Internet DRAFT - draft-gao-flexible-session-protocol
draft-gao-flexible-session-protocol
Network Working Group J. Gao
Internet-Draft Individual
Intended status: Experimental 17 October 2023
Expires: 19 April 2024
Flexible Session Protocol
draft-gao-flexible-session-protocol-11
Abstract
FSP is a connection-oriented transport layer protocol that provides
mobility and multihoming support by introducing the concept of 'upper
layer thread ID', which is associated with some shared secret that is
applied with some authenticated encryption algorithm to protect
authenticity of the origin of the FSP packets. It is able to provide
following services to the upper layer application:
* Stream-oriented send-receive with native message boundary
* Flexibility to exploit authenticated encryption
* On-the-wire compression
* Light-weight session management
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on 19 April 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Features . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 6
1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . 6
2. Abbreviations and Idioms . . . . . . . . . . . . . . . . . . 7
3. Key Mechanisms . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Underlying Layer Services Required . . . . . . . . . . . 9
3.2. Identifying Connection by Local ULTID . . . . . . . . . . 10
3.3. Defending Against Connection Hijacking with ICC . . . . . 10
3.4. Synchronizing Key Installation with Transmit
Transaction . . . . . . . . . . . . . . . . . . . . . . . 11
3.5. 0-RTT Connection Multiplication with OOB Packet . . . . . 11
4. Packet Structure . . . . . . . . . . . . . . . . . . . . . . 12
4.1. FSP over UDP/IPv4 . . . . . . . . . . . . . . . . . . . . 12
4.2. FSP over IPv6 . . . . . . . . . . . . . . . . . . . . . . 13
4.3. Generic FSP Header . . . . . . . . . . . . . . . . . . . 15
4.4. FSP Header Signature and Code-Mark-Length Prefix . . . . 15
4.5. Preliminary FSP Packets . . . . . . . . . . . . . . . . . 18
4.6. Normal Fixed Header . . . . . . . . . . . . . . . . . . . 21
4.7. Sink Parameter . . . . . . . . . . . . . . . . . . . . . 23
4.8. Selective Negative Acknowledgment . . . . . . . . . . . . 24
4.9. RESET . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5. The Finite State Machine . . . . . . . . . . . . . . . . . . 26
5.1. NON_EXISTENT . . . . . . . . . . . . . . . . . . . . . . 26
5.2. LISTENING . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3. CONNECT_BOOTSTRAP . . . . . . . . . . . . . . . . . . . . 27
5.4. CONNECT_AFFIRMING . . . . . . . . . . . . . . . . . . . . 27
5.5. CHALLENGING . . . . . . . . . . . . . . . . . . . . . . . 28
5.6. ACTIVE . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.7. COMMITTING . . . . . . . . . . . . . . . . . . . . . . . 29
5.8. COMMITTED . . . . . . . . . . . . . . . . . . . . . . . . 29
5.9. PEER_COMMIT . . . . . . . . . . . . . . . . . . . . . . . 30
5.10. COMMITTING2 . . . . . . . . . . . . . . . . . . . . . . . 30
5.11. CLOSABLE . . . . . . . . . . . . . . . . . . . . . . . . 31
5.12. SHUT_REQUESTED . . . . . . . . . . . . . . . . . . . . . 32
5.13. PRE_CLOSED . . . . . . . . . . . . . . . . . . . . . . . 32
5.14. CLOSED . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.15. CLONING . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.16. Passive Multiplication . . . . . . . . . . . . . . . . . 33
5.17. Typical State Transitions . . . . . . . . . . . . . . . . 33
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6. End-to-End Negotiation . . . . . . . . . . . . . . . . . . . 39
6.1. Connect Initialization . . . . . . . . . . . . . . . . . 39
6.2. Response to Connect Initialization . . . . . . . . . . . 40
6.3. Connection Incarnation Request . . . . . . . . . . . . . 40
6.4. Connection Incarnation Response . . . . . . . . . . . . . 41
6.5. The Last Confirmation . . . . . . . . . . . . . . . . . . 42
6.6. Retransmission . . . . . . . . . . . . . . . . . . . . . 42
7. Quad-party Session Key Installation . . . . . . . . . . . . . 42
7.1. API for Session Key Installation . . . . . . . . . . . . 43
7.2. Time to Call API for Session Key Installation . . . . . . 44
7.3. Time to Take New Session Key into Effect . . . . . . . . 44
7.4. Generating the Initial Session Key . . . . . . . . . . . 44
7.5. Internal Rekeying . . . . . . . . . . . . . . . . . . . . 45
7.6. Sample Sequence of Installing Session Key . . . . . . . . 46
8. Send and Receive . . . . . . . . . . . . . . . . . . . . . . 47
8.1. Packet Integrity Protection . . . . . . . . . . . . . . . 47
8.2. Start a New Transmit Transaction . . . . . . . . . . . . 49
8.3. Send a Pure Data Packet . . . . . . . . . . . . . . . . . 50
8.4. Commit a Transmit Transaction . . . . . . . . . . . . . . 50
8.5. Retransmission . . . . . . . . . . . . . . . . . . . . . 51
8.6. Flow Control . . . . . . . . . . . . . . . . . . . . . . 54
8.7. Congestion Control . . . . . . . . . . . . . . . . . . . 54
8.8. On-the-Wire Compression . . . . . . . . . . . . . . . . . 55
8.9. Milk Like Payload and Minimal Delay Service . . . . . . . 56
9. Connection Multiplication . . . . . . . . . . . . . . . . . . 56
9.1. Request to Multiply Connection . . . . . . . . . . . . . 56
9.2. Response to Connection Multiplication Request . . . . . . 57
9.3. Duplicate Detection of Connection Multiplication
Request . . . . . . . . . . . . . . . . . . . . . . . . . 58
9.4. Retransmission . . . . . . . . . . . . . . . . . . . . . 58
9.5. Key Derivation for Branch Connection . . . . . . . . . . 58
10. Mobility and Multihome Support . . . . . . . . . . . . . . . 59
10.1. Heartbeat Signals . . . . . . . . . . . . . . . . . . . 59
10.2. Active Address Change Signaling . . . . . . . . . . . . 60
10.3. Heuristic Remote Address Change Adaptation . . . . . . . 60
10.4. Heuristic Address Change Acknowledgement . . . . . . . . 60
10.5. NAT-traversal and Multihoming . . . . . . . . . . . . . 61
10.6. Explicit Multi-home Informing . . . . . . . . . . . . . 61
11. Graceful Shutdown . . . . . . . . . . . . . . . . . . . . . . 61
11.1. Initiation of Graceful Shutdown . . . . . . . . . . . . 62
11.2. Acknowledgment of Graceful Shutdown . . . . . . . . . . 62
11.3. Finalization of Graceful Shutdown . . . . . . . . . . . 62
11.4. Retransmission of RELEASE Packet . . . . . . . . . . . . 63
12. Timeouts and Abrupt Close . . . . . . . . . . . . . . . . . . 63
12.1. Timeouts in End-to-End Negotiation . . . . . . . . . . . 63
12.2. Timeouts in Multiply . . . . . . . . . . . . . . . . . . 63
12.3. Timeout of Transmit Transaction Commitment . . . . . . . 63
12.4. Timeout of Graceful Shutdown . . . . . . . . . . . . . . 64
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12.5. Idle Timeout . . . . . . . . . . . . . . . . . . . . . . 64
12.6. Session Key Timeout . . . . . . . . . . . . . . . . . . 64
12.7. Abrupt Close . . . . . . . . . . . . . . . . . . . . . . 64
13. Security Considerations . . . . . . . . . . . . . . . . . . . 64
13.1. Deny of Service Attack . . . . . . . . . . . . . . . . . 64
13.2. Replay Attack . . . . . . . . . . . . . . . . . . . . . 64
13.3. Passive Attacks . . . . . . . . . . . . . . . . . . . . 64
13.4. Masquerade Attack . . . . . . . . . . . . . . . . . . . 65
13.5. Active Man-In-The-Middle Attack . . . . . . . . . . . . 65
13.6. Privacy Concerns . . . . . . . . . . . . . . . . . . . . 65
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 65
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 65
15.1. Normative References . . . . . . . . . . . . . . . . . . 65
15.2. Informative References . . . . . . . . . . . . . . . . . 67
Appendix A. Issues for Further Study . . . . . . . . . . . . . . 69
A.1. Resolution of ULTID in DNS . . . . . . . . . . . . . . . 69
A.2. Proxy Pattern for Syndicated Name Resolution . . . . . . 70
A.3. Asymmetric Transmission . . . . . . . . . . . . . . . . . 71
Appendix B. Choices of Design Goals . . . . . . . . . . . . . . 71
B.1. Optimizing towards IPv6 . . . . . . . . . . . . . . . . . 71
B.2. Hardware-Accelerated Cryptography . . . . . . . . . . . . 72
B.3. On-the-wire Compression . . . . . . . . . . . . . . . . . 72
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 73
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 73
1. Introduction
The dominating transport layer protocols, TCP and UDP that take use
of the IP address to identifying the end node, introduce the
controversial role of IP address both as the identifier and as the
routing locater.
Flexible Session Protocol, introduces the concept of 'upper layer
thread ID' (ULTID), which was firstly suggested in [Gao2002]. The
ULTID is unique in the local context of the FSP node. Its
significance may be compared with the Security Parameter Index (SPI)
in MOBIKE [RFC4555].
An integrity check code (ICC) field is designed in the FSP packet
header to protect authenticity and optionally privacy of the FSP
packet. The ICC field is designed to be associated with some shared
secret indexed by the source or destination ULTID in the local
context of the source or destination node, respectively. An FSP
packet is assumed to originate from the same source if the ICC value
associated the ULTID passes validation, regardless of the full source
or destination address. In such a way FSP provides provides
mobility, multi-homing and multi-path support.
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ICC is either calculated by [CRC64] which protects FSP against
unintended modification, or cryptographically calculated with some
Authenticated Encryption with Additional Data [R01] algorithm, each
of which requires a shared secret key.
In the former case a weak key meant to obfuscate the CRC64 checksum
is agreed by the FSP participants. In the latter two cases, the
shared secret key is assumed to be installed by the upper layer
application (ULA).
Either the weak key or the shared secret key is indexed by the source
or destination ULTID in the local context of the sender or the
receiver, respectively.
FSP facilitates secret key installation by introducing the concept of
transmit transaction. Mechanism of transmit transaction also
provides the session-connection synchronization service to the upper
layer.
FSP is a transport layer protocol as specified in [RFC1122], provides
services alike TCP [STD5] to ULA, with session layer features as
suggested in [OSI_RM], most noticeably session-connection
synchronization by introducing the concept of transmit transaction.
1.1. Features
1.1.1. Transport Layer Mobility Support
FSP is meant to be transport layer protocol that keeps the IP address
as the routing locater but keeps it from being the key constituent of
the end point identifier of FSP or any upper layer protocol built
upon FSP.
1.1.2. Flexibility to exploit Authenticated Encryption
By optionally applying authenticated encryption with additional data
on each FSP packet, FSP provides both authentication of message
origin and privacy protection service to the upper layer application.
The shared key required by the authenticated encryption algorithm is
supposed to be established and installed onto the FSP layer by the
upper layer application (ULA), and by introducing the concept of
transmit tranaction FSP provides mechanism for the connected ULAs to
synchronize installation of the shared key. Thus FSP makes it
flexible to test, try or apply new key establish algorithms.
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1.1.3. Transmit Transaction
FSP introduces the concept of transmit transaction, which makes it
able to mark end of message inherently at the transport layer,
effectively eliminate the requirement of message delimiters at the
application layer. Besides, it still provides byte-stream-oriented
transfer service to its upper layer application which is familiar and
friendly to application developers.
1.1.4. Light-weight session management
In addition to transmit transaction mechanism, which is arguably a
feature of session-connection synchronization, the FSP upper layer
application is able to fork branch connections of an established
connection in zero round-trip mode without compromising security. In
this way FSP provides light-weight session management service to ULA.
1.1.5. On-the-wire Compression
FSP provides on-the-wire compression service through the on-the-wire
compression and fragmentation function module.
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying significance described in RFC 2119.
1.3. Conventions
Conventions in describing the finite state machine (FSM) of FSP are:
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ESTABLISHED The string of alphabetic characters designates
the name of the state
[API: Reset] Upper Layer Application Programming Interface
Call
{Notify} Call back/notify the upper layer application
{new context} Additional action before or after state
transition
[Send Send some FSP packet
OPCODE_OF_FSP_PACKET]
[Retransmit Retransmit some FSP packet
OPCODE_OF_FSP_PACKET]
{On transient state Timed-out event
Timeout}
{&& additional Together with some additional condition
condition}
--> state transition
|-- branch
2. Abbreviations and Idioms
Connection An FSP connection is the binding of two network nodes
established through some end-to-end negotiation process. It is
identified by the ULTID in the local context of each network node,
respectively.
EoT End of Transaction. A transmit transaction is said to reach EoT
if the EoT flag is set in a legitimate ACK_CONNECT_REQ, PURE_DATA,
PERSIST or MULTIPLY packet. We said that the packet terminates
the transmit transaction if the EoT flag is set. An FSP end node
SHALL NOT send further data if it has initiated EoT of its
transmit direction unless the packet with EoT flag set, together
with all of the packets before this particular packet have all
been acknowledged. EoT, i.e. termination of transmit transaction
is unilateral.
FREWS Flags and advertised REceive Window Size. It is the 32-bit
combined word next to the ICC field in the normal FSP fixed
header.
