Internet DRAFT - draft-kaippallimalil-tsvwg-media-hdr-wireless
draft-kaippallimalil-tsvwg-media-hdr-wireless
TSVWG WG J. Kaippallimalil
Internet-Draft Futurewei
Intended status: Standards Track S. Gundavelli
Expires: 24 August 2023 Cisco
20 February 2023
Media Header Extensions for Wireless Networks
draft-kaippallimalil-tsvwg-media-hdr-wireless-01
Abstract
Wireless networks like 5G cellular or Wi-Fi experience significant
variations in link capacity over short intervals due to wireless
channel conditions, interference, or the end-user's movement. These
variations in capacity take place in the order of hundreds of
milliseconds and is much too fast for end-to-end congestion signaling
by itself to convey the changes for an application to adapt. Media
applications on the other hand demand both high throughput and low
latency, and are able to dynamically adjust the size and quality of a
stream to match available network bandwidth. However, catering to
such media flows over a radio link where the capacity changes rapidly
requires the buffers and QoS in general to be managed carefully.
This draft proposes additional information about the media
transported in each packet to manage the buffers and optimize the
scheduling of radio resources. The set of information proposed here
includes importance of the packet, burst length and time budget to be
conveyed by the media application in a new UDP option. The metadata
in the UDP option is used to provide the wireless network the
flexibility to prioritize packets that are essential when the radio
capacity is temporarily low, defer packets that can tolerate some
additional delay, or even drop packets selectively in more extreme
conditions.
This draft defines media metadata, a new UDP option to carry this
metadata and the operational aspects for using it between a UDP
source and a on-path wireless entity.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 24 August 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Media Metadata . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Design Criteria . . . . . . . . . . . . . . . . . . . . . 7
4.2. Metadata Parameters . . . . . . . . . . . . . . . . . . . 8
4.2.1. Profile . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.2. Timestamp . . . . . . . . . . . . . . . . . . . . . . 9
4.2.3. Media Data Unit Sequence . . . . . . . . . . . . . . 9
4.2.4. Packet Counter . . . . . . . . . . . . . . . . . . . 10
4.2.5. Importance . . . . . . . . . . . . . . . . . . . . . 10
4.2.6. Data Burst . . . . . . . . . . . . . . . . . . . . . 11
4.2.7. Delay Budget . . . . . . . . . . . . . . . . . . . . 12
4.3. Metadata Handling . . . . . . . . . . . . . . . . . . . . 12
5. Metadata Transport . . . . . . . . . . . . . . . . . . . . . 13
6. Common Deployments . . . . . . . . . . . . . . . . . . . . . 14
6.1. Data Center Deployment . . . . . . . . . . . . . . . . . 14
6.2. Security Gateways . . . . . . . . . . . . . . . . . . . . 15
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 17
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
Wireless networks inherently experience large variations in link
capacity due to a number of factors. These include the change in
wireless channel conditions, interference between proximate cells and
channels or as a result of the end user's movement. These variations
in link capacity take place in a short time in the order of hundreds
of milliseconds. End-to-end congestion control at the IP layer does
not react fast enough to these changes when a combination of high
throughput and low latency are required. Media packets on the other
hand typically demand both high throughput and low latency. The
application is able to adapt, but when the feedback signal (i.e., via
end-to-end congestion signaling or application level feedback) is of
low resolution and frequency compared to the changes in the network,
the result is that there is no means by which the application can
adjust the flow rate just enough, or to signal which packet (or group
of packets) have priority or which can tolerate more delay. If there
are short periods of low radio channel capacity, random packet drops
may also result in more damage than if a packet dropped is of a lower
importance (e.g., encoding of an enhanced layer and not a base
layer). 3GPP has studied enhancements in the wireless network in
[TR.23.700-60-3GPP] for such media applications that demand high
bandwidth and low latency. Some of the recommendations include
providing the wireless network with information on groups of media
packets that should be handled similarly (e.g., packets of a video
I-frame), the importance of a media packets and others that allow the
wireless network to schedule and forward packets more optimally.
