As per Relevance of the word signalling, we have this rfc below:
Network Working Group M.
Request for Comments: 2331 USC/
Category: Standards Track April 1998
ATM Signalling Support for IP over ATM - UNI Signalling 4.0
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
This memo describes how to efficiently use the ATM call
signalling procedures defined in UNI Signalling 4.0 [SIG40]
support IP over ATM environments as described in RFC 2225 [LAUB98]
and in RFC 2332 [LUC98]. Among the new features found in
Signalling 4.0 are Available Bit Rate signalling and
parameter negotiation. This memo highlights the features of
Signalling 4.0 that provide IP entities capabilities for
ATM service in sites with SVC support, whether it is private ATM
publicly provisioned ATM, in which case the SVC support is
configured inside PVPs
This document is only relevant to IP when used as the well
"best effort" connectionless service. In particular, this means
this document does not pertain to IP in the presence of
IP Integrated Services. The topic of IP with Integrated
over ATM will be handled by a different specification or set
specifications being worked on in the ISSLL WG
This specification is a follow-on to RFC 1755, "ATM Signaling
for IP over ATM", which is based on UNI 3.1 signalling [UNI95].
Readers are assumed to be familiar with RFC 1755.
Maher Standards Track [Page 1]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
Table of
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.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
document are to be interpreted as described in RFC 2119 [BRA97].
2.
UNI Signalling version 4.0 (SIG 4.0) is the ATM Forum follow-
specification to UNI 3.1 signalling (UNI 3.1). Among the new
in SIG 4.0, those of particular interest to IP over ATM
are
o Available Bit Rate (ABR) Signalling for Point-to-Point
o Traffic Parameter
o Frame Discard
o Leaf Initiated Join (LIJ)
o ATM Anycast
o Switched Virtual Path (VP)
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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
This memo highlights the first three capabilities listed above.
last three capabilities are not discussed because models for
use in IP over ATM environments have not yet been defined. The
WG is considering the applicability of LIJ and Group Addressing
the RFC2022 problem space. Furthermore, Anycast addressing is
explored as a technique for supporting server discovery in
networks
3. Use of Protocol
Section 3 in RFC 1755 introduces requirements of virtual circuit (VC
management intended to prevent VC thrashing, excessive
consumption, and other related problems. This section updates
1755's requirements related to VC teardown
3.1. VC
In environments running layer 3 (L3) signalling protocols, such
RSVP [RSVP], over ATM, data VCs might correspond to L3 reserved
(even if the VC is a 'best effort' VC). In such environments it
beneficial for VCs to be torn down only when the L3 reservation
expired. In other words, it is more efficient for the sender of a L
reserved flow to initiate VC tear-down when the receiver(s)
ceased refreshing the reservation. To support such L3 behavior
systems implementing a Public ATM UNI interface and serving as
_called_ party of a VCC MUST NOT use an inactivity timer on such
VCC by default. A system MAY use an inactivity timer on such a
if configured to do so
4. Overview of Call Establishment Message
Signalling messages are structured to contain mandatory and
variable length information elements (IEs). A SETUP message
establishes an ATM connection to be used for IP and
interconnection calls MUST contain the following IEs
AAL
ATM Traffic
Broadband Bearer
Broadband Low Layer
QoS
Called Party
Calling Party
and MAY, under certain circumstance contain the following IEs
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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
Calling Party
Called Party
Transit Network
(New in SIG 4.0:)
Minimum Acceptable ATM Traffic
Alternative ATM Traffic
ABR Setup
ABR Additional
Connection Scope
Extended QoS
End-to-End Transit
In SIG 4.0, like UNI 3.1, the AAL Parameters and the Broadband
Layer Information IEs are optional in a SETUP message. However,
support of IP over ATM these two IEs MUST be included. Appendix
shows a sample setup message
5. Description of Information
This section describes the coding of, and procedures surrounding
information elements in SETUP and CONNECT messages. The first two
described, ATM Adaptation Layer Parameters and Broadband Low
Information, are categorized as having significance only to the end
points of an ATM call supporting IP. That is, the network does
process these IEs
5.1. ATM Adaptation Layer (AAL)
The AAL Parameters IE carries information about the ATM
layer to be used on the connection. The parameters specified in
IE are the same as specified in [PER95].
