RFC 3496

Protocol Extension for Support of Asynchronous Transfer Mode (ATM) Service Class-aware Multiprotocol Label Switching (MPLS) Traffic Engineering

📅 published March 2003, from ietf

RFC 3496 🎀 Title Block Tea ☕

Okay bestie, this one's a real one. 💅 It's RFC 3496, from the Network Working Group, dated March 2003. Its title is Protocol Extension for Support of Asynchronous Transfer Mode (ATM) Service Class-aware Multiprotocol Label Switching (MPLS) Traffic Engineering ✨.

The authors are A. G. Malis (Andrew G. Malis) and T. Hsiao (Tony Hsiao), both from Vivace Networks 🦋. The category is Informational 🌸. The title block doesn't list anything it obsoletes or updates. Blank space, no drama 🙈.

Status of this Memo 🫶

Okay so this doc is giving information for the Internet community. It is NOT an Internet standard, no cap 🧢. Distribution is unlimited, so share it with everyone 💖.

Copyright Notice ©️

Abstract ✨

So the big idea is this: it's a Resource ReSerVation Protocol-Traffic Engineering (RSVP-TE) signaling extension that supports Asynchronous Transfer Mode (ATM) Service Class-aware Multiprotocol Label Switching (MPLS) Traffic Engineering 🔥.

Table of Contents 🗂️

1.  Overview......................................................2
2.  Extended RSVP-TE Path Message Format..........................2
    2.1 PATH Message Format.......................................3
3.  ATM_SERVICECLASS Object.......................................3
4.  Handling the ATM_SERVICECLASS Object..........................4
5.  Non-support of the ATM_SERVICECLASS Object....................4
6.  Security Considerations.......................................4
7.  IANA Considerations...........................................5
8.  References....................................................5
9.  Authors' Addresses............................................5
10. Full Copyright Statement......................................6

1. Overview 🌈

Okay so this doc defines an RSVP-TE protocol addition that brings ATM Service Class-aware MPLS Traffic Engineering to the party 🎉.

This addition works with all MPLS Label Switched Routers (LSRs) and all link types, including (but not limited to) Packet over SONET, Ethernet, and ATM links 🔗. It's used to signal traffic engineered paths that can support the ATM service classes defined by the ATM Forum [TM] 💜.

Now here's the tea ☕: this doc does not explain HOW the MPLS LSRs actually pull off those ATM service classes (stuff like queuing and scheduling). It only covers how to signal that the TE path has to support those classes 🙈. A super useful use case is carrying ATM cells inside IP or MPLS packets, so MPLS networks can act as drop-in replacements for ATM networks 🧚.

2. Extended RSVP-TE Path Message Format 💅

So this doc adds exactly one new RSVP-TE Object: the ATM_SERVICECLASS Object 🎀. Its full details are down below. It goes in PATH messages, and only the ones used to set up LSP (Label Switched Path) Tunnels under [RSVP-TE] 🦋. Those PATH messages carry a Session Object with a C-Type equal to LSP_TUNNEL_IPv4, plus a LABEL_REQUEST object 🍓.

All the [RSVP-TE] restrictions for setting up LSP Tunnels also apply to these ATM Service Class-aware tunnels 🔒. For example, only unicast LSPs are supported, and multicast LSPs are "for further study" 🌸.

Also, the ATM_SERVICECLASS object is optional from RSVP-TE's point of view 💖. That means general RSVP-TE implementations that don't care about ATM Service Class-aware MPLS LSP setup don't have to support it ✨.

2.1 PATH Message Format 🧾

The extended PATH message looks like this 👀:

<PATH Message> ::=      <Common Header> [ <INTEGRITY> ]
                             <SESSION> <RSVP_HOP>
                         <TIME_VALUES>
                         [ <EXPLICIT_ROUTE> ]
                         <LABEL_REQUEST>
                         [ <SESSION_ATTRIBUTE> ]
                         [ <DIFFSERV> ]
                         [ <ATM_SERVICECLASS> ]
                         [ <POLICY_DATA> ... ]
                         [ <sender descriptor> ]

<sender descriptor> ::=  <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
                         [ <ADSPEC> ]
                         [ <RECORD_ROUTE> ]

3. ATM_SERVICECLASS Object 🦄

The ATM_SERVICECLASS object is laid out like this 💜. Its Class Number is 227 and its C_Type is 1 🔥.

