Network Working Group M. Pullen
Request for Comments: 2502 George Mason University
Category: Informational M. Myjak
The Virtual Workshop
C. Bouwens
SAIC
February 1999
Network Working Group M. Pullen
Request for Comments: 2502 George Mason University
Category: Informational M. Myjak
The Virtual Workshop
C. Bouwens
SAIC
February 1999
Limitations of Internet Protocol Suite for Distributed Simulation in the Large Multicast Environment
大型多播环境下用于分布式仿真的Internet协议套件的局限性
Status of this Memo
本备忘录的状况
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (1999). All Rights Reserved.
版权所有（C）互联网协会（1999年）。版权所有。
Abstract
摘要
The Large-Scale Multicast Applications (LSMA) working group was chartered to produce documents aimed at a consensus based development of the Internet protocols to support large scale multicast applications including real-time distributed simulation. This memo defines services that LSMA has found to be required, and aspects of the Internet protocols that LSMA has found to need further development in order to meet these requirements.
大型多播应用程序（LSMA）工作组被授权编制文件，旨在基于共识开发互联网协议，以支持大规模多播应用程序，包括实时分布式仿真。本备忘录定义了LSMA发现需要的服务，以及LSMA发现需要进一步开发以满足这些要求的互联网协议方面。
The Large-Scale Multicast Applications working group (LSMA) was formed to create a consensus based requirement for Internet Protocols to support Distributed Interactive Simulation (DIS) [DIS94], its successor the High Level Architecture for simulation (HLA) [DMSO96], and related applications. The applications are characterized by the need to distribute a real-time applications 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. The network supporting such an system necessarily will be capable of multicast [IEEE95a,IEEE95b].
大规模多播应用程序工作组（LSMA）的成立是为了创建一个基于共识的互联网协议需求，以支持分布式交互仿真（DIS）[DIS94]，其后续产品高层仿真体系结构（HLA）[DMSO96]，以及相关应用程序。这些应用程序的特点是需要以可扩展的方式在共享广域网上分发实时应用程序，以便从几台到数万台的主机能够以足够的可靠性和及时性交换状态数据，以维持三维虚拟网络，包含大量移动对象的视觉环境。支持这种系统的网络必须能够多播[IEEE95a，IEEE95b]。
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 systems for military training, rehearsal, and other purposes. More information on DIS can be found in [SSM96].
分布式交互仿真是一系列协议的名称，用于在分布式系统中的主机之间交换有关虚拟环境的信息，这些主机模拟该环境中对象的行为。物体能够进行物理交互，并且可以通过视觉和其他方式（红外等）相互感知。DIS由美国国防部（DoD）开发，用于实施军事训练、演习和其他用途的系统。有关DIS的更多信息，请参见[SSM96]。
The feature of distributed simulation 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 distributed simulation 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 thousands of multicast groups where objects may move between groups in large numbers at high rates. Because the number of simulators is known in advance and their maximum output rate in packets per second and bits per second is specified, the overall total data rate (the sum of all multicast groups) is bounded. However the required data rate in any particular group cannot be predicted, and may change quite rapidly during the simulation.
驱动网络需求的分布式仿真的特点是，它旨在跨分布式模拟器实时处理人类的输出和输入。这严格限制了主机之间的延迟。这也意味着任何实际网络都需要多播来实现所有数据到所有参与模拟器的所需分发。大型分布式仿真配置预计将基于虚拟环境中共享相同传感器输入的多播组上的主机分组。这可能意味着需要数千个多播组，其中对象可能以高速率在大量组之间移动。由于预先知道模拟器的数量，并且指定了模拟器的最大输出速率（以每秒分组数和每秒比特数为单位），因此总数据速率（所有多播组的总和）是有界的。但是，无法预测任何特定组中所需的数据速率，并且在模拟过程中可能会发生非常迅速的变化。
DIS real time flow consists of packets of length around 2000 bits at rates from .2 packets per second per simulator to 15 packets per second per simulator. This information is intentionally redundant and is normally transmitted with a best effort transport protocol (UDP). In some cases it 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.