Format and field values of AAL Parameters
----------------------------------------------------------
| 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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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
This shows maximum size MTUs. In practice, most sites have used 9180
IP MTUs for ATM [RFC1626].
5.2. Broadband Low Layer
Selection of an encapsulation to support IP over an ATM VCC is
using the Broadband Low Layer Information (B-LLI) IE, along with
AAL Parameters IE, and the B-LLI negotiation procedure. B-
negotiation is described in [PER95] in Appendix D. The
remain the same for this SIG 4.0 based specification
Format of B-LLI IE indicating LLC/SNAP
----------------------------------------------------------
| bb_low_layer_information |
----------------------------------------------------------
| layer_2_id 2 |
| user_information_layer 12 (lan_llc - ISO 8802/2) |
----------------------------------------------------------
5.3. Traffic Management Issues and Related
The ATM Forum Traffic Management Sub-working group has
version 4.0 of their specification [TMGT40]. This latest
focuses primarily on the definition of the ABR service category.
opposed to the Unspecified Bit Rate (UBR) traffic class, ABR uses
rate-based flow control mechanism to assure certain
guarantees (bandwidth and delay). There has been much debate
whether IP benefits from ABR, and if so, how IP should use ABR.
IP Integrated Services (IIS) and RSVP models in IP add complexity
this issue because mapping IIS traffic classes to ATM traffic
is not straightforward
This document attempts only to present the required IP to
signaling interface for IP over ATM systems that do not support
as yet. It is an attempt to cause IP over ATM vendors to
enough options for signalling the traffic characteristics of
serving non-IIS IP datagrams. This specification also aims to
guidance to ATM system administrators so that they can
their IP over ATM entities to conform to the varied services
their ATM provider may have sold to them. By definition, IP
IIS cannot be expected to provide a signalling interface that
flexible and allows application specific traffic descriptors.
topic of IP over ATM signalling for IP _with_ IIS is to be
in other specifications being produced by the ISSLL WG of the IETF
An IP over ATM interface may be configured to support all the
ATM Service Categories (ASC). They are
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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
-
- CBR with CLR specified (loss-permitting CBR
-
-
- real time
- non-real time
The ATM Traffic Descriptor IE, Broadband Bearer Capability IE,
the QoS Parameter IE together define the signalling view of
traffic management. Additionally, the Extended QoS parameters IE
the End-to-end Transit Delay IE may be used to provide more
about traffic requirements, however this note does not
explicit recommendations on their use. Annex 9 of [SIG40]
a set of allowable combinations of traffic and QoS
paramenters defined for SIG 4.0. This set includes all forms
non-IIS IP signaling configurations that MUST be implemented in
endsystems to accommodate varied sites' needs. The principle is
IP over ATM service may be available in different sites by
types of procured ATM service; for one site, a CBR PVP might
cost-effective and then the SVCs that IP over ATM without IIS
establish must be CBR. Similarly, VBR or ABR PVPs could
provisioned. The intent of this document is to specify the use
the most sensible parameters within this non-IIS configuration.
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-
with a 0 MCR
For the reader's convenience, we have replicated the tables found
Annex 9 of [SIG40] in Appendix C of this document. Ideally
document could recommend specific values for the various
parameters that would offer the most sensible IP over ATM service
Nevertheless, it is not possible to mandate specific values given
varied scenarios of procured ATM service
5.3.1. ATM Traffic
Even with the newly defined ABR ASC, the most convenient model
supporting IP still corresponds to the best effort capability,
UBR ASC. The rationale for this assertion stems from the fact that
non-IIS IP service has no notion of the performance requirements
the higher layers it supports. Therefore, if a site's
allows use of UBR, users SHOULD signal for it using the IE's
parameters pertaining to the UBR ATC. See Appendix C for the list
those IE's and parameters
Although we consider the UBR ASC the most natural ASC for best-
IP, ATM vendors that implement VBR and ABR services could
create hooks for convenient use of these services. If this is
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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
