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- Network Working Group M. Maher
- Request for Comments: 2331 USC/ISI
- Category: Standards Track April 1998
-
-
- ATM Signalling Support for IP over ATM - UNI Signalling 4.0 Update
-
- Status of this Memo
-
- This document specifies an Internet standards track protocol for the
- Internet community, and requests discussion and suggestions for
- improvements. Please refer to the current edition of the "Internet
- Official Protocol Standards" (STD 1) for the standardization state
- and status of this protocol. Distribution of this memo is unlimited.
-
- Copyright Notice
-
- Copyright (C) The Internet Society (1998). All Rights Reserved.
-
- Abstract
-
- This memo describes how to efficiently use the ATM call control
- signalling procedures defined in UNI Signalling 4.0 [SIG40] to
- support IP over ATM environments as described in RFC 2225 [LAUB98]
- and in RFC 2332 [LUC98]. Among the new features found in UNI
- Signalling 4.0 are Available Bit Rate signalling and traffic
- parameter negotiation. This memo highlights the features of UNI
- Signalling 4.0 that provide IP entities capabilities for requesting
- ATM service in sites with SVC support, whether it is private ATM or
- publicly provisioned ATM, in which case the SVC support is probably
- configured inside PVPs.
-
- This document is only relevant to IP when used as the well known
- "best effort" connectionless service. In particular, this means that
- this document does not pertain to IP in the presence of implemented
- IP Integrated Services. The topic of IP with Integrated Services
- over ATM will be handled by a different specification or set of
- specifications being worked on in the ISSLL WG.
-
- This specification is a follow-on to RFC 1755, "ATM Signaling Support
- for IP over ATM", which is based on UNI 3.1 signalling [UNI95].
- Readers are assumed to be familiar with RFC 1755.
-
-
-
-
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- Maher Standards Track [Page 1]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- Table of Contents
-
- 1. Conventions ............................................... 2
- 2. Overview .................................................. 2
- 3. Use of Protocol Procedures ................................ 3
- 3.1 VC Teardown........................................... 3
- 4. Overview of Call Establishment Message Content ............ 3
- 5. Description of Information Elements ....................... 4
- 5.1 ATM Adaptation Layer Parameters ...................... 4
- 5.2 Broadband Low Layer Information ..................... 5
- 5.3 Traffic Management Issues and Related IEs............. 5
- 5.3.1 ATM Traffic Descriptor ........................ 6
- 5.3.1.1 Tagging vs. Dropping ................. 7
- 5.3.2 Traffic Parameter Negotiation .................. 7
- 5.3.3 Broadband Bearer Capability .................... 8
- 5.3.4 QoS Parameter .................................. 8
- 5.3.4.1 Signalling of Individual QoS Parameters 8
- 5.4 ATM Addressing Information ........................... 9
- 6. ABR Signalling In More Detail ............................ 9
- 7. Frame Discard Capability .................................. 10
- 8. Security Considerations ................................... 10
- 9. Acknowledgements........................................... 10
- 10. References ................................................ 10
- 11. Author's Address .......................................... 12
- Appendix A Sample Signalling Messages ........................ 13
- Appendix B ABR and nrt-VBR Signalling Guidelines for IP Routers 15
- Appendix C Combinations of Traffic Related Parameters ........ 18
- Full Copyright Statement ...................................... 26
-
- 1. Conventions
-
- 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 [BRA97].
-
- 2. Overview
-
- UNI Signalling version 4.0 (SIG 4.0) is the ATM Forum follow-on
- specification to UNI 3.1 signalling (UNI 3.1). Among the new features
- in SIG 4.0, those of particular interest to IP over ATM environments
- are:
-
- o Available Bit Rate (ABR) Signalling for Point-to-Point Calls
- o Traffic Parameter Negotiation
- o Frame Discard Support
- o Leaf Initiated Join (LIJ) Capability
- o ATM Anycast Capability
- o Switched Virtual Path (VP) Service
-
-
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- Maher Standards Track [Page 2]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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-
- This memo highlights the first three capabilities listed above. The
- last three capabilities are not discussed because models for their
- use in IP over ATM environments have not yet been defined. The ION
- WG is considering the applicability of LIJ and Group Addressing to
- the RFC2022 problem space. Furthermore, Anycast addressing is being
- explored as a technique for supporting server discovery in ATM
- networks.
-
- 3. Use of Protocol Procedures
-
- Section 3 in RFC 1755 introduces requirements of virtual circuit (VC)
- management intended to prevent VC thrashing, excessive VC
- consumption, and other related problems. This section updates RFC
- 1755's requirements related to VC teardown.
-
- 3.1. VC Teardown
-
- In environments running layer 3 (L3) signalling protocols, such as
- RSVP [RSVP], over ATM, data VCs might correspond to L3 reserved flows
- (even if the VC is a 'best effort' VC). In such environments it is
- beneficial for VCs to be torn down only when the L3 reservation has
- expired. In other words, it is more efficient for the sender of a L3
- reserved flow to initiate VC tear-down when the receiver(s) has
- ceased refreshing the reservation. To support such L3 behavior,
- systems implementing a Public ATM UNI interface and serving as the
- _called_ party of a VCC MUST NOT use an inactivity timer on such a
- VCC by default. A system MAY use an inactivity timer on such a VCC
- if configured to do so.