Class Number = 227, C_Type = 1

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Reserved                          | SC  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Reserved: 29 bits 🫧 This field is reserved. It must be set to zero on transmission and must be ignored on receipt.

SC: 3 bits 🌷 This tells you the ATM Service Class. The values currently allowed are:

0: UBR (Unspecified Bit Rate)
1: VBR-NRT (Variable Bit Rate, Non-Real Time)
2: VBR-RT (Variable Bit Rate, Real Time)
3: CBR (Constant Bit Rate)
4-7: reserved

4. Handling the ATM_SERVICECLASS Object 🎬

So to set up an LSP tunnel with RSVP-TE, the sender LSR builds a PATH message with a session type of LSP_Tunnel_IPv4 and a LABEL_REQUEST object, as described in [RSVP-TE] 🍭. The sender LSR may also include the DIFFSERV object, following [DIFF-MPLS] ✨.

If the LSP is tied to an ATM Service Class, the sender LSR must include the ATM_SERVICECLASS object in the PATH message, with the Service-Class (SC) field set to the class it wants 💖.

If a path message has multiple ATM_SERVICECLASS objects, only the first one counts 🙃. The later ones must be ignored, and they must not be forwarded 🚫.

Every ATM_SERVICECLASS-aware LSR along the path records the ATM_SERVICECLASS object (when it's there) in its path state block 📝.

The destination LSR answers the PATH message with a RESV message that has no ATM_SERVICECLASS object in it. This is true whether or not the PATH message had one 🌈.

5. Non-support of the ATM_SERVICECLASS Object 🥀

Okay this part is kinda important, so pay attention 👀.

If an LSR doesn't recognize the ATM_SERVICECLASS Class Number, it must act according to the [RSVP] rules for an unknown Class Number with the binary format 11bbbbbb, where b=0 or 1. In other words, RSVP ignores the object but still forwards it unexamined and unmodified 🫥.

If an LSR recognizes the Class Number but not the C-Type, it must act according to the [RSVP] rules for an unknown C-type. That means it must send a PathErr with the error code 'Unknown object C-Type' back toward the sender 🚨.

In both cases, the path setup fails 💀. The sender should tell management that the LSP can't be set up, and it might try to retry the reservation without the ATM_SERVICECLASS object 🔁.

6. Security Considerations 🔐

The solution is not expected to add specific security requirements beyond those of Diff-Serv and existing TE 🚨. The security mechanisms currently used with Diff-Serv and existing TE can be used with this solution 🛡️.

7. IANA Considerations 📋

IANA has registered a new RSVP Class Number for ATM_SERVICECLASS, which is 227 🎀. You can check the registry at http://www.iana.org/assignments/rsvp-parameters 🦋.

8. References 📚

[DIFF-MPLS] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
            P., Krishnan, R., Cheval, P. and J. Heinanen, "Multi-
            Protocol Label Switching (MPLS) Support of Differentiated
            Services", RFC 3270, May 2002.

[RSVP]      Braden, R., Ed., Zhang, L., Berson, S., Herzog, S. and S.
            Jazmin , "Resource ReSerVation Protocol (RSVP) -- Version
            1 Functional Specification", RFC 2205, September 1997.

[RSVP-TE]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
            and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
            Tunnels", RFC 3209, December 2001.

[TM]        ATM Forum Traffic Management Specification Version 4.0,
            af-tm-0056.000, April 1996.

9. Authors' Addresses 📮

Andrew G. Malis
Vivace Networks, Inc.
2730 Orchard Parkway
San Jose, CA 95134

EMail: Andy.Malis@vivacenetworks.com

Tony Hsiao
Vivace Networks, Inc.
2730 Orchard Parkway
San Jose, CA 95134

EMail: Tony.Hsiao@VivaceNetworks.com

10. Full Copyright Statement ⚖️

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement 🙏

Funding for the RFC Editor function is currently provided by the Internet Society 💜.

📦 where this page comes from

ietf: rfc3496 2003-03
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