Media packets that are fully encrypted and carry fragments of
multiple media streams in a packet are not easy to classify since it
depends on the sets of media being encoded and the application's
choices on packetization of the various streams. Examining or
inferring based on patterns or other heuristics is expensive,
unreliable and defeats the goal of minimizing sojourn time in the
wireless network. The simplest way is to examine metadata inserted
by the application as a basis for classification in the wireless
network. This is also inline with the recommendations in [RFC8558]
that discuss explicit signals to on-path network elements. Section 4
proposes a set of metadata that the wireless network can use to
optimize media packet forwarding in the wireless network.
Metadata inserted by a media application is transported across
trusted networks between the application server that inserts metadata
and the on-path wireless entity that uses it. The transport is
designed to allow carrying metadata for a range of media transports
including SRTP [RFC3711] and HTTP/3 media over QUIC. A new UDP
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option [I-D.ietf-tsvwg-udp-options] is proposed here to carry the
metadata. The trade-off in terms of lookup efficiency, protocol
overhead, the constraints for transporting metadata across trusted
networks and other related aspects are discussed in Section 3.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Terminology
The following terms is used in this document:
* Media Data Unit (MDU) - a set of one or more IP packets carrying a
media payload that should be treated as unit in the wireless
network. For example, packets of an MDU may be of a low priority
and all packets may be dropped in case of extreme congestion. In
protocols like RTP, the payload may consist of data of one media
type (e.g., a video I-frame) and in protocols like HTTP/3 that
carry multiple streams, each stream in the packet can potentially
carry a payload of different media types. In either case, the
application should classify the MDU that a packet belongs to and
in turn the network applies policies that treat the set of packets
of an MDU as a unit.
* Importance - The importance of a packet (or group of packets
belonging to an MDU) identify the priority of the packet(s),
dependency between packet(s) of an MDU to another (e.g., packets
of a video P-frame depend on an I-frame) and delivery preferences
when packet(s) are delayed due to congestion or temporary lack of
wireless resources. The application marks importance (and other
metadata) and the wireless network interprets the marking as
preferences when handling these media packets under reduced
wireless capacity. If an application marks all packets with the
same priority, the result would be random packet drop in the
wireless network in the presence of extreme congestion.
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3. Architecture
Section 1 has outlined the the issue around changes in link capacity
in a wireless network changes and the need for additional information
to handle such flows in the wireless network. This section provides
an end-to-end view of what the wireless network needs to optimize its
resource handling and the actions of clients, servers and entities in
the network to facilitate it.
UDP encrypted payload UDP encrypted payload + metadata
+-------------------+ +=========================+
/ \ / _____ \
/ _____ \ / ( ) \
/ ( ) +---V----+ ( ) \
+---V----+ (Wireless) |Wireless| ( IP ) +----o-----+
| Client +---( Network )--+ Node +--( Network )------+ Server |
+--------+ ( ) +--------+ ( ) +----------+
(UDP dest) (_____) ( ) (UDP source)
(_____)
Wireless Network Appl Network
|------------------------| |--------------|
Figure 1: Media Metadata in Application and Wireless network
Figure 1 shows an end-to-end view where a packet containing a media
payload from a server (e.g., a media server or relay) is sent to a
client (i.e., a wireless end point). The general assumption here is
that the server and on-path wireless node that serves the wireless
end point in Figure 1 are in two networks. These two networks share
a trust relationship that allows entities in these networks to
exchange media metadata. The relationship also limits the exposure
of the media metadata to authorized entities within the two networks.
A trusted domain (e.g., as outlined in [RFC8799]) associated to the
wireless and application networks with a public key and trust anchors
within each network have the ability to perform operations to
authorize, enroll, and manage nodes with specific policy and roles
(i.e., server, wireless node, gateways) for managing media metadata
handling in a secure manner. When the application (server, UDP
source) and wireless network are not directly connected, a secure
overlay network with encryption MUST be used between the two domains.
