home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Internet Info 1997 December
/
Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso
/
drafts
/
draft_ietf_i
/
draft-ietf-issll-atm-imp-guide-01.txt
< prev
next >
Wrap
Text File
|
1997-07-15
|
14KB
|
409 lines
Internet Draft L. Berger
Expires: January 1998 FORE Systems
File: draft-ietf-issll-atm-imp-guide-01.txt
RSVP over ATM Implementation Guidelines
July 11, 1997
Status of Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ds.internic.net (US East Coast), nic.nordu.net
(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
Rim).
Abstract
This note presents specific implementation guidelines for running
RSVP over ATM switched virtual circuits (SVCs). The general problem
is discussed in [8]. Implementation requirements are discussed in
[3]. Integrated Services to ATM service mappings are covered in [6].
The full set of documents present the background and information
needed to implement Integrated Services and RSVP over ATM.
Berger Expires: January 1998 [Page 1]
Internet Draft RSVP over ATM Guidelines July 1997
1. Introduction
This note discusses running IP over ATM in an environment where SVCs
are used to support QoS flows and RSVP is used as the internet level
QoS signaling protocol. It applies when using CLIP/ION, LANE2.0 and
MPOA methods for supporting IP over ATM. The general issues related
to running RSVP[7] over ATM have been covered in several papers
including [8,4,2,5]. This document is intended as a companion to
[8,3] and as a guide to implementers. The reader should be familiar
with both documents.
This document will provide a recommended set of functionality for
implementations using ATM UNI3.x and 4.0, while allowing for more
sophisticated approaches. We expect some vendors to additionally
provide some of the more sophisticated approaches described in [8],
and some networks to only make use of such approaches. The
recommended set of functionality is defined to ensure predictability
and interoperability between different implementations. Requirements
for RSVP over ATM implementations are provided in [3].
This document uses the same terms and assumption stated in [3].
2. Implementation Recommendations
This section provides implementation guidelines for implementation of
RSVP over ATM. Several recommendations are common for all, both
unicast and multicast, RSVP sessions. There are also recommendations
that are unique to unicast and multicast session types.
2.1 RSVP Message VC Usage
The general issues related to which VC should be used for RSVP
messages is covered in [8]. It discussed several implementation
options including: mixed control and data, single control VC per
session, single control VC multiplexed among sessions, and
multiple VCs multiplexed among sessions. QoS for control VCs was
also discussed. The general discussion is not repeated here and
[8] should be reviewed for detailed information.
RSVP over ATM implementations SHOULD send RSVP control (messages)
over the best effort data path, see figure 1. It is permissible
to allow a user to override this behavior. The stated approach
minimizes VC requirements since the best effort data path will
need to exist in order for RSVP sessions to be established and in
order for RSVP reservations to be initiated. The specific best
effort paths that will be used by RSVP are: for unicast, the same
VC used to reach the unicast destination; and for multicast, the
same VC that is used for best effort traffic destined to the IP
Berger Expires: January 1998 [Page 2]
Internet Draft RSVP over ATM Guidelines July 1997
multicast group. Note that for multicast there may be another
best effort VC that is used to carry session data traffic, i.e.,
for data that is both in the multicast group and matching a
sessions protocol and port.
Data Flow ==========>
QoS VCs
+-----+ --------------> +----+
| | --------------> | |
| Src | | R1 |
| | Best Effort VC(s) | |
+-----+ <-----------------> +----+
/\
||
||
RSVP Control
Messages
Figure 1: RSVP Control Message VC Usage
The disadvantage of this approach is that best effort VCs may not
provide the reliability that RSVP needs. However the best-effort
path is expected to satisfy RSVP reliability requirements in most
networks. Especially since RSVP allows for a certain amount of
packet loss without any loss of state synchronization.
2.2 Aggregation
As discussed in [8], data associated with multiple RSVP sessions
could be sent using the same shared VCs. Implementation of such
"aggregation" models is still a matter for research. Therefore,
RSVP over ATM implementations SHOULD use independent VCs for each
RSVP reservation.
2.3 Short-Cuts
Short-cuts allow ATM attached routers and hosts to directly
establish point-to-point VCs across LIS boundaries, i.e., the VC
end-points are on different IP sub-nets. Short-cut support for
unicast traffic has been defined in [9] and [1]. The ability for
short-cuts and RSVP to interoperate has been raised as a general
question. The area of concern is the ability to handle asymmetric
short-cuts. Specifically how RSVP can handle the case where a
downstream short-cut may not have a matching upstream short-cut.
In this case, which is shown in figure 2, PATH and RESV messages
Berger Expires: January 1998 [Page 3]
Internet Draft RSVP over ATM Guidelines July 1997
following different paths.
______
/ \
+-------- / Router \ <-------+
| \ / | <....... RESVs Follow
| \______/ | Hop-by-hop Path
| |
| |
V QoS VCs |
+-----+ ==============> +----+
| | ==============> | |
| Src | | R1 |
| | Best Effort VC(s) | |
+-----+ <=================> +----+
/\
:: Data Paths:
:: ----> Hop-by-hop (routed)
PATHs and Data ====> Short-cut
Follow Short-cut
Path
Figure 2: Asymmetric RSVP Message Forwarding With ATM Short-Cuts
Examination of RSVP shows that the protocol already includes
mechanisms that allows support of short-cuts. The mechanism is
the same one used to support RESV messages arriving at the wrong
router and the wrong interface. The key aspect of this mechanism
is RSVP only processing messages that arrive at the proper
interface and RSVP forwarding of messages that arrive on the wrong
interface. The proper interface is indicated in the NHOP object
of the message. So, existing RSVP mechanisms will support
asymmetric paths.