ICC Identity Check Code. It is a 64-bit value that depends on both
the session key and all of the headers of the FSP packet to
include the ICC, calculated with the same algorithm in the context
of each FSP participant. Only a packet with correct ICC can be
accepted by any FSP participant as soon as the connection has been
established. Initially CRC64 is exploited to make a checksum that
weekly protects the FSP packet against unintentional modification.
The checksum is obfuscated with the initial session key to get the
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ICC. After the ULA installed the long-term session key some
Authenticated Encryption with Additional Data algorithm shall be
applied to obtain or check the ICC.
Session An FSP session is the transport-layer association of two
network nodes. A full FSP session consists of one connection that
was established from scratch and all of its branches. However for
this version of FSP specification the idioms session and
connection are interchangeable if not explicitly specified.
Session Key The session key is a bit string of at least 128 bits
that means to resist against masquerade attack. It is either
initiated during the end-to-end negotiation phase or installed by
the ULA after the FSP connection is established. The session key
installed by the ULA is called the long-term session key. Here
long-term means that the key could be used until the packet
sequence space is exhausted. The packet sequence space is
exhausted if the number of packets that use the same key reaches
or exceeds 2,147,483,647(2^31-1).
SN Sequence Number. It is the unsigned 32-bit integer number
assigned to every FSP packet except the preliminary packets.
Difference of two sequence number is represented by a 32-bit
signed integer. If the result of SN B subtracting SN A is greater
than zero, we say that B is greater than A and the packet of the
sequence number B is later than the packet of the sequence number
A, although the unsigned integer representation of B may be far
less that A. Consequently, as the result of A subtracting B is
less than zero, we say that A is less than B and the packet of the
sequence number A is earlier than the packet of the sequence
number A.
Transmit Transaction A transmit transaction in FSP is a sequence of
FSP packets that were sent and marked by the ULA as one continuous
stream where all packets in the stream must be acknowledged before
any further packet is allowed to be sent. A ACK_CONNECT_REQ,
PERSIST or MULTIPLY packet always starts a new transmit
transaction. Any packet with EoT flag set, including the PERSIST
packet that is exploited to acknowledge the ACK_CONNECT_REQ or
MULTIPLY packet, terminates the transmit transaction. .
ULA Upper Layer Application
ULTID The Upper Layer Thread Identifier (ULTID) is a 32-bit word
that was allocated by particular network end node of an FSP
connection and is unique in the local context of the network end
node. Theoretically all of the ULAs of a network end node MAY
establish up to 2^31-1 FSP connections totally. Each connection
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MUST have a unique thread identifier (ULTID) assigned in the local
context of the network end node. A session or connection in FSP
does not require a global ID.
3. Key Mechanisms
3.1. Underlying Layer Services Required
FSP requires that the underlying layer provides packet delivery
service. In addition FSP supposes that the underlying layer has
following features:
3.1.1. Handling of High Mobility
Here high mobility refers to scenarios such as high-speed train or
airplane.
FSP solves somewhat coarse-grain or low-speed mobility problem.
Fine-grain or high-speed mobility is left to the underlying physical
network. To make mobility support work effectively it is assumed
that one end-node MUST keep its lower layer address reasonably stable
while the other end-node SHOULD NOT change its lower layer address
too frequently.
Here the meaning of physical network conforms to what was depicted in
[RFC1122].
3.1.2. Network Address Change Notification
Network address change notification is mandatory only in the IPv6
network.
We split the IPv6 address of the IPv6 packet underlying FSP into
three parts. The leftmost 64-bit long word is the network prefix,
which SHOULD be the unique IPv6 prefix assigned to the host
[RFC8273]. The centermost 32-bit word is called the aggregation host
ID, and the rightmost 32-bit word is the ULTID. While the ULTID MUST
be kept stable even during the life of an FSP session, the network
prefix part MAY change when an endpoint is roaming. The aggregation
host ID may change as well. The network prefix part together with
the aggregation host ID part act as the traditional routing locator
at the network layer.
The aggragation host ID SHOULD NOT be 0, nor hexadecimal value
FDFFFFFFF, nor hexadecimal value FFFFFFFFF so that the final IPv6
address assigned can not be an IPv6 subnet anycast address[RFC2526].
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It is supposed that the network layer immediately notifies the FSP
layer if the network prefix or aggregation host ID changes.
An participant of an FSP connection SHALL immediately notify its peer
whenever its underlying IPv6 address is changed with a KEEP_ALIVE
packet. The peer shall send packet to the participant that has
notified the address change with the new address.
It is supposed that the packet to inform the remote end to update the
lower layer address association could reach its destination in a
satisfying success rate.
3.1.3. Network Congestion Control
Network layer congestion control is mandatory only in future IPv6
network.
It is supposed that end-to-end congestion control is provided at some
sub-layer of the network layer. Implementation of FSP MUST include a
congestion manager [RFC3124] if such sub-layer service of the network
layer is not provided.
3.2. Identifying Connection by Local ULTID
Each FSP connection prepares a pair of ULTIDs. An ULTID uniquely
indexes a connection in the local context of an FSP end node. An FSP
end node relies neither source IP address nor destination IP address,
except the ULTID part of the near end's IPv6 address to identify an
FSP connection.
Each ULTID is allocated in the local context of the two FSP
participant respectively. The source ULTID and the destination ULTID
of an FSP packet usually differ in their values. However, the secret
keys indexed in the local contexts of the two end-points must have
the same value.
3.3. Defending Against Connection Hijacking with ICC
An integrity check code (ICC) field associated with the ULTID is
designed in the FSP header to protect authenticity and optionally
privacy of the FSP packet. An FSP packet is assumed to originate
from the same source if the ICC value associated with certain
destination ULTID passes validation, regardless of the source or
destination address in the underlying layer.
On initiating FSP takes use of [CRC64] to make checksum of the FSP
packet to protect it against unintentional modification. The
checksum is taken as the ICC.
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After the ULA has installed a shared secret key, value of ICC is
calculated by firstly getting the secret key associated indexed by
the local ULTID, then calculating the tag value with the AES-GCM
[GCM] authenticated encryption with additional data algorithm.
3.4. Synchronizing Key Installation with Transmit Transaction
It is proposed that it is the ULA to do key establishment and/or end-
point user-agent authentication while the FSP layer provides
authenticated, optionally encrypted data transfer service.
A dedicate application program interface (API) is designed for the
ULA to install the secret key established by the ULA participants.
FSP facilitates shared secret key installation by introducing the
concept of transmit transaction.
A transmit transaction of FSP is a sequence of FSP packets that were
sent and requested by ULA as one continuous stream where all packets
in the stream MUST be acknowledged before any further packet is
allowed to be sent.
A flag called 'End of Transaction' (EoT) is designed in the FSP
header. When it is set, it marks that the transmit transaction in
the direction from the source of the FSP packet towards the
destination of the FSP packet is 'committed'.
As the FSP node knows when a transmit transaction at FSP layer is
terminated there is no ambiguity which packet is to be applied with
the new session key when the key is installed by ULA through the
dedicated API.
3.5. 0-RTT Connection Multiplication with OOB Packet
An FSP connection MAY be multiplied to get a branch or branches of
the connection. Multiplication of a connection is protected by
deriving new session key from the original security context of the
connection.
The packet that carries the command to multiply an established FSP
connection MUST be sent from a new allocated local ULTID towards the
destination ULTID of the original connection. It is an out-of-band
(OOB) packet in the context of the original connection and it MUST be
cryptographically protected by the secret key of the original
connection. The packet MAY carry payload.
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The receiver of the packet MUST allocate a new local ULTID, accept
the optional payload in the new context associated with the new
ULTID, derive a new secret key from the secret key of the original
connection, and responds from the new context. The response MAY
carry payload.
The very first response packet MUST be protected by the new secret
key. The sender of the multiply command packet MUST automatically
inaugurate the same secret key, derived from the secret key of the
same original connection. And it MUST treat the response packet as
though a transmit transaction had been committed by the responder,
i.e. authenticity of the response packet is verified with the new
secret key.
Thus the branch connection of a new pair of ULTIDs is established
with zero round-trip overhead. This mechanism may be exploited to
provide expedited data transfer or parallel data transfer service.
4. Packet Structure
4.1. FSP over UDP/IPv4
In this version of FSP, when FSP is implemented in the IPv4 network,
every FSP packet MUST be encapsulated in a UDP [STD6] datagram. The
UDP datagram encapsulated the FSP packet SHALL have the checksum
disabled (i.e. set its value to 0) [RFC8085]. The Source and the
destination ULTIDs are put at the leading position of the UDP
payload. FSP fixed header, optional extension headers and FSP
payload follow the ULTIDs:
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0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ FSP Fix Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional FSP Extension Headers ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ FSP payload (may be empty) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2. FSP over IPv6
When FSP is implemented over IPv6 [RFC8200], the ULTID part is
embedded in the IPv6 address. FSP fixed header follows the IPv6
headers:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~ IPv6 Header: ~
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Network Prefix +
| |
+ Source Address ----------------------------+
| Source Aggregation Host ID |
+ ----------------------------+
| Source Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Destination Network Prefix +
| |
+ Destination Address ---------------------------------+
| Destination Aggregation Host ID |
+ ---------------------------------+
| Destination Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Optional IPv6 Headers ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ FSP Fix Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional FSP Extension Headers ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ FSP payload (may be empty) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Prefix The leftmost 64-bit of the IPv6 address which MAY and
usually do have different value at the difference interface of an
IPv6 end- node.
Aggregation Host ID The left 32-bit part of the rightmost 64-bit
long word of the IPv6 address. All of the aggregation host ID
parts of an IPv6 end- node's IPv6 addresses MUST have the same
value for this version of FSP.
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Network prefix and aggregation host ID make the IPv6 prefix part of
the IPv6 address under the context of FSP. It is assumed that there
is a unique IPv6 prefix per host [RFC8273].
RFCs related to IPv6 address configuration such as ND for IPv6
[RFC4861], SLAAC [RFC4862], 'IPv6 Subnet Model' [RFC5942], 'IPv6
Address Assignment to End Sites' [RFC6177], 'Discovery of the IPv6
Prefix Used for IPv6 Address Synthesis' [RFC7050], DHCP [RFC8415] and
'IPv6 Node Requirements' [RFC8504] would be reviewed in separate
documents.
4.3. Generic FSP Header
FSP headers include the fixed header and the extension headers. A
general fixed header consists of a 32-bit FSP Header Signature and
20-byte operation-code specific fields. An extension header consists
of a 32-bit Code-Mark-Length Prefix and the operation-code specific
content. The length of the extension header content may be variable,
provided that the tail of the full extension header align on 64-bit
boundary.
Integers in the FSP fix header are transmitted in network byte order.
Integers in the FSP extension headers are of little-endian.
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Operation Code Specific Fields ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.4. FSP Header Signature and Code-Mark-Length Prefix
0 7 8 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Operation Code| Major | Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 7 8 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Operation Code| Mark | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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4.4.1. Operation Code
The operation code is an octet that stores the code of the command
which indicates the function of the FSP packet, or specifies the type
of some extension header.
+==================+======+========================================+
| Synonym | Code | Meaning |
+==================+======+========================================+
| INIT_CONNECT | 1 | Initialize Connection |
+------------------+------+----------------------------------------+
| ACK_INIT_CONNECT | 2 | Acknowledge Initialization of |
| | | Connection |
+------------------+------+----------------------------------------+
| CONNECT_REQUEST | 3 | Formally Request to Connect |
+------------------+------+----------------------------------------+
| ACK_CONNECT_REQ | 4 | Acknowledge the Connection Request |
+------------------+------+----------------------------------------+
| RESET | 5 | Reset a connection. Abort the |
| | | connection, or refuse to establish the |
| | | connection at the very beginning. |
+------------------+------+----------------------------------------+
| KEEP_ALIVE | 7 | Keep the peer alive. It is an out-of- |
| | | band control packet acting as the |
| | | heart-beating signal. An out-of-band |
| | | control packet does not consume send |
| | | sequence space itself. FSP takes use |
| | | of the KEEP_ALIVE packet to inform the |
| | | peer about the change of the source IP |
| | | addresses. Besides, when the MIND |
| | | flag is set, the KEEP_ALIVE packet is |
| | | meant to tell the peer which packets |
| | | should be retransmitted. |
+------------------+------+----------------------------------------+
| PERSIST | 8 | Make a connection persistent. It is |
| | | meant to start a new transmit |
| | | transaction after a connection |
| | | migrated to CLOSABLE state. It can |
| | | also acknowledge ACK_CONNECT_REQ or |
| | | MULTIPLY. It MUST carry payload. It |
| | | always consumes a slot of the send |
| | | sequence space. |
+------------------+------+----------------------------------------+
| PURE_DATA | 9 | Pure Data. It does not carry any |
| | | optional header. |
+------------------+------+----------------------------------------+
| RELEASE | 11 | Release the connection. RELEASE |
| | | packet does not carry payload, but it |
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| | | always consumes a slot of the send |
| | | sequence space. |
+------------------+------+----------------------------------------+
| MULTIPLY | 12 | Multiply the connection. It is sent |
| | | in the context of the original |
| | | connection and may carry payload and/ |
| | | or optional headers as an out-of-band |
| | | packet. |
+------------------+------+----------------------------------------+
| PEER_SUBNETS | 17 | Tell the remote end how to address the |
| | | sender of the packet in the reverse |
| | | direction. It is the code of the Sink |
| | | Parameter extension header. |
+------------------+------+----------------------------------------+
| SELECTIVE_NACK | 18 | Tell the remote end to retransmit the |
| | | packets that were negatively |
| | | acknowledged. It is the code of the |
| | | Selective Negative Acknowledgment |
| | | extension header. |
+------------------+------+----------------------------------------+
Table 1
4.4.2. Major
It is an octet that states current FSP major version. For this FSP
version it MUST be 0.
It is not mandatory for different major versions of FSP to be
compatible.