The server and client in Figure 1 have signalled to setup the media
session (e.g., using SDP, HTTP) prior to sending media packets. The
UDP source (e.g., an Application Server) is responsible for inserting
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relevant metadata based on the media content of the packet and using
the metadata format specified in Section 4. The metadata in the UDP
option is delivered to the wireless node (e.g., a 3GPP UPF) that
classifies it using the metadata in the packet along with other
network policies. The metadata and its transport are designed to be
efficient in processing and byte overhead per packet. The metadata
is expected to work with any UDP media including RTP, SRTP and
HTTP/3. Metadata parameters are encoded in binary format for compact
representation. Details are in Section 4.
The UDP option and metadata defined in this specification must only
be exchanged between entities that are trusted. The server (UDP
source) and Wireless Node (access router in wireless network) are
configured with data that allow establishment of trust between the
entities and the network(s) in between prior to the exchange of
metadata using the UDP option defined in this specification. When
there are insecure network segments in between, all packets that
carry the metadata in the MED UDP option must be secured with
encryption between these segments (e.g., secure GRE/VXLAN tunnel) or
at a flow level (e.g., with MASQUE proxies). Section 6 describes a
few common deployments.
The application server (server in Figure 1) is responsible for
inserting the metadata in the UDP option. The application server
determines the importance and other metadata parameters based on the
type of media encoded as well other information (e.g., configured
information on destination wireless network, live feedback from the
session). The application encrypts the payload (i.e., media content)
in the UDP packet and adds the MED UDP option to be processed in the
wireless network. Entities on-path do not process the UDP option,
but security gateways or other network entities at the boundary of a
trust domain may remove the option if there is an untrusted network
segment on-path. The wireless node receives UDP packet, inspects the
metadata in the UDP option and applies local policies to the metadata
to derive optimal scheduling and forwarding on the wireless path.
The wireless node does not examine the content of the packet which
may use various encrypted application transports like SRTP cryptex,
HTTP/3 and may have variable number of media streams.
4. Media Metadata
Media packets are encoded and formatted to enable efficient and
reliable processing of the data at both the encoding and decoding
endpoints. Media may consist of audio, live video, static pictures
and overlaid objects among others. Each of these may have different
tolerance to delays in the network, resiliency (i.e., the ability to
recover from loss) or even subjective importance (e.g., a loss of a
video base layer I-frame packets is more significant than enhanced
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layer P-frame). Media encoding is evolving continually and modern
codecs use complex prediction structures and make various dynamic
decisions in the encoding process. However, it is expected that
there are differences in priority, delay and acceptable loss across
sets of packets. This is information that the wireless network can
use to provide a better forwarding service especially when there is a
high demand of network resources and poor radio conditions.
The wireless network, unlike encoders and decoders, is not concerned
with decoding the media, but rather on deciding the best forwarding
options when its link capacity is limited. Since applications may
deliver media across 5G, WiFi or wired networks the attempt is for a
minimal set of metadata that is useful for optimizing handling of
media packets. The end-to-end aspects and metadata parameters are
described below.
4.1. Design Criteria
A media application that uses this specification provides a set of
metadata about the media packet that an authorized wireless network
can inspect and use to optimize handling during adverse radio
conditions. Metadata for media packets are carried in a new UDP
option discussed further in Section 5.
Metadata defined in Section 4.2 is broad enough to be applied
regardless of whether the application uses RTP, HTTP or another
application transport protocol.
The media application(server, or UDP source) is responsible for and
retains control over the metadata that is inserted at the UDP source.
