HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 04:49:32 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Wed, 08 Jan 1997 00:15:00 GMT ETag: "361c0c-1e6b-32d2e704" Accept-Ranges: bytes Content-Length: 7787 Connection: close Content-Type: text/plain INTERNET DRAFT J.M.Pullen Expiration: 25 April 1997 George Mason U. M.Myjak U.of Central Florida C.Bouwens SAIC, Inc. 25 November 1996 Limitations of Internet Protocol Suite for Distributed Simulation in the Large Multicast Environment draft-ietf-lsma-limitations-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 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 sufficent reliability and timeliness to sustain a three-dimensional virtual, visual environment containing large numbers of moving objects. The network supporting such an 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. 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 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 all data to all participating simulators. Large DIS configurations are expected to group hosts on 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 is normally 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 is 100 milliseconds between any two hosts. At relatively rare intervals events (e.g. collisions) may occur which require reliable transmission of some data on a unicast basis, to any other host in the system. 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 netowrking 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 low packet loss (less than 2%), predictable latency on the order of a few hundred milliseconds, and low jitter (variation of latency), on the order of a few 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. multicasting using a many-to-many paradigm in which 90% or more of the group members act as receivers and senders to a group d. support for resource reservation because of the impracticality of over-provisioning the WAN and the LAN e. support for secure networking, needed for classified military simulations 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. resource reservation available in production systems (RSVP seems to be on a path to achieving this but a mechanism is needed to group streams such that multiple multicast groups can share the same capacity) b. resource-sensitive routing to be used with the resource reservation mechanism c. IP multicast that is capable of taking advantage of link-layer multicast (such as ATM) for packet replication across multiple logical IP subnets d. 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 e. network management for DIS systems (this appears to require only a DIS MIB for use with SNMP) f. a session protocol to start, pause, and stop a DIS exercise over an IP network (MMUSIC or an adaptation might work) g. an integrated security architecture (it is likely that the IPv6 security architecture will meet this need) 4. References RFC1667, "Modeling and Simulation Requirements for IPng" August 1994 "The DIS Vision", DIS Steering Committee, Institute for Simulation and Training, University of Central Florida, May 1994 IEEE 1278.1-1995, Standard for Distributed Interactive Simulation - Application Protocols IEEE 1278.2-1995, Standard for Distributed Interactive Simulation - Communication services and Profiles 5. Authors' Addresses J. Mark Pullen Computer Science/4A5 George Mason University Fairfax, VA 22032 Michael Myjak Institute for Simulation and Training Orlando, FL Christina Bouwens SAIC Inc. Orlando FL Expiration: 25 April 1997