4.4.3. Mark
It is an octet that marks current minor version of the extension
header, under the major FSP version specified in the fixed header,
and/or serves as the flag, depending on the type of the extension
header.
It is mandatory for implementations to be compatible with different
minor versions of FSP extension header under the same major FSP
version.
It is not mandatory for minor versions of FSP extension header under
the different major FSP version to be compatible, even if the minor
versions happen to be the same.
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4.4.4. Offset
The offset field is a 16-bit unsigned integer that specifies the
offset of the first octet of the payload, starting from the begin of
the FSP fixed header. If its value equals the size of the fixed
header the packet has no extension.
4.4.5. Length
The length field is a 16-bit unsigned integer that specifies the
length, including the Type-Version-Length Header and the size of the
the operation code specific content of the extension header.
4.5. Preliminary FSP Packets
Preliminary FSP packets are the packets exchanged during the end-to-
end negotiation phase of FSP connection establishment when it is
impossible to calculate ICC normally.
4.5.1. Connect Initialization
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Init-Check-Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Host Name of the Responder (optional) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Operation Code of this type of packet is INIT_CONNECT.
Salt It a 32-bit random bit string that may be exploited to make
secret key agreement.
Timestamp It is a 64-bit unsigned integer that represents number of
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microseconds elapsed since 00:00, Jan.1, 1970, Coordinated
Universal Time. It may be exploited to synchronize the clocks of
the participants and/or estimate delay during data transmission in
the network.
Init-Check-Code It is a 64-bit random [RFC4086] bit string that
means to uniquely associated with the connection initiated.
Host Name of the Responder The optional payload of the Connect
Initialization packet is the host name of the responder. It MUST
be encoded in UTF-8 [RFC3629] and SHOULD be resolvable in DNS,
4.5.2. Acknowledgment to Connect Initialization
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time Delta |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Init-Check-Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Sink Parameter ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Operation Code of this type of packet is ACK_INIT_CONNECT.
Time Delta It is a 32-bit signed integer which is the difference
between the near-end's time and the timestamp value sent in the
Connection Initialization packet. The units and the epoch of the
near-end's time value and the timestamp value MUST be the same.
However, the precision or resolution of the time delta value is
chosen arbitrarily by the responder.
Cookie It is a 64-bit bit string cryptographically generated by the
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responder in a represent-transfer state manner. More specifically
when the same timestamp, time delta, Init-Check-Code, salt, source
and destination ULTIDs are sent to the responder, the responder
MUST be able to generate the identical cookie value.
Init-Check-Code It MUST be identical to the corresponding field in
the Connect Initialization packet acknowledged.
o Sink Parameter It is an extension header specified in 4.7.
4.5.3. Connect Request
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Init-Check-Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Time Stamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Sink Parameter ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time Delta |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Host Name of the Initiator (optional) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Operation Code of this type of packet is CONNECT_REQUEST.
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The value of each field that has the identical name with the one in
the associated Connect Initialization and Acknowledgment to Connect
Initialization packet MUST be assigned the same value as in these two
packets, except header signature in the packet.
Note that the initiator SHALL fill in the time delta field as it is
and SHALL NOT assume endian-ness of the time delta field.
Sink Parameter It is an extension header specified in 4.7.
Host Name of the Initiator The optional payload of the Connect
Request packet is the host name, which is encoded in UTF-8 and
SHOULD be resolvable in DNS, of the initiator. It could be
exploited by the responder to look up the address of the initiator
that may receive packets in the reverse direction.
4.6. Normal Fixed Header
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Advertised Receive Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Integrity Check Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Expected Sequence Number/Out-of-Band Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Operation Code of a normal fixed header may be ACK_CONNECT_REQ,
PURE_DATA, PERSIST, KEEP_ALIVE, RELEASE or MULTIPLY.
Flags It is bit-field of width 8. From left to right:
End of Transaction (EoT): If the EoT flag of a packet is set,
it is the last packet of a transmit transaction. A packet with
the EoT flag set MAY be the start and the single packet of the
transmit transaction as well.
Minimal-Delay (MIND): If the MIND flag of the Connect Request
or Acknowledgment to Connect Request packet is set, the ULA
prefers minimal delay and is willing to tolerate packet loss.
FSP SHALL drop the packet received earliest when there is no
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enough receive buffer so that the latest packet received can be
saved and the delay to deliver data to ULA is minimized. If
the MIND flag has been set the EoT flag of any following packet
is simply ignored. The MIND flag of an FSP packet may be set
only if the packet does not belong to a compressed transmit
transaction. Payload of each FSP packet is delivered to the
ULA as an independent message if the MIND flag has been set.
Compressed (CPR): If the CPR flag of the first packet of a
transmit transaction is set, compression is applied on the
octet stream of the payloads of the continuous packets that
constitute the transmit transaction, or to put it simply, the
payload octet stream of the transaction transaction. Such
transmit transaction is called a compressed transmit
transaction. When the CPR flag of a packet is set, CPR flag of
each following packet is ignored until reaching termination of
the transmit transaction. If the payload octet stream of the
transmit transaction is compressed the Minimal-Delay flag of
any packet in the transmit transaction MUST be cleared.
ECN-Echo (ECE): The Explicit Congestion Notification Echo flag
of a packet is set if the sender of the packet has received an
underlying IPv6 packet with Congestion Experienced code point
set for its peer as stated in "The Addition of Explicit
Congestion Notification (ECN) to IP" [RFC3168].
Send Rate Reduced (SRR): The SRR flag of each packet SHALL be
set as soon as the sender has received a legitimate packet with
ECE flag set and has informed the congestion manager to reduce
the send rate, until a sent packet with SRR flag set is
acknowledged.
The remaining 3 bits are reserved.
Advertised Receive Window Size It is a 20-bit unsigned integer that
stores number of the free blocks in the receive buffer of the
sender of the packet that contains the receive window size field.
It is count from the slot meant to accept the packet with the
expected sequence number. The sender must ensure that the
difference between the latest sequence number sent out and the
largest expected sequence number received does not exceed the
value of the latest advertised receive window size received.
Sequence Number Each in-band FSP packet is assigned a 32-bit
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unsigned integer as the sequence number. The sequence number
assigned for in-band FSP packets MUST be in strict order. An out-
of-band packet that has the operation code of KEEP_ALIVE or
MULTIPLY MUST be assigned a sequence number that falls in the
receive window.
Expected Sequence Number The 'expected sequence number/out-of-band
serial number' field stores the earliest sequence number of the
packets that were not yet received in the receive window of the
sender for in-band packet. It is an accumulative acknowledgment.
Any packet with the sequence number before the received Expected
Sequence Number is supposed to have been received by the remote
end.
Out-of-band Serial Number The 'expected sequence number/out-of-band
serial number' field stores a 32-bit unsigned integer that numbers
the out-of-band FSP packet separately from the sequence space of
the in-band packets. Each time an out-of-band packet is sent the
out-of-band serial number SHALL increase by one. It is assumed
that in the life of the session no two packets have the same
sequence number and the same out-of-band serial number
simultaneously.
Integrity Check Code The ICC of the packet.
4.7. Sink Parameter
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code-Mark-Length Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Listener ID/Host ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Addressable Network Prefixes ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Operation Code in the Header Signature of this extension header is
PEER_SUBNETS.
Listener ID It is the ULTID of the responder that is in LISTENING
state.
Host ID It is the aggregation host id of the sender. It SHALL be 0
if it is in the IPv4 network.
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Addressable Network Prefixes These are up to 4 64-bit words that
specify the network prefixes of the lower layer interfaces that
are addressable by the receiver in the reverse direction. In this
version of the FSP 'Addressable Network Prefixes' field is of
fixed length. The last network prefix which is non-zero is the
last resort one. There MUST be at least one non-zero network
prefix. If there are more than one non-zero network prefixes
those other than the last resort are load-balanced preferred. In
an IPv6 network, the addressable network prefix is the leftmost 64
bits of the IPv6 address. The receiver of the Addressable Network
Prefixes SHALL send packet in the reverse direction, i.e. to the
sender of the field with the destination IPv6 address generated by
combining a preferred network prefix with the aggregation host id
and the ULTID part of the source address in the IPv6 header of the
received packet that eventually carries the Addressable Network
Prefixes. Such feature MAY be exploited to handle links with
unidirectional connectivity, but it is NOT RECOMMENTED. In an
IPv4 network for compatibility with the IPv6 addressed ULA the
64-bit word of the addressable network prefix specified is
composed as following Figure:
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x2002 (IPv6 6to4 prefix) |IPv4 address (leftmost 16 bits)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IPv4 address(rightmost 16 bits)| UDP port number (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sender of the Sink Parameter packet SHOULD be NAT-aware in the IPv4
network. If it is able to obtain the from the NAT box (as defined in
"Traditional IP Network Address Translator (Traditional NAT)"
[RFC3022]) through Port Control Protocol (PCP) [RFC6887] SHOULD fill
in the IPv4 address and UDP port number fields with the public IP
value that were obtained. If it does not have such capability, it
SHALL fill in the addressable network prefix with all binary zeroes.
4.8. Selective Negative Acknowledgment
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0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code-Mark-Length Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Expected Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delay Sample Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgement Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Width |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Further pairs of (Gap Width, Data Length) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The operation code of this type of extension header is SELECTIVE_NACK
Expected Sequence Number It stores the earliest sequence number of
the packets that were not yet received in the receive window of
the sender. It is an accumulative acknowledgment. Any packet
with the sequence number before the received Expected Sequence
Number is supposed to have been received by the remote end. The
expected sequence number is represented in little endian.
Delay Sample Sequence Number It stores the sequence number of the
packet that the acknowledgement delay was calculated on. The
delay sample sequence number is represented in little endian.
Acknowledgement Delay A 32-bit unsigned integer specifies the delay
in microseconds between sending the packet containing the SNACK
extension header and accepting the last packet that is
accumulatively acknowledged by the SNACK extension header. The
acknowledgement delay is represented in little endian.
Gap Width and Data Length The SNACK header contains the descriptor
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of the receive window gaps. The descriptor itself is a list of
entries. The length of the list can be zero which means that
there is no gap in the receive window. If the list is not empty,
each entry contains the width of one gap (Gap Width) in the
receive window and the length of the continuously received data
following the gap (Data Length), respectively. The unit of
aforementioned length of gaps or number of packets is buffer block
which size is agreed upon connection establishment. Gap width and
data length MUST be transmitted in little endian.
4.9. RESET
The 'RESET' packet is a special command packet meant to interrupt
connection setup process or disconnect abruptly. Operation Code of
the packet is RESET.
Structure of a RESET packet in C code snippet with unnamed union
applied:
struct FSP$HeaderSignature { octet opCode; octet major; uint16_t
offset; }; struct FSP_RejectConnect { FSP$HeaderSignature hs; /* bit
field to describe reasons for reset */ uint32_t reasons; /* sequence
numbers */ union { timestamp_t timeStamp; struct { uint32_t initial;
uint32_t expected; } sn; }; /* uniqueness proof */ union { uint64_t
integrityCode; uint64_t cookie; uint64_t initCheckCode; }; };
When the RESET packet is the response to a Connect Initialization
packet both the timeStamp and the initCheckCode fields of the RESET
packet MUST be set to the same values of Time Stamp and Init-Check-
Code in the Connect Initialization packet, respectively.
When the RESET packet is the response to a Connect Request packet
both the timeStamp and the cookie fields of the RESET packet MUST be
set to the same value of Time Stamp and Cookie in the Connect Request
packet, respectively.
When the RESET packet is the response to a packet with a normal fixed
header, the sn.initial, the sn.expected and the integrityCode of the
RESET packet MUST be set as to specification of normal fixed header
field Sequence Number, Expected Sequence Number and Integrity Check
Code, respectively.
5. The Finite State Machine
5.1. NON_EXISTENT
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---[API: Listen]-->LISTENING
|--[API: Connect]-->CONNECT_BOOTSTRAP-->[Send INIT_CONNECT]
|--[API: Multiply]-->CLONING-->[Send MULTIPLY]
NON_EXISTENT is a pseudo-state before a connection is created by the
ULA calling API Listen, Connect or Multiply (or after a connection is
reset).
5.2. LISTENING
---[API: Reset]-->NON_EXISTENT
|<-->[Rcv.INIT_CONNECT]{&& accepted}[Send ACK_INIT_CONNECT]
|<-->[Rcv.CONNECT_REQUEST]
|--{&& duplication detected}--[Retransmit ACK_CONNECT_REQ]
|--{&& no duplication}-->{Notify}
|-->[API: Accept]
-->{new context}CHALLENGING-->[Send ACK_CONNECT_REQ]
|-->[API: Reject]-->[Send RESET]{abort new context, if any}
LISTENING is a state entered by the ULA calling API Listen.
5.3. CONNECT_BOOTSTRAP
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|-->[Rcv.ACK_INIT_CONNECT]-->CONNECT_AFFIRMING
-->[Send CONNECT_REQUEST]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CONNECT_BOOTSTRAP is a state entered by the ULA calling API Connect,
before receiving the acknowledgement of the remote end to the
connection initialization packet.
5.4. CONNECT_AFFIRMING
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---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.ACK_CONNECT_REQ]-->[Notify]
|-->{Callback return to accept}
|-->{EoT}
|-->{ULA-flushing}-->COMMITTING2
-->[Send PERSIST with EoT]
|-->{Not ULA-flushing}-->PEER_COMMIT
-->[Send PERSIST with EoT]
|-->{Not EoT}
|-->{ULA-flushing}-->COMMITTING
-->[Send PERSIST without EoT]
|-->{Not ULA-flushing}-->ESTABLISHED
-->[Send PERSIST without EoT]
|-->{Callback return to reject]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CONNECT_AFFIRMING is a state entered by the ULA affirming to send
connect request after receiving the acknowledgement to the connection
initialization packet.