DIS实时流由长度约为2000位的数据包组成，速率从每个模拟器每秒0.2个数据包到每个模拟器每秒15个数据包。此信息是有意冗余的，通常使用尽力而为传输协议（UDP）传输。在某些情况下，它也被压缩。延迟和物理模拟所需的精度随预期目的而变化，但通常必须至少足以满足人类感知。例如，在紧密耦合的模拟中，如高性能飞机，任何两台主机之间的最大可接受延迟为100毫秒。在相对罕见的时间间隔内，可能会发生事件（例如冲突），这些事件需要在单播基础上可靠地将某些数据传输到系统中的任何其他主机。
The U.S. DoD has a goal to build distributed simulation 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 distributed simulation 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.
美国国防部的目标是用多达100000个模拟对象建立分布式模拟系统，其中许多是计算机生成的部队，在最少的人为干预下运行，充当无法参与的敌对部队或模拟友军。国防部希望使用共享广域网进行此类模拟。除了国防部，许多人认为分布式仿真能力可能会被商业化为娱乐。这种娱乐系统的范围很难预测，但可以想象，其规模可能会超过国防部100000的目标。
The High Level Architecture (HLA) is a DoD development beyond DIS that aims at bringing DIS and other forms of distributed simulation into a unifying system paradigm. From a distributed systems standpoint HLA is considerably more sophisticated than DIS. For example attributes of distributed objects may be controlled by different simulators. From the standpoint of the supporting network the primary difference between HLA and DIS is that HLA does not call for redundant transmission of object attributes; instead it specifies a "Run Time Infrastructure" (RTI) that is responsible to transmit data reliably, and may choose to do so by various means including redundant transmission using best effort protocols. It is reasonable to say that any network that can meet the needs of DIS can support HLA by DIS-like redundant transmission, however this approach ignores the possibility that under HLA some mixture of redundant and reliable transmission can make significantly better use of network resources than is possible using DIS. While HLA, like DIS, does not specify use of a multicasting network, it has similar requirements for many-to-many transmission of object attributes at rates in excess of one update per object per second that cannot be met without multicasting. Further, HLA calls for transmission of semantically organized data (for example, groups of objects with similar capabilities such as tanks or aircraft) in this many-to-many context.
高层体系结构（HLA）是国防部在DIS之外的一项发展，旨在将DIS和其他形式的分布式仿真纳入统一的系统范式。从分布式系统的角度来看，HLA比DIS复杂得多。例如，分布式对象的属性可以由不同的模拟器控制。从支持网络的角度来看，HLA和DIS的主要区别在于HLA不要求对象属性的冗余传输；相反，它指定了一个“运行时基础设施”（RTI），负责可靠地传输数据，并且可以通过各种方式选择这样做，包括使用尽力而为协议进行冗余传输。可以合理地说，任何能够满足DIS需求的网络都可以通过类似DIS的冗余传输来支持HLA，但是这种方法忽略了这样一种可能性，即在HLA下，某些冗余和可靠传输的混合可以比使用DIS更好地利用网络资源。虽然HLA和DIS一样，没有规定使用多播网络，但它对对象属性的多对多传输有类似的要求，传输速率超过每秒每个对象一次更新，这在没有多播的情况下是无法满足的。此外，HLA要求在这种多对多上下文中传输语义组织的数据（例如，具有类似能力的对象组，如坦克或飞机）。
One solution that has been employed to deal with these challenges is to aggregate the contents of many multicast groups into a single multicast transmission [PuWh95, CSTH95]. Termed "dual-mode" or "bi-level" multicast, this approach takes advantage of the fact that although the amount of traffic in any particular multicast group can vary greatly, the aggregate of all transmissions is bounded. If the traffic is all aggregated into one large flow, an underlying ATM network can create multicast SVCs with acceptable QoS to support the requirement. It also bounds the network control problem of group joins, in that the joins take place among dedicated collections of routers and across the dedicated SVCs, rather than contending with other LSMAs that may be sharing the same network. But it does this at the cost of adding to the network a new, nonstandard aggregation element that is a hybrid of the Internet and ATM protocols. We address below the requirement to achieve such a result using a purely IP network with aggregated reservation via RSVP.
