INTERNET DRAFT                                  J.M.Pullen
                                                  George Mason U.
                                                M.Myjak
                                                  U.of Central Florida
                                                C.Bouwens
                                                  SAIC, Inc.
                                                20 September 1996
                                                Expire in six months


    Limitations of Internet Protocol Suite for Distributed Simulation
               in the Large Multicast Environment
                   <draft-pullen-lame-00.txt>

Status of this 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 ftp.is.co.za (Africa),
     nic.nordu.net (Europe), munnari.oz.au (Pacific Rim),
     ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast).


Abstract

     The characteristics of distributed simulation in the Large
     Multicast Environment are described.  Mechanics and rates
     of data exchange are elaborated.  Required network
     characteristics are described.  Using this information,
     additional capabilities needed to use the Internet Protocol
     Suite for support of large-scale distributed simulation
     are enumerated.





1.  The Large Multicast Environment

     The Large Multicast User's Group (LAMUG) was formed to create a
     consensus-based requirement for Internet Protocols to support
     Distributed Interactive Simulation (DIS), its successor the High
     Level Architecture for simulation (HLA), and related applications.
     The applications are characterized by the need to distribute a
     real-time application over a shared wide-area network in a
     scalable manner such that numbers of hosts from a few to tens of
     thousands are able to interchange state data with sufficient
     reliability and timeliness to sustain a three-dimensional virtual,
     visual environment containing large numbers of moving objects.
     Each such host may simulate a number of battlefield entities
     that may be as few as one or an many as thousands.  The network
     supporting such a system necessarily will be capable of multicast.

     Distributed Interactive Simulation is the name of a family of
     protocols used to exchange information about a virtual
     environment among hosts in a distributed system that are
     simulating the behavior of objects in that environment.  The
     objects are capable of physical interactions and can sense each
     other by visual and other means (infrared, etc.).  DIS was
     developed by the U.S. Department of Defense (DoD) to implement
     system for military training, rehearsal, and other purposes.
     DIS standards are used for the same purposes by defense and other
     organizations in other countries as well.  More information on DIS
     can be found in the references.

     The feature of DIS that drives network requirements is that it
     is intended to work with output to and input from humans across
     distributed simulators at both local and distant locations in real
     time.  This places tight limits on latency between hosts.  It also
     means that any practical network will require multicasting to
     implement the required distribution of large amounts of data to all
     participating simulators.  Large DIS configurations are expected to
     place hosts in multicast groups based on sharing the same sensor
     inputs in the virtual environment.  This can mean a need for
     hundreds of multicast groups where objects may move between groups
     in large numbers at high rates.

     DIS real time flow consists of packets of length around 2000
     bits at rates from .2 per second per simulator to 15 per second
     per simulator.  This information is intentionally redundant and
     normally is transmitted with a best-effort transport protocol
     (UDP), and in some cases also is compressed.  Required accuracy
     both of latency and of physical simulation varies with the
     intended purpose but generally must be at least sufficient to
     satisfy human perception, for example in tightly coupled




     simulations such as high performance aircraft maximum acceptable
     latency between applications end-to-end is 100 milliseconds between
     any two hosts.  At relatively rare intervals events (e.g.
     collisions between battlefield entities) may occur which require
     reliable transmission of some data on a unicast basis, to any other
     host in the system.  Other protocols supporting the DIS environment
     (e.g. Network Time and Simulation Management) may require
     information transport in addition to the flow of DIS entity-state
     data.

     DoD has a goal to build DIS systems with up to 100,000 simulated
     objects, many of them computer-generated forces that run with
     minimal human intervention, acting as opposing force or simulating
     friendly forces that are not available to participate.  DoD would
     like to carry out such simulations using a shared WAN.  Beyond
     DoD many people see a likelihood that DIS-like capabilities may
     be commercialized as entertainment.  The scope of such an
     entertainment system is hard to predict but conceivably could be
     larger than the DoD goal of 100,000.

     The High Level Architecture (HLA) is a development beyond DIS
     that aims at bringing DIS and other forms of distributed
     simulation into a unifying system paradigm.  Thus HLA has
     networking requirements at least as demanding as DIS.  HLA is
     still under development, therefore this document will focus on
     the requirements of DIS.


2.  DIS network requirements.

     a.  real-time packet delivery, with a small fraction (less than
     two percent), of packets exceed an established latency, in no case
     more than a few hundred milliseconds, in a shared network

     b.  multicasting with thousands of multicast groups that can
     sustain join/leave in less than one second at rates of hundreds
     of join/leaves per second

     c.  support for secure networking, needed for classified military
     simulations

     d.  A high degree of flexibility in constructing networks depending
     on the working environment, such as leased lines, ISDN, ATM, and/or
     mobile links on instrumented ranges.





3.  Internet Protocol Suite facilities needed and not yet available for
large-scale DIS in shared networks.

     These derive from the need for real-time multicast with established
     quality of service:

     a.  Requirement: resource reservation available in production
     systems.  Work needed: RSVP seems to be on a path to achieving
     this, however a mechanism is needed to group streams such that
     multiple multicast groups can share the same network capacity.
     The RSVP Working Group recognizes a need for this and is
     planning to consider it after they complete a draft standard
     based on their current work (experimental RSVP version 12).

