Network Working Group J. Rosenberg
Request for Comments: 2871 dynamicsoft
Category: Informational H. Schulzrinne
Columbia University
June 2000
Network Working Group J. Rosenberg
Request for Comments: 2871 dynamicsoft
Category: Informational H. Schulzrinne
Columbia University
June 2000
A Framework for Telephony Routing over IP
一种基于IP的电话路由框架
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 (2000). All Rights Reserved.
版权所有（C）互联网协会（2000年）。版权所有。
Abstract
摘要
This document serves as a framework for Telephony Routing over IP (TRIP), which supports the discovery and exchange of IP telephony gateway routing tables between providers. The document defines the problem of telephony routing exchange, and motivates the need for the protocol. It presents an architectural framework for TRIP, defines terminology, specifies the various protocol elements and their functions, overviews the services provided by the protocol, and discusses how it fits into the broader context of Internet telephony.
本文档作为IP电话路由（TRIP）的框架，支持提供商之间IP电话网关路由表的发现和交换。该文档定义了电话路由交换的问题，并激发了对该协议的需求。它提出了TRIP的体系结构框架，定义了术语，指定了各种协议元素及其功能，概述了协议提供的服务，并讨论了它如何适应更广泛的互联网电话环境。
Table of Contents
目录
1 Introduction ........................................ 2
2 Terminology ......................................... 2
3 Motivation and Problem Definition ................... 4
4 Related Problems .................................... 6
5 Relationship with BGP ............................... 7
6 Example Applications of TRIP ........................ 8
6.1 Clearinghouses ...................................... 8
6.2 Confederations ...................................... 9
6.3 Gateway Wholesalers ................................. 9
7 Architecture ........................................ 11
8 Elements ............................................ 12
8.1 IT Administrative Domain ............................ 12
8.2 Gateway ............................................. 13
8.3 End Users ........................................... 14
8.4 Location Server ..................................... 14
9 Element Interactions ................................ 16
1 Introduction ........................................ 2
2 Terminology ......................................... 2
3 Motivation and Problem Definition ................... 4
4 Related Problems .................................... 6
5 Relationship with BGP ............................... 7
6 Example Applications of TRIP ........................ 8
6.1 Clearinghouses ...................................... 8
6.2 Confederations ...................................... 9
6.3 Gateway Wholesalers ................................. 9
7 Architecture ........................................ 11
8 Elements ............................................ 12
8.1 IT Administrative Domain ............................ 12
8.2 Gateway ............................................. 13
8.3 End Users ........................................... 14
8.4 Location Server ..................................... 14
9 Element Interactions ................................ 16
9.1 Gateways and Location Servers ....................... 16
9.2 Location Server to Location Server .................. 16
9.2.1 Nature of Exchanged Information ..................... 17
9.2.2 Quality of Service .................................. 18
9.2.3 Cost Information .................................... 19
10 The Front End ....................................... 19
10.1 Front End Customers ................................. 19
10.2 Front End Protocols ................................. 20
11 Number Translations ................................. 21
12 Security Considerations ............................. 22
13 Acknowledgments ..................................... 23
14 Bibliography ........................................ 23
15 Authors' Addresses .................................. 24
16 Full Copyright Statement ............................ 25
9.1 Gateways and Location Servers ....................... 16
9.2 Location Server to Location Server .................. 16
9.2.1 Nature of Exchanged Information ..................... 17
9.2.2 Quality of Service .................................. 18
9.2.3 Cost Information .................................... 19
10 The Front End ....................................... 19
10.1 Front End Customers ................................. 19
10.2 Front End Protocols ................................. 20
11 Number Translations ................................. 21
12 Security Considerations ............................. 22
13 Acknowledgments ..................................... 23
14 Bibliography ........................................ 23
15 Authors' Addresses .................................. 24
16 Full Copyright Statement ............................ 25
1 Introduction
1导言
This document serves as a framework for Telephony Routing over IP (TRIP), which supports the discovery and exchange of IP telephony gateway routing tables between providers. The document defines the problem of telephony routing exchange, and motivates the need for the protocol. It presents an architectural framework for TRIP, defines terminology, specifies the various protocol elements and their functions, overviews the services provided by the protocol, and discusses how it fits into the broader context of Internet telephony.