5.5. CHALLENGING
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|<-->[API: Send{new data}]{just pre-buffer}
|--[Rcv.PERSIST]
|-->{EoT}
|-->{ULA-flushing}-->CLOSABLE-->[Notify]
-->[Send SNACK]
|-->{Not ULA-flushing}-->PEER_COMMIT-->[Notify]
-->[Send SNACK]
|-->{Not EoT}
|-->{ULA-flushing}-->COMMITTED-->[Notify]
-->[Send delay SNACK]
|-->{Not ULA-flushing}-->ESTABLISHED-->[Notify]
-->[Send delay SNACK]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CHALLENGING is a state entered by the ULA accepting the connection
request after a new connection context has been incarnated. The new
connection is incarnated by the FSP context of the near end in the
LISTENING state as a legitimate CONNECT_REQUEST packet is received.
5.6. ACTIVE
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[
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{flush}]-->COMMITTING{Urge to commit}
|<-->[API: Send{more data}][Send PURE_DATA]
|<-->[Rcv.PERSIST][Send KEEP_ALIVE]
|--[Rcv.PURE_DATA]
|--{EoT}-->PEER_COMMIT
|-->[Send SNACK]-->[Notify]
|--{Not EoT}-->[Send SNACK]-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
ACTIVE, also known as ESTABLISHED, is a state that the FSP
participant has finished end-to-end negotiation but has not committed
current transmit transaction nor fully received the latest transmit
transaction of the remote end.
5.7. COMMITTING
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.SNACK]{Acknowledge-All}-->COMMITTED-->[Notify]
|--[Rcv.PURE_DATA]
|--{EoT}-->COMMITTING2-->[Send SNACK]-->[Notify]
|--{Not EoT}-->[Send SNACK]-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RELEASE]
|--{All-Acknowledged}-->SHUT_REQUESTED
|-->[Send SNACK]-->[Notify]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
COMMITTING is a state that the FSP participant has committed the
transmit transaction but has not fully received the latest transmit
transaction of the remote end, nor the acknowledgement to the
transmit transaction commitment has been received.
The participant in COMMITTING state SHALL NOT transmit further data
until current transmit transaction commitment is acknowledged.
5.8. COMMITTED
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---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{more data}]-->ACTIVE-->[Send PERSIST]
|--[API: Send{flush}]-->COMMITTING-->{Flush the send queue}
|<-->[Rcv.PERSIST][Send KEEP_ALIVE]
|--[Rcv.PURE_DATA]
|-->{EoT}-->CLOSABLE
-->[Send SNACK]-->[Notify]
|-->{Not EoT}-->[Send SNACK]-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RELEASE]-->SHUT_REQUESTED
-->[Send SNACK]-->[Notify]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
COMMITTED is a state that the FSP participant has committed current
transmit transaction and has received the acknowledgement to the
transmit transaction commitment, but has not fully received the
latest transmit transaction of the remote end.
5.9. PEER_COMMIT
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{flush}]
-->{Mark EoT or append payload-less PURE_DATA with EoT set}
-->COMMITTING2-->{Do Send}
|--[API: Shutdown]-->PRE_CLOSED-->{Append RELEASE}
-->{Do Send}
|<-->[API: Send{more data}][Send PURE_DATA]
|<-->[Rcv.PURE_DATA]{just prebuffer}
|--[Rcv.PERSIST]
|<-->{EoT}-->[Send SNACK]
--{&& is new transaction}-->[Notify]
|-->{Not EoT}-->ACTIVE-->[Send SNACK]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
PEER_COMMIT is a state that the FSP participant has not committed
current transmit transaction but has fully received the latest
transmit transaction of the remote end, and the acknowledgement to
the transmit transaction commitment has not been received yet.
5.10. COMMITTING2
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---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{flush}]
-->{Mark EoT or append payload-less PURE_DATA with EoT set}
-->COMMITTING2-->{Do Send}
|--[API: Shutdown]-->PRE_CLOSED-->{Append RELEASE}
-->{Do Send}
|<-->[API: Send{more data}][Send PURE_DATA]
|<-->[Rcv.PURE_DATA]{just prebuffer}
|--[Rcv.PERSIST]
|<-->{EoT}-->[Send SNACK]
--{&& is new transaction}-->[Notify]
|-->{Not EoT}-->COMMITTING-->[Send SNACK]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RELEASE]
|--{All-Acknowledged}-->SHUT_REQUESTED
|-->[Send SNACK]-->[Notify]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
COMMITTING2 is a state that the FSP participant has committed current
transmit transaction and has fully received the latest transmit
transaction of the remote end, but the acknowledgement to the
transmit transaction commitment has not been received yet.
The participant in COMMITTING2 state SHALL NOT transmit further data
until current transmit transaction commitment is acknowledged.
5.11. CLOSABLE
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Shutdown]-->PRE_CLOSED-->{Append RELEASE}-->{Do Send}
|<-->[Rcv.PURE_DATA]{just prebuffer}
|--[Rcv.SNACK]{Acknowledge All}-->CLOSABLE-->[Notify]
|--[Rcv.PERSIST]
|--{EoT}--{but a new transaction}
-->[Send SNACK]-->[Notify]
|--{Not EOT}-->COMMITTING-->[Send SNACK]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RELEASE]-->SHUT_REQUESTED
-->[Send SNACK]-->[Notify]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
CLOSABLE is a state that the FSP participant has committed current
transmit transaction and has received the acknowledgement to the
transmit transaction commitment, and has fully received the latest
transmit transaction of the remote end.
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5.12. SHUT_REQUESTED
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Shutdown]-->CLOSED-->[Notify]
|<-->[Rcv.RELEASE]-->[Send SNACK]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
SHUT_REQUESTED is a state entered when a legitimate RELEASE packet
was received in COMMITTED or CLOSABLE state. It may be entered as
well if the RELEASE packet was received in COMMITTING or COMMITTING2
state and all packets in flight were accumulatively acknowledged.
A connection context MAY persist in SHUT_REQUESTED state until the
session key runs out of life, or the host system needs to recycle the
resource allocated. A connection in SHUT_REQUESTED state MAY be
resurrected.
5.13. PRE_CLOSED
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.SNACK]{Acknowledge All}-->CLOSED-->[Notify]
|--[Rcv.RELEASE]-->[Notify]-->CLOSED
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->CLOSED-->[Notify]
PRE_CLOSED is a state entered on the ULA calling the API Shutdown in
PEER_COMMIT or CLOSABLE state.
Note that the ULA may call the API Shutdown in COMMITTING2 state as
well, where it SHALL wait the FSP layer to get the accumulative
acknowledgement to all packets in flight before sending the RELEASE
packet.
5.14. CLOSED
|--{On Recycling Needed}-->NON_EXISTENT
CLOSED is a state migrated from PRE_CLOSED state on receiving a
legitimate KEEP_ALIVE packet which acknowledges all packet in flight
from the remote end, or from SHUT_REQUESTED state on the ULA calling
the API Shutdown.
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Unlike TCP [STD7], CLOSED state in FSP is not fictional. Instead a
connection context MAY persist in CLOSED state until the session key
runs out of life, or the host system needs to recycle the resource
allocated to the CLOSED session. A connection in CLOSED state MAY be
resurrected.
5.15. CLONING
---[API: Reset]-->NON_EXISTENT
|<-->[API: Send{new data}]{just prebuffer}
|<-->[Rcv.PURE_DATA]{just prebuffer}
|--[Rcv.PERSIST]
|-->{Not EoT}
|--{&& Not ULA-flushing}-->ACTIVE
-->[Send SNACK]-->[Notify]
|--{&& ULA-flushing}-->COMMITTED
-->[Send SNACK]-->[Notify]
|-->{EoT}
|--{&& Not ULA-flushing}-->PEER_COMMIT
-->[Send SNACK]-->[Notify]
|--{&& ULA-flushing}-->CLOSABLE
-->[Send SNACK]-->[Notify]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CLONING is a state entered by ULA calling the API Multiply from any
state that may accepting an out-of-band packet.
5.16. Passive Multiplication
{ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT, COMMITTING2, CLOSABLE}
|-->/MULTIPLY/-->[API{Callback}]-->{new context}
|-->[{Return Accept}]
|-->{Send packet(s) starting with PERSIST}
|-->[{Return Reject}]-->{abort creating new context}
-->[Send RESET]
In the ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT, COMMITTING2 or
CLOSABLE state an FSP end node MAY accept its peer's connection
multiplication request and transit to the unnamed, temporary passive
multiplication state.
5.17. Typical State Transitions
This section is informative.
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5.17.1. Typical Main Connection
*** Bootstrapping ***
CONNECT_BOOTSTRAP ------ INIT_CONNECT -------> LISTENING
| <---- ACK_CONNECT_INIT -----
CONNECT_AFFIRMING ------ CONNECT_REQUEST ----> |
*** Connection affirmation, carrying welcome messages ***
|
{Accept}
{and send a single packet welcome message immediately}
|
| <- ACK_CONNECT_REQ c/w EoT - CHALLENGING
PEER_COMMITTED
|
{Callback, to send ticket immediately}
{(a fictional identification token of a single packet)}
|
COMMITTING2 ----- PERSIST c/w EoT -----> |
CLOSABLE
| <---- KEEP_ALIVE(SNACK) ---- |
CLOSABLE
|
{Send Server's Challenge}
|
| <----- PERSIST w/o EoT ----- PEER_COMMITED
COMMITTED ---- KEEP_ALIVE(SNACK) ---->
.
.
. |
{Flush}
|
| <---- PURE_DATA c/w EoT ---- COMMITTING2
CLOSABLE
---- KEEP_ALIVE(SNACK) ----> |
CLOSABLE
|
{Send Client's Response}
|
PEER_COMMITTED ----- PERSIST w/o EoT -----> |
COMMITTED
| <--- KEEP_ALIVE(SNACK) ----- |
.
| ---- PURE_DATA w/o EoT ----> COMMITTED
PEER_COMMITTED <--- KEEP_ALIVE(SNACK) ---- |
.
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.
| .
{Flush}
|
COMMITTING2 ---- PURE_DATA c/w EoT ----> |
CLOSABLE
| <---- KEEP_ALIVE(SNACK) ----
CLOSABLE
** Typical C/S request-response exchange on application layer **
|
{Send Request}
|
PEER_COMMITTED ----- PERSIST w/o EoT -----> |
COMMITTED
| <--- KEEP_ALIVE(SNACK) ----- |
.
| ---- PURE_DATA w/o EoT ----> COMMITTED
PEER_COMMITTED <--- KEEP_ALIVE(SNACK) ----- |
.
.
| .
{Flush}
|
COMMITTING2 ---- PURE_DATA c/w EoT ----> |
CLOSABLE
| <---- KEEP_ALIVE(SNACK) ----
CLOSALBE
{Send Response}
|
| <----- PERSIST w/o EoT ----- PEER_COMMITED
COMMITTED
---- KEEP_ALIVE(SNACK) ----> |
.
| <---- PURE_DATA w/o EoT ---- PEER_COMMITED
COMMITTED ---- KEEP_ALIVE(SNACK) ----> |
.
.
.
{Flush}
|
| <---- PURE_DATA c/w EoT ---- COMMITTING2
CLOSABLE
---- KEEP_ALIVE(SNACK) ----> |
CLOSALBE
.
.
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.
*** Following request-responses, e.g. HTTP pipelining ***
.
.
.
CLOSABLE CLOSALBE
.
.
*** End of connection, in a typical C/S application ***
|
{Shutdown}
|
| <---------- RELEASE -------- PRE_CLOSED
SHUT_REQUESTED
---- KEEP_ALIVE(SNACK) ----> |
| CLOSED
{Shutdown}
|
CLOSED
5.17.2. Typical Clone Connection for Get Resource
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Client Server
*** Suppose the browser fork a new connection to request ***
*** some resource and the URI is short enough to be ***
*** encapsulated in a single packet ***
{MultiplyAndWrite}
| {In Clonable State}
CLONING ---- MULTIPLY c/w EoT ----> *
{Make Clone Connection}
{and return resource data immediately}
|
| <---- PERSIST w/o EoT ------ PEER_COMMITTED
COMMITTED ---- KEEP_ALIVE(SNACK) ---->
<---- PUER_DATA w/o EoT ---- PEER_COMMITTED
COMMITTED ---- KEEP_ALIVE(SNACK) ---->
.
.
. |
{Flush}
|
| <--- PURE_DATA c/w EoT ----- COMMITTING2
CLOSABLE
---- KEEP_ALIVE(SNACK) ----> |
CLOSABLE
.
.
*** End of Connection ***
5.17.3. Typical Clone Connection for Push Message
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Initiator of Multiplication Responder of Multiplication
*** Suppose the server fork a new connection to push message ***
(Used to be server side) (Used to be client side)
|
{MultiplyAndWrite}
| {In Clonable State}
CLONING ---- MULTIPLY w/o EoT ----> *
{Make Clone Connection}
*** suppose no immediately available responding data ***
|
COMMITTING
| <--- PERIST(c/w EoT) ---- |
PEER_COMMITTED
| ---- KEEP_ALIVE(SNACK) ----> COMMITTED
.
| ---- PURE_DATA w/o EoT ----> COMMITTED
PEER_COMMITTED <--- KEEP_ALIVE(SNACK) ---- |
.
.
| .
{Flush}
|
COMMITTING2 ---- PURE_DATA c/w EoT ----> |
CLOSABLE
| <---- KEEP_ALIVE(SNACK) ----
CLOSABLE
.
.