为应对这些挑战而采用的一种解决方案是将多播组的内容聚合到单个多播传输中[PuWh95，CSTH95]。这种方法被称为“双模”或“双层”多播，它利用了这样一个事实，即尽管任何特定多播组中的通信量可以变化很大，但所有传输的总量是有界的。如果流量全部聚合为一个大流量，则底层ATM网络可以创建具有可接受QoS的多播SVC来支持该需求。它还限制了组联接的网络控制问题，因为联接发生在专用路由器集合之间和专用SVC之间，而不是与共享同一网络的其他LSMA竞争。但它这样做的代价是向网络中添加一个新的非标准聚合元素，它是互联网和ATM协议的混合体。我们通过RSVP使用具有聚合保留的纯IP网络来满足以下要求，以实现这样的结果。
The defense distributed simulation community has created a number of multicast-capable networks for various simulated exercises, ranging from tens to hundreds of simulated objects distributed across numbers of sites ranging from two to twenty. As the number of objects has increased they have found that building multicasting networks potentially supporting thousands of simultaneous multicast groups with large group change rates is a hard problem. This defense problem is the precursor of similar problems that can be expected in
国防分布式仿真社区为各种模拟演习创建了大量支持多播的网络，范围从数十个到数百个模拟对象，分布在两到二十个站点之间。随着对象数量的增加，他们发现构建多播网络可能支持数千个具有较大组更改率的同时多播组是一个困难的问题。这一防御问题是未来可能出现的类似问题的前兆
commercial networks. Therefore the following sections describe the services required and the shortcomings that have been found in using today's Internet protocols in providing these services, with the intention of informing the IETF to enable it to produce protocols that meet the needs in these areas.
商业网络。因此，以下各节描述了在提供这些服务时使用当今互联网协议所需的服务和发现的缺点，旨在通知IETF，使其能够生成满足这些领域需求的协议。
2. Distributed Simulation (DIS and HLA) network service requirements.
2. 分布式仿真（DIS和HLA）网络服务需求。
a. real-time packet delivery, with low packet loss (less than 2%), predictable latency on the order of a few hundred milliseconds, after buffering to account for jitter (variation of latency) such that less than 2% of packets fail to arrive within the specified latency, in a shared network
a. 实时数据包交付，在共享网络中，在缓冲以考虑抖动（延迟变化）后，具有低数据包丢失（小于2%）的可预测延迟，约为几百毫秒，这样在指定的延迟内，不到2%的数据包无法到达
b. multicasting with thousands of multicast groups that can support join latencies of less than one second, at rates of hundreds of joins per second
b. 具有数千个多播组的多播，可支持小于1秒的连接延迟，每秒连接数百次
c. multicasting using a many-to-many paradigm in which 90% or more of the group members act as receivers and senders within any given multicast group
c. 使用多对多模式的多播，其中90%或更多的组成员充当任何给定多播组中的接收者和发送者
d. support for resource reservation; because of the impracticality of over-provisioning the WAN and the LAN for large distributed simulations, it is important to be able to reserve an overall capacity that can be dynamically allocated among the multicast groups
d. 支持资源预留；由于为大型分布式仿真过度配置WAN和LAN是不切实际的，因此能够保留可在多播组之间动态分配的总体容量非常重要
e. support for a mixture of best-effort and reliable low-latency multicast transport, where best-effort predominates in the mixture, and the participants in the reliable multicast may be distributed across any portion of the network
e. 对尽力而为和可靠的低延迟多播传输的混合的支持，其中尽力而为在混合中占主导地位，并且可靠多播的参与者可以分布在网络的任何部分
f. support for secure networking, in the form of per-packet encryption and authentication needed for classified military simulations
f. 支持安全网络，以保密军事模拟所需的每包加密和身份验证的形式
3. Internet Protocol Suite facilities needed and not yet available for large-scale distributed simulation in shared networks: These derive from the need for real-time multicast with established quality of service in a shared network. (Implementation questions are not included in this discussion. For example, it is not clear that implementations of IP multicast exist that will support the required scale of multicast group changes for LSMA, but that appears to be a question of implementation, not a limitation of IP multicast.)
