rfc1821.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   not particularly care what mechanisms a network element (such as an
   ATM network) uses to provide a certain QoS; what matters is whether
   the ATM service model is capable of offering services that can
   support the end-to-end IP service model. Most of the hard problems
   for IP over ATM therefore revolve around the service models for IP
   and ATM.  The one piece of mechanism that is important in an IP/ATM
   context is signalling or resource reservation, a topic we return to
   below.

   The following paragraphs enumerate some of the areas in which we
   believe significant work is needed. The work falls into three areas:
   extending the IP over ATM standards; extensions to the ATM service
   model; and extensions to the IP service model. In general, we expect
   that practical experience with providing IP QoS over ATM will suggest
   more enhancements to the service models.

   We need to define ways of mapping the QoS and traffic
   characterizations (Tspecs and Rspecs) of IP flows to suitable
   characterizations for ATM connections.  An agreement is needed so
   that some sort of uniform approach is taken. Whatever agreement is
   made for such mappings, it needs to be done so that when traversing
   several networks, the requested QoS is obtained end-to-end (when
   admission is possible). Practical experience should be gained with
   these mappings to establish that the ATM service classes can in fact
   provide suitable QoS to IP flows in a reasonably efficient way.
   Enhancement of the ATM service classes may be necessary, but
   experience is needed to determine what is appropriate.

   We need to determine how the resource reservation models of IP (RSVP
   and ST-II) interact with ATM signalling. Mechanisms for establishing
   appropriate connection state with suitable QoS in ATM networks that
   are part of a larger integrated services Internet need to be defined.
   It is possible that the current IP/ATM mechanisms such as ARP servers
   and MARS can be extended to help to manage this state.

   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



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   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.








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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",
       RFC 1825, NRL, August 1995.

   3.  Atkinson, R., "IP Authentication Header", RFC 1826, 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", RFC 1633, 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", RFC 1636, 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+", RFC 1819,
       ST2 Working Group, August 1995.

   13. Dykeman, D., Ed., "PNNI Draft Specification", ATM Forum/94-0471R8,
       IBM Zurich Research Lab, May 1995.



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   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", RFC 1577, HP,
       January 1994.

   16. Moy, J., "OSPF Version 2", RFC 1583, Proteon, March 1994.

   17. Moy, J., "Multicast Extensions to OSPF," RFC 1584, Proteon, March
       1994.

   18. Partridge, C., "A  Proposed Flow Specification", RFC 1363, BBN,
       September 1992.

   19. Perez, M., Liaw, F., Mankin, A., Hoffman, E., Grossman, D. and
       A. Malis, "ATM Signaling Support for IP over ATM", RFC 1755,
       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)", RFC 1190, BBN, October 1990.



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   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
   [e-mail]
   [e-mail]


   Bruce S. Davie
   Bellcore
   445 South Street
   Morristown, New Jersey 07960-6438
   201-829-4838
   [e-mail]


   Stephen G. Batsell
   Naval Research Laboratory
   Code 5521
   Washington, DC 20375-5337
   202-767-3834
   [e-mail]






















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