*** End of Connection ***
5.17.4. Simultaneous Shutdown
CLOSABLE CLOSABLE
| |
{Shutdown} {Shutdown}
| |
PRE_CLOSED PRE_CLOSED
| \ / |
| \ / |
| \ / |
| \------------- RELEASE --------------/----->+
+<------------------- RELEASE ------------/ |
| CLOSED
CLOSED
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6. End-to-End Negotiation
End-to-end negotiation of FSP session occurs in the connection
establishment phase. Connection establishment process of FSP
consists of two and a half pairs of packet exchanges for connection
initialization, connection incarnation and the last confirmation.
During the process various optional header or payload MAY be carried
in the FSP preliminary packets to negotiate end-to-end session
parameters.
6.1. Connect Initialization
The initiator sends the INIT_CONNECT packet to the responder:
(INIT_CONNECT, Salt, Timestamp, Init-Check-Code [, Responder's Host
Name])
Connection initialization MAY be syndicated with optional address
resolution at the gateway in the IPv6 network by carrying the
responder's host name in the INIT_CONNECT packet.
If it does carry the responder's host name it MUST take the link-
local interface address [RFC4291] as the source IPv6 address and the
default link-local gateway address, FE80::1, as the destination IPv6
address no matter whether the global unicast IP address of the
default gateway is configured.
If the gateway that relays the INIT_CONNECT packet finds that the
responder is on the same link-local network with the initiator it
SHALL change the source and the destination IP addresses of the
INIT_CONNECT packet to the link-local IP addresses of the initiator
and the responder respectively, and relay the packet onto the same
link-local network.
On receiving the INIT_CONNECT packet that carries the responder's
host name the link-local gateway MUST resolute the responder's global
unicast IPv6 address and map the initiator's global unicast IPv6
address, and replace the destination and source address of the
INIT_CONNECT packet respectively, unless it finds that the initiator
and the responder are on the same link-local network, where the
gateway SHALL process the packet as stated in the previous statement.
The gateway SHALL silently ignore the INIT_CONNECT packet if it is
unable to resolve the IP address of the responder.
If the destination address is the default link-local gateway address
while the INIT_CONNECT does not carry the responder's host name
payload, it is supposed that the gateway is the intent destination of
the connection to initialize.
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6.2. Response to Connect Initialization
The responder sends acknowledgment to the initiator:
(ACK_INIT_CONNECT, Time-delta, Cookie, Init-Check-Code Reflected,
Responder's Sink Parameter)
If the responder is ready to accept the connection, it SHALL generate
a cookie which is meant to be reflected by the initiator. The
responder MUST send the ACK_INIT_CONNECT packet with the new
allocated local ULTID instead of the original listening ULTID. The
initiator should be able to find out the original listening ULTID by
searching its own connection context.
In the Responder's Sink Parameter the original listener ULTID MUST be
set to the right value.
The destination address of the packet sent back MUST be set to the
source address of the corresponding Connect Initialization packet
whose source and destination address MAY be updated by some
intermediary such as the link-local gateway of the initiator.
The responder SHALL NOT make state transition on receiving
INIT_CONNECT packet.
If the responder refuses to accept the connection, it SHALL silently
discard the INIT_CONNECT packet.
6.3. Connection Incarnation Request
(CONNECT_REQUEST, Salt, Timestamp, Init-Check-Code, Initial SN, Time-
delta Reflected, Cookie Reflected, Initiator's Sink Parameter [,
Initiator's Host Name])
The initiator accepts the Response to Connect Initialization packet
if and only if both the destination ULTID of the response packet
matches the source ULTID of the connect initialization packet and the
Init-Check-Code reflected in the response packet matches the Init-
Check-Code in the connect initialization packet.
If the response packet is accepted the initiator formally requests to
establish the connection by sending the CONECT_REQUEST packet.
In the CONNECT_REQUEST packet the value of the Timestamp, the Init-
Check-Code and the Salt field MUST be the same as in the INIT_CONNECT
packet while the value of the Cookie Reflected field and the Time-
delta Reflected field MUST be the same as in the ACK_INIT_ CONNECT
packet, respectively.
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The initiator MUST send the packet towards the remote ULTID that the
responder has preserved and sent with the ACK_INIT_CONNECT packet.
It MUST fill the original listener ID field in the Initiator's Sink
Parameter with the right value.
The source address of the CONNECT_REQUEST packet MUST be set to the
destination address of the received ACK_INIT_CONNECT packet, while
the network prefix and host-id part of the destination address MUST
be set to the source address of the received ACK_INIT_CONNECT packet
in the IPv6 network.
The initiator SHALL save the cookie value that the responder has
given to make up the weak session key.
The initiator MUST fill the Initial SN field with the sequence number
of the packet that will follow CONNECT_REQUEST. The CONNECT_REQUEST
packet is payload free and does not consume the sequence space.
The optional fields Initiator's Host Name is put as the payload of
the CONNECT_REQUEST packet. If presented it MAY be exploited by the
responder as the last resort to resolute the most recent IP address
of the initiator in some extraordinary scenarios such as the
initiator has hibernated for a considerably long time.
6.4. Connection Incarnation Response
Case 1: (ACK_CONNECT_REQ, FREWS, Initial SN, Expected SN, ICC[,
Payload])
Case 2: (RESET, Reason of Failure, Timestamp Reflected, Copy of
Cookie Reflected)
The responder responds as in case 1 if the reflected cookie was
validated, resources were successfully allocated and the initial
context of the connection was setup. Otherwise it SHOULD respond as
in case 2.
However, if the cookie is invalid, the responder SHALL silently
discard the CONNECT_REQUEST packet.
The Initial SN in case 1 is the initial sequence number of the
responder. The responder should fill in the field with a random 32-
bit unsigned integer. As the ACK_CONNECT_REQ packet may carry
payload the sequence number of the responder starts from the
ACK_CONNECT_REQ packet.
The Expected SN MUST equal to the Initial SN specified in the
corresponding CONNECT_ REQUEST packet.
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6.5. The Last Confirmation
Case 1: (PERSIST, FREWS, Initial SN, Expected SN, ICC, payload)
Case 2: (RESET, Reason of Failure, Initial SN, Expected SN, ICC)
The initiator of the connection MUST eventually confirm to the
responder that the connection is established by sending a PERSIST
packet (case 1).
Of course the initiator MAY quit to establish the connection by
sending a legitimate RESET packet (case 2).
6.6. Retransmission
The initiator SHALL retransmit the INIT_CONNECT packet if the
corresponding ACK_INIT_CONNECT packet is not received in some limit
time (by default 15 seconds).
The initiator SHALL retransmit the CONNECT_CONNECT packet if the
corresponding ACK_CONNECT_REQ packet is not received in some limit
time (by default 15 seconds).
The responder SHALL NOT retransmit ACK_INIT_CONNECT or
ACK_CONNECT_REQ packet.
The initiator SHOULD retransmit the right INIT_CONNECT packet or
CONNECT_CONNECT packet until the legitimate ACK_CONNECT_REQ packet is
eventually received.
It SHALL give up if the time starting from the very first
INIT_CONNECT packet was sent has exceed a longer timed-out value (by
default 60 seconds) before the legitimate ACK_CONNECT_REQ packet is
received.
7. Quad-party Session Key Installation
It is assumed that in the scenarios applying FSP it is the ULA to do
key establishment and/or end-point authentication while the FSP layer
provides authenticated, optionally encrypted data transfer service.
The ULA installs the established shared secret key as the new session
key of the FSP layer. Together they establish a secure channel
between two application end-points.
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In a typical scenario the ULA endpoints first setup the FSP
connection where resistance against connection redirection is weakly
enforced by CRC64. After the pair of ULA endpoints have established
a shared secret key, they install the secret key. Authenticity of
the FSP packets sent later is cryptographically protected by the new
secret key and resistance against various attacks is secured.
Although transmit transaction is actually uni-directional the secret
key is shared bi-directionally in this version of FSP.
Protocol for installation of the shared secret key is quad-party in
the sense that both the upper layer application and the FSP layer of
both the participant nodes MUST agree on the moment of certain state
to install the shared secret key.
It is arguably much more flexible for the application layer protocols
to adopt new key establishment algorithm while offloading routine
authentication and optionally encryption of the data to the
underlying layers where it may be much easier to exploit hardware-
acceleration.
7.1. API for Session Key Installation
A dedicate application program interface (API) is designed for the
ULA to install the secret key established by the ULA participants.
The API SHOULD take four parameters:
* A 'handle' to state the connection context for installing the
session key
* A octet string of initial key materials (IKM)
* An integer to state the length of IKM. The unit is octet.
* An integer to state the desired length of the effective session
key if AEAD is applied. The unit is bit. For this version of FSP
desired length of the effective session key is either 128 or 256.
The peer MUST have commit a transmit transaction and it SHALL install
the same secret key on receiving the FSP packet with the EoT flag
set.
The ULA SHOULD have installed the new shared secret key, or install
it instantly after accepting the packet with the EoT flag set. If
the new secret key has ever been installed the packet received after
the one with the EoT flag set MUST adopt the new secret key.
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7.2. Time to Call API for Session Key Installation
A participant MAY install new session key if and only if the packet
with the latest sequence number it has received has EoT flag marked.
7.3. Time to Take New Session Key into Effect
By committing a transmit transaction a ULA participant clearly tells
the underlying FSP layer that the next packet sent MAY adopt a new
secret key. On receiving a packet with the EoT flag set the ULA is
informed that the next packet received MAY adopt a new shared secret
key.
After the ULA of a network node installed a new session key, every
packet to send with sequence number later than the one with the EoT
flag set just before the API to install session key was called MUST
adopt the new session key in the FSP layer of the network node.
Every packet received with the sequence number later than the one
with EoT flag set when the ULA called the API to install session key
MUST be validated with the new session key. If the new secret key
has ever been installed the packet received after the one with the
EoT flag set MUST adopt the new secret key.
7.4. Generating the Initial Session Key
When the ULA install the secret key, it is required to provide the
initial key material which might have unbalanced bit randomness, not
the session key itself. HMAC-based Extract-and-Expand Key Derivation
Function (HKDF) [RFC5869] is applied to generate the initial session
key.
Given raw key material ikm, length of the ikm nB in octets, intended
master key length lenb in bits, || is octet string concatenation,
If AEAD is designated, the initial session key, or the first secret
key for packet authentication and payload encryption is obtained as
specified in [RFC5869]:
Key Extract phase Let Km = HMAC-SM3k512(zeros, ikm), where:
zeros is 64 octets of zeroes
ikm is the input initial key material
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HMAC-SM3k512 is applied. HMAC-SM3k512 is the HMAC algorithm
[RFC2104] that exploits SM3 secure hash algorithm [ISO-SM3]
with a slight modification that exploits initial key with
length of 512 bits instead of 256 bits.
Km is the result master key.
Key Expand phase: Let Ks = HMAC-SM3k512(Km, info), where:
Km is the master key generated in previous phase, padded to 512
bits with zeroes at right.
info is concatenation of the arbitrary ASCII string
"Establishes an FSP session", which is 26-octet long, 3 octets
of integer 0, and 1 octet of integer 1.
HMAC-SM3k512 algorithm is applied.
Ks is the result of 256 bits in length. If the requested key
length is 128-bit or 192-bit, Ks is the final result. If the
requested key length is 256-bit, the second iteration of HKDF
MUST be applied to get the final result of 512 bits in lenth.
For this version of FSP the final result is split into three parts,
the initial session key of requested key length, the 32-bit salt, and
the remain bits that are simply discarded. The salt is to be applied
to compose the initialization vector(IV), which would be passed to
AES-GCM, together with the sequence number and expected sequence
number fields in the normal FSP fixed header:
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Expected Sequence Number/Out-of-band Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7.5. Internal Rekeying
Let Ks' = HMAC-SM3k512(Km, H || info') , where:
Km is the master key generated as in section 7.4, padded to 512 bits
with zeros at right.
H is the 16-octet internal hash sub-key of AES-GCM of previous
session key
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info' is concatenation of the arbitrary ASCII string "Sustains an
FSP connection", which is 26-octet long and the 4 octets in
network order of the 32-bit unsigned integer that specifies the
batch index of the session key.
HMAC-SM3k512 is applied.
Ks' is the result of 256 bits in length.
For this version of FSP, if the session key length is 128-bit or
192-bit, the leftmost bits in key length of the result Ks' is taken
as the new session key, the following 32 bits is taken as the new
salt that is to be applied to compose the IV as the input to AES-GCM.
If the key length is 256-bit, the result is taken as the new session
key and the salt SHALL NOT be changed.
The batch index of the initial session key is 1, and it is increased
by 1 every time before it is to re-key.
7.6. Sample Sequence of Installing Session Key
This section is informative.
Node A Node B
ULA-A FSP-A FSP-B ULA-B
{Send Km-A}
->[seq_a2b_0] ->
{Send Km-B}
<- [seq_b2a_0]<-
.
.
.
{Commit}
->[seq_a2b_m c/w EoT] ->
{Install Key}
.
{Wait} .
.
{Commit}
<- [seq_b2a_n c/w EoT]<-
{Install Key}
.
. {Send Further}
<- [seq_b2a_n+1]<-
.
{Send Further} .
->[seq_a2b_m+1] ->
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Send Km-A, Send Km-B ULA of node A and node B send there key
material for key establishment, respectively.
Commit ULA of node A or node B informs the FSP layer to set the End
of Transaction flag of the last packet to send and flush the send
buffer.
Install Key ULA of node A or node B informs the FSP layer to install
new session key, giving key materials for deriving the session
key. A node may call Install Key if and only if its peer has just
committed a transmit transaction.