3. 共享网络中的大规模分布式仿真需要Internet协议套件设施，但目前尚不可用：这些设施源于对共享网络中具有既定服务质量的实时多播的需求。（本讨论不包括实现问题。例如，不清楚是否存在支持LSMA所需的多播组更改规模的IP多播实现，但这似乎是一个实现问题，而不是IP多播的限制。）
The Resource reSerVation Protocol (RSVP) is aimed at providing setup and flow-based information for managing information flows at pre-committed performance levels. This capability is generally seen as needed in real-time systems such as the HLA RTI. Concerns have been raised about the scalability of RSVP, and also about its ability to support highly dynamic flow control changes. In terms of existing RTI capabilities, the requirement in LSMA is for rapid change of group membership, not for rapid change of group reservations. This is because in existing RTIs the aggregate requirement for all groups in a large scale distributed simulation is static. However the current RSVP draft standard for LSMA does not support aggregation of reservation resources for groups of flows and therefore does not meet the needs of existing RTIs. Moreover, there is at least one RTI development underway that intends to use individual, dynamic reservations for large numbers of groups, and therefore will require a dynamic resource reservation capability that scales to thousands of multicast groups.
资源预留协议（RSVP）旨在提供基于设置和流的信息，以便以预先承诺的性能级别管理信息流。这种能力通常被认为是实时系统（如HLA RTI）所需要的。人们对RSVP的可伸缩性以及其支持高度动态流控制更改的能力提出了担忧。就现有RTI功能而言，LSMA中的要求是快速更改组成员资格，而不是快速更改组保留。这是因为在现有RTI中，大规模分布式仿真中所有组的总体需求是静态的。但是，当前LSMA的RSVP标准草案不支持流组的保留资源聚合，因此不满足现有RTI的需求。此外，至少有一个RTI开发正在进行中，它打算对大量组使用单独的动态保留，因此需要扩展到数千个多播组的动态资源保留功能。
Further, RSVP provides support only for communicating specifications of the required information flows between simulators and the network, and within the network. Distributing routing information among the routers within the network is a different function altogether, performed by routing protocols such as Multicast Open Shortest Path First (MOSPF). In order to provide effective resource reservation in a large shared network function, it may be necessary to have a routing protocol that determines paths through the network within the context of a quality of service requirement. An example is the proposed Quality Of Service Path First (QOSPF) routing protocol [ZSSC97]. Unfortunately the requirement for resource-sensitive routing will be difficult to define before LSMA networks are deployed with RSVP.
此外，RSVP仅支持在模拟器和网络之间以及网络内通信所需信息流的规范。在网络中的路由器之间分发路由信息是完全不同的功能，由多播开放最短路径优先（MOSPF）等路由协议执行。为了在大型共享网络功能中提供有效的资源预留，可能需要具有在服务质量要求的上下文中确定通过网络的路径的路由协议。一个例子是提出的服务质量路径优先（QOSPF）路由协议[ZSSC97]。不幸的是，在使用RSVP部署LSMA网络之前，很难定义资源敏感路由的要求。
3.2 IP multicast that is capable of taking advantage of all common link layer protocols (in particular, ATM)
3.2 能够利用所有通用链路层协议（特别是ATM）的IP多播
Multicast takes advantage of the efficiency obtained when the network can recognize and replicate information packets that are destined to a group of locations. Under these circumstances, the network can take on the job of providing duplicate copies to all destinations, thereby greatly reducing the amount of information flowing into and through the network.
多播利用了当网络能够识别和复制发送到一组位置的信息包时所获得的效率。在这些情况下，网络可以承担向所有目的地提供副本的工作，从而大大减少流入和通过网络的信息量。
When IP multicast operates over Ethernet, IP multicast packets are transmitted once and received by all receivers using Ethernet-layer multicast addressing, avoiding replication of packets. However, with wide-area Asynchronous Transfer Mode (ATM), the ability to take
当IP多播在以太网上运行时，IP多播数据包只发送一次，并由所有接收器使用以太网层多播寻址来接收，从而避免数据包的复制。然而，在广域异步传输模式（ATM）下
advantage of data link layer multicast capability is not yet available beyond a single Logical IP Subnet (LIS). This appears to be due to the fact that (1) the switching models of IP and ATM are sufficiently different that this capability will require a rather complex solution, and (2) there has been no clear application requirement for IP multicast over ATM multicast that provides for packet replication across multiple LIS. Distributed simulation is an application with such a requirement.