The media application only inserts metadata if the destination
(wireless end point) is a device in a trusted wireless network. For
example, a range of IP addresses that belong to the trusted wireless
network. The wireless network verifies that a packet with MED UDP
option metadata has originated from a trusted server. The wireless
network that inspects metadata may defer or drop packets to optimize
the use of radio resources. The application may receive out of band
feedback on the quality and other statistics of the data received at
the UDP destination (e.g., RTCP receiver report). The application
may use heuristics or other algorithms on the feedback, explicit
network congestion information, encoding characteristics of the media
or other aspects of the data to obtain the desired handling in the
wireless network. Details of the mechanisms an application uses is
not in the scope of this document. The feedback provided allows the
application server (or UDP sender) to remain in control and determine
if there is any potential malicious or incoherent handling of media
packets. In such cases, the the application server (or UDP sender)
can revert to marking all packets with the same level of importance.
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The on-path wireless network entity that inspects metadata does not
rely on packets arriving in order. The metadata itself should
provide sufficient information and the network entity should factor
in these assumptions when calculating jitter and burst length using
the metadata in each packet. For example jitter may be calculated as
a moving average across multiple packets and burst length should
compensate for potential out-of-order packet arrivals especially
towards the tail end of a burst.
Metadata is transported in a new UDP option, MED, defined in
Section 5. The metadata in MED UDP option is carried in each packet
that the application server (or UDP source) inserts. Thus, the
wireless entity keeps some state information to use the metadata.
For example, a sequence counter is used to track the set of packets
that belong to a media data unit (MDU), and a series of timestamps
may be used to derive jitter. The different metadata parameters are
described below in Section 4.2.
This specification describes one set of metadata described as a
profile. A Profile field makes this specification extendable to
future specifications that describe a new metadata profile.
4.2. Metadata Parameters
The media application provides a set of metadata about the content of
the packet and the wireless network inspects the metadata and uses to
optimize handling during adverse radio conditions. Some information
that is useful to wireless networks include the importance of a
packet (or a group of packets), the number of packets in a burst,
timestamps and acceptable end-to-end latency of the packet.
Importance of a packet (or group of packets) is useful to provide
some flexibility to the radio scheduler to prioritize packets that
are essential during low capacity intervals and to defer packets that
can tolerate some additional delay, or even drop the packet. For
example, if some set of packets carry a stored video image that is
stored in advance, it may be able to tolerate some additional delay
over a real-time video encoding carried in another stream. Only the
media application is able to provide such information since even
inspecting a clear media header (e.g., RTP packet carrying an I-frame
fragment) does not provide the on-path network entity with sufficient
information as whether that represents live media, the length of a
data burst or the actual delay budget where the packet is useful for
decoding.
The parameters below identify a minimum set that an on-path network
entity can use for optimizing the use of wireless network resources.
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4.2.1. Profile
This parameter allows for more metadata profiles to be carried by the
MED UDP option. This specification only defines one profile.
0
0 1 2 3 4
+-+-+-+-+-+
| Profile |
+-+-+-+-+-+
Value Meaning
-----------------------------------------------------
0 RESERVED
1 Basic - defined in this specification
2-31 Unassigned (assignable by IANA)
Specifications may define a new metadata format in future using one
of the unassigned values.
4.2.2. Timestamp
Timestamp contains the wallclock time (absolute date and time) of
transmission of the packet and is represented in a compact format
where the first 16 bits represent seconds relative to 0h UTC on 1
January 1900, and the second 16 bits represent the fractional part of
a second.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A pair of timestamps S2 and S1 represent a time interval between them
of (S2 - S1) that have sequential Packet counter values. The
transmission time contained in the field may be used for network
jitter calculations.
4.2.3. Media Data Unit Sequence
The Media Data Unit (MDU) sequence is a cyclical counter that has the
same value for a set of packets identified by an application to be
treated as a unit (i.e., an MDU), and is incremented for the next
MDU.