case, IP routers may perhaps have the most to gain from use of VBR
ABR services because of the large aggregated traffic volume they
required to forward. See Appendix B for detailed suggestions on
and ABR signalling for IP routers. We simply note here that,
support of ABR service, two new subfields have been added in SIG 4.0
to the Traffic Descriptor IE. These fields are the forward
backward 'Minimum Cell Rate' fields
5.3.1.1. Tagging vs.
The Traffic Descriptor IE contains a 'tagging' subfield used
indicating whether the network is allowed to tag the source's
cells. Tagging in the network may occur during periods of
or when the source's traffic has violated the traffic contract
the connection. See Section 4 of [TMGT40] for an explanation of
connection conformance and the Usage Parameter Control (UPC
function
SIG 4.0 and TMGT 4.0 define two modes of UBR, UBR.1 which
tagging and UBR.2 which enables tagging (see Appendix C). In
network environments there is no potential for UBR traffic sources
violate the connection traffic contract because, either the user'
terminal equipment supports traffic shaping, or the network does
enforce PCR. In such environments, the user SHOULD specify '
tagging' in the SETUP message (UBR.1). Specifying 'no tagging
indicates to the network that cells should be dropped during
of congestion instead of being randomly marked/tagged as
priority. Cells of packets that the source itself has marked as
priority are dropped first, thereby preserving the source'
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
source, the source has the potential to violate the traffic
and SHOULD therefore signal for tagging (UBR.2). Tagging allows
source's non-conforming cells to be tagged and forwarded instead
dropped
5.3.2. Traffic Parameter
SIG 4.0 allows certain traffic parameters to be negotiated during
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
negotiation of PCR
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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
- the Alternative ATM Traffic Descriptor IE allows negotiation
other traffic
A SETUP or CONNECT message may include ONLY one of the above IEs
That is, the calling party may only offer an 'alternative'
'minimum' to the requested traffic parameters. (See Section 8
[SIG40].) IP over ATM entities SHOULD take advantage of
capability whenever possible. In order to do so, IP over ATM
SHOULD specify PCR _equal_ to the link rate in the ATM
Descriptor IE of the SETUP message and a minimum of zero PCR in
Minimum Acceptable ATM Traffic Descriptor IE
5.3.3. Broadband Bearer
A new field in UNI signalling 4.0 called, 'ATM Transfer Capability
(ATC), has been defined in the Broadband Bearer Capability IE for
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
-------------------------------------------------------------
| 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
Inclusion of the QoS Parameter IE is not mandatory in SIG 4.0.
may be omitted from a SETUP message _if and only if_ the Extended
Parameters IE is included (see next section). This
makes no explicit recommendation on the use of the QoS related IEs
5.3.4.1. Two IEs for Signalling of Individual QoS
SIG 4.0 allows for signalling of individual QoS parameters for
purpose of giving the the network and called party a more
description of the desired delay and cell loss characteristics.
two individual QoS related IEs, Extended QoS Parameters IE and End
to-End Transit Delay IE, can be used in the SETUP and
signaling messages in place of the 'generic' QoS Parameter IE.
that inclusion of these two IEs depends on the type of ATM
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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
category requested (see Annex 9 in [SIG40]).
5.4. ATM Addressing
ATM addressing information is carried in the Called Party Number
Calling Party Number, and, under certain circumstance, Called
Subaddress, and Calling Party Subaddress IE. The ATM Forum
Specification 4.0 [ILMI40] provides the procedure for an
endsystem to learn its own ATM address from the ATM network, for
in populating the Calling Party Number IE
Format and field values of Called Party Number
----------------------------------------------------------
| 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
The IEs and procedures pertaining to ABR signalling are
described in this section. Nevertheless, this document makes
specific recommendation on when to use the ABR service category
IP VCCs or give suggestions on appropriate values for the
parameters in the ABR related IEs
Two new IEs have been defined for ABR signaling
o ABR Setup
o ABR Additional
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
- Forward/Backward ABR Transient Buffer
- Cumulative RM Fixed Round Trip
- Forward/Backward Rate Increment
- Forward/Backward Rate Decrease
The ABR Additional Parameters IE contains one subfield
- Forward/Backward Additional Parameters
Maher Standards Track [Page 9]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
The Additional Parameters Record value is a compressed encoding of
set of ABR parameters (see [SIG40] and [ABRS]).