-
- 4. Overview of Call Establishment Message Content
-
- Signalling messages are structured to contain mandatory and optional
- variable length information elements (IEs). A SETUP message which
- establishes an ATM connection to be used for IP and multiprotocol
- interconnection calls MUST contain the following IEs:
-
- AAL Parameters
- ATM Traffic Descriptor
- Broadband Bearer Capability
- Broadband Low Layer Information
- QoS Parameter
- Called Party Number
- Calling Party Number
-
- and MAY, under certain circumstance contain the following IEs:
-
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- Maher Standards Track [Page 3]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- Calling Party Subaddress
- Called Party Subaddress
- Transit Network Selection
-
- (New in SIG 4.0:)
- Minimum Acceptable ATM Traffic Descriptor
- Alternative ATM Traffic Descriptor
- ABR Setup Parameters
- ABR Additional Parameters
- Connection Scope Selection
- Extended QoS Parameters
- End-to-End Transit Delay
-
- In SIG 4.0, like UNI 3.1, the AAL Parameters and the Broadband Low
- Layer Information IEs are optional in a SETUP message. However, in
- support of IP over ATM these two IEs MUST be included. Appendix A
- shows a sample setup message.
-
- 5. Description of Information Elements
-
- This section describes the coding of, and procedures surrounding,
- information elements in SETUP and CONNECT messages. The first two IEs
- described, ATM Adaptation Layer Parameters and Broadband Low Layer
- Information, are categorized as having significance only to the end-
- points of an ATM call supporting IP. That is, the network does not
- process these IEs.
-
- 5.1. ATM Adaptation Layer (AAL) Parameters
-
- The AAL Parameters IE carries information about the ATM adaptation
- layer to be used on the connection. The parameters specified in this
- IE are the same as specified in [PER95].
-
-
- Format and field values of AAL Parameters IE
-
- ----------------------------------------------------------
- | aal_parameters |
- ----------------------------------------------------------
- | aal_type 5 (AAL 5) |
- | fwd_max_sdu_size_identifier 140 |
- | fwd_max_sdu_size 65,535 (desired IP MTU) |
- | bkw_max_sdu_size_identifier 129 |
- | bkw_max_sdu_size 65,535 (desired IP MTU) |
- | sscs_type identifier 132 |
- | sscs_type 0 (null SSCS) |
- ----------------------------------------------------------
-
-
-
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- Maher Standards Track [Page 4]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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-
- This shows maximum size MTUs. In practice, most sites have used 9180
- IP MTUs for ATM [RFC1626].
-
- 5.2. Broadband Low Layer Information
-
- Selection of an encapsulation to support IP over an ATM VCC is done
- using the Broadband Low Layer Information (B-LLI) IE, along with the
- AAL Parameters IE, and the B-LLI negotiation procedure. B-LLI
- negotiation is described in [PER95] in Appendix D. The procedures
- remain the same for this SIG 4.0 based specification.
-
- Format of B-LLI IE indicating LLC/SNAP encapsulation
-
- ----------------------------------------------------------
- | bb_low_layer_information |
- ----------------------------------------------------------
- | layer_2_id 2 |
- | user_information_layer 12 (lan_llc - ISO 8802/2) |
- ----------------------------------------------------------
-
- 5.3. Traffic Management Issues and Related IEs
-
- The ATM Forum Traffic Management Sub-working group has completed
- version 4.0 of their specification [TMGT40]. This latest version
- focuses primarily on the definition of the ABR service category. As
- opposed to the Unspecified Bit Rate (UBR) traffic class, ABR uses a
- rate-based flow control mechanism to assure certain traffic
- guarantees (bandwidth and delay). There has been much debate on
- whether IP benefits from ABR, and if so, how IP should use ABR. The
- IP Integrated Services (IIS) and RSVP models in IP add complexity to
- this issue because mapping IIS traffic classes to ATM traffic classes
- is not straightforward.
-
- This document attempts only to present the required IP to ATM
- signaling interface for IP over ATM systems that do not support IIS
- as yet. It is an attempt to cause IP over ATM vendors to support
- enough options for signalling the traffic characteristics of VCs
- serving non-IIS IP datagrams. This specification also aims to give
- guidance to ATM system administrators so that they can configure
- their IP over ATM entities to conform to the varied services that
- their ATM provider may have sold to them. By definition, IP without
- IIS cannot be expected to provide a signalling interface that is
- flexible and allows application specific traffic descriptors. The
- topic of IP over ATM signalling for IP _with_ IIS is to be presented
- in other specifications being produced by the ISSLL WG of the IETF.
-
- An IP over ATM interface may be configured to support all the defined
- ATM Service Categories (ASC). They are:
-
-
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- Maher Standards Track [Page 5]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- - CBR
- - CBR with CLR specified (loss-permitting CBR)
- - ABR
- - UBR
- - real time VBR
- - non-real time VBR
-
- The ATM Traffic Descriptor IE, Broadband Bearer Capability IE, and
- the QoS Parameter IE together define the signalling view of ATM
- traffic management. Additionally, the Extended QoS parameters IE and
- the End-to-end Transit Delay IE may be used to provide more specifics
- about traffic requirements, however this note does not provide
- explicit recommendations on their use. Annex 9 of [SIG40] describes
- a set of allowable combinations of traffic and QoS related
- paramenters defined for SIG 4.0. This set includes all forms of
- non-IIS IP signaling configurations that MUST be implemented in ATM
- endsystems to accommodate varied sites' needs. The principle is that
- IP over ATM service may be available in different sites by different
- types of procured ATM service; for one site, a CBR PVP might be
- cost-effective and then the SVCs that IP over ATM without IIS must
- establish must be CBR. Similarly, VBR or ABR PVPs could be
- provisioned. The intent of this document is to specify the use of
- the most sensible parameters within this non-IIS configuration. For
- instance, for non-IIS VBR, the SCR value may need to be hand-
- configured for IP users, or for ABR, the PCR value may be link-rate
- with a 0 MCR.