The short-cut model of VC establishment still poses several issues
when running with RSVP. The major issues are dealing with
established best-effort short-cuts, when to establish short-cuts,
and QoS only short-cuts. These issues will need to be addressed by
RSVP implementations.
The key issue to be addressed by any RSVP over ATM solution is
when to establish a short-cut for a QoS data flow. RSVP over ATM
implementations SHOULD simply follow best-effort traffic. When a
short-cut has been established for best-effort traffic to a
destination or next-hop, that same end-point SHOULD be used when
Berger Expires: January 1998 [Page 4]
Internet Draft RSVP over ATM Guidelines July 1997
setting up RSVP triggered VCs for QoS traffic to the same
destination or next-hop. This will happen naturally when PATH
messages are forwarded over the best-effort short-cut. Note that
in this approach when best-effort short-cuts are never
established, RSVP triggered QoS short-cuts will also never be
established.
2.4 Data VC Management for Heterogeneous Sessions
Heterogeneous sessions can only occur with multicast RSVP
sessions. The issues relating to data VC management of
heterogeneous sessions are covered in detail in [8] and are not
repeated. In summary, heterogeneity occurs when receivers request
different levels of QoS within a single session and also when some
receivers do not request any QoS. Both types of heterogeneity are
shown in figure 3.
+----+
+------> | R1 |
| +----+
|
| +----+
+-----+ -----+ +--> | R2 |
| | ---------+ +----+ Receiver Request Types:
| Src | ----> QoS 1 and QoS 2
| | .........+ +----+ ....> Best-Effort
+-----+ .....+ +..> | R3 |
: +----+
/\ :
|| : +----+
|| +......> | R4 |
|| +----+
Single
IP Mulicast
Group
Figure 3: Types of Multicast Receivers
[8] provides four models for dealing with heterogeneity: full
heterogeneity, limited heterogeneity, homogeneous, and modified
homogeneous models. The key issue to be addressed by an
implementation is providing requested QoS downstream. One of or
some combination of the discussed models [8] may be used to
provide requested QoS. Unfortunately, none of the described
models is the right answer for all cases. For some networks, e.g.
public WANs, it is likely that the limited heterogeneous model or
a hybrid limited-full heterogeneous model will be desired. In
Berger Expires: January 1998 [Page 5]
Internet Draft RSVP over ATM Guidelines July 1997
other networks, e.g. LANs, it is likely that a the modified
homogeneous model will be desired.
Since there is not one model that satisfies all cases,
implementations SHOULD implement one of either the limited
heterogeneity model or the modified homogeneous model.
Implementations SHOULD support both approaches and provide the
ability to select which method is actually used, but are not
required to do so.
3. Security
The same considerations stated in [7] and [10] apply to this
document. There are no additional security issues raised in this
document.
4. Acknowledgments
This work is based on earlier drafts [2,4] and comments from the
ISSLL working group. The author would like to acknowledge their
contribution, most notably Steve Berson who coauthored [4].
5. Author's Address
Lou Berger
FORE Systems
6905 Rockledge Drive
Suite 800
Bethesda, MD 20817
Phone: +1 301 571 2534
EMail: lberger@fore.com
REFERENCES
[1] The ATM Forum, "MPOA Baseline Version 1", May 1997.
[2] Berger, L., "RSVP over ATM: Framework and UNI3.0/3.1 Method",
Internet Draft, June 1996.
[3] Berger, L., "RSVP over ATM Implementation Requirements, Internet
Draft, July 1997.
[4] Berson, S., Berger, L., "IP Integrated Services with RSVP over ATM,"
Internet Draft, draft-ietf-issll-atm-support-02.txt, November 1996.
[5] Borden, M., Crawley, E., Krawczyk, J, Baker, F., and Berson, S.,
"Issues for RSVP and Integrated Services over ATM," Internet Draft,
Berger Expires: January 1998 [Page 6]
Internet Draft RSVP over ATM Guidelines July 1997
February 1996.
[6] Borden, M., and Garrett, M., "Interoperation of Controlled-Load and
Guaranteed-Service with ATM," Internet Draft, March 1997.
[7] Braden, R., Zhang, L., Berson, S., Herzog, S., and Jamin, S.,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification," Internet Draft, June 1997.
[8] Crawley, E., Berger, L., Berson, S., Baker, F., Borden, M., and
Krawczyk, J, "Issues for Integrated Services and RSVP over ATM,"
Internet Draft, July 1997.
[9] Luciani, J., Katz, D., Piscitello, D., Cole, B., "NBMA Next Hop
Resolution Protocol (NHRP)," Internet Draft, January 1997.
[10] Perez, M., Liaw, F., Grossman, D., Mankin, A., Hoffman, E., and
Malis, A., "ATM Signalling Support for IP over ATM," RFC 1755.
Berger Expires: January 1998 [Page 7]