Wait The ULA MUST wait until it has received some packet with EoT
set from its peer before it may install new session key. There is
no mandatory calling order of Commit and Install Key. However, if
a node Commit before Install Key and it wants to apply new session
key for the transmit transaction next to the one it has just
committed, it SHALL NOT send further data until Install Key has
returned successfully. In the above example, for node A packet
with sequence number [seq_a2b_m+1] will be sent by applying the
new session key, for node B packet with sequence number
[seq_b2a_n+1] will be sent by applying the new session key.
Send Further ULA of node A or node B sends further data in the new
transmit transaction, respectively. There is no mandatory order
on which node should start new transmit transaction firstly.
8. Send and Receive
8.1. Packet Integrity Protection
8.1.1. Application of CRC64
Starting from ACK_CONNECT_REQUEST, until the ULAs have installed the
shared secret CRC64 is applied to calculate the value of the ICC
field. The algorithm:
1. Take pair of the ULDs as the initial value of accumulative CRC64
2. Accumulate the value of the Init-Check-Code field
3. Accumulate the value of the Cookie field successively
4. Accumulate the combined value of the salt and the timeDelta field
where the former is the leftmost 32 bits and the latter is the
rightmost 32 bits
5. Accumulate the value of the Time Stamp field
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6. Save the accumulated CRC64 value as the pre-computed CRC64 value
The pair of the ULDs is composed of the near end's ULTID and the
remote end's ULTID, where the former is the leftmost 32 bits and the
latter is the rightmost 32 bits of initial value for the send
direction, and the order is reversed for the receive direction.
When calculate the value ICC of a particular FSP packet, firstly set
ICC to the pre-computed CRC64 value, then calculate the CRC64
checksum of the whole FSP packet, while ULTIDs are NOT included if
the FSP packet is encapsulated in UDP. The result is set as the
final value of the ICC field.
8.1.2. Authenticated Encryption with Additional Data
FSP provides per-packet authenticated encryption service. Only one
authenticated encryption algorithm is allowed for a determined
version of FSP. For this FSP version, the authenticated encryption
algorithm selected is GCM-AES [GCM][AES], it is applied to protect
integrity of the full FSP packets, and privacy of the payload
together with the extension headers, if any. The four inputs to GCM-
AES authenticated encryption are:
K: the key derived by the master key installed by ULA. The length of
the session key is determined by the ULA.
IV: the initial vector, 96-bit string made by concatenating a 32-bit
salt, the 32-bit sequence number of the packet and the 32-bit
expected sequence number field of the packet. The salt is derived by
the master key installed by ULA.
P: the plaintext are the bytes following the fixed header up to the
end of the original payload.
AAD: additional authenticated data, for this version of FSP it
consists of first 128 bits of the fixed header of the FSP packet.
The source ULTID MUST be stored in the leftmost 32-bit of the ICC
field while the destination ULTID MUST be stored in the rightmost
32-bit of the ICC field before the ICC value is calculated.
The length of the authentication tag MUST be 64 bits for FSP version
0 and 1. The authentication tag is stored in the ICC finally.
The inputs to GCM-AES decryption are:
K: the key derived by the master key installed by ULA. The length of
the session key is determined by the ULA.
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IV: the initial vector, 96-bit string made by concatenating consisted
of the 32-bit salt, the 32-bit sequence number of the packet and the
32-bit expected sequence number field of the packet.
C: the cipher-text are the bytes following the fixed header up to the
end of the received payload.
AAD: additional authenticated data, for this version of FSP it
consists of the first 128 bits of the fixed header of the FSP packet.
The sender's ULTID MUST be stored in the leftmost 32-bit of the ICC
field while the receiver's ULTID MUST be stored in the rightmost
32-bit of the ICC field before the ICC value is calculated.
T: The authentication tag, which is fetched from the ICC field
received.
Only when the outputs of GCM-AES decryption tell that the
authentication tag passed verification may the receiver deliver the
decrypted payload to the ULA.
8.1.3. ICC of the Out-of-Band Packet
When calculating the ICC of an out-band packet (KEEP_ALIVE or
MULTIPLY), the ExpectedSN field SHALL be filled with the out-of- band
serial number. The first 32-bit word of the fixed header is taken as
the second salt.
To get or check the ICC of the out-of-band packet the original salt
value that is set on deriving the session key and stored in the
internal security context MUST be XORed with the second salt value
before applying GCM-AES. The original salt value MUST be recovered
instantly after GCM-AES is applied.
8.2. Start a New Transmit Transaction
The responder starts a transmit transaction by send the
ACK_CONNECT_REQ packet which MAY terminate the transmit transaction
at the same time.
Any party MAY start a new transmit transaction by sending a PERSIST
packet:
(PERSIST, FREWS, SN, ExpectedSN, ICC, Payload)
PERSIST packet sent by the initiator firstly acknowledges the
ACK_CONNECT_REQ packet as well.
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8.3. Send a Pure Data Packet
(PURE_DATA, FREWS, SN, ExpectedSN, ICC, Payload)
After a new transmit transaction has been started further PURE_DATA
packet MAY be sent until a packet with EoT flag set is sent.
8.4. Commit a Transmit Transaction
8.4.1. Initiate Transmit Transaction Commitment
A participant of an FSP connection MAY notify its peer that a
transmit transaction shall be committed by setting the EoT flag of
the last packet of the transmit transaction, be it PERSIST, PURE_DATA
or MULTIPLY.
8.4.2. Respond to Transmit Transaction Commitment
(KEEP_ALIVE, FREWS, SN, ExpectedSN, ICC, Sink Parameter, SNACK)
Whenever a legitimate packet falls in the receive window of the
receiver, and the packet fills in the last gap of the sequence of
current transmit transaction on receiving direction, or the packet
with same sequence number has been accepted already, a responding
KEEP_ALIVE packet that accumulatively acknowledges all the packets
sent by the remote end SHALL be sent back immediately, and the FSP
layer MUST immediately notify the ULA that a transmit transaction has
been committed.
The sequence number (SN) of the KEEP_ALIVE packet MUST equal the
latest sequence number of the legitimate packets that have been sent.
The out-of-band serial number SHALL increase by one whenever a new
KEEP_ALIVE packet is sent.
Here the KEEP_ALIVE packet SHALL contain a SNACK extension header,
although number of gap descriptors in the SNACK header MUST be 0.
8.4.3. Finalize Transmit Transaction Commitment
After receiving the KEEP_ALIVE packet that accumulatively
acknowledges all the packets sent the sender of the EoT flag migrates
to the COMMITTED or CLOSABLE state from the COMMITTING or COMMITTING2
state, respectively.
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8.4.4. Time-out for Committing Transmit Transaction
The ULA SHALL be timed-out if there is no packet was acknowledged in
some hard-coded time-out. For this version of FSP the time-out is
set to 30 seconds.
8.5. Retransmission
8.5.1. Calculation of RTT
We borrows specifications for calculating RTT (and RTO) considerably
from Computing TCP's Retransmission Timer [RFC6298] to calculate
Retransmission Time Out (RTO).
The sender maintains two state variables, SRTT (smoothed round-trip
time) and RTTVAR (round-trip time variation). In addition, we assume
a clock granularity of G seconds.
Initial round trip time (RTT) for the Connection Initiator: Equals to
the mean of the time elapsed when ACK_ INIT_CONNECT was received
since INIT_CONNECT was sent, and the time elapsed till
ACK_CONNECT_REQ was received since CONNECT_REQUEST was sent.
Initial RTT for the Connection Responder: Equals to the time elapsed
when the CONNECT_REQUEST packet was received since the
ACK_INIT_CONNECT packet had been received.
Initial RTT for the Initiator of Connection Multiplication: Equals to
the most recent RTT of the multiplied connection.
Initial RTT for the Responder of Connection Multiplication: Equals to
the most recent RTT of the multiplied connection.
When the Initial RTT measurement R is made, the host MUST set
SRTT <- R
RTTVAR <- R/2
When a subsequent RTT measurement R' is made, a host MUST set
RTTVAR <- (1 - beta) * RTTVAR + beta * |SRTT - R'|
SRTT <- (1 - alpha) * SRTT + alpha * R'
The value of SRTT used in the update to RTTVAR is its value before
updating SRTT itself using the second assignment. That is, updating
RTTVAR and SRTT MUST be computed in the above order.
The above SHOULD be computed using alpha=1/8 and beta=1/4.
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R' SHOULD be measured whenever a packet with the SNACK extension
header is received.
Suppose the packet with the latest SN that is accumulatively
acknowledged is P-latest, R' equals the time when the SNACK header is
received, minus the time when P-latest was sent, minus the delay that
the acknowledgment was made.
The delay that the acknowledgment was made is stored in the
"Acknowledgement Delay" field of the SNACK header. It equals the
time difference between the time when the acknowledgement was sent
and the time when P-latest was received.
Note that the no packet with SN later than any gap described in the
SNACK header is considered as the packet with the latest SN that is
accumulatively acknowledged.
8.5.2. Generation and transmission of SNACK
Whenever the receiver receives a packet it SHALL shift the time to
send next heartbeat signal earlier to the time of RTT since current
time, if the time to send next heartbeat signal used to be later. If
the time is already earlier than the time of RTT since current time,
it needs not be shifted.
On the time to send the heartbeat signal the FSP node generates the
SNACK header, then generate and send a new KEEP_ALIVE packet to carry
the SNACK header.
8.5.3. Negative acknowledgment of Packets Sent
KEEP_ALIVE packets in FSP carry the SNACK extension headers. We call
them SNACK packets. A SNACK packet P1 is said to be later than P0,
if and only if SN of P1 is later than SN of P0, or SN of P1 equals SN
of P0 while the out-of-band sequence number of P1 is later than that
of P0.
By convention when we specify the range, the left square bracket
meant to be inclusive, while the right parenthesis meant to be
exclusive, the packets with SN in the ranges:
[expectedSN, expectedSN + 1st Gap Width),
[expectedSN + 1st Gap Width + 1st Data Length, expectedSN + 1st Gap
Width + 1st DataLength + 2nd Gap Width), ...
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[expectedSN + 1st Gap Width + 1st Data Length... + (n-1)th Gap Width
+ (n-1)th Data Length, expectedSN + 1st Gap Width + 1st DataLength...
+ n-th Gap Width)
together with the packets with SN later than (expectedSN + 1st Gap
Width + 1st DataLength + ... + n-th Gap Width), these packets are
assumed to be negatively acknowledged.
8.5.4. Retransmission Interval
Until RTT measurement has been made for a packet sent between the
sender and receiver, the sender SHOULD set RTO <- 1 second.
After computing new SRTT, a host MUST updated RTO <- SRTT + max (G,
K*RTTVAR) where K = 4.
Clock granularity SHOULD be finer than 100msec, that is, it SHOULD be
that G <= 0.1 second.
Whenever RTO is computed, if it is less than 1 second, then the RTO
SHOULD be rounded up to 1 second.
An implementation MUST manage the retransmission timer(s) in such a
way that A packet is never retransmitted less than one RTO after the
previous transmission of that packet.
Every time an in-band packet is sent (including a retransmission), if
the timer is not running, start it running so that it will expire
after RTO seconds (for the current value of RTO).
When all outstanding data has been acknowledged, turn off the
retransmission timer.
When the retransmission timer expires, retransmit the packets that
have not been acknowledged by the receiver, but limit by the rate
throttling mechanism.
Rate of retransmission MUST be throttled in a way that No more that
M/2 packets may be retransmitted in a clock interval, suppose in each
clock interval M packets were sent averagely.
Packet retransmission SHALL be subjected to congestion control as
well.
However, at least one packet MAY be retransmitted in one clock
interval, provide that the retransmission timer expires for the first
packet that has not been acknowledged yet.
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8.6. Flow Control
The participants of an FSP connection negotiate the initial receive
window size with the FREWS field in the ACK_CONNECT_REQ packet, and
the first PERSIST packet that acknowledges the ACK_CONNECT_REQ
packet, respectively. The receive window size SHALL NOT be less than
4 and SHALL be less than 2^24.
An FSP participant advertises current receive window size in the
FREWS field.
An FSP participant SHALL NOT send a packet whose sequence number is
later than the value of the ExpectedSN field plus the advertised
receive window size, where both value come from the very packet
received with the latest sequence number.
8.7. Congestion Control
FSP supposes that end-to-end congestion control is provided by some
shim layer, such as the congestion manager [RFC3124] between the
"traditional" IP layer and the FSP transport layer. The shim layer
is considered as a sub-layer of the network layer. Implementation of
FSP MUST provide such shim layer if the network layer of the end node
does not provide end-to-end congestion management service.
FSP layer SHALL provide following information to the congestion
manager as soon as the first packet on the fly was acknowledged by
any mean, or a legitimate packet falling in the receive window with
the ECE flag set is received:
* The local interface number that the packet carrying the ECE signal
is accepted.
* The remote network prefix that the congestion information is meant
to associate. Note that the aggregated host ID part is NOT
included in the prefix.
* The traffic class. For FSP it is bisected: MIND flag set or not.
* Number of outstanding octets, including all of those in the
payload AND the FSP headers.
* The effective round trip time calculated in the most recent
period. Note that retransmitted packets MUST be excluded on
calculating the effective RTT.
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* Whether an ECN-Echo signal was received. The ECE flag of a
legitimate packet falling in the receive window is the ECN-Echo
signal.
* Whether a sent packet with SRR flag set is acknowledged.
The congestion manager SHOULD reduce the send rate if the FSP sender
informed it that an ECN-Echo signal was received.
The sender SHALL NOT inform the congestion manager to reduce the send
rate again even if further packet with ECE flag set is received,
until at least one sent packet with SRR flag set is acknowledged.
A packet with ECE flag set received after the packet with SRR flag
set is acknowledged SHOULD make the congestion manager reduce the
send rate again.