数据链路层多播功能的优势在单个逻辑IP子网（LIS）之外尚不可用。这似乎是由于以下事实造成的：（1）IP和ATM的交换模型完全不同，因此该功能需要一个相当复杂的解决方案；（2）对于通过ATM多播的IP多播没有明确的应用要求，该多播可提供跨多个LIS的包复制。分布式仿真就是这样一种应用。
In general the Internet protocol suite uses the Transmission Control Protocol (TCP) for reliable end-to-end transport, and the User Datagram Protocol (UDP) for best-effort end-to-end transport, including all multicast transport services. The design of TCP is only capable of unicast transmission.
通常，Internet协议套件使用传输控制协议（TCP）进行可靠的端到端传输，使用用户数据报协议（UDP）进行尽力而为的端到端传输，包括所有多播传输服务。TCP的设计只能进行单播传输。
Recently the IETF has seen proposals for several reliable multicast transport protocols (see [Mont97] for a summary). A general issue with reliable transport for multicast is the congestion problem associated with delivery acknowledgments, which has made real-time reliable multicast transport infeasible to date. Of the roughly 15 attempts to develop a reliable multicast transport, all have shown to have some problem relating to positive receipt acknowledgments (ACK) or negative acknowledgments (NAK). In any event, its seems clear that there is not likely to be a single solution for reliable multicast, but rather a number of solutions tailored to different application domains. Approaches involving distributed logging seem to hold particular promise for the distributed simulation application.
最近，IETF已经看到了几种可靠的多播传输协议的提案（见[Mont97]的摘要）。多播可靠传输的一个普遍问题是与发送确认相关的拥塞问题，这使得实时可靠多播传输迄今不可行。在开发可靠多播传输的大约15次尝试中，所有尝试都显示出与肯定接收确认（ACK）或否定确认（NAK）相关的一些问题。无论如何，似乎很清楚，不可能有一个单一的可靠多播解决方案，而是有许多针对不同应用领域的解决方案。涉及分布式日志记录的方法似乎对分布式仿真应用有着特殊的前景。
In the DIS/HLA environment, five different transmission needs can be identified:
在DIS/HLA环境中，可以确定五种不同的传输需求：
(1) best-effort low-latency multicast of object attributes that often
change continuously, for example position of mobile objects;
(2) low-latency reliable multicast of object attributes that do not
change continuously but may change at arbitrary times during the
simulation, for example object appearance (An important
characteristic of this category is that only the latest value of
any attribute is needed by the receiver.);
(3) low-latency, reliable unicast of occasional data among arbitrary
members of the multicast group (This form of transmission was
specified for DIS "collisions"; it is not in the current HLA
specification but might profitably be included there. The
requirement is for occasional transaction-like exchange of data
between two arbitrary hosts in the multicast group, with a low
latency that makes TCP connection impractical.);
(1) best-effort low-latency multicast of object attributes that often
change continuously, for example position of mobile objects;
(2) low-latency reliable multicast of object attributes that do not
change continuously but may change at arbitrary times during the
simulation, for example object appearance (An important
characteristic of this category is that only the latest value of
any attribute is needed by the receiver.);
(3) low-latency, reliable unicast of occasional data among arbitrary
members of the multicast group (This form of transmission was
specified for DIS "collisions"; it is not in the current HLA
specification but might profitably be included there. The
requirement is for occasional transaction-like exchange of data
between two arbitrary hosts in the multicast group, with a low
latency that makes TCP connection impractical.);
(4) reliable but not necessarily real-time multicast distribution of supporting bulk data such as terrain databases and object enumerations; and (5) reliable unicast of control information between individual RTI components (this requirement is met by TCP).
