There is a need for better QoS routing. While this functionality is
needed even in the pure ATM or pure IP environment, there is also an
eventual need for integrated QoS routing between ATM and IP. Further
research and practical experience is needed in the areas of QoS
routing in IP in order to support more than the shortest best-effort
path, especially when this path may traverse ATM networks. In many
IP networks, there are multiple paths between a given source and
destination pair but current routing technologies only pay attention
to the current shortest path. As resources on the shortest path are
reserved, it will be necessary and viable to explore other paths in
order to provide QoS to a flow.
Enrichment of the ATM model to support dynamic QoS would greatly help
the IP over ATM situation. At present, the QoS objectives for ATM are
established at call set-up and then fixed for the duration of a call.
It would be advantageous to have the ability to provide a dynamic QoS
in ATM, so that an existing call could be modified to provide altered
services.
Another possible area of enhancement to the ATM service model is in
the area of multicasting. The multicast QoS offered is equal for all
receivers, and thus may be determined by the least favorable path
through the tree or by the most demanding receiver. Furthermore,
there is no current provision for multipoint to multipoint
connections. This limitation may rule out some of the services
envisioned in the IP service model.
There are areas of potential enrichment of the IP model as well.
While the receiver-based approach of RSVP has nice scaling properties
and handles receiver heterogeneity well, it is not clear that it is
ideal for all applications or for establishing state in ATM networks.
It is possible that a sender-oriented mode for RSVP might ease the
IP/ATM integration task.
Since the widespread availability of QoS raises new security concerns
(e.g., denial of service by excessive resource reservation), it seems
prudent that the IP and ATM communities work closely to adopt
compatible approaches to handling these issues.
This list is almost certainly incomplete. As work progresses to
define IP over ATM standards to support QoS and to implement
integrated services internetworks that include ATM, more issues are
likely to arise. However, we believe that this paper has described
the major issues that need to be taken into consideration at this
time by those who are defining the standards and building
implementations.
9.0 References
1. Armitage, G., "Support for Multicast over UNI 3.1 based ATM
Networks", Work in Progress, Bellcore, February 1995.
2. Atkinson, R., "Security Architecture for the Internet Protocol",
RFC1825, NRL, August 1995.
3. Atkinson, R., "IP Authentication Header", RFC1826, NRL,
August 1995.
4. Ballardie, A., and J. Crowcroft, "Multicast-Specific Security
Threats and Counter-Measures", Proceedings of ISOC Symposium on
Network and Distributed System Security, San Diego, Feb. 1995,
pp. 2-16.
5. Ballardie, T., Jain, N., Reeve, S. "Core Based Trees (CBT)
Multicast, Protocol Specification", Work In Progress, University
College London, Bay Networks, June, 1995.
6. Braden, R., Clark, D., and S. Shenker, "Integrated Services in
the Internet Architecture: an Overview", RFC1633, ISI/MIT/Xerox
PARC, July 1994.
7. Braden, R., Zhang, L., Estrin, Herzog, D., and S. Jamin,
"Resource ReSerVation Protocol (RSVP) - Version 1 Functional
Specification", Work in Progress, ISI/PARC/UCS, July 1995.
8. Braden, R., Clark, D., Crocker, S., and C. Huitema, "Report of IAB
Workshop on Security in the Internet Architecture", RFC1636, ISI,
MIT, TIS, INRIA, June 1994.
9. Callon, R., and B. Salkewicz, An Outline for Integrated PNNI for
IP Routing", ATM Forum/ 95-0649, Bay Networks, July 1995.
10. Cole, R., Shur, D., and C. Villamizar, "IP over ATM: A Framework
Document", Work in Progress, AT&T Bell Laboratories/ ANS, April
1995.
11. Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC
1112, Stanford University, August 1989.
12. Delgrossi, L., and L. Berger, Editors, "Internet Stream Protocol
Version 2 (ST-2) Protocol Specification - Version ST2+", RFC1819,
ST2 Working Group, August 1995.
13. Dykeman, D., Ed., "PNNI Draft Specification", ATM Forum/94-0471R8,
IBM Zurich Research Lab, May 1995.
14. Goyal, P., Lam, S., and Vin, H., "Determining End-to-End Delay
Bounds in Heterogeneous Networks," 5th International Workshop on
Network and Operating System Support for Digital Audio and Video,
April, 1995.(Available via URL http://www.cs.utexas.edu/users/dmcl)
15. Laubach, M., "Classical IP and ARP over ATM", RFC1577, HP,
January 1994.
16. Moy, J., "OSPF Version 2", RFC1583, Proteon, March 1994.
17. Moy, J., "Multicast Extensions to OSPF," RFC1584, Proteon, March
1994.
18. Partridge, C., "A Proposed Flow Specification", RFC1363, BBN,
September 1992.
19. Perez, M., Liaw, F., Mankin, A., Hoffman, E., Grossman, D. and
A. Malis, "ATM Signaling Support for IP over ATM", RFC1755,
ISI, Fore, Motorola Codex, Ascom Timeplex, February 1995.
20. Perkins, D., and Liaw, Fong-Ching, "Beyond Classical IP-Integrated
IP and ATM Architecture Overview", ATM Forum/94-0935, Fore Systems,
September 1994.
21. Perkins, D. and Liaw, Fong-Ching, "Beyond Classical IP-Integrated
IP and ATM Protocol Specifications", ATM Forum/94-0936, Fore
Systems, September 1994.
22. Romanow, A., and S. Floyd, "The Dynamics of TCP Traffic over ATM
Networks", Proceedings of ACM SIGCOMM U94, London, August 1994,
pp.79-88.
23. Shenker, S., and C. Partridge. "Specification of Guaranteed Quality
of Service", Work in Progress, Xerox/BBN, July 1995.
24. Shenker, S., and C. Partridge. "Specification of Predictive Quality
of Service", Work in Progress, Xerox/BBN, March 1995.
25. Shenker, S., C. Partridge and J. Wroclawski. "Specification of
Controlled Delay Quality of Service", Work in Progress,
Xerox/BBN/MIT, June 1995.
26. Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP:
A Transport Protocol for Real-time Applications", Work in Progress,
GMD/ISI/Xerox/LBL, March 1995.
27. Topolcic, C., "Experimental Internet Stream Protocol, Version 2
(ST-II)", RFC1190, BBN, October 1990.
28. Wang, Z., and J. Crowcroft, "QoS Routing for Supporting Resource
Reservation", University College of London white paper, 1995.
10. Authors' Addresses
Eric S. Crawley
Marty Borden
Bay Networks
3 Federal Street
Billerica, Ma 01821
508-670-8888
esc@baynetworks.com
mborden@baynetworks.com
Bruce S. Davie
Bellcore
445 South Street
Morristown, New Jersey 07960-6438
201-829-4838
bsd@bellcore.com
Stephen G. Batsell
Naval Research Laboratory
Code 5521
Washington, DC 20375-5337
202-767-3834