7. Frame Discard
The frame discard capability in SIG 4.0 is primarily based on
'Partial and Early Packet Discard' strategy [ROM94]. Its use
defined for any of the ATM services, except for loss-less CBR.
discard signaling MUST be supported by all IP over ATM entities
it is RECOMMENDED that frame discard be signaled for all IP
because it has been proven to increase throughput under
congestion. Signaling for frame discard is done by setting the
discard bit in the 'Traffic Management Options' subfield in
Traffic Descriptor IE. It is possible that not all network
in the SVC path support frame discard, but it is required that
all forward the signaling
8. Security
The ATM Forum Security sub-working group is currently
security mechanisms in ATM. The group has yet to produce
specification, therefore it is premature to begin defining IP
ATM signalling's use of ATM security. The ATM Forum is working
authentication mechanisms for signalling and on mechanisms
providing data integrity and confidentiality (e.g encryption).
of these ATM security mechanisms prevents the authentication of
originator of signalling messages, such as, connection setup
or connection teardown request. IP Security (RFC1825) can be
to IP datagrams over ATM VCs to overcome the lack of security at
ATM layer
9.
The authors would like to thank the members of the ION working
for their input. Special thanks to K.K. Ramakrishnan and
Fendick who contributed Appendix B of this document
[ABRS] ATM Forum, "Addendum to UNI Signalling v4.0 for ABR
Negotiation", af-sig-0076.000; available
ftp://ftp.atmforum.com/pub
[ABRT] ATM Forum, "Addendum to Traffic Management v4.0 for
Parameter Negotiation", af-tm-0077.000; available
ftp://ftp.atmforum.com/pub
Maher Standards Track [Page 10]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
[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
in the Internet Architecture: An Overview", RFC 1633, June 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC1483] Heinanen, J., "Multiprotocol Encapsulation over
Adaptation Layer 5", RFC 1483, July 1993.
[ILMI40] ATM Forum, "Integrated Local Management Interface (ILMI
Specification Version 4.0", af-ilmi-0065.000, finalized
1996; available at ftp://ftp.atmforum.com/pub
[ISO8473] ISO/IEC 8473, Information processing systems -
communications - Protocol for providing the connectionless-
network service, 1988.
[ISO9577] Information Technology - Telecommunication and
exchange between systems - Protocol identification in the
layer ISO/IEC TR9577 (International Standards Organization: Geneva
1990)
[LAUB98] Laubach, M., and J. Halpern, "Classical IP and ARP
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
ATM", RFC 1755, February 1995. (* see author's information below
[ROM94] Romanow, A., and Floyd, S., Dynamics of TCP Traffic over
Networks. IEEE JSAC, V. 13 N. 4, May 1995, p. 633-641. Abstract.
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
Specification", RFC 2205, September 1997.
[SIG40] ATM Forum, "ATM User-Network Interface (UNI)
Specification Version 4.0", af-sig-0061.000, finalized July 1996;
available at ftp://ftp.atmforum.com/pub
Maher Standards Track [Page 11]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
[TMGT40] ATM Forum, "Traffic Management Specification Version 4.0",
af-tm-0056.000, finalized April 1996; available
ftp://ftp.atmforum.com/pub
[UNI95] ATM Forum, "ATM User-Network Interface Specification
3.1", Prentice Hall, Upper Saddle River, NJ, 1995.
Author's
Maryann P. Maher (formerly Maryann Perez
USC/
4350 N. Fairfax Drive, Suite 620
Arlington VA 22203
EMail: maher@isi.