-
- For the reader's convenience, we have replicated the tables found in
- Annex 9 of [SIG40] in Appendix C of this document. Ideally this
- document could recommend specific values for the various table
- parameters that would offer the most sensible IP over ATM service.
- Nevertheless, it is not possible to mandate specific values given the
- varied scenarios of procured ATM service.
-
- 5.3.1. ATM Traffic Descriptor
-
- Even with the newly defined ABR ASC, the most convenient model for
- supporting IP still corresponds to the best effort capability, the
- UBR ASC. The rationale for this assertion stems from the fact that a
- non-IIS IP service has no notion of the performance requirements of
- the higher layers it supports. Therefore, if a site's configuration
- allows use of UBR, users SHOULD signal for it using the IE's and
- parameters pertaining to the UBR ATC. See Appendix C for the list of
- those IE's and parameters.
-
- Although we consider the UBR ASC the most natural ASC for best-effort
- IP, ATM vendors that implement VBR and ABR services could possibly
- create hooks for convenient use of these services. If this is the
-
-
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- Maher Standards Track [Page 6]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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-
- case, IP routers may perhaps have the most to gain from use of VBR or
- ABR services because of the large aggregated traffic volume they are
- required to forward. See Appendix B for detailed suggestions on VBR
- and ABR signalling for IP routers. We simply note here that, in
- support of ABR service, two new subfields have been added in SIG 4.0
- to the Traffic Descriptor IE. These fields are the forward and
- backward 'Minimum Cell Rate' fields.
-
- 5.3.1.1. Tagging vs. Dropping
-
- The Traffic Descriptor IE contains a 'tagging' subfield used for
- indicating whether the network is allowed to tag the source's data
- cells. Tagging in the network may occur during periods of congestion
- or when the source's traffic has violated the traffic contract for
- the connection. See Section 4 of [TMGT40] for an explanation of ATM
- connection conformance and the Usage Parameter Control (UPC)
- function.
-
- SIG 4.0 and TMGT 4.0 define two modes of UBR, UBR.1 which disables
- tagging and UBR.2 which enables tagging (see Appendix C). In some
- network environments there is no potential for UBR traffic sources to
- violate the connection traffic contract because, either the user's
- terminal equipment supports traffic shaping, or the network does not
- enforce PCR. In such environments, the user SHOULD specify 'no
- tagging' in the SETUP message (UBR.1). Specifying 'no tagging'
- indicates to the network that cells should be dropped during periods
- of congestion instead of being randomly marked/tagged as low
- priority. Cells of packets that the source itself has marked as low
- priority are dropped first, thereby preserving the source's
- characterization of the traffic.
-
- On the other hand, when the network applies PCR to the UPC function,
- meaning it enforces PCR, and traffic shaping is not enabled at the
- source, the source has the potential to violate the traffic contract
- and SHOULD therefore signal for tagging (UBR.2). Tagging allows the
- source's non-conforming cells to be tagged and forwarded instead of
- dropped.
-
- 5.3.2. Traffic Parameter Negotiation
-
- SIG 4.0 allows certain traffic parameters to be negotiated during the
- call establishment phase Traffic parameters cannot be 'renegotiated'
- after the call is active. Two new IEs make negotiation possible:
-
- - the Minimum Acceptable ATM Traffic Descriptor IE allows
- negotiation of PCR parameters
-
-
-
-
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- Maher Standards Track [Page 7]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- - the Alternative ATM Traffic Descriptor IE allows negotiation of
- other traffic parameters
-
- A SETUP or CONNECT message may include ONLY one of the above IEs.
- That is, the calling party may only offer an 'alternative' or
- 'minimum' to the requested traffic parameters. (See Section 8 of
- [SIG40].) IP over ATM entities SHOULD take advantage of this
- capability whenever possible. In order to do so, IP over ATM entities
- SHOULD specify PCR _equal_ to the link rate in the ATM Traffic
- Descriptor IE of the SETUP message and a minimum of zero PCR in the
- Minimum Acceptable ATM Traffic Descriptor IE.
-
- 5.3.3. Broadband Bearer Capability
-
- A new field in UNI signalling 4.0 called, 'ATM Transfer Capability'
- (ATC), has been defined in the Broadband Bearer Capability IE for the
- purpose of explicitly specifying the desired ATM traffic category.
- The figure below shows the allowable ATC values.
-
- Format and field values of Broadband Bearer Capability IE
-
- -------------------------------------------------------------
- | bb_bearer_capability |
- ------------------------------------------------------------|
- | spare 0 |
- | bearer_class bcob-x,c,a or VP |
- | transfer_capability cbr, rt-vbr, nrt-vbr, abr |
- | susceptibility_to_clipping 0 (not suscept) |
- | spare 0 |
- | user_plane_configuration pt-to-pt, pt-to-mpt |
- -------------------------------------------------------------
-
- 5.3.4. QoS Parameter
-
- Inclusion of the QoS Parameter IE is not mandatory in SIG 4.0. It
- may be omitted from a SETUP message _if and only if_ the Extended QoS
- Parameters IE is included (see next section). This specification
- makes no explicit recommendation on the use of the QoS related IEs.
-
- 5.3.4.1. Two IEs for Signalling of Individual QoS Parameters
-
- SIG 4.0 allows for signalling of individual QoS parameters for the
- purpose of giving the the network and called party a more exact
- description of the desired delay and cell loss characteristics. The
- two individual QoS related IEs, Extended QoS Parameters IE and End-
- to-End Transit Delay IE, can be used in the SETUP and CONNECT
- signaling messages in place of the 'generic' QoS Parameter IE. Note
- that inclusion of these two IEs depends on the type of ATM service
-
-
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- Maher Standards Track [Page 8]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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-
- category requested (see Annex 9 in [SIG40]).
