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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] (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,” October 2000.) and also describes how this TML addresses all the requirements described in [RFC3654] (Khosravi, H. and T. Anderson, “Requirements for Separation of IP Control and Forwarding,” November 2003.) and the ForCES protocol [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,” July 2007.) draft.
1.
Definitions
2.
Introduction
3.
Protocol Framework Overview
3.1.
The PL
3.2.
The TML layer
3.2.1.
TML Parameterization
3.3.
The TML-PL interface
4.
SCTP TML overview
4.1.
Introduction to SCTP
4.2.
Rationale for using SCTP for TML
4.3.
Meeting TML requirements
4.3.1.
Reliability
4.3.2.
Congestion control
4.3.3.
Timeliness and prioritization
4.3.4.
Addressing
4.3.5.
HA
4.3.6.
DOS prevention
4.3.7.
Encapsulation
5.
IANA Considerations
6.
Security Considerations
7.
Manageability Considerations
8.
Acknowledgements
9.
References
9.1.
Normative References
9.2.
Informative References
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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The following definitions are taken from [RFC3654] (Khosravi, H. and T. Anderson, “Requirements for Separation of IP Control and Forwarding,” November 2003.)and [RFC3746] (Yang, L., Dantu, R., Anderson, T., and R. Gopal, “Forwarding and Control Element Separation (ForCES) Framework,” April 2004.):
ForCES Protocol -- The protocol used at the Fp reference point in the ForCES Framework in [RFC3746] (Yang, L., Dantu, R., Anderson, T., and R. Gopal, “Forwarding and Control Element Separation (ForCES) Framework,” April 2004.).
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] (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,” July 2007.).
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.
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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] (Khosravi, H. and T. Anderson, “Requirements for Separation of IP Control and Forwarding,” November 2003.) and [RFC3746] (Yang, L., Dantu, R., Anderson, T., and R. Gopal, “Forwarding and Control Element Separation (ForCES) Framework,” April 2004.) respectively define architectural and protocol requirements for the communication between CE and FE. The ForCES protocol layer specification [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,” July 2007.) 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 (Message exchange between CE and FE to establish an NE association).
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] (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,” July 2007.).
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The reader is referred to the Framework document [RFC3746] (Yang, L., Dantu, R., Anderson, T., and R. Gopal, “Forwarding and Control Element Separation (ForCES) Framework,” April 2004.), and in particular sections 3 and 4, for an architectural overview and explanation of where and how the ForCES protocol fits in.
There is some content overlap between the ForCES protocol draft [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,” July 2007.) 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 (Message exchange between CE and FE to establish an NE association).
+----------------------------------------------
| 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 |
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).
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The PL is common to all implementations of ForCES and is standardized by the IETF [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,” July 2007.). 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.
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The TML layer is responsible for transport of the PL layer messages. The TML provides the following services on behalf of the ForCES protocol:
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.
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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:
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[TML‑API] (M. Wang, W., Hadi Salim, J., and A. Audu, “ForCES Transport Mapping Layer (TML) Service Primitives,” Feb. 2007.) defines an interface between the PL and the TML layers. The end goal of [TML‑API] (M. Wang, W., Hadi Salim, J., and A. Audu, “ForCES Transport Mapping Layer (TML) Service Primitives,” Feb. 2007.) 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 (TML Parameterization).
,''''''''''''''''''''''|
| |
| 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] (M. Wang, W., Hadi Salim, J., and A. Audu, “ForCES Transport Mapping Layer (TML) Service Primitives,” Feb. 2007.) as a background.
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SCTP [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,” October 2000.) 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. SCTP as well can do most of what a combination of the other transport protocols can achieve (eg TCP and DCCP or TCP and UDP).
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:
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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.
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,''''''''''''''''''''|
| |
| PL |
| |
|........ .+.........|
|
+ TML API
|
,''''''''''+'''''''''`.
| |
| TML |
| |
'`'''''''''+'''''''''''
|
+ SCTP socket API
|
,''''''''''+'''''''''`.
| |
| SCTP |
| (over IP) |
| |
'`'''''''''''''''''''''
| Figure 3: The TML-SCTP interface |
Figure 3 (The TML-SCTP interface) above shows the interfacing between the TML and SCTP. There is only one socket connection open with two streams used. The first 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.
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As mentioned earlier, a shade of reliability ranges is possible in SCTP. Therefore this requirement is met.
Redirected control traffic in ForCES is not expected to be reliably delivered but MUST at the same time be congestion aware. This requirement is also met by SCTP.
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Congestion control is built into SCTP. Therefore, this requirement is met.
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By using multiple streams in conjunction with the partial-reliability feature, both timeliness and prioritization can be achieved.
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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, unlike other proposed TMLs, that there are no extra headers required for SCTP.
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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.
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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.
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There is no extra encapsulation added by this TML. SCTP provides for extensions to be added to it by defining new chunks. In the future, should the need arise, a new SCTP extension can be defined to meet newer ForCES requirements.
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This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an RFC.
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TBA: how to use TLS,IPSEC
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TBA
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| [RFC2434] | Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” BCP 26, RFC 2434, October 1998 (TXT, HTML, XML). |
| [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 (TXT). |
| [RFC3654] | Khosravi, H. and T. Anderson, “Requirements for Separation of IP Control and Forwarding,” RFC 3654, November 2003 (TXT). |
| [RFC3746] | Yang, L., Dantu, R., Anderson, T., and R. Gopal, “Forwarding and Control Element Separation (ForCES) Framework,” RFC 3746, April 2004 (TXT). |
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| [FE-MODEL] | Halpern, J. and E. Deleganes, “ForCES Forwarding Element Model,” Oct. 2007. |
| [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,” July 2007. |
| [TML-API] | M. Wang, W., Hadi Salim, J., and A. Audu, “ForCES Transport Mapping Layer (TML) Service Primitives,” Feb. 2007. |
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| Jamal Hadi Salim | |
| ZNYX Networks | |
| Ottawa, Ontario | |
| Canada | |
| Email: | hadi@znyx.com |
| Kentaro Ogawa | |
| NTT Network Service Systems Laboratories | |
| 3-9-11 Midori-cho | |
| Musashino-shi, Tokyo 180-8585 | |
| Japan | |
| Email: | ogawa.kentaro@lab.ntt.co.jp |
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