Internet DRAFT - draft-hadi-forces-sctptml

draft-hadi-forces-sctptml






Network Working Group                                      J. Hadi Salim
Internet-Draft                                             ZNYX Networks
Expires: December 20, 2006                                 June 18, 2006


      SCTP based TML (Transport Mapping Layer) for ForCES protocol
                      draft-hadi-forces-sctptml-00

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines the SCTP based TML (Transport Mapping Layer)
   for the ForCES protocol.  It explains the rationale for choosing the
   SCTP (Stream Control Transmission Protocol) [RFC2960] and also
   describes how this TML addresses all the requirements described in
   [RFC3654] and the ForCES protocol [FE-PROTO] draft.







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Table of Contents

   1.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Protocol Framework Overview  . . . . . . . . . . . . . . . . .  3
     3.1.  The PL . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  The TML layer  . . . . . . . . . . . . . . . . . . . . . .  5
       3.2.1.  TML Parameterization . . . . . . . . . . . . . . . . .  6
     3.3.  The TML-PL interface . . . . . . . . . . . . . . . . . . .  6
   4.  SCTP TML overview  . . . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Introduction to SCTP . . . . . . . . . . . . . . . . . . .  7
     4.2.  Rationale for using SCTP for TML . . . . . . . . . . . . .  9
     4.3.  Meeting TML requirements . . . . . . . . . . . . . . . . .  9
       4.3.1.  Reliability  . . . . . . . . . . . . . . . . . . . . . 10
       4.3.2.  Congestion control . . . . . . . . . . . . . . . . . . 10
       4.3.3.  Timeliness and prioritization  . . . . . . . . . . . . 10
       4.3.4.  Addressing . . . . . . . . . . . . . . . . . . . . . . 10
       4.3.5.  HA . . . . . . . . . . . . . . . . . . . . . . . . . . 10
       4.3.6.  DOS prevention . . . . . . . . . . . . . . . . . . . . 11
       4.3.7.  Encapsulation  . . . . . . . . . . . . . . . . . . . . 11
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
   Intellectual Property and Copyright Statements . . . . . . . . . . 14























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1.  Definitions

   The following definitions are taken from [RFC3654]and [RFC3746]:

   ForCES Protocol -- The protocol used at the Fp reference point in the
   ForCES Framework in [RFC3746].

   ForCES Protocol Layer (ForCES PL) -- A layer in ForCES protocol
   architecture that defines the ForCES protocol architecture and the
   state transfer mechanisms as defined in [FE-PROTO].

   ForCES Protocol Transport Mapping Layer (ForCES TML) -- A layer in
   ForCES protocol architecture that specifically addresses the protocol
   message transportation issues, such as how the protocol messages are
   mapped to different transport media (like TCP, IP, ATM, Ethernet,
   etc), and how to achieve and implement reliability, multicast,
   ordering, etc.


2.  Introduction

   The ForCES (Forwarding and Control Element Separation) working group
   in the IETF is defining the architecture and protocol for separation
   of control and forwarding elements in network elements such as
   routers.  [RFC3654] and [RFC3746] respectively define architectural
   and protocol requirements for the communication between CE and FE.
   The ForCES protocol layer specification [FE-PROTO] describes the
   protocol semantics and workings.  The ForCES protocol layer operates
   on top of an inter-connect hiding layer known as the TML.  The
   relationship is illustrated in Figure 1.

   This document defines the SCTP based TML for the ForCES protocol
   layer.  It also addresses all the requirements for the TML including
   security, reliability, etc as defined in [FE-PROTO].


3.  Protocol Framework Overview

   The reader is referred to the Framework document [RFC3746], and in
   particular sections 3 and 4, for an architectural overview and
   explanation of where and how the ForCES protocol fits in.

   There may be some content overlap between the ForCES protocol draft
   [FE-PROTO] and this section in order to provide clarity.

   The ForCES layout constitutes two pieces: the PL and TML layer.  This
   is depicted in Figure 1.




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               +----------------------------------------------
               |                   CE PL                      |
               +----------------------------------------------
               |              CE TML                          |
               +----------------------------------------------
                                         ^
                                         |
                            ForCES       |   (i.e. Forces data + control
                            PL           |    packets )
                            messages     |
                            over         |
                            specific     |
                            TML          |
                            encaps       |
                            and          |
                            transport    |
                                         |
                                         v
               +------------------------------------------------
               |                   FE TML                      |
               +------------------------------------------------
               |                   FE PL                       |
               +------------------------------------------------



   Figure 1: Message exchange between CE and FE to establish an NE
   association

   The PL layer is in charge of the ForCES protocol.  Its semantics and
   message layout are defined in [FE-PROTO].  The TML Layer is necessary
   to connect two ForCES PL layers as shown in Figure 1.

   Both the PL and TML are standardized by the IETF.  While only one PL
   is defined, different TMLs are expected to be standardized.  The TML
   at each of the peers (CE and FE) is expected to be of the same
   definition in order to inter-operate.

   When transmitting, the PL delivers its messages to the TML.  The TML
   then delivers the PL message to the destination peer TML(s) as
   defined by the addressing in the PL message.

   On reception of a message, the TML delivers the message to its
   destination PL layer(s).

3.1.  The PL

   The PL is common to all implementations of ForCES and is standardized



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   by the IETF [FE-PROTO].  The PL layer is responsible for associating
   an FE or CE to an NE.  It is also responsible for tearing down such
   associations.  An FE uses the PL layer to throw various subscribed-to
   events to the CE PL layer as well as respond to various status
   requests issued from the CE PL.  The CE configures both the FE and
   associated LFBs attributes using the PL layer.  In addition the CE
   may send various requests to the FE to activate or deactivate it,
   reconfigure its HA parameterization, subscribe to specific events
   etc.

3.2.  The TML layer

   The TML layer is responsible for transport of the PL layer messages.
   The TML provides the following services on behalf of the ForCES
   protocol:

   1.  Reliability
       As defined by RFC 3654, section 6 #6.

   2.  Security
       TML provides security services to the ForCES PL.  The TML
       definition needs to define how the following are achieved:

       *  Endpoint authentication of FE and CE

       *  Message authentication

       *  Confidentiality service

   3.  Congestion Control
       The congestion control mechanism defined by the TML should
       prevent the FE from being overloaded by the CE.  Additionally,
       the circumstances under which notification is sent to the PL to
       notify it of congestion must be defined.

   4.  Uni/multi/broadcast addressing/delivery, if any
       If there is any mapping between PL and TML level uni/multi/
       broadcast addressing it needs to be defined.

   5.  Transport High Availability
       It is expected that availability of transport links is the TML's
       responsibility.  However, on config basis, the PL layer may wish
       to participate in link failover schemes and therefore the TML
       must allow for this.

   6.  Encapsulations used
       Different types of TMLs will encapsulate the PL messages on
       different types of headers.  The TML needs to specify the



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       encapsulation used.

   7.  Prioritization
       The TML SHOULD will be able to handle up to 8 priority levels
       needed by the PL and will provide preferential treatment.
       The TML needs to define how this is achieved.

   8.  Protection against DoS attacks
       As described in the Requirements RFC 3654, section 6

   It is expected more than one TML will be standardized.  The different
   TMLs each could implement things differently based on capabilities of
   underlying media and transport.  However, since each TML is
   standardized, interoperability is guaranteed as long as both
   endpoints support the same TML.

3.2.1.  TML Parameterization

   It is expected that it should be possible to use a configuration
   reference point, such as the FEM or the CEM, to configure the TML.

   Some of the configured parameters may include:

   o  PL ID

   o  Connection Type and associated data.  For example if a TML uses
      IP/TCP/UDP then parameters such as TCP and UDP ports and IP
      addresses need to be configured.

   o  Number of transport connections

   o  Connection Capability, such as bandwidth, etc.

   o  Allowed/Supported Connection QoS policy (or Congestion Control
      Policy)

3.3.  The TML-PL interface

   [TML-API] defines an interface between the PL and the TML layers.
   The end goal of [TML-API] is to provide a consistent top edge
   semantics for all TMLs to adhere to.  Conforming to such an interface
   makes it easy to plug in different TMLs over time.  It also allows
   for simplified TML parameterization requirement stated in
   Section 3.2.1.







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                  ,''''''''''''''''''''''|
                  |                      |
                  |     PL Layer         |
                  |                      |
                  |........ .............|
                             ^
                             |
                             |   TML API
                             |
                             |
                             V
                  ,''''''''''''''''''''''`.
                  |                       |
                  |     TML Layer         |
                  |                       |
                  '`'''''''''''''''''''''''


   Figure 2: The TML-PL interface

   We are going to assume the existence of such an interface and not
   discuss it further.  The reader is encouraged to read [TML-API] as a
   background.


4.  SCTP TML overview

4.1.  Introduction to SCTP

   SCTP [RFC2960] is an end-to-end transport protocol that is equivalent
   to TCP, UDP, or DCCP in many aspects.  With a few exceptions, SCTP
   can do most of what UDP, TCP, or DCCP can achieve.

   Like TCP, it provides ordered, reliable, connection-oriented, flow-
   controlled, congestion controlled data exchange.  Unlike TCP, it does
   not provide byte streaming and instead provides message boundaries.

   Like UDP, it can provide unreliable, unordered data exchange.  Unlike
   UDP, it does not provide multicast support

   Like DCCP, it can provide unreliable, ordered, congestion controlled,
   connection-oriented data exchange.

   SCTP also provides other services that none of the 3 transport
   protocols mentioned above provide.  These include:

   o  Multi-homing
      An SCTP connection can make use of multiple destination IP



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      addresses to communicate with its peer.

   o  Runtime IP address binding
      With the SCTP ADDIP feature, a new address can be bound at
      runtime.  This allows for migration of endpoints without
      restarting the association (valuable for high availability).

   o  A range of reliability shades with congestion control
      SCTP offers a range of services from full reliability to none, and
      from full ordering to none.  With SCTP, on a per message basis,
      the application can specify a message's time-to-live.  When the
      expressed time expires, the message can be "skipped".

   o  Built-in heartbeats
      SCTP has built-in heartbeat mechanism that validate the
      reachability of peer addresses.

   o  Multi-streaming
      A known problem with TCP is head of line (HOL) blocking.  If you
      have independent messages, TCP enforces ordering of such messages.
      Loss at the head of the messages implies delays of delivery of
      subsequent packets.  SCTP allows for defining upto 64K independent
      streams over the same socket connection, which are ordered
      independently.

   o  Message boundaries with reliability
      SCTP allows for easier message parsing (just like UDP but with
      reliability built in) because it establishes boundaries on a PL
      message basis.  On a TCP stream, one would have to peek into the
      message to figure the boundaries.

   o  Improved SYN DOS protection
      Unlike TCP, which does a 3 way connection setup handshake, SCTP
      does a 4 way handshake.  This improves against SYN-flood attacks
      because listening sockets do not set up state until a connection
      is validated.

   o  Simpler transport events
      An application (such as the TML) can subscribe to be notified of
      both local and remote transport events.  Events such as indication
      of association changes, addressing changes, remote errors, expiry
      of timed messages, etc, are off by default and require explicit
      subscription.

   o  Simplified replicasting
      Although SCTP does not allow for multicasting it allows for a
      single message from an application to be sent to multiple peers.
      This reduces the messaging that typically crosess different memory



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      domains within a host.

4.2.  Rationale for using SCTP for TML

   SCTP has all the features required to provide a robust TML.  As a
   transport that is all-encompassing, it negates the need for having
   multiple transport protocols, as has been suggested so far in the
   other proposals for TMLs.  As a result it allows for simpler coding
   and therefore reduces a lot of the interoperability concerns.

   SCTP is also very mature and widely deployed completing the equation
   that makes it a superior choice in comparison with other proposed
   TMLs.