-
- 5.4. ATM Addressing Information
-
- ATM addressing information is carried in the Called Party Number,
- Calling Party Number, and, under certain circumstance, Called Party
- Subaddress, and Calling Party Subaddress IE. The ATM Forum ILMI
- Specification 4.0 [ILMI40] provides the procedure for an ATM
- endsystem to learn its own ATM address from the ATM network, for use
- in populating the Calling Party Number IE.
-
- Format and field values of Called Party Number IE
-
- ----------------------------------------------------------
- | called_party_number |
- ----------------------------------------------------------
- | type_of_number (international number / unknown) |
- | addr_plan_ident (ISDN / ATM Endsystem Address) |
- | addr_number (E.164 / ATM Endsystem Address) |
- ----------------------------------------------------------
-
- 6. ABR Signaling In More Detail
-
- The IEs and procedures pertaining to ABR signalling are briefly
- described in this section. Nevertheless, this document makes no
- specific recommendation on when to use the ABR service category for
- IP VCCs or give suggestions on appropriate values for the various
- parameters in the ABR related IEs.
-
- Two new IEs have been defined for ABR signaling:
-
- o ABR Setup Parameters
- o ABR Additional Parameters
-
- These IEs may be optionally included in a SETUP or CONNECT message.
- The ABR Setup Parameters IE contains the following subfields:
-
- - Forward/Backward ABR Initial Cell Rate
- - Forward/Backward ABR Transient Buffer Exposure
- - Cumulative RM Fixed Round Trip Time
- - Forward/Backward Rate Increment Factor
- - Forward/Backward Rate Decrease Factor
-
- The ABR Additional Parameters IE contains one subfield:
-
- - Forward/Backward Additional Parameters Record
-
-
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- Maher Standards Track [Page 9]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- The Additional Parameters Record value is a compressed encoding of a
- set of ABR parameters (see [SIG40] and [ABRS]).
-
- 7. Frame Discard Capability
-
- The frame discard capability in SIG 4.0 is primarily based on the
- 'Partial and Early Packet Discard' strategy [ROM94]. Its use is
- defined for any of the ATM services, except for loss-less CBR. Frame
- discard signaling MUST be supported by all IP over ATM entities and
- it is RECOMMENDED that frame discard be signaled for all IP SVCs
- because it has been proven to increase throughput under network
- congestion. Signaling for frame discard is done by setting the frame
- discard bit in the 'Traffic Management Options' subfield in the
- Traffic Descriptor IE. It is possible that not all network entities
- in the SVC path support frame discard, but it is required that they
- all forward the signaling.
-
- 8. Security Considerations
-
- The ATM Forum Security sub-working group is currently defining
- security mechanisms in ATM. The group has yet to produce a
- specification, therefore it is premature to begin defining IP over
- ATM signalling's use of ATM security. The ATM Forum is working on
- authentication mechanisms for signalling and on mechanisms for
- providing data integrity and confidentiality (e.g encryption). Lack
- of these ATM security mechanisms prevents the authentication of the
- originator of signalling messages, such as, connection setup request
- or connection teardown request. IP Security (RFC1825) can be applied
- to IP datagrams over ATM VCs to overcome the lack of security at the
- ATM layer.
-
- 9. Acknowledgements
-
- The authors would like to thank the members of the ION working group
- for their input. Special thanks to K.K. Ramakrishnan and Kerry
- Fendick who contributed Appendix B of this document.
-
- REFERENCES
-
- [ABRS] ATM Forum, "Addendum to UNI Signalling v4.0 for ABR Parameter
- Negotiation", af-sig-0076.000; available at
- ftp://ftp.atmforum.com/pub.
-
- [ABRT] ATM Forum, "Addendum to Traffic Management v4.0 for ABR
- Parameter Negotiation", af-tm-0077.000; available at
- ftp://ftp.atmforum.com/pub.
-
-
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- Maher Standards Track [Page 10]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- [RFC1122] Braden, R., Editor, "Requirements for Internet Hosts --
- Communication Layers", STD 3, RFC 1122, October 1989.
-
- [RFC1633] Braden, R., Clark, D., and S. Shenker, "Integrated Service
- in the Internet Architecture: An Overview", RFC 1633, June 1994.
-
- [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
- Requirement Levels", BCP 14, RFC 2119, March 1997.
-
- [RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM
- Adaptation Layer 5", RFC 1483, July 1993.
-
- [ILMI40] ATM Forum, "Integrated Local Management Interface (ILMI)
- Specification Version 4.0", af-ilmi-0065.000, finalized September
- 1996; available at ftp://ftp.atmforum.com/pub.
-
- [ISO8473] ISO/IEC 8473, Information processing systems - Data
- communications - Protocol for providing the connectionless-mode
- network service, 1988.
-
- [ISO9577] Information Technology - Telecommunication and information
- exchange between systems - Protocol identification in the network
- layer ISO/IEC TR9577 (International Standards Organization: Geneva,
- 1990)
-
- [LAUB98] Laubach, M., and J. Halpern, "Classical IP and ARP over
- ATM", RFC 2225, April 1998.
-
- [LUC98] Luciani, J., Katz, D., Piscitello, D., Cole, B., and N.
- Doraswamy, "NBMA Next Hop Resolution Protocol (NHRP)", RFC 2332,
- April 1998.
-
- [RFC1755] Perez*, M., et. al., "ATM Signaling Support for IP over
- ATM", RFC 1755, February 1995. (* see author's information below)
-
- [ROM94] Romanow, A., and Floyd, S., Dynamics of TCP Traffic over ATM
- Networks. IEEE JSAC, V. 13 N. 4, May 1995, p. 633-641. Abstract. An
- earlier version appeared in SIGCOMM '94, August 1994, pp. 79-88.