本文档作为IP电话路由（TRIP）的框架，支持提供商之间IP电话网关路由表的发现和交换。该文档定义了电话路由交换的问题，并激发了对该协议的需求。它提出了TRIP的体系结构框架，定义了术语，指定了各种协议元素及其功能，概述了协议提供的服务，并讨论了它如何适应更广泛的互联网电话环境。
2 Terminology
2术语
We define the following terms. Note that there are other definitions for these terms, outside of the context of gateway location. Our definitions aren't general, but refer to the specific meaning here:
我们定义以下术语。请注意，在网关位置上下文之外，这些术语还有其他定义。我们的定义不是一般性的，而是指此处的具体含义：
Gateway: A device with some sort of circuit switched network connectivity and IP connectivity, capable of initiating and terminating IP telephony signaling protocols, and capable of initiating and terminating telephone network signaling protocols.
网关：具有某种电路交换网络连接和IP连接的设备，能够启动和终止IP电话信令协议，并且能够启动和终止电话网络信令协议。
End User: The end user is usually (but not necessarily) a human being, and is the party who is the ultimate initiator or recipient of calls.
最终用户：最终用户通常（但不一定）是人，是呼叫的最终发起人或接收人。
Calling Device: The calling device is a physical entity which has IP connectivity. It is under the direction of an end user who wishes to place a call. The end user may or may not be directly controlling the calling device. If the calling device is a PC,
呼叫设备：呼叫设备是具有IP连接的物理实体。它在希望拨打电话的最终用户的指导下进行。最终用户可以直接控制呼叫设备，也可以不直接控制呼叫设备。如果呼叫设备是PC，
the end user is directly controlling it. If, however, the calling device is a telephony gateway, the end user may be accessing it through a telephone.
最终用户直接控制它。然而，如果呼叫设备是电话网关，则最终用户可以通过电话访问它。
Gatekeeper: The H.323 gatekeeper element, defined in [1].
网守：H.323网守元素，在[1]中定义。
SIP Server: The Session Initiation Protocol proxy or redirect server defined in [2].
SIP服务器：在[2]中定义的会话启动协议代理或重定向服务器。
Call Agent: The MGCP call agent, defined in [3].
呼叫代理：MGCP呼叫代理，在[3]中定义。
GSTN: The Global Switched Telephone Network, which is the worldwide circuit switched network.
GSTN：全球交换电话网，即全球电路交换网络。
Signaling Server: A signaling server is an entity which is capable of receiving and sending signaling messages for some IP telephony signaling protocol, such as H.323 or SIP. Generally speaking, a signaling server is a gatekeeper, SIP server, or call agent.
信令服务器：信令服务器是能够接收和发送某些IP电话信令协议（如H.323或SIP）的信令消息的实体。一般来说，信令服务器是网守、SIP服务器或呼叫代理。
Location Server (LS): A logical entity with IP connectivity which has knowledge of gateways that can be used to terminate calls towards the GSTN. The LS is the main entity that participates in Telephony Routing over IP. The LS is generally a point of contact for end users for completing calls to the telephony network. An LS may also be responsible for propagation of gateway information to other LS's. An LS may be coresident with an H.323 gatekeeper or SIP server, but this is not required.
位置服务器（LS）：具有IP连接的逻辑实体，了解可用于终止对GSTN的呼叫的网关。LS是参与IP电话路由的主要实体。LS通常是终端用户完成电话网络呼叫的联络点。LS还可以负责将网关信息传播到其他LS。LS可以与H.323网守或SIP服务器协同工作，但这不是必需的。
Internet Telephony Administrative Domain (ITAD): The set of resources (gateways and Location Servers) under the control of a single administrative authority. End users are customers of an ITAD.
Internet电话管理域（ITAD）：由单个管理机构控制的一组资源（网关和位置服务器）。最终用户是ITAD的客户。
Provider: The administrator of an ITAD.
提供者：ITAD的管理员。
Location Server Policy: The set of rules which dictate how a location server processes information it sends and receives via TRIP. This includes rules for aggregating, propagating, generating, and accepting information.
位置服务器策略：指定位置服务器如何处理通过TRIP发送和接收的信息的一组规则。这包括聚合、传播、生成和接受信息的规则。
End User Policy: Preferences that an end user has about how a call towards the GSTN should be routed.
终端用户策略：终端用户关于如何路由到GSTN的呼叫的首选项。
Peers: Two LS's are peers when they have a persistent association between them over which gateway information is exchanged.
对等点：当两个LS之间存在持久关联并通过该关联交换网关信息时，它们就是对等点。
Internal peers: Peers that both reside within the same ITAD.
内部对等点：位于同一ITAD中的对等点。
External peers: Peers that reside within different ITADs.
外部对等点：位于不同ITAD中的对等点。
Originating Location Server: A Location Server which first generates a route to a gateway in its ITAD.
起始位置服务器：首先在其ITAD中生成到网关的路由的位置服务器。
Telephony Routing Information Base (TRIB): The database of gateways an LS builds up as a result of participation in TRIP.
电话路由信息库（TRIB）：LS因参与TRIