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Versions: 00 01                                                         
Internet Draft                                                 S. Berson
Expiration: September 1997                                           ISI
File: draft-berson-classy-approach-00.txt                     S. Vincent

      A ``Classy'' Approach to Aggregation for Integrated Services

                             March 26, 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
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   The current Integrated Services (IS) architecture has a fundamental
   scaling problem in that per flow state is maintained everywhere.  Our
   approach is to use aggregation as a technique to address this
   problem.  There is a wide spectrum of approaches towards aggregation
   of IS state, with different tradeoffs in the amount of state
   required.  This draft describes one promising approach to aggregating
   IS state within defined regions of a network.  Service classes are
   configured on all of the routers in a region.  At the edges of the
   region, routers keep detailed IS state and map packets into the
   configured traffic service classes.  In the interior of this region,
   routers need keep only a bounded amount of IS state.

Table of Contents

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1. Introduction

   In order to deploy Integrated Services (IS) in the Internet,
   resources are needed in the routers to keep state and to process
   packets.  As currently defined [1], this state is on a per session
   basis, where a session is a unicast destination or a multicast group.
   Thus, widespread use of IS would mean a large amount of state at
   routers in the core of the internet.  This large amount of state and
   related processing could overwhelm routers, so aggregation models
   that do not require per-session state need to be explored.  This memo
   describes a particular approach to reducing this IS state.

   Several types of per-session state are used with integrated services.
   First, there is scheduling state that consists of the different
   traffic service queues for packet forwarding.  Second, there is
   packet classifier state.  Classifier state is used to assign each
   arriving packet to a packet scheduling queue for forwarding.  Third,
   there is the state for the setup protocol, e.g. state carried in RSVP
   PATH and RESV messages.  Finally, current multicast routing
   algorithms also store state, either per source and session (e.g.
   DVMRP, PIM-DM) or per session shared-tree (e.g. CBT, PIM-SM).  While
   approaches to aggregation of routing state are similar to aggregation
   of RSVP state, they are beyond the scope of this note.

   Any aggregation scheme entails some tradeoffs.  Keeping full
   integrated services state at all routers allows the resources
   dedicated to the flow of packets from each admitted session to be
   isolated from the resources for packets from all other sessions.
   This isolation means that resources reserved for one session, if
   needed, will be used only on the reserving session.  The disadvantage
   of doing aggregation is the lesser degree of flow isolation,
   since with aggregation many flows would share the same traffic
   service class.  The benefits of additional flow isolation achievable
   from keeping full IS state is unknown.

2. Framework

   This draft proposes an approach to reducing the amount of IS state
   based on configured traffic service classes within aggregating
   regions.  Configuring a fixed number of traffic service classes
   bounds the amount of scheduler state.  Establishing aggregating
   regions (described below) and storing full IS state only at the edges
   reduces the classifier state and setup protocol state.

   We make several assumptions:

   1.   We assume that an explicitly definable region (e.g. one or more

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        contiguous autonomous systems), called an "aggregating region",
        will aggregate and will implement supporting mechanisms at its
        boundary points.

   2.   We assume that the choice to aggregate and the mechanism used to
        do so is an intra-domain issue, not an inter-domain issue and
        therefore there can be variability across regions so long as at
        the boundaries routers continue to pass along adequate messages
        to support RSVP upstream and downstream.

   3.   We assume current multicast and unicast routing within the
        aggregating region; but with no other enhancements.

3. Approach

   In our approach, traffic service classes are defined at all routers
   in an aggregating region.  While the exact form of these traffic
   service classes is the subject of continuing research, the scheduling
   algorithms used by these service classes could include features such
   as priority queueing and/or weighted fair queueing.  Each traffic
   service class is subject to admission control and traffic policing
   (additional subjects of continuing research) but only at the ingress
   to the region.  Note that no changes to packet forwarding are needed
   in the interior of the aggregating region.  Similarly, no RSVP
   processing is needed in the interior of the region.  When an RSVP
   reservation message arrives at an ingress to the region (from an
   egress), and that reservation passes admission control, then packets
   from that flow are assigned to a traffic service class.  Data packets
   belonging to a traffic class are "tagged" on entry to the aggregating
   region with some identifier indicating which class of service the
   packets should receive.  This identifier can consist of some bits in
   the packet header (e.g. type of service bits) or the packet could be
   encapsulated.  The tag (or encapsulation) encodes the traffic service
   class that this packet will receive across the aggregating region.
   Tagging or encapsulating each packet minimizes the classifier state
   in the interior of the aggregating region.

   In summary our approach provides for reduction of packet scheduler
   state, packet classifier state, and setup protocol (e.g. RSVP) state
   in the following ways.  A bounded amount of packet scheduler state at
   all routers in an aggregating region is achieved by using
   preconfigured traffic service classes.  A bounded amount of packet
   classifier state at all interior routers in the aggregating region is
   accomplished by tagging or encapsulating each packet with its traffic
   service class.  No setup protocol state at interior routers is
   achieved by doing admission control and policing only at the edges of
   the aggregating region.

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4. Open Issues

   Aggregation provides opportunities for increased multiplexing and
   resource usage efficiency, but it also brings up several challenges
   in admission control and policing.  First there is an issue of how
   many service classes are to be used and of how to configure the
   service classes on the routers.  Second, there is an issue of how and
   when to assign flows to the service classes, i.e. aggregate admission
   control.  Finally, there is the issue of how and when to police an
   aggregate reservation.  Good solutions to these problems will provide
   integrated services across aggregating regions with greatly reduced
   state requirements.

5. Acknowledgements

   This draft is the result of discussions with many people particularly
   Bob Braden, Deborah Estrin, and Daniel Zappala.


[1] Braden, R., Zhang, L., Berson, S., Herzog, S., and Jamin, S.,
    "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
    Specification," Internet Draft, November 1996.

[2] Floyd, S., and Jacobson, V., "Link-sharing and Resource Management
    Models for Packet Networks," IEEE/ACM Transactions on Networking,
    Vol. 3 No. 4, pp. 365-386, August 1995.

[3] Rampal, S., "Flow Grouping for Reducing Reservation Requirements for
    Guaranteed Delay Service," Internet Draft, December 1996.

Security Considerations

   Security considerations have not been addressed in this draft.

Author's Address

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   Steven Berson
   USC Information Sciences Institute
   4676 Admiralty Way
   Marina del Rey, CA 90292

   Phone: +1 310 822 1511
   EMail: berson@isi.edu

   Subramaniam Vincent
   USC Information Sciences Institute
   4676 Admiralty Way
   Marina del Rey, CA 90292

   Phone: +1 310 822 1511
   EMail: svincent@isi.edu

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