(4) 可靠但不一定实时的支持海量数据的多播分发，如地形数据库和对象枚举；（5）单个RTI组件之间的可靠控制信息单播（TCP满足此要求）。
All of these transmissions take place within the same large-scale multicasting environment. The value of integrating categories (1) and (2) into a single selectively reliable protocol was proposed by Cohen [Cohe94]. Pullen and Laviano implemented this concept [PuLa95] and demonstrated it within the HLA framework [PLM97] as the Selectively
所有这些传输都发生在相同的大规模多播环境中。Cohen[Cohen 94]提出了将类别（1）和（2）集成到单个选择性可靠协议中的价值。普伦和拉维亚诺实施了这一概念[PuLa95]，并在HLA框架[PLM97]中对其进行了演示，作为有选择的解决方案
Reliable Transmission Protocol (SRTP) for categories (1) through (3). Category (4) could be supported by a reliable multicast protocol such as the commercial multicast FTP offering from Starburst [MRTW97], however adequate congestion control has not been demonstrated in any such protocol. There has been some discussion of using the Real-Time Streaming Protocol, RTSP, for this purpose, however as the databases must be transmitted reliably and RTSP uses a best-effort model, it does not appear to be applicable.
类别（1）至（3）的可靠传输协议（SRTP）。类别（4）可以由可靠的多播协议（如Starburst[MRTW97]提供的商业多播FTP）支持，但在任何此类协议中均未证明有足够的拥塞控制。对于使用实时流协议RTSP，已经进行了一些讨论，但是，由于数据库必须可靠传输，并且RTSP使用尽力而为模型，因此它似乎不适用。
In summary, it is clear that a hybrid of best-effort and reliable multicast (not necessarily all in the same protocol) is needed to support DIS and HLA, and that the low-latency, reliable part of this hybrid is not available in the Internet protocol suite.
总之，很明显，需要一种尽力而为和可靠多播的混合（不一定都在同一协议中）来支持DIS和HLA，并且这种混合的低延迟、可靠部分在Internet协议套件中不可用。
Coordinated, integrated network management is one of the more difficult aspects of a large distributed simulation exercise. The network management techniques that have been used successfully to support the growth of the Internet for the past several years could be expanded to fill this need. The technique is based on a primitive called a Management Information Base (MIB) being polled periodically at very low data rates. The receiver of the poll is called an Agent and is collocated with the remote process being monitored. The agent is simple so as to not absorb very many resources. The requesting process is called a Manager, and is typically located elsewhere on a separate workstation. The Manager communicates to all of the agents in a given domain using the Simple Network Management Protocol (SNMP). It appears that SNMP is well adapted to the purpose of distributed simulation management, in addition to managing the underlying simulation network resources. Creating a standard distributed simulation MIB format would make it possible for the simulation community to make use of the collection of powerful, off-the-shelf network management tools that have been created around SNMP.
协调、集成的网络管理是大型分布式仿真演习中比较困难的方面之一。过去几年中成功地支持互联网发展的网络管理技术可以扩展以满足这一需求。该技术基于一个称为管理信息库（MIB）的原语，该原语以极低的数据速率定期轮询。轮询的接收者称为代理，并与被监视的远程进程并置。代理很简单，因此不会占用很多资源。请求进程称为管理器，通常位于单独工作站的其他位置。管理器使用简单网络管理协议（SNMP）与给定域中的所有代理进行通信。除了管理底层仿真网络资源外，SNMP似乎还很适合用于分布式仿真管理。创建标准的分布式仿真MIB格式将使仿真社区能够利用围绕SNMP创建的功能强大的现成网络管理工具。
3.5 A session protocol to start, pause, and stop a distributed simulation exercise
3.5 用于启动、暂停和停止分布式模拟练习的会话协议
Coordinating start, stop, and pause of large distributed exercises is a complex and difficult task. The Session Initiation Protocol (SIP) recently proposed by the Multiparty Multimedia Session Control (MMUSIC) working group serves a similar purpose for managing large scale multimedia conferences. As proposed, SIP appears to offer sufficient extensibility to be used for exercise session control, if standardized by the IETF.
协调大型分布式演习的开始、停止和暂停是一项复杂而困难的任务。多方多媒体会话控制（MMUSIC）工作组最近提出的会话发起协议（SIP）也用于管理大型多媒体会议。正如所提议的，如果IETF标准化，SIP似乎提供了足够的可扩展性，可用于训练会话控制。
It appears that this requirement will be met by IPv6 deployment. A shortcoming of the current Internet Protocol (IPv4) implementation is the lack of integrated security. The new IPv6 protocol requires implementers to follow an integrated security architecture that provides the required integrity, authenticity, and confidentiality for use of the Internet by communities with stringent security demands, such as the financial community. The possibility that the IPv6 security architecture may meet military needs, when combined either with military cryptography or government-certified commercial cryptography, merits further study.