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0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MDU Sequence |
+-+-+-+-+-+-+-+-+
The wireless network uses this field to provide consistent treatment
to the set of packets that belong to the same MDU. In some cases,
based on the priority and tolerance to delay and loss, the wireless
network may delay or drop the sequence of packets that has the same
MDU sequence value. An MDU sequence of 8-bits means that there can
be upto 256 (2^8) concurrent MDU sequences for a UDP source/
destination pair that a wireless network can distinguish.
The MDU sequence value is not itself associated to any set of media
properties. These media properties are defined in Importance, burst
length and delay in the sections that follow.
4.2.4. Packet Counter
This parameter provides a counter starting at "0" that is incremented
for each subsequent packet belonging to a Media Data Unit (MDU).
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The delay between subsequent packets of an MDU may be averaged or
otherwise used to extrapolate jitter in the arrival stream at the
wireless node.
4.2.5. Importance
Importance represents the media characteristics of the set of packets
that that form a media data unit (MDU) relative to the
characteristics of another MDU. The characteristics represented in
importance are the priority level, the ability to tolerate delay and
transmission errors.
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0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| L | D | P |
+-+-+-+-+-+-+-+-+
Value Meaning
-----------------------------------------------------
L Delay Tolerance
00 limited value if delayed
01 should be forwarded even if delayed
D Inter-MDU Dependency
000 No dependency Information provided
001 Independent
010 Base MDU
011 Enhanced MDU (dependent on previous base MDU)
P Priority level
001 high priority
010 medium priority
100 low priority
The application determines the priority of a packet in terms of how
critical the loss of packets of an MDU is for a destination/decoding
end. Some media frames may be extremely important but not as
sensitive to delay, others may be important and should be delivered
even past a delay deadline. There are various other factors such as
packets with medium or lower priority and varying tolerance for delay
that need to be considered.
The dependency flags indicate whether the packet is independent or
dependent on packets of other MDUs. TBD - specification/behavior of
the different values of priority.
4.2.6. Data Burst
The data burst field represents the number of byptes of data in a
continuous burst of packets. This may be the result of a large
amount of media encoded at a particular time. In many cases, the
distribution of packets tend to be heavy tailed and this information,
if available to the wireless network at the beginning of the burst,
is useful to let the wireless network know so that it can plan for
radio resources in advance. In RTP streams, a burst may for example
represent the number of bytes to send in a video I-frame. However,
in more complex encodings where the media in a packet belongs to
multiple streams (e.g., AR/VR), the application should determine the
length of a burst of data.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Burst |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If the value is set to "zero", it indicates that the application does
not provide the size of the data burst. All other values indicate
the actual size of the data burst in bytes upto a maximum of 2^32
bytes. The wireless node keeps track of the number of bytes in each
packet payload to determine the total number of bytes in a burst.
4.2.7. Delay Budget
The delay budget represents an upper bound in milliseconds between
the reception of the first packet of the MDU to the last packet of
the MDU.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Delay |
+-+-+-+-+-+-+-+-+
The delay budget along with data burst and importance (priority) is
used to convey to the wireless network in advance the duration of
time over which the burst of packets is sent. This can allow the
wireless scheduler to plan for the appropriate level of resources.
4.3. Metadata Handling
Metadata in this specification consists of the set of parameters in
Section 4.2 and always uses Profile value of "1".
The application server (UDP source) inserts the metadata into each
packet. The application server should only prepare metadata in UDP
MED option if the UDP destination belongs to a wireless network that
has a trust relationship with the application network. Importance,
data burst and delay budget parameters are the same for all packets
of an MDU (identified by an MDU sequence value for the UDP source/
destination). The timestamp indicates the sending time of each
packet while the packet counter is incremented for each packet in an
MDU.
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The wireless node that receives metadata in the UDP MED option should
verify that it orinated from an application network with which it has
a trust relationship. The metadata is used to prioritize, defer or
drop packets of an MDU when radio resources are limited.
5. Metadata Transport
Transport of metadata between the application and wireless network
may be based on one of several protocol options but it would be
preferable to have one mechanism (or limited number) so that wireless
network entities do not have to support a large number of options.