Maher Standards Track [Page 12]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
Appendix A. A Sample SIG 4.0 SETUP
+--------------------------------------------------------------------+
Information Elements
Fields Value/(Meaning
-------------------- ---------------
aal_
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_
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_
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
Maher Standards Track [Page 13]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
bb_low_layer_
layer_2_id 2
user_information_layer 12 (lan_llc - ISO 8802/2)
qos_
qos_class_fwd 0 (class 0)
qos_class_bkw 0 (class 0)
called_party_
type_of_number (international number / unknown
addr_plan_ident (ISDN / ATM Endsystem Address
number (E.164 / ATM Endsystem Address
calling_party_
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
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RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
Appendix B. ABR and VBR Signaling Guidelines for IP
When ATM is used to interconnect routers that are supporting a
effort service, the ATM connection typically carries an
of IP flows, e.g., all best effort IP traffic between a pair
routers. With the efforts undertaken by ATM to be more "
friendly" (e.g., frame discard), it is useful to examine ways that
VC can provide service comparable to or better than that of
dedicated or leased "link" in terms of performance and packet loss
For ATM connections used to interconnect routers, a non-
bandwidth reservation may be required to achieve
adequate performance for the aggregate set of flows. The support
bandwidth commitments for an ATM connection carrying IP traffic
to assure that a certain fraction of each link's capacity is
for the total IP traffic between the routers. Reserving
for the aggregation of best-effort traffic between a pair of
is analogous to provisioning a particular link bandwidth between
routers. There are at least 3 service classes defined in the
Traffic Management specification that provide varying degrees
capability that are suitable for interconnecting IP routers: UBR,
and VBR non-real-time. Although the use of best-effort service (UBR
at the ATM layer is the most straightforward and uncomplicated,
lacks the capability to enforce bandwidth commitments
Note that we are talking of providing a "virtual link"
routers, for the aggregate traffic. The provisioning is for
aggregate. It is therefore distinct from the per-flow
reservations that might be appropriate for Integrated Services
Even best-effort IP flows, when supported on an aggregate basis,
some broad service goals. The primary one is that of keeping
loss rate reasonably small. A service class that strives to
this, keeping in mind the tradeoff between complexity and
service, is desirable. It has been recommended in this memo that
be the default service for this. UBR with (some form of)
discard has the desirable goal of being simple in function, and
appears that vendors will be supporting it. However, when available
it may be quite worthwhile to consider ABR and VBR non-real-
service classes
Because AAL5 frames with missing cells are discarded by the receiver
ATM bandwidth commitments are most useful if supported in the form
a committed rate of cell delivery in complete, non-errored AAL
frames delivered to the receiver. In addition, it is desirable
the ATM connection to deliver additional complete frames, beyond
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
category through the use of a Minimum Cell Rate, if the ABR
is supported by the ATM endpoints and if efficient frame discard
supported at the ABR source. The mechanisms put in place for the
service strive to keep loss quite low within the ATM network
The parameters that should be specified by the end system are (i)
Peak Cell Rate (likely the link rate), (ii) the Minimum Cell
(the committed rate), and (iii) the Cumulative RM Fixed Round-
Time. The remaining parameter values, if left unspecified by
calling party, are selected by the network or are chosen from
default values specified in the ATM Forum Traffic
specification
Parameters (i) and (ii) are contained in the mandatory
Descriptor IE, whereas parameter (iii) is contained in the
ABR Setup Parameters IE. Other paramenters in the ABR
Parameters IE may be omitted. (Note that the third IE which
to ABR signalling, the ABR Additional Parameters IE, is an
IE and therefore need not be included.) Parameter (iii) is
on the hardware of the end system, so that the default
specified for that hardware should be used. In the absense of such
default, a value of zero MAY be specified by the end system.
using ABR connections for IP over ATM SHOULD take advantage
parameter negotiation by specifying Peak Cell Rate equal to the
rate in the ATM Traffic Descriptor IE of the SETUP message. The
selected for the Minimum Cell Rate is implementation specific.