IPv6部署似乎可以满足这一要求。当前Internet协议（IPv4）实现的一个缺点是缺乏集成的安全性。新的IPv6协议要求实施者遵循集成的安全体系结构，该体系结构为具有严格安全要求的社区（如金融社区）使用互联网提供所需的完整性、真实性和保密性。IPv6安全体系结构与军事密码学或政府认证的商业密码学相结合时满足军事需求的可能性值得进一步研究。
Name-to-address mapping in the Internet is performed by the Domain Name Service (DNS). DNS has a distributed architecture tuned to the needs of unicast networking with reliable transmission (TCP) that is not considered problematic if its latency is on the order of a second or more. The requirement of distributed simulation for agile movement among multicast groups implies a need for name-to-multicast-address mapping with latency of under one second for the name resolution and group join combined. This problem has been circumvented in military simulations by using group IP addresses rather than names. While military simulations may be satisfied to communicate using a known mapping from grid squares to multicast groups, growth of distributed simulation into commercial entertainment cannot be based on such a simple capability. The players in distributed entertainment simulations will want to be organized symbolically by virtual world and role. A low-latency multicast naming service will be required.
Internet中的名称到地址映射由域名服务（DNS）执行。DNS具有一个分布式体系结构，可根据具有可靠传输（TCP）的单播网络的需要进行调整，如果其延迟在一秒或更长的时间内，则不会被认为是有问题的。多播组间敏捷移动的分布式仿真需求意味着需要名称到多播地址的映射，对于名称解析和组加入的组合，延迟不超过1秒。在军事模拟中，这个问题通过使用组IP地址而不是名称来规避。虽然军事仿真可能满足于使用从网格正方形到多播组的已知映射进行通信，但分布式仿真向商业娱乐的发展不能基于这样一种简单的能力。分布式娱乐模拟中的玩家希望通过虚拟世界和角色象征性地组织起来。需要低延迟多播命名服务。
While military LSMAs typically take place within a single administrative domain, future entertainment LSMAs can be expected to involve heavy inter-domain multicast traffic so that players can be supported by multiple service providers. Standardized protocols able
虽然军事LSMA通常发生在单个管理域内，但未来的娱乐LSMA可能会涉及大量域间多播流量，因此玩家可以由多个服务提供商支持。标准化协议
to support large numbers of multicast flows across domain boundaries will be needed for this purpose. Current work to create a Border Gateway Multicast Protocol (BGMP) shows promise of meeting this need.
为此，需要跨域边界支持大量多播流。目前创建边界网关多播协议（BGMP）的工作显示了满足这一需求的希望。
[CSTH95] Calvin, J., et. al., "STOW Realtime Information Transfer and Networking Architecture," 12th DIS Workshop on Standards for the Interoperability Distributed Simulations, March 1995.
[CSTH95]Calvin，J.等人，“STOW实时信息传输和网络体系结构”，第12届分布式仿真互操作性标准研讨会，1995年3月。
[Cohe94] Cohen, D., "Back to Basics," Proceedings of the 11th Workshop on Standards for Distributed Interactive Simulation, Orlando, FL, September 1994.
[Cohen，D.，“回到基础”，第11届分布式交互仿真标准研讨会论文集，佛罗里达州奥兰多，1994年9月。
[DIS94] DIS Steering Committee, "The DIS Vision," Institute for Simulation and Training, University of Central Florida, May 1994.
[DIS94] DIS指导委员会，“DIS愿景”，中佛罗里达大学模拟与训练研究所，1994年5月。
[DMSO96] Defense Modeling and Simulation Office, High Level Architecture Rules Version 1.0, U.S. Department of Defense, August 1996.