4.3.  Meeting TML requirements




                  ,''''''''''''''''''''|
                  |                    |
                  |     PL             |
                  |                    |
                  |........ .+.........|
                             |
                             +   TML API
                             |
                  ,''''''''''+'''''''''`.
                  |                     |
                  |     TML             |
                  |                     |
                  '`'''''''''+'''''''''''
                             |
                             +   SCTP socket API
                             |
                  ,''''''''''+'''''''''`.
                  |                     |
                  |         SCTP        |
                  |       (over IP)     |
                  |                     |
                  '`'''''''''''''''''''''



   Figure 3: The TML-SCTP interface

   Figure 3 above shows the interfacing between the TML and SCTP.  There
   is only one socket connection open with two streams used.  The first



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   stream which is high priority will be dedicated for configuration
   data and the second lower priority stream is used for data path
   redirect.  The TML will use information passed by the TML API to
   select which of the two streams to use when sending.  The TML will
   also subscribe to events from SCTP associated with the two streams.

4.3.1.  Reliability

   As mentioned earlier, a shade of reliability ranges is possible in
   SCTP.  Therefore this requirement is met.

4.3.2.  Congestion control

   Congestion control is built into SCTP.  Therefore, this requirement
   is met.

4.3.3.  Timeliness and prioritization

   By using multiple streams in conjunction with the partial-reliability
   feature, both timeliness and prioritization can be achieved.

4.3.4.  Addressing

   SCTP can be told to replicast packets to multiple destinations.  The
   TML will translate PL level addresses, to a variety of unicast IP
   addresses in order to emulate multicast and broadcast.  Note,
   however, that there are no extra headers required.

4.3.5.  HA

   Transport link resiliency is SCTP's strongest point (where it totally
   outclasses all other TML proposals).  Failure detection and recovery
   is built in as mentioned earlier.

   o  With multi-homing, path diversity is provided.  Should one of the
      peer IP addresses become unreachable, the other(s) can be used
      without involving lower layer (routing, for example) convergence
      or even the TML becoming aware.

   o  With heartbeats and data transmission thresholds, on a per peer IP
      address, reachability faults can be detected.  The faults could be
      a result of an unreachable address or peer, which may be caused by
      a variety of reasons, like interface, network, or endpoint
      failures.

   o  With the ADDIP feature, one can migrate IP addresses to other
      nodes at runtime.  This is not unlike the VRRP protocol use.




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4.3.6.  DOS prevention

   Two separate streams are used within any FE-CE setup: the higher
   priority one is for configuration and the lower priority one for data
   redirection.  The design is strict priority to further guarantee that
   lower priority is starved if lack of resources happen.

4.3.7.  Encapsulation

   There is no extra encapsulation added by this TML.  In the future,
   should the need arise, SCTP provides for extensions to be added to it
   by defining new chunks.


5.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.


6.  Security Considerations

   TBA: how to use TLS,IPSEC


7.  Acknowledgements


8.  References

8.1.  Normative References

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC2960]  Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
              Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
              Zhang, L., and V. Paxson, "Stream Control Transmission
              Protocol", RFC 2960, October 2000.

   [RFC3654]  Khosravi, H. and T. Anderson, "Requirements for Separation
              of IP Control and Forwarding", RFC 3654, November 2003.

   [RFC3746]  Yang, L., Dantu, R., Anderson, T., and R. Gopal,
              "Forwarding and Control Element Separation (ForCES)



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              Framework", RFC 3746, April 2004.

8.2.  Informative References

   [FE-MODEL]
              Yang, L., Halpern, J., Gopal, R., DeKok, A., Haraszti, Z.,
              and S. Blake, "ForCES Forwarding Element Model",
              Mar. 2006.

   [FE-PROTO]
              Doria (Ed.), A., Haas (Ed.), R., Hadi Salim (Ed.), J.,
              Khosravi (Ed.), H., M. Wang (Ed.), W., Dong, L., and R.
              Gopal, "ForCES Protocol Specification", Mar. 2006.

   [TML-API]  M. Wang, W. and J. Hadi Salim, "ForCES Transport Mapping
              Layer (TML) Service Primitives", Apr. 2006.



































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Author's Address

   Jamal Hadi Salim
   ZNYX Networks
   Ottawa, Ontario
   Canada

   Email: hadi@znyx.com











































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