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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET DRAFT J.M.Pullen 2 Expiration: 25 April 1997 George Mason U. 3 M.Myjak 4 U.of Central Florida 5 C.Bouwens 6 SAIC, Inc. 7 25 November 1996 9 Limitations of Internet Protocol Suite for Distributed Simulation 10 in the Large Multicast Environment 12 draft-ietf-lsma-limitations-00.txt 14 Status of this Memo 16 This document is an Internet-Draft. Internet-Drafts are working 17 documents of the Internet Engineering Task Force (IETF), its 18 areas, and its working groups. Note that other groups may also 19 distribute working documents as Internet-Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six 22 months and may be updated, replaced, or obsoleted by other 23 documents at any time. It is inappropriate to use Internet- 24 Drafts as reference material or to cite them other than as 25 ``work in progress.'' 27 To learn the current status of any Internet-Draft, please check 28 the ``1id-abstracts.txt'' listing contained in the Internet- 29 Drafts Shadow Directories on ftp.is.co.za (Africa), 30 nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), 31 ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). 33 Abstract 35 1. The Large Multicast Environment 37 The Large Multicast User's Group (LAMUG) was formed to create a consensus- 38 based requirement for Internet Protocols to support Distributed Interactive 39 Simulation (DIS), its successor the High Level Architecture for simulation 40 (HLA), and related applications. The applications are characterized by 41 the need to distribute a real-time application over a shared wide-area network 42 in a scalable manner such that numbers of hosts from a few to tens of 43 thousands are able to interchange state data with sufficent reliability 44 and timeliness to sustain a three-dimensional virtual, visual environment 45 containing large numbers of moving objects. The network supporting 46 such an system necessarily will be capable of multicast. 48 Distributed Interactive Simulation is the name of a family of protocols 49 used to exchange information about a virtual environment among 50 hosts in a distributed system that are simulating the behavior of objects 51 in that environment. The objects are capable of physical interactions 52 and can sense each other by visual and other means (infrared, etc.). 54 DIS was developed by the U.S. Department of Defense (DoD) to 55 implement system for military training, rehearsal, and other purposes. 56 More information on DIS can be found in the references. 58 The feature of DIS that drives network requirements is that it is 59 intended to work with output to and input from humans across 60 distributed simulators in real time. This places tight limits on latency 61 between hosts. It also means that any practical network will require 62 multicasting to implement the required distribution of all data to all 63 participating simulators. Large DIS configurations are expected to 64 group hosts on multicast groups based on sharing the same sensor 65 inputs in the virtual environment. This can mean a need for hundreds 66 of multicast groups where objects may move between groups in large 67 numbers at high rates. 69 DIS real time flow consists of packets of length around 2000 bits at 70 rates from .2 per second per simulator to 15 per second per simulator. 71 This information is intentionally redundant and is normally 72 transmitted with a best-effort transport protocol (UDP), and in some 73 cases also is compressed. Required accuracy both of latency and of 74 physical simulation varies with the intended purpose but generally 75 must be at least sufficient to satisfy human perception, for example in 76 tightly coupled simulations such as high performance aircraft 77 maximum acceptable latency is 100 milliseconds between any two 78 hosts. At relatively rare intervals events (e.g. collisions) may occur 79 which require reliable transmission of some data on a unicast basis, to 80 any other host in the system. 82 DoD has a goal to build DIS systems with up to 100,000 simulated 83 objects, many of them computer-generated forces that run with 84 minimal human intervention, acting as opposing force or simulating 85 friendly forces that are not available to participate. DoD would like to 86 carry out such simulations using a shared WAN. Beyond DoD many 87 people see a likelihood that DIS-like capabilities may be 88 commercialized as entertainment. The scope of such an entertainment 89 system is hard to predict but conceivably could be larger than the DoD 90 goal of 100,000. 92 The High Level Architecture (HLA) is a development beyond DIS that aims 93 at bringing DIS and other forms of distributed simulation into a unifying 94 system paradigm. Thus HLA has netowrking requirements at least as 95 demanding as DIS. HLA is still under development, therefore this 96 document will focus on the requirements of DIS. 98 2. DIS network requirements. 100 a. real-time packet delivery, with low packet loss (less than 2%), 101 predictable latency on the order of a few hundred milliseconds, and 102 low jitter (variation of latency), on the order of a few milliseconds, in 103 a shared network 104 b. multicasting with thousands of multicast groups that can sustain 105 join/leave in less than one second at rates of hundreds of join/leaves 106 per second 108 c. multicasting using a many-to-many paradigm in which 90% or more 109 of the group members act as receivers and senders to a group 111 d. support for resource reservation because of the impracticality 112 of over-provisioning the WAN and the LAN 114 e. support for secure networking, needed for classified military 115 simulations 117 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: 119 a. resource reservation available in production systems (RSVP seems 120 to be on a path to achieving this but a mechanism is needed to group 121 streams such that multiple multicast groups can share the same 122 capacity) 124 b. resource-sensitive routing to be used with the resource reservation 125 mechanism 127 c. IP multicast that is capable of taking advantage of link-layer 128 multicast (such as ATM) for packet replication across multiple logical 129 IP subnets 131 d. a hybrid transport protocol that can support best-effort multicast of 132 most data, lightweight reliable multicast of critical reference data, and 133 reliable unicast of occasional data 135 e. network management for DIS systems (this appears to require only 136 a DIS MIB for use with SNMP) 138 f. a session protocol to start, pause, and stop a DIS exercise over an IP 139 network (MMUSIC or an adaptation might work) 141 g. an integrated security architecture (it is likely that the IPv6 security 142 architecture will meet this need) 144 4. References 146 RFC1667, "Modeling and Simulation Requirements for IPng" 147 August 1994 149 "The DIS Vision", DIS Steering Committee, Institute for Simulation and Training, University of Central Florida, May 1994 150 IEEE 1278.1-1995, Standard for Distributed Interactive Simulation - Application Protocols 152 IEEE 1278.2-1995, Standard for Distributed Interactive Simulation - Communication services and Profiles 154 5. Authors' Addresses 156 J. Mark Pullen 157 Computer Science/4A5 158 George Mason University 159 Fairfax, VA 22032 161 Michael Myjak 162 Institute for Simulation and Training 163 Orlando, FL 165 Christina Bouwens 166 SAIC Inc. 167 Orlando FL 169 Expiration: 25 April 1997