     Note: Some current DIS networks allow for quality of service in
     terms of reserved/prioritized bandwidth and/or minimal delay
     (ST-2 or RSVP) or private dial-up links with bandwidth on
     demand and compression (ISDN), but no commercial, production
     system using open standards is available to meet the performance
     requirements projected above.


     b.  Requirement: resource-sensitive routing to be used with the
     resource reservation mechanism.  Work needed: a routing protocol
     for IP multicast, derived from the current versions (DVMRP or
     MOSPF) but sensitive to resource requirements.  A new protocol
     called Quality of Service Open Shortest Path First (QOSPF) has
     been proposed and a working group is being formed to investigate
     its potential.  QOSPF will work with RSVP.  It is likely to
     require at least two years to develop such a protocol.

     c.  Requirement: IP multicast that is capable of taking advantage
     of link-layer multicast (such as ATM) for packet replication across
     multiple logical IP subnets (LIS). Work needed: Extend or replace
     the current standards-track IP multicast over ATM multicast, which
     uses a Multicast Address Resolution Server (MARS) to resolve the
     fact that ATM provides no mechanism to distribute IP multicast
     group information.  It only works within an LIS and hence will not
     support high-performance, wide-area, shared-use IP/ATM networks
     in multicast mode.  An approach to solving this problem has been
     developed in the DARPA Real time Information Transport Network
     (RITN) program and was briefed to the IETF in December, 1995 but
     no working group is pursuing it.

     d.  Requirement: a hybrid transport protocol that can support best-
     effort multicast of most data, lightweight reliable multicast of
     critical reference data, and reliable unicast of occasional data.
     Without such a protocol the application must become responsible
     for reliability of transport in the real time multicast
     environment. Work needed:  A Selectively Reliable Transport
     Protocol (SRTP) has been proposed by the Distributed Interactive
     Simulation Communications and Security (DIS-CAS) working group.
     This work needs to be brought into the IETF and pursued there.  A
     new IETF working group on multicast transport has been proposed.
     Such a group would provide a logical home for SRTP development.




     e.  Requirement: network management for DIS systems.  Work needed:
     Create a DIS/HLA Management Information Base (MIB) for use with the
     Internet standard Simple Network Management Protocol (SNMP).  This
     could be undertaken by the LAMUG.

     f.  Requirement: a session protocol to start, pause, and stop a DIS
     exercise over an IP network.  Work needed: a new subgroup of the
     Multiparty Multimedia Session Control working group to investigate
     use of that session protocol for DIS/HLA.

     g.  Requirement: an integrated security architecture. Work needed:
     Investigate use of the IPv6 security architecture to meet this
     need.


4.  References

   [1] Symington et. al, "Modeling and Simulation Requirements for IPng",
       RFC 1667, August 1994

   [2] DIS Steering Committee, "The DIS Vision", Institute for
       Simulation and Training, University of Central Florida, May 1994

   [3] IEEE 1278.1-1995, Standard for Distributed Interactive Simulation
       Application Protocols

   [4] IEEE 1278.2-1995, Standard for Distributed Interactive Simulation
       Communication services and Profiles

   [5] Deering, "Host Requirements for IP Multicasting", RFC 1112,
       August 1989

   [6] Case et. al., "Simple Network Management Protocol", RFC 1067,
       May 1990

   [7] Moy, "MOSPF: Analysis and Experience", RFC1585, March 1994

   [8] Estrin et. al., "Protocol Independent Multicast-Sparse Mode",
       work in progress (draft-ietf-idmr-pim-sm-spec-06), September 1996

   [9] Pusateri, "Distance Vector Multicast Routing Protocol",
       work in progress (draft-ietf-idmr-dvmrp-v3-03), September 1996

   [10] Atkinson, "IPv6 Security Architecture", work in progress
        (draft-ietf-ipngwg-sec-00), March 1996

   [11] Braden et. al., "Resource Reservation Protocol Version 1 Functional
        Specification", work in progress (draft-ietf-rsvp-policy-arch-12)

   [12] Zhang et. al., "Quality of Service Extensions to OSPF", work in
        progress (Internet Draft) June, 1996

   [13] Armitage, "Support for Multicast over UNI 3.0/3.1 based ATM
        Networks", work in progress (draft-ietf-ipatm-ipmc-12),
        February 1996




   [14] Bormann et. al., "Simple Conference Control Protocol", work in
        progress (draft-ietf-mmusic-sccp-00), June 1996

   [15] Pullen et. al. "Implementation of A Selectively Reliable Transport
        Protocol for DIS", Proceedings of the 14th Distributed Interactive
        Simulation Workshop, March 1996

5.  Authors' Addresses

  J. Mark Pullen
  Computer Science/4A5
  George Mason University
  Fairfax, VA 22032
  mpullen@gmu.edu

  Michael Myjak
  Institute for Simulation and Training
  University of Central Florida
  3800 Progress Drive
  Orlando, FL  32826
  mmyjak@ist.ucf.edu

  Christina Bouwens
  SAIC Inc.
  Orlando FL
  chris_bouwens@cpqm.saic.com