Retransmitted packet SHALL be subjected to send rate control at the
underlying congestion management service sub-layer as well.
Quota or other means to enforce fairness among various FSP
connections SHOULD be provided directly to the ULA by the congestion
management service.
Requirement of an FSP congestion manager would be detailed in a
separate document.
8.8. On-the-Wire Compression
FSP exploits the lossless compression algorithm as per [LZ4].
If the CPR flag of the first packet of a transmit transaction is set,
compression is applied on the payload octet stream of the transaction
transaction.
When applying compression FSP divides source stream into multiple
blocks. For this version of FSP length of each block is 128KiB
(131072 octets), except the final block whose length may be less than
or equal to 128KiB. The final block is the one that terminate the
transmit transaction, i.e. which contains the last FSP packet of the
transmit transaction. The last FSP packet of the transmit
transaction has the EoT flag set. The "LZ4_compress_fast_continue"
method SHALL be applied on each block. That is, data from previous
compressed blocks are taken use for better compression ratio.
When transferring the result data of compressing each block, the
result data is prefixed with its length. The length is expressed by
a 4-octets little-endian integer.
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On-the-wire compression of each transmit transactions is independent.
It is the upper layer application that SHALL make agreement on which
transmit transaction utilizes on-the-wire compression.
8.9. Milk Like Payload and Minimal Delay Service
An ordinary data flow is wine-like in the sense that the older data
are more valuable. If it has to, data packet sent latest are dropped
first. In the contrary, milk-like payload is that the newer data are
more precious and outdated data packet can be discarded.
When ULA is willing to accept incomplete message the peer of the
underling FSP node SHALL set the MIND flag of the first PERSIST
packet that starts the first transmit transaction, and set the MIND
flag of every following PURE_DATA packet, while set the Traffic Class
of the underlying IPv6 packet to some registered value.
In the transmission path, any relaying middle box, be it router or
switch, should reserve a reasonably short queue for the packet flow
of such flow to minimize delay.
When the receive buffer overflows the receiver discards the
undelivered packet received first to free buffer space for the latest
packet received. However it keeps order on delivering the packets to
he ULA. ULA may choose to discard packets received earlier than some
threshold.
The receiver SHOULD NOT make any acknowledgement to the packet
received with the MIND flag set.
Minimal delay service is asymmetric in the sense that one
transmission direction the data flow may be milk-like while in the
reverse direction the data flow may be wine-like.
A minimal delay service data flow is terminated by ULA via some out-
of-band control mechanism.
9. Connection Multiplication
Connection multiplication is the process of incarnating a new
connection context by re-using security context of an established
connection.
9.1. Request to Multiply Connection
(MULTIPLY, FREWS, SN, Salt, ICC [, Sink Parameter] [, payload])
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The initiator's initial sequence number of the new connection is the
sequence number of the packet that piggybacks the connection
multiplication header. The ExpectedSN field of the normal packet
store a Salt value instead.
The FREWS field MUST be processed in the new connection context while
the ICC MUST be calculated with the session key of the original
connection.
The new connection inherits the remaining key life. ULA SHOULD
negotiate new session key and/or install new session key as soon as
possible.
The optional payload of the MULTIPLY packet MUST be processed in the
new connection context.
The MULTIPLY packet is an out-of-band command packet in the original
connection context.
9.2. Response to Connection Multiplication Request
Case 1: (PERSIST, FREWS, SN, ExpectedSN, ICC, Payload)
Case 2: (RESET, Reason of Failure, SN, ExpectedSN, ICC)
In all of these cases the ULTID of the remote-end MUST be the value
of the initiator's ULTID in the connection multiplication header.
It is REQUIRED that only a connection in the ESTABLISHED, COMMITTING,
COMMITTED, PEER_COMMIT, COMMITTING2 or CLOSABLE state may accept a
connection multiplication request.
In case 1 the responder admits the multiplication request AND commit
the transmit transaction, the new connection enters into the
PEER_COMMIT or CLOSABLE state immediately, on request of ULA.
In case 2 the responder admits the multiplication request and the new
connection enters into the ESTABLISHED, PEER_COMMIT, COMMITTING or
CLOSABLE state immediately, depending whether the ULA of the
multiplication initiator has requested to commit the transmit
transaction immediately and whether the ULA of the multiplication
responder has requested to commit the transmit transaction in the
reverse direction immediately.
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In case 3 the responder rejects the multiplication request. To
defend against spoofing attack ICC MUST be valid. The value of the
SN field MUST equal the value of the 'Expected SN' field of the
requesting MULTIPLY packet while the value of ExpectedSN field MUST
equal the value of the 'Sequence No' field.
The new connection MUST derive new session key from the session key
of the original connection where the out-of-band requesting MULTIPLY
packet is received immediately.
9.3. Duplicate Detection of Connection Multiplication Request
Every time the responder of connection multiplication receives a
MULTIPLY packet it MUST check the suggested responder's ULTID and the
initiator's ULTID.
The responder MUST reject the multiplication request if the suggested
responder's ULTID equals the near-end ULTID of some connection and
the remote-end ULTID of that connection does not equal the
initiator's ULTID.
The responder MUST recognize the MULTIPLY packet as a duplicate
connection request if some connection matches the request and SHOULD
response by retransmitting the head packet of the send queue of the
matching connection. A connection matches the MULTIPLY request if
and only if the suggested responder's ULTID in the MULTIPLY packet
equals the near-end ULTID of the connection and the initiator's ULTID
equals the remote-end ULTID of the connection.
9.4. Retransmission
The initiating side SHALL retransmit the MULTIPLY packet if the
corresponding PERSIST packet is not received in some limit time (by
default 15 seconds).
9.5. Key Derivation for Branch Connection
Let K_out = HMAC-SM3k512(Km, [d] || Label || 0x00 || Context || L),
where:
Km is the master key, padded to 512 bits with zeros at right,
[d] is one octet of integer Depth. For this version of FSP it is
the fixed number 1 for the first iteration,
Label is the fixed ASCII string "Multiply an FSP connection" which
is 26-octet long for this version of FSP,
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Context is concatenation of two 32-bit words idB and idR idB is
the ULTID allocated for the branch connection in the context of
the multiplication initiator. idB is byte-order neutral. idR is
the receiver side ULTID of the original connection that is to
accept the connection multiplication request. idI or idR is byte-
order neutral.
L is a 32-bit network byte-order integer specifying the length in
bits of the derived key K-out
The result K_out is of 256 bits in length. If the requested key
length is 128-bit or 192-bit, leftmost bits of the key requested
length of K_out is taken as the session key of the new branch
connection, the following 32 bits is taken as the salt to be
applied to compose the IV for AES-GCM.
If the requested key length is 256-bit, K_out is taken as the
session key of the new branch connection while the salt to be
applied to compose the IV for AES-GCM in the original connection
is simply inheritted.
10. Mobility and Multihome Support
10.1. Heartbeat Signals
FSP requires that the participants periodically send the heartbeat
signals.
The participant in the ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT,
COMMITING2 or CLOSABLE state MUST send the KEEP_ ALIVE packet as the
heart-beat signal periodically to retain the connection in case that
underlying IP address has changed.
(KEEP_ALIVE, FREWS, SN, ExpectedSN, ICC, Sink Parameter, SNACK)
Heartbeat signal packet is an out-of-band control packet. It does
not carry payload. The sequence number of the packet SHALL be set to
the latest sequence number of all of the packets that have been sent.
Only the FSP node in the ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT,
COMMITING2 or CLOSABLE state MAY process the heartbeat signal.
In this version of FSP the heartbeat period is arbitrarily set to 600
seconds.
The sequence number (SN) of the heartbeat signal packet MUST equal
the latest sequence number of the legitimate packets that have been
sent.
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The out-of-band serial number SHALL increase by one whenever a new
hearbeat signal packet is sent.
10.2. Active Address Change Signaling
During communication process the FSP participant whose underlying IP
address is changed SHOULD inform its peer such change by transmit a
heartbeat signal packet so that the peer can retransmit the packets
that were negatively acknowledged, if any.
Such informing hearbeat signal packet SHALL be sent in the ACTIVE,
COMMITTING, COMMITTED, PEER_COMMIT, COMMITING2 or CLOSABLE state.
Informing heartbeat signal packet SHOULD be sent more frequently than
a normal heartbeat signaling packet.
For this version of FSP informing heartbeat signal packet SHALL be
retransmitted every 4 RTT interval until the heuristic
acknowledgement is received.
10.3. Heuristic Remote Address Change Adaptation
A participant of the FSP connection SHALL set the source address of
the packet to be transmitted (or retransmitted) to the new IPv6
address as soon as the near-end IPv6 address has changed. However,
the ULTID field MUST remain the same.
When a new packet with a later sequence number is received and the
source IP address of the packet is found to be different with the
preserved IP address of the remote end, the receiver SHOULD
automatically update the preserved IP address of the remote end to
the source IP address of the new packet, unless there is a Sink
Parameter header in the packet.
If the sequence number of the packet received is not the latest in
the receive window the preserved IP address of the remote end SHALL
NOT be updated even if the source address of the received packet has
changed.
10.4. Heuristic Address Change Acknowledgement
The address change signaling heartbeat signal packet is supposed to
be acknowledged if a packet targeted at the new IP address that the
heartbeat signal packet has informed is received.
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10.5. NAT-traversal and Multihoming
When FSP is implemented over UDP in the IPv4 network, each endpoint
of the FSP connection is bound one and only one IPv4 address as soon
as the connection is established. Each endpoint SHALL choose the
source IPv4 address of the last packet received as the destination
IPv4 address of the packet that it is to send later. By this mean
FSP over UDP is NAT-friendly.
When FSP is implemented over IPv6, as soon as the connection is
established the IPv6 address may be changed dynamically, and one more
alternate IP address may be added or removed dynamically for
individual endpoint as well, provided that ULTIDs and host-IDs all
IPv6 addresses of the endpoint keep the same value at any given
moment.
The sender may choose as the source IP address by selecting any
network prefix that it has most-recently sent to its peer in the
allowed address list field of the Sink Parameter header, joining with
the host ID in the Sink Parameter header and the stable ULTID of the
sender, and choose as the destination IP address by selecting any
network prefix in the allowed address list field of the Sink
Parameter header most-recently received from its peer, joining with
the peer's host ID and the peer's ULTID. Thus multiple multi-homed
paths MAY co-exist between the two FSP endpoints.
10.6. Explicit Multi-home Informing
If an FSP end node is configured with multiply global unicast IPv6
address, it MAY advertise multiple underlying addresses to the remote
end by put them in the addressable network prefix list of the Sink
Parameter extension header. The Sink Parameter extension header may
be carried in the CONNECT_REQUEST, ACK_CONNECT_REQ, PERSIST, MULTIPLY
or KEEP_ALIVE packet.
Any participant of the communication SHALL NOT make discrimination of
the source or destination IP address of any packet provided that both
the source ULTID and the destination ULTID keep unchanged and the ICC
field passes verification.
11. Graceful Shutdown
One participant of an FSP connection MAY initiate graceful shutdown
of the connection if and only if its peer has committed the most
recent transmit transaction.
By initiating graceful shutdown the participant tells its peer that
current transmit transaction is to be committed as well.
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11.1. Initiation of Graceful Shutdown
(RELEASE, FREWS, SN, ExpectedSN, ICC)
An FSP end node MAY initiate graceful shutdown if it is in the
PEER_COMMIT, COMMITTING2 or CLOSABLE state. It SHALL NOT initiate
graceful shutdown if its peer has not committed current transmit
transaction.
Graceful shutdown is signaled to the remote end by sending a RELEASE
command packet. The FSP end node SHALL migrate to the PRE_CLOSED
state just before sending the RELEASE packet.
11.2. Acknowledgment of Graceful Shutdown
The RELEASE packet may be accepted in the COMMITTING, COMMITTED,
COMMITTING2, CLOSABLE or PRE_CLOSED state.
If the legitimate RELEASE packet is received in the COMMITTING or
COMMITTING2 state, the FSP end node SHALL buffer the RELEASE packet,
wait each packet of the last transmit transaction of its peer has
been received, deliver all the buffered payload and then migrate to
the SHUT_REQUESTED state.
If the legitimate RELEASE packet is received in the COMMITTED or
CLOSABLE state, the FSP end node SHALL migrate to the SHUT_REQUESTED
state immediately.
In either of the two cases the receiver of the RELEASE packet SHALL
acknowledge the sender of the RELEASE packet with a legitimate out-
of-band KEEP_ALIVE packet.
Note that out-of-order RELEASE packet MAY be discarded in the
COMMITTED or CLOSABLE state.
If the RELEASE packet is received in the PRE_CLOSED state, it is to
finalize the graceful shutdown procedure.
11.3. Finalization of Graceful Shutdown
If either the legitimate RELEASE packet or the legitimate KEEP_ALIVE
packet is received in the PRE_CLOSED state the grace shutdown request
is supposed to be acknowledged and the shutdown procedure SHALL be
finalized by that the FSP end node migrates to the CLOSED state
immediately.
In SHUT_REQUESTED state the FSP node SHALL migrate to CLOSED state
immediately on the Shutdown API called by the ULA.
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11.4. Retransmission of RELEASE Packet
The FSP end node in the PRE_CLOSED state SHALL retransmit the RELEASE
packet until it migrates to CLOSED state or it is timed out.
As RELEASE is the in-band packet retransmission of the RELEASE packet
is subjected to the normal retransmission rule.
12. Timeouts and Abrupt Close
12.1. Timeouts in End-to-End Negotiation
Initially the initiator is in the CONNECT_BOOTSTRAP state. It
migrates to the CONNECT_ AFFIRMING state after it received the
legitimate ACK_INIT_CONNECT packet. Then it migrates to the
PEER_COMMIT or CLOSABLE state after it received the legitimate
ACK_CONNECT _REQ packet, depending on the hint of ULA.