Some considerations include the ease with which an application can
encode the metadata in a transport header, compactness and efficiency
for lookup in the wireless network as this is applied per packet, and
the security of the metadata itself (not unique to wireless
networks). In this specification, the media metadata is transported
in UDP options. UDP transport of metadata is efficient and
applicable to not only HTTP/3 media but also RTP/SRTP for any further
extensions related to wireless networks.
A new UDP option, MED, that conforms to [I-D.ietf-tsvwg-udp-options]
is defined to carry media metadata. Figure 2 shows the parameters in
the MED UDP option. The Kind value for this option is (TBD - IANA
assigned). The MED option is a SAFE option as it does not alter the
UDP data payload in any manner and should therefore be assigned a
value in the 0..191 range as defined in [I-D.ietf-tsvwg-udp-options].
The length of this option can be variable since another specification
can define a new media "Profile" of a different length.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Kind=TBA2 | Len=17 | RES | Profile | Importance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MDU Sequence | Packet Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Burst |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delay |
+-+-+-+-+-+-+-+-+
Figure 2: MED UDP Option in Long Format
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The MED UDP option in this specification has a size of 17 bytes. In
this specification, the Profile option MUST be set to "1". Following
the length field, 3 bits are left reserved (RES) for future use. The
MDU sequence indicates the set of media data unit packets of the UDP/
IP datagram 5-tuple). The MDU sequence value should be the same for
all packets that form a media data unit (MDU) Other UDP/IP datagrams
(e.g., from the same server to another client) that have the same
value of MDU sequence represents a different MDU set. The Importance
of a packet includes its priority relative to other MDUs of the same
UDP/IP datagram (5-tuple). The Timestamp value in this option
represents the transmission time of the packet and along with Packet
counter may be used to derive latency and jitter information. For a
media flow/sequence identified by IP 5-tuple, the MDU sequence is
incremented for every subsequent MDU. The Packet counter represents
a sequence of packets of an MDU and may be used along with timestamps
to derive jitter. The wireless node does not attempt to sequence
packets arriving out of order using the Packet counter. The Data
burst when provided indicates the number of bytes of the MDU and this
value remains the same for all packets of the MDU. The Delay field
conveys the upper bound in milliseconds between the reception of the
first packet of the MDU to the last packet of the MDU. All packets
of an MDU have the same value of Delay.
The UDP source (application server) MUST NOT add the UDP MED option
if the UDP destination (wireless client) does not belong to a
wireless network that has a trust relationship with the application
network. The wireless network MUST NOT use metadata in the UDP MED
option of the UDP source (application server) does not belong to an
application network that has a trust relationship with it. The
wireless network MUST remove the UDP MED option before forwarding the
packet to the wireless node regardless of whether it originated from
a trusted or untrusted network.
A security gateway at the boundary of an application network or
wireless network that share a trust relationship should inspect the
UDP MED option to ensure that the origin/destination network comply
with the policies of the domain.
6. Common Deployments
This section provides a few examples of common deployments and the
use of the MED UDP option to carry media metadata.
6.1. Data Center Deployment
In this deployment scenario, the UDP source (i.e., App Server) and
the wireless network entity (i.e., Wireless Node) are within the same
Data Center and within a secure network.
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Wireless Network Provider App Provider
|----------------------------------| |---------------|
______ +--------------------------------+
( ) | +--------+ +----------+ |
+------+ (Wireless) | |Wireless| | App | |
|client/---------------------------/ /=======/ Server | |
+------+ (Network ) | | Node | +----------+ |
(______) | +--------+ |
+--------------------------------+
Data Center
/======/ UDP Packet with MED option
/------/ UDP Packet (no MED option)
Figure 3: Server and Wireless entity in Data Center
The UDP MED option is inserted by the Application Server and
forwarded. The network in between is within the boundaries of the
trust domain. The Wireless Node processes the metadata in the MED
UDP option and before forwarding the packet to the client (wireless
end point), the MED UDP option is removed.