[DMSO96]国防建模与仿真办公室，高级体系结构规则1.0版，美国国防部，1996年8月。
[IEEE95a] IEEE 1278.1-1995, Standard for Distributed Interactive Simulation - Application Protocols
[IEEE95a]IEEE 1278.1-1995，分布式交互仿真标准-应用协议
[IEEE95b] IEEE 1278.2-1995, Standard for Distributed Interactive Simulation - Communication services and Profiles
[IEEE95b]IEEE 1278.2-1995，分布式交互仿真标准-通信服务和配置文件
[MRTW97] Miller, K., et. al. "StarBurst Multicast File Transfer Protocol (MFTP) Specification", Work in Progress.
[MRTW97]Miller，K.等人，“星突发多播文件传输协议（MFTP）规范”，正在进行的工作。
[Mont97] Montgomery, T., Reliable Multicast Links webpage,
http://research.ivv.nasa.gov/RMP/links.html
[Mont97] Montgomery, T., Reliable Multicast Links webpage,
http://research.ivv.nasa.gov/RMP/links.html
[PuLa95] Pullen, M. and V. Laviano, "A Selectively Reliable Transport Protocol for Distributed Interactive Simulation", Proceedings of the 13th Workshop on Standards for Distributed Interactive Simulation, Orlando, FL, September 1995.
[Pulla95]Pullen，M.和V.Laviano，“分布式交互仿真的选择性可靠传输协议”，第13届分布式交互仿真标准研讨会论文集，佛罗里达州奥兰多，1995年9月。
[PuWh95] Pullen, M. and E. White, "Dual-Mode Multicast: A New Multicasting Architecture for Distributed Interactive Simulation," 12th DIS Workshop on Standards for the Interoperability of Distributed Simulations, Orlando, FL, March 1995.
[PuWh95]Pullen，M.和E.White，“双模多播：分布式交互仿真的新多播架构”，第12届分布式仿真互操作性标准DIS研讨会，佛罗里达州奥兰多，1995年3月。
[PLM97] Pullen, M., Laviano, V. and M. Moreau, "Creating A Light-Weight RTI As An Evolution Of Dual-Mode Multicast Using Selectively Reliable Transmission," Proceedings of the Second Simulation Interoperability Workshop, Orlando, FL, September 1997.
[PLM97]Pullen，M.，Laviano，V.和M.Moreau，“创建轻型RTI作为使用选择性可靠传输的双模多播的一种演变”，第二次仿真互操作性研讨会论文集，佛罗里达州奥兰多，1997年9月。
[SPW94] Symington, S., Pullen, M. and D. Wood, "Modeling and Simulation Requirements for IPng", RFC 1667, August 1994.
[SPW94]Symington，S.，Pullen，M.和D.Wood，“IPng的建模和仿真要求”，RFC 1667，1994年8月。
[SSM96] Seidensticker, S., Smith, W. and M. Myjak, "Scenarios and Appropriate Protocols for Distributed Interactive Simulation", Work in Progress.
[SSM96]Seidensticker，S.，Smith，W.和M.Myjak，“分布式交互仿真的场景和适当协议”，正在进行中。
[ZSSC97] Zhang, Z., et. al., "Quality of Service Path First Routing Protocol", Work in Progress.
[ZSSC97]Zhang，Z.等，“服务质量路径优先路由协议”，正在进行中。
Security issues are discussed in section 3.6.
第3.6节讨论了安全问题。
J. Mark Pullen Computer Science/C3I Center MS 4A5 George Mason University Fairfax, VA 22032
J.马克·普伦计算机科学/C3I中心MS 4A5乔治梅森大学费尔法克斯，弗吉尼亚州22032
EMail: mpullen@gmu.edu
EMail: mpullen@gmu.edu
Michael Myjak The Virtual Workshop P.O. Box 98 Titusville, FL 32781
Michael Myjak虚拟车间地址：佛罗里达州提图斯维尔98号邮政信箱32781
EMail: mmyjak@virtualworkshop.com
EMail: mmyjak@virtualworkshop.com
Christina Bouwens ASSET Group, SAIC Inc. Orlando, FL
Christina Bouwens资产集团，上汽集团，佛罗里达州奥兰多
EMail: christina.bouwens@cpmx.mail.saic.com
EMail: christina.bouwens@cpmx.mail.saic.com
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