-
- [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S.
- Jamin, "Resource ReSerVation Protocol (RSVP) - Version 1 Functional
- Specification", RFC 2205, September 1997.
-
- [SIG40] ATM Forum, "ATM User-Network Interface (UNI) Signalling
- Specification Version 4.0", af-sig-0061.000, finalized July 1996;
- available at ftp://ftp.atmforum.com/pub.
-
-
-
-
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- Maher Standards Track [Page 11]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- [TMGT40] ATM Forum, "Traffic Management Specification Version 4.0",
- af-tm-0056.000, finalized April 1996; available at
- ftp://ftp.atmforum.com/pub.
-
- [UNI95] ATM Forum, "ATM User-Network Interface Specification Version
- 3.1", Prentice Hall, Upper Saddle River, NJ, 1995.
-
- Author's Address
-
- Maryann P. Maher (formerly Maryann Perez)
- USC/ISI
- 4350 N. Fairfax Drive, Suite 620
- Arlington VA 22203
-
- EMail: maher@isi.edu
-
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- Maher Standards Track [Page 12]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- Appendix A. A Sample SIG 4.0 SETUP Message
-
- +--------------------------------------------------------------------+
- SETUP
-
- Information Elements/
- Fields Value/(Meaning)
- -------------------- ---------------
-
- aal_parameters
- aal_type 5 (AAL 5)
- fwd_max_sdu_size_ident 140
- fwd_max_sdu_size (xmit IP MTU value)
- bkw_max_sdu_size_ident 129
- bkw_max_sdu_size (recv IP MTU, 0 for disallowing return traffic)
- sscs_type identifier 132
- sscs_type 0 (null SSCS)
-
- traffic_descriptor
- fwd_peak_cell_rate_0_1_ident 132
- fwd_peak_cell_rate_0_1 (link rate)
- bkw_peak_cell_rate_0_1_ident 133
- bkw_peak_cell_rate_0_1 (link rate)
- traff_mngt_options_ident 191
- fwd_frame_discard 1 (on)
- bkw_frame_discard 1 (on if return traffic indicated)
- spare 0
- tagging_bkw 1 (on)
- tagging_fwd 1 (on if return traffic indicated)
- best_effort_indication 190 (on)
-
- minimum_acceptable_traffic_descriptor
- fwd_peak_cell_rate_0_1_ident 132
- fwd_peak_cell_rate_0_1 0
- bkw_peak_cell_rate_0_1_ident 133
- bkw_peak_cell_rate_0_1 0
-
- bb_bearer_capability /* a coding for specifying UBR like service */
- spare 0
- bearer_class 16 (BCOC-X)
- spare 0
- atm_transfer_capability 10 (nrt-vbr)
- susceptibility_to_clipping 0 (not susceptible to clipping)
- spare 0
- user_plane_configuration 0 (point_to_point)
-
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-
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- Maher Standards Track [Page 13]
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- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
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- bb_low_layer_information
- layer_2_id 2
- user_information_layer 12 (lan_llc - ISO 8802/2)
-
- qos_parameter
- qos_class_fwd 0 (class 0)
- qos_class_bkw 0 (class 0)
-
- called_party_number
- type_of_number (international number / unknown)
- addr_plan_ident (ISDN / ATM Endsystem Address)
- number (E.164 / ATM Endsystem Address)
-
- calling_party_number
- type_of_number (international number / unknown)
- addr_plan_ident (ISDN / ATM Endsystem Address)
- presentation_indic (presentation allowed)
- spare 0
- screening_indic (user_provided verified and passed)
- number (E.164 / ATM Endsystem Address)
-
- +--------------------------------------------------------------------+
-
- Figure 1.
- Sample contents of SETUP message
-
-
-
-
-
-
-
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- Maher Standards Track [Page 14]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- Appendix B. ABR and VBR Signaling Guidelines for IP Routers
-
- When ATM is used to interconnect routers that are supporting a best
- effort service, the ATM connection typically carries an aggregation
- of IP flows, e.g., all best effort IP traffic between a pair of
- routers. With the efforts undertaken by ATM to be more "packet
- friendly" (e.g., frame discard), it is useful to examine ways that a
- VC can provide service comparable to or better than that of a
- dedicated or leased "link" in terms of performance and packet loss.
-
- For ATM connections used to interconnect routers, a non-zero
- bandwidth reservation may be required to achieve consistently
- adequate performance for the aggregate set of flows. The support of
- bandwidth commitments for an ATM connection carrying IP traffic helps
- to assure that a certain fraction of each link's capacity is reserved
- for the total IP traffic between the routers. Reserving bandwidth
- for the aggregation of best-effort traffic between a pair of routers
- is analogous to provisioning a particular link bandwidth between the
- routers. There are at least 3 service classes defined in the ATM
- Traffic Management specification that provide varying degrees of
- capability that are suitable for interconnecting IP routers: UBR, ABR
- and VBR non-real-time. Although the use of best-effort service (UBR)
- at the ATM layer is the most straightforward and uncomplicated, it
- lacks the capability to enforce bandwidth commitments.
-
- Note that we are talking of providing a "virtual link" between
- routers, for the aggregate traffic. The provisioning is for the
- aggregate. It is therefore distinct from the per-flow bandwidth
- reservations that might be appropriate for Integrated Services.