6.2. Security Gateways
In this deployment scenario, the UDP sender (i.e, App Server) and the
wireless network entity (i.e., Wireless Node) have a trust
relationship between them and security gateways are used to encrypt
all traffic traversing an insecure network segment in between.
Wireless Network Provider Application Provider
|------------------------------| |------------------|
______
( ) +--------+ +---+ +---+ +--------+
+------+ (Wireless) |Wireless| |Sec|_________|Sec| | App |
|client/--------------/ /===+GW O____+____O GW+====/ Server |
+------+ (Network ) | Node | | | | | | +--------+
(______) +--------+ +---+ | +---+
V
Secure Tunnel
/======/ UDP Packet with MED option
/------/ UDP Packet (no MED option)
Figure 4: Security Gateways between Server and Wireless network
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The UDP MED option is sent between App Server and Wireless Node. The
Wireless Node removes the MED UDP option before forwarding the packet
onwards.
7. Acknowledgements
Thanks to Tiru Reddy for extensive discussions on security, metadata
and UDP options formats in this draft. Thanks to Dan Wing for input
on security and reliability of messages for this draft. Xavier De
Foy and the authors of this draft have discussed the similarities and
differences of this draft with the MoQ draft for carrying media
metadata.
8. IANA Considerations
IANA request to assign new kind from UDP option registry to be set by
IANA for [I-D.ietf-tsvwg-udp-options].
Kind Length Meaning
-----------------------------------------------------
TBA1 17 Media Metadata (MED)
9. Security Considerations
Metadata in the UDP option MED must only be exchanged between
entities that have a trust relationship that permits sending/
receiving this UDP option.
Metadata in the MED UDP option MUST NOT be sent to a wireless network
that does not have a trust relationship with the application network
(UDP source). A wireless network that receives a MED UDP option MUST
verify that the origin of the metadata is from a trusted network.
After processing the MED option, the wireless network node MUST
delete the option before forwarding the packet.
If the application network that sends the media packet with MED UDP
option and the wireless network that receives the UDP packet/MED
option are separated by an untrusted network, the traffic must be
encrypted across the untrusted network segment. Security gateways at
the boundary of the origin /destination networks SHOULD inspect to
verify that the MED UDP option to verify that the origin or
destination of the packet with UDP MED option are across the two
trusted networks.
10. References
10.1. Normative References
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[I-D.ietf-tsvwg-udp-options]
Touch, J. D., "Transport Options for UDP", Work in
Progress, Internet-Draft, draft-ietf-tsvwg-udp-options-19,
27 December 2022, <https://www.ietf.org/archive/id/draft-
ietf-tsvwg-udp-options-19.txt>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[draft-ietf-avtcore-cryptex-08]
IETF, "Encrypting RTP Header Extensions and Contributing
Sources", August 2022.
[I-D.iab-path-signals-collaboration]
Arkko, J., Hardie, T., Pauly, T., and M. Kühlewind,
"Considerations on Application - Network Collaboration
Using Path Signals", Work in Progress, Internet-Draft,
draft-iab-path-signals-collaboration-03, 3 February 2023,
<https://datatracker.ietf.org/doc/html/draft-iab-path-
signals-collaboration-03>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>.
[RFC8558] Hardie, T., Ed., "Transport Protocol Path Signals",
RFC 8558, DOI 10.17487/RFC8558, April 2019,
<https://www.rfc-editor.org/info/rfc8558>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
[TR.23.700-60-3GPP]
3rd Generation Partnership Project (3GPP), "Study on XR
(Extended Reality) and media services (Release 18)",
August 2022.
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Authors' Addresses
John Kaippallimalil
Futurewei
United States of America
Email: john.kaippallimalil@futurewei.com
Sri Gundavelli
Cisco
United States of America
Email: sgundave@cisco.com
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