The responder incarnates a new connection context which is initially
in the CHALLENGING state after accepting a legitimate Connect Request
packet. Then it migrates to the COMMITTING or CLOSABLE state,
depending on the packet received from its peer.
If the initiator or the responder is unable to migrate to a new state
in some limit time (by default 60 seconds, except in LISTENING state)
it aborts the connection by recycling the connection context.
12.2. Timeouts in Multiply
Initially the initiating side of Connection Multiplication is in the
CLONING state. It migrates to the ACTIVE, COMMITTED, PEER_COMMIT or
CLOSABLE state after it received the legitimate PERSIST packet.
Which state to migrated depends on the EoT flag of the initiating
MULTIPLY packet and the responding PERSIST packet.
If the initiating side is unable to migrate to a new state in some
limit time (by default 60 seconds) it aborts multiplication by
recycling the new connection context.
12.3. Timeout of Transmit Transaction Commitment
The FSP node MUST abort the connection if the time of no packet
having arrived has exceed certain limit in the COMMITTING or
COMMITTING2 state.
In this FSP version, timeout of transmit transaction commitment is
set to 5 minutes.
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12.4. Timeout of Graceful Shutdown
It simply migrates to the NON_EXISTENT pseudo-state if timeout in the
PRE_CLOSED state.
In this FSP version, timeout of Graceful Shutdown is set to 1 minute.
12.5. Idle Timeout
If one participant has not received any packet nor has it sent any
packet in some limit time, it MUST be abruptly closed.
In this FSP version the time limit, or the idle timeout, is set to 4
hours.
12.6. Session Key Timeout
For this FSP version if a secret key is applied for more than 2^30
times the FSP node MUST abruptly closed instantly.
12.7. Abrupt Close
An FSP node abruptly shutdown a session by sending a RESET packet and
release all of the resource occupied by the the session immediately.
(RESET, Reason of Failure, SN, ExpectedSN, ICC)
13. Security Considerations
13.1. Deny of Service Attack
FSP is designed to mitigate effect of DoS attack by exploiting
Cookie.
However, resistance against distributed DoS attack relies on external
mechanism.
13.2. Replay Attack
In-band sequence number and out-of-band sequence number are exploited
to resist against replay attack.
13.3. Passive Attacks
AEAD MAY be exploited by the ULA to protect it against passive
attacks such as eavesdropping, gaining advantage by analyzing the
data sent.
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MAC only service MAY also be utilized. Together with application
layer stream-mode encryption it protects the ULA against passive
attacks as well.
13.4. Masquerade Attack
Both AEAD and MAC only service may be exploited to protect the
endpoints against masquerade attack.
If proxy pattern for syndicated name resolution is exploited for FSP
over IPv6, secure neighbor discovery [RFC3971] SHOULD be applied
instead of common neighbor discovery whenever it is feasible.
13.5. Active Man-In-The-Middle Attack
The ULA SHALL take account to protect itself against MITM attack when
making client authentication and key establishment.
13.6. Privacy Concerns
It is beneficial for privacy protection that the ULTID of each
endpoints of an FSP connection is generated randomly [RFC7721].
14. IANA Considerations
It should be requested that the port number registered for UDP
packets encapsulating FSP in the IPv4 network. The port number 18003
is exploited in the concept prototype implementation. The number is
the decimal presentation of ASCII codes of the character 'F' ('x46')
and 'S' ('x53') concatenated in network byte order.
It should be requested that the 'Next Header'/protocol number is
assigned for FSP over IPv6. Decimal number 144 is exploited in the
concept prototype implementation.
15. References
15.1. Normative References
[AES] NIST, "Advanced Encryption Standard (AES)", November 2001.
[CRC64] ECMA, "Data Interchange on 12.7 mm 48-Track Magnetic Tape
Cartridges - DLT1 Format Standard, Annex B", December
1992.
[GCM] NIST, "Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC", November 2007.
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[LZ4] "LZ4: Extremely Fast Compression algorithm",
<https://lz4.github.io/lz4/>.
[OSI_RM] ISO and IEC, "Information technology-Open Systems
Interconnection - Basic Reference Model: The Basic Model",
November 1994.
[R01] Rogaway, P., "Authenticated encryption with Associated
Data", 2002.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, DOI 10.17487/RFC2526, March 1999,
<https://www.rfc-editor.org/info/rfc2526>.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, DOI 10.17487/RFC2663, August 1999,
<https://www.rfc-editor.org/info/rfc2663>.
[RFC3124] Balakrishnan, H. and S. Seshan, "The Congestion Manager",
RFC 3124, DOI 10.17487/RFC3124, June 2001,
<https://www.rfc-editor.org/info/rfc3124>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
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[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 4106, DOI 10.17487/RFC4106, June 2005,
<https://www.rfc-editor.org/info/rfc4106>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007,
<https://www.rfc-editor.org/info/rfc5056>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
<https://www.rfc-editor.org/info/rfc8273>.
[STD5] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981, <https://www.rfc-editor.org/rfc/rfc791>.
[STD6] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980, <https://www.rfc-editor.org/rfc/rfc768>.
[STD7] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981,
<https://www.rfc-editor.org/rfc/rfc793>.
15.2. Informative References
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[Gao2002] Gao, J., "Fuzzy-layering and its suggestion", IETF Mail
Archive, September 2002,
<https://mailarchive.ietf.org/arch/msg/ietf/u-6i-6f-
Etuvh80-SUuRbSCDTwg>.
[ISO-SM3] Standardization, I. O. F., "IT Security techniques --
Hash-functions -- Part 3: Dedicated hash-functions", ISO/
IEC 10118-3:2018, October 2018,
<https://www.iso.org/standard/67116.html>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
DOI 10.17487/RFC3022, January 2001,
<https://www.rfc-editor.org/info/rfc3022>.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<https://www.rfc-editor.org/info/rfc3596>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
<https://www.rfc-editor.org/info/rfc4555>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
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[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC5942] Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
Model: The Relationship between Links and Subnet
Prefixes", RFC 5942, DOI 10.17487/RFC5942, July 2010,
<https://www.rfc-editor.org/info/rfc5942>.
[RFC6177] Narten, T., Huston, G., and L. Roberts, "IPv6 Address
Assignment to End Sites", BCP 157, RFC 6177,
DOI 10.17487/RFC6177, March 2011,
<https://www.rfc-editor.org/info/rfc6177>.
[RFC6298] Paxson, V., Allman, M., Chu, J., and M. Sargent,
"Computing TCP's Retransmission Timer", RFC 6298,
DOI 10.17487/RFC6298, June 2011,
<https://www.rfc-editor.org/info/rfc6298>.
[RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis",
RFC 7050, DOI 10.17487/RFC7050, November 2013,
<https://www.rfc-editor.org/info/rfc7050>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
Appendix A. Issues for Further Study
A.1. Resolution of ULTID in DNS
There are two patterns of IP address resolution in FSP: the DNS-
compatible pattern and the proxy pattern. The former pattern relies
on some name service to resolve the IP address of the responder for
the initiator before they exchange end-to-end negotiation packets.
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In the DNS-compatible pattern, the responder side of the FSP
participants registered its address identifier, such as 'domain name'
in some name service such as DNS [RFC1034][RFC1035], according to
some pre-agreement at first. The initiator resolves the current IP
address of the responder by consulting the name service, such as
looking after the A or AAAA record [RFC3596] of the domain name in
DNS.
If UDP over IPv4 is exploited as the under layer data packet delivery
service the port number of the responder is firstly resolved just
alike normal network application such as HTTP. Then it is extended
to 32-bit ULTID, and ULTIDs of FSP can be considered as the superset
of TCP port numbers.
If the string representation of IPv4/IPv6 address is applied directly
as the peer's address identifier instead of the domain name there is
no need for some real address resolution. But from the API caller's
point of view it is a DNS-compatible mode address resolution.
A.2. Proxy Pattern for Syndicated Name Resolution
The proxy pattern of IP address resolution in FSP is to embed the
address resolution information in the connection initialization
packets and is designed to work in FSP over IPv6 mode only.
In IPv6 network the rightmost 32 bits of the IPv6 address directly
maps to the ULTID so FSP does not need additional multiplexing
mechanism such as port number. And it needs not consult SRV record
or look for some entry in some 'services' file.
If the INIT_CONNECT packet carries the responder's host name it MUST
take the link-local interface address as the source IPv6 address and
the default link-local gateway address, FE80::1, as the destination
IPv6 address no matter whether the global unicast IP address of the
default gateway is configured. In such scenario the link-local
gateway MUST be able to resolute the responder's host name to its
global unicast IPv6 address, and the gateway MUST be able to map the
initiator's link local address to its global unicast IPv6 address.
If the gateway that relays the INIT_CONNECT packet finds that the
responder is on the same link-local network with the initiator it
SHALL change the source and the destination IP addresses of the
INIT_CONNECT packet to the link-local IP addresses of the initiator
and the responder respectively, and relay the packet onto the same
link-local network.
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On receiving the INIT_CONNECT packet that carries the responder's
host name the link-local gateway MUST resolute the responder's global
unicast IPv6 address and map the initiator's global unicast IPv6
address, and replace the destination and source address of the
INIT_CONNECT packet respectively, unless it finds that the initiator
and the responder are on the same link-local network, where the
gateway SHALL process the packet as stated in the previous statement.
A.3. Asymmetric Transmission
If there is one participant whose receive interface is not the same
as the send interface the participant is called an asymmetric-
transmission node.
Asymmetric transmission itself is asymmetric in the sense that one
participant may be asymmetric-transmission node while its peer is a
normal node that the send interface is the same receive interface.
An end node is asymmetric-transmission if it received an
ACK_CONNECT_REQ packet or PERSIST packet whose source IP address that
the network interface accepting the packets reported is not in the
allowed IP address list in the Sink Parameter header of the packet.
For an asymmetric-transmission remote end, the near end cannot rely
on automatic IP address change detection. Instead IP address change
notification mechanism shall be utilized.
However for this version of FSP asymmetric transmission support is
optional.
Appendix B. Choices of Design Goals
B.1. Optimizing towards IPv6
FSP intends to promote IPv6 for sake of transparent end-to-end
connectivity.
B.1.1. Goal: More Efficient Use of the IPv6 Address Space
The length of an IPv6 address is 128 bits. Practices of IPv4 NAPT
show that address space of 48 bits is sufficient. There could be
optimization space for more efficient use of the IPv6 address space.
It could be argued that every IPv6 network node is effectively a
router. And it could be argued that this opinion is implicitly
supported by "Unique IPv6 Prefix per Host" [RFC8273].
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It could be argued that the upper layer application is the ultimate
IPv6 end-point as well.
B.1.2. Goal: NAT friendliness in IPv4 network
Network Address Translation and Port Translation (NAPT) [RFC2663]
works well for conserving global addresses and addressing multihoming
requirements because an IPv4 NAPT router implements three functions:
source address selection, next-hop resolution, and (optionally) DNS
resolution. It is mandatory for FSP to keep NAT-friendliness in the
IPv4 internetwork because NAT middleboxes are ubiquitous.
B.1.3. Non-Goal: NAT friendliness in IPv6 network
It is both feasible and preferable to avoid NAT in the IPv6
internetwork for sake of transparent end-to-end connectivity.
B.2. Hardware-Accelerated Cryptography
Hardware implementation efficiency and popularity shall be the most
important factors of selecting the data integrity and confidentiality
protection algorithm.
First version of FSP exploits AES-GCM[AES][GCM], like in The Use of
Galois/Counter Mode (GCM) in IPsec Encapsulating Security Payload
(ESP) [RFC4106].
Here it is explicitly proposed that the upper layer application
should take care of key establishment, and install the key
established onto the FSP layer, alike to the Use of Channel Bindings
to Secure Channels[RFC5056]. Reason behind the proposal is alike to
channel binding as well: 'the main goal of channel binding is to be
able to delegate cryptographic session protection to network layers
below the application in hopes of being able to better leverage
hardware implementations of cryptographic protocols'.
B.3. On-the-wire Compression
Because lots of content is compressible and compression saves
bandwidth, it is proposed that FSP shall support on-the-wire
compression.
LZ4 algorithm is chosen for it "features extremely fast decoder"
[LZ4]. Few well-known loss-less compression algorithm has higher
performance than LZ4 in terms of decompression speed.
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Besides, LZ4 offers a high compression derivative called LZ4_HC that
shares the same "extremely fast decoder" with the default compressor.
It is possible to pre-compress some content with LZ4_HC and serve it
to mass client, while each client decodes and gets the original
content with on-the-wire speed.
B.3.1. Goal: Compatibility with Pre-compression
From the sender side of view lots of content is pre-determined and
pre-compressible. It would be welcomed if the on-the-wire
compression algorithm chosen offers a high compression branch that
share the same on-the-wire speed decoder with the on-the-wire
encoder.
B.3.2. Goal: Goal: Decompression Speed
The decoder should run as fast as possible.
B.3.3. Goal: System Robustness
From the receiver point of view decompression may consume
unpredictable amount of memory resource. On-the-wire compression
service SHOULD be provided in the user space for sake of system
robustness. And the decoder should consume memory resource less than
the amount reasonably provided by a constrained node.
B.3.4. Non-Goal: Versatility of On-the-Wire Compression
Speed and system robustness should take precedence over compression
ratio on selecting the on-the-wire compression algorithm for FSP.
Appendix C. Acknowledgements
Author's Address
Jun-an Gao
Beijing Capital Highway Development Group Co.,Ltd.
Shoufa Plaza-A, Liuliqiao South, Fengtai
Beijing
People's Republic of China
Email: jagao@outlook.com
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