that the MCR also MAY be negotiated if an MCR parameter is
by the end system in the Minimum Acceptable ATM Traffic
IE. The use of MCR negotiation by the end system is
specific. Also, note that Frame Discard MAY be requested for
connections as well as for UBR connections. Although the ABR
attempts to minimize cell loss, the use of Frame Discard may
throughput when cell loss is not eliminated
ATM recognizes in addition to the service class (UBR, ABR, etc.),
notion of a QoS class. The QoS class specifies the type of
requested of the network when the call is setup. This is
from the service class requested for the connection, and
specification of the traffic parameters (which specify what
source's traffic will look like). QoS class 0 is the "simplest",
is called the Unspecified QoS class. In the context of ABR (and
non-realtime below), we are only concerned with the QoS
providing an assurance of acceptable loss behavior for
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
connections. In this context, QoS Class 0 corresponds to a network
specific objective for the cell loss ratio. Networks in general
expected to support a low Cell Loss Ratio for ABR sources that
cell flow in response to control information
The VBR-nrt service category provides an alternate means of
these characteristics. These characteristics may be obtained
VBR-nrt connections for which (i) the VBR.3 conformance definition
used, (ii) a Sustainable Cell Rate (SCR) and Maximum Burst
(MBS), and Peak Cell Rate (PCR) are specified, and (iii) both
and frame discard are requested. A request for tagging
that best-effort delivery is desired for traffic offered in excess
the SCR and MBS. A request for frame discard indicates to
network that the user desires allocations of committed and
bandwidth to translate into corresponding throughputs at the
level
As with UBR connections, entities using VBR-nrt connections for
over ATM should take advantage of parameter negotiation by
PCR equal to the link rate in the ATM Traffic Descriptor IE of
SETUP message and PCR equal to SCR in the Minimum Acceptable
descriptor. The selection of SCR, MBS, and CLR (cell loss ratio
should be implementation specific. However, for IP over ATM, an
value of N*(Maximum MTU) is RECOMMENDED, where N>=1 with a default
2 and where Maximum MTU is equal to 192 cells (consistent with an
MTU size of 9180 bytes [RFC1626]).
Maher Standards Track [Page 17]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
Appendix C. Combinations of Traffic Related
This appendix contains a copy of the five tables found in Annex 9
[SIG40] which show the allowable combinations of traffic and
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
parameters information element or the end-to-end
information element; or
- objectives implied from the QoS class If an
QoS Parameters IE is not present in the message, then
value of this parameter is acceptable. If neither
parameter nor the Extended QoS Parameters IE is present
then the objective for this parameter is determined
the QoS class in the QoS Parameter IE
S = Specified
(blank) = Unspecified
* = allowed QoS class values are a network option. Class 0
always for alignment with ITU-T
^ = (note 5).
~ = (note 11).
Note 1 - Values 0,1,2,4,6, and 8 are not used on
but shall be understood on reception
Note 2 - Maximum end-2-end transit delay objectives may only
specified for the forward direction
Note 3 - Maximum end-2-end transit delay objectives may
specified for the ATM Service Category of Non-
Time VBR for reasons of backward compatibility
ITU-T Recommendations
Note 4 - Included for reasons of backward compatibility
UNI 3.1and ITU-T Recommendations. With
conformance definitions, the CLR commitment is
for the CLP=0 traffic stream
Note 5 - Included to allow switched virtual paths to use
UNI 3.1 conformance definitions
Note 6 - Optional in the user-to-network direction.
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
PCR (CLP=0) parameter were a SCR (CLP=0) parameter
a MBS (CLP=0) parameter with a value of 1.
Note 8 - This combination should be treated as if an
SCR (CLP=0) parameter were received with the
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
and backward directions
Note 10 - This combination should only be used when the
commitment on CLP=0+1 is required versus
commitment on CLP=0 traffic, since these
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
entries to indicated explicitly whether the
commitment is for the CLP=0 or the CLP=0+1 cells
Maher Standards Track [Page 25]
RFC 2331 IP over ATM Signalling - SIG 4.0 Update April 1998
Full Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Maher Standards Track [Page 26]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
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