-
- Even best-effort IP flows, when supported on an aggregate basis, have
- some broad service goals. The primary one is that of keeping packet
- loss rate reasonably small. A service class that strives to achieve
- this, keeping in mind the tradeoff between complexity and adequate
- service, is desirable. It has been recommended in this memo that UBR
- be the default service for this. UBR with (some form of) packet
- discard has the desirable goal of being simple in function, and it
- appears that vendors will be supporting it. However, when available,
- it may be quite worthwhile to consider ABR and VBR non-real-time
- service classes.
-
- Because AAL5 frames with missing cells are discarded by the receiver,
- ATM bandwidth commitments are most useful if supported in the form of
- a committed rate of cell delivery in complete, non-errored AAL5
- frames delivered to the receiver. In addition, it is desirable for
- the ATM connection to deliver additional complete frames, beyond this
- commitment, on a best-effort basis.
-
-
-
-
- Maher Standards Track [Page 15]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- These characteristics can be achieved through the ABR service
- category through the use of a Minimum Cell Rate, if the ABR service
- is supported by the ATM endpoints and if efficient frame discard is
- supported at the ABR source. The mechanisms put in place for the ABR
- service strive to keep loss quite low within the ATM network.
-
- The parameters that should be specified by the end system are (i) the
- Peak Cell Rate (likely the link rate), (ii) the Minimum Cell Rate
- (the committed rate), and (iii) the Cumulative RM Fixed Round-Trip
- Time. The remaining parameter values, if left unspecified by the
- calling party, are selected by the network or are chosen from the
- default values specified in the ATM Forum Traffic Management
- specification.
-
- Parameters (i) and (ii) are contained in the mandatory Traffic
- Descriptor IE, whereas parameter (iii) is contained in the mandatory
- ABR Setup Parameters IE. Other paramenters in the ABR Setup
- Parameters IE may be omitted. (Note that the third IE which pertains
- to ABR signalling, the ABR Additional Parameters IE, is an optional
- IE and therefore need not be included.) Parameter (iii) is dependent
- on the hardware of the end system, so that the default value
- specified for that hardware should be used. In the absense of such a
- default, a value of zero MAY be specified by the end system. Entities
- using ABR connections for IP over ATM SHOULD take advantage of
- parameter negotiation by specifying Peak Cell Rate equal to the link
- rate in the ATM Traffic Descriptor IE of the SETUP message. The value
- selected for the Minimum Cell Rate is implementation specific. Note
- that the MCR also MAY be negotiated if an MCR parameter is included
- by the end system in the Minimum Acceptable ATM Traffic Descriptor
- IE. The use of MCR negotiation by the end system is implementation
- specific. Also, note that Frame Discard MAY be requested for ABR
- connections as well as for UBR connections. Although the ABR service
- attempts to minimize cell loss, the use of Frame Discard may improve
- throughput when cell loss is not eliminated.
-
- ATM recognizes in addition to the service class (UBR, ABR, etc.), a
- notion of a QoS class. The QoS class specifies the type of guarantee
- requested of the network when the call is setup. This is distinct
- from the service class requested for the connection, and the
- specification of the traffic parameters (which specify what the
- source's traffic will look like). QoS class 0 is the "simplest", and
- is called the Unspecified QoS class. In the context of ABR (and VBR
- non-realtime below), we are only concerned with the QoS class
- providing an assurance of acceptable loss behavior for the
- connection.
-
-
-
-
-
-
- Maher Standards Track [Page 16]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- The Unspecified QoS Class (QoS Class 0) MUST be requested for ABR
- connections. In this context, QoS Class 0 corresponds to a network-
- specific objective for the cell loss ratio. Networks in general are
- expected to support a low Cell Loss Ratio for ABR sources that adjust
- cell flow in response to control information.
-
- The VBR-nrt service category provides an alternate means of achieving
- these characteristics. These characteristics may be obtained with
- VBR-nrt connections for which (i) the VBR.3 conformance definition is
- used, (ii) a Sustainable Cell Rate (SCR) and Maximum Burst Size
- (MBS), and Peak Cell Rate (PCR) are specified, and (iii) both tagging
- and frame discard are requested. A request for tagging indicates
- that best-effort delivery is desired for traffic offered in excess of
- the SCR and MBS. A request for frame discard indicates to the
- network that the user desires allocations of committed and excess
- bandwidth to translate into corresponding throughputs at the frame
- level.
-
- As with UBR connections, entities using VBR-nrt connections for IP
- over ATM should take advantage of parameter negotiation by specifying
- PCR equal to the link rate in the ATM Traffic Descriptor IE of the
- SETUP message and PCR equal to SCR in the Minimum Acceptable Traffic
- descriptor. The selection of SCR, MBS, and CLR (cell loss ratio)
- should be implementation specific. However, for IP over ATM, an MBS
- value of N*(Maximum MTU) is RECOMMENDED, where N>=1 with a default of
- 2 and where Maximum MTU is equal to 192 cells (consistent with an IP
- MTU size of 9180 bytes [RFC1626]).
-
-
-
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-
-
- Maher Standards Track [Page 17]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- Appendix C. Combinations of Traffic Related Parameters
-
- This appendix contains a copy of the five tables found in Annex 9 of
- [SIG40] which show the allowable combinations of traffic and QoS
- related parameters in a SIG 4.0 SETUP message.
-
- +--------------------------------------------------------------------+
- |ATM Service Category| CBR |
- |--------------------|---------------|---------------|---------------|
- | Conformance |CBR.1 (note 10)| (note 4) | (note 4) |
- |--------------------|---------------|---------------|---------------|
- | Bearer Capability | | | |
- |--------------------|---------------|---------------|---------------|
- | BB Bearer Class | A | X | VP | A | X | VP^| A | X | VP^|
- |--------------------|---------------|----|-----|----|----|-----|----|
- | ATM Transfer | | | 4,5,| | | 4,5,| |
- | Capability (note 1)| 7 | abs| or 6| 5 | abs| or 6| 5 |
- |--------------------|---------------|---------------|---------------|
- | Traffic Descriptor | | | |
- | for a given dir. | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0) | | | S |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0+1) | S | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0) | | | |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0+1) | | | |
- |--------------------|---------------|---------------|---------------|
- | Best Effort | | | |
- |--------------------|---------------|---------------|---------------|
- | Tagging | N | N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | Frame Discard | Y/N | Y/N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | QoS Classes | * | * | * |
- |--------------------|---------------|---------------|---------------|
- | Transit Delay | O | O | O |
- |--------------------|---------------|---------------|---------------|
- | Peak-to-Peak CDV | O | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0)~ | | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0+1)~ | O | | |
- +--------------------------------------------------------------------+
-
-
-
-
-
-
- Maher Standards Track [Page 18]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- +--------------------------------------------------------------------+
- |ATM Service Category| Real Time VBR |
- |--------------------|---------------|---------------|---------------|
- | Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
- |--------------------|---------------|---------------|---------------|
- | Bearer Capability | | | |
- |--------------------|---------------|---------------|---------------|
- | BB Bearer Class | C | X | VP | C | X | VP | C | X | VP |
- |--------------------|---------------|----|-----|----|----|-----|----|
- | ATM Transfer | | | 1 | | | 1 | |
- | Capability | 19 | 9 | or 9| 9 | 9 | or 9| 9 |
- |--------------------|---------------|---------------|---------------|
- | Traffic Descriptor | | | |
- | for a given dir. | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0) | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0+1) | S | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0) | | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0+1) | S | | |
- |--------------------|---------------|---------------|---------------|
- | Best Effort | | | |
- |--------------------|---------------|---------------|---------------|
- | Tagging | N | N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | Frame Discard | Y/N | Y/N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | QoS Classes | * | * | * |
- |--------------------|---------------|---------------|---------------|
- | Transit Delay(nt.2)| O | O | O |
- |--------------------|---------------|---------------|---------------|
- | Peak-to-Peak CDV | O | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0)~ | | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0+1)~ | O | | |
- +--------------------------------------------------------------------+
-
-
-
-
-
-
-
-
-
-
-
-
- Maher Standards Track [Page 19]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- +--------------------------------------------------------------------+
- |ATM Service Category| Real Time VBR |
- |--------------------|---------------|---------------|---------------|
- | Conformance | (note 4,7) | (note 4,8) | (note 4) |
- |--------------------|---------------|---------------|---------------|
- | Bearer Capability | | | |
- |--------------------|---------------|---------------|---------------|
- | BB Bearer Class | X | X | X | C or VP^|
- |--------------------|---------------|---------------|-----|---------|
- | ATM Transfer | | | | |
- | Capability | 1 or 9 | 1 or 9 | 1or9| 9 |
- |--------------------|---------------|---------------|---------------|
- | Traffic Descriptor | | | |
- | for a given dir. | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0) | S | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0+1) | S | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0) | | | |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0+1) | | | S |
- |--------------------|---------------|---------------|---------------|
- | Best Effort | | | |
- |--------------------|---------------|---------------|---------------|
- | Tagging | Y/N | N | N |
- |--------------------|---------------|---------------|---------------|
- | Frame Discard | Y/N | Y/N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | QoS Classes | * | * | * |
- |--------------------|---------------|---------------|---------------|
- | Transit Delay(nt.2)| O | O | O |
- |--------------------|---------------|---------------|---------------|
- | Peak-to-Peak CDV | O | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0)~ | O | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0+1)~ | | | |
- +--------------------------------------------------------------------+
-
-
-
-
-
-
-
-
-
-
-
-
- Maher Standards Track [Page 20]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- +--------------------------------------------------------------------+
- |ATM Service Category| Non-Real Time VBR |
- |--------------------|---------------|---------------|---------------|
- | Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
- |--------------------|---------------|---------------|---------------|
- | Bearer Capability | | | |
- |--------------------|---------------|---------------|---------------|
- | BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
- |--------------------|---------------|--|--------|---|--|--------|---|
- | ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
- | Capability | 11 |ab| 8,10 |10 |ab| 8,10 |10 |
- |--------------------|---------------|---------------|---------------|
- | Traffic Descriptor | | | |
- | for a given dir. | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0) | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0+1) | S | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0) | | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0+1) | S | | |
- |--------------------|---------------|---------------|---------------|
- | Best Effort | | | |
- |--------------------|---------------|---------------|---------------|
- | Tagging | N | N | Y |
- |--------------------|---------------|---------------|---------------|
- | Frame Discard | Y/N | Y/N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | QoS Classes | * | * | * |
- |--------------------|---------------|---------------|---------------|
- | Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
- |--------------------|---------------|---------------|---------------|
- | Peak-to-Peak CDV | | | |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0)~ | | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0+1)~ | O | | |
- +--------------------------------------------------------------------+
-
-
-
-
-
-
-
-
-
-
-
-
- Maher Standards Track [Page 21]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- +--------------------------------------------------------------------+
- |ATM Service Category| Non-Real Time VBR |
- |--------------------|---------------|---------------|---------------|
- | Conformance | (note 4,7) | (note 4,8) | (note 4) |
- |--------------------|---------------|---------------|---------------|
- | Bearer Capability | | | |
- |--------------------|---------------|---------------|---------------|
- | BB Bearer Class | C | X | C | X |C | X |VP^|
- |--------------------|-------|-------|-------|-------|--|--------|---|
- | ATM Transfer | |abs,0,2| |abs,0,2| |abs,0,2,|abs|
- | Capability | abs |8 or 10| |8 or 10|ab| 8 or10 |10 |
- |--------------------|---------------|---------------|---------------|
- | Traffic Descriptor | | | |
- | for a given dir. | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0) | S | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0+1) | S | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0) | | | |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0+1) | | | S |
- |--------------------|---------------|---------------|---------------|
- | Best Effort | | | |
- |--------------------|---------------|---------------|---------------|
- | Tagging | Y/N | N | N |
- |--------------------|---------------|---------------|---------------|
- | Frame Discard | Y/N | Y/N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | QoS Classes | * | * | * |
- |--------------------|---------------|---------------|---------------|
- | Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
- |--------------------|---------------|---------------|---------------|
- | Peak-to-Peak CDV | | | |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0)~ | O | O | O |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0+1)~ | | | |
- +--------------------------------------------------------------------+
-
-
-
-
-
-
-
-
-
-
-
-
- Maher Standards Track [Page 22]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- +--------------------------------------------------------------------+
- |ATM Service Category| ABR | UBR |
- |--------------------|---------------|---------------|---------------|
- | Conformance | ABR | UBR.1 | UBR.2 |
- |--------------------|---------------|---------------|---------------|
- | Bearer Capability | | | |
- |--------------------|---------------|---------------|---------------|
- | BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
- |--------------------|---------------|--|--------|---|--|--------|---|
- | ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
- | Capability | 12 |ab| 8,10 |10 |ab| 8,10 |10 |
- |--------------------|---------------|---------------|---------------|
- | Traffic Descriptor | | | |
- | for a given dir. | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0) | | | |
- |--------------------|---------------|---------------|---------------|
- | PCR (CLP=0+1) | S | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0) | | S | S |
- |--------------------|---------------|---------------|---------------|
- | SCR, MBS (CLP=0+1) | S | | |
- |--------------------|---------------|---------------|---------------|
- | ABR MCR | (note 6) | | |
- |--------------------|---------------|---------------|---------------|
- | Best Effort | | S (note 9) | S (note 9) |
- |--------------------|---------------|---------------|---------------|
- | Tagging | N | N | N |
- |--------------------|---------------|---------------|---------------|
- | Frame Discard | Y/N | Y/N | Y/N |
- |--------------------|---------------|---------------|---------------|
- | QoS Classes | 0 | 0 | 0 |
- |--------------------|---------------|---------------|---------------|
- | Transit Delay(nt.2)| | | |
- |--------------------|---------------|---------------|---------------|
- | Peak-to-Peak CDV | | | |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0)~ | | | |
- |--------------------|---------------|---------------|---------------|
- | CLR (CLP=0+1)~ | | | |
- +--------------------------------------------------------------------+
-
- ab, abs = absent.
-
- Y/N = either "Yes" or "No" is allowed.
-
-
-
-
-
-
- Maher Standards Track [Page 23]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- O = Optional. May be specified using:
-
- - an additional QoS parameter encoded i the Extended QoS
- parameters information element or the end-to-end transit
- information element; or,
-
- - objectives implied from the QoS class If an Extended
- QoS Parameters IE is not present in the message, then any
- value of this parameter is acceptable. If neither the
- parameter nor the Extended QoS Parameters IE is present,
- then the objective for this parameter is determined from
- the QoS class in the QoS Parameter IE.
-
- S = Specified.
-
- (blank) = Unspecified.
-
- * = allowed QoS class values are a network option. Class 0 is
- always for alignment with ITU-T.
-
- ^ = (note 5).
-
- ~ = (note 11).
-
- Note 1 - Values 0,1,2,4,6, and 8 are not used on transmission
- but shall be understood on reception.
-
- Note 2 - Maximum end-2-end transit delay objectives may only be
- specified for the forward direction.
-
- Note 3 - Maximum end-2-end transit delay objectives may be
- specified for the ATM Service Category of Non-real
- Time VBR for reasons of backward compatibility with
- ITU-T Recommendations.
-
- Note 4 - Included for reasons of backward compatibility with
- UNI 3.1and ITU-T Recommendations. With these
- conformance definitions, the CLR commitment is only
- for the CLP=0 traffic stream.
-
- Note 5 - Included to allow switched virtual paths to use the
- UNI 3.1 conformance definitions.
-
- Note 6 - Optional in the user-to-network direction. Specified
- in the network-to-user direction.
-
-
-
-
-
-
- Maher Standards Track [Page 24]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- Note 7 - This combination should be treated as if the received
- PCR (CLP=0) parameter were a SCR (CLP=0) parameter and
- a MBS (CLP=0) parameter with a value of 1.
-
- Note 8 - This combination should be treated as if an additional
- SCR (CLP=0) parameter were received with the same
- value as a PCR (CLP=0+1) parameter and a MBS (CLP=0)
- parameter with a value of 1.
-
- Note 9 - The best effort parameter applies to both the forward
- and backward directions.
-
- Note 10 - This combination should only be used when the CLR
- commitment on CLP=0+1 is required versus CLR
- commitment on CLP=0 traffic, since these combinations
- are not supported by UNI 3.0/3.1 nor ITU-T Q.2931.
-
- Note 11 - In this table the CLR commitment is shown as two
- entries to indicated explicitly whether the CLR
- commitment is for the CLP=0 or the CLP=0+1 cells.
-
-
-
-
-
-
-
-
-
-
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- Maher Standards Track [Page 25]
-
- RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
-
- Full Copyright Statement
-
- Copyright (C) The Internet Society (1998). All Rights Reserved.
-
- 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.
-
-
-
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- Maher Standards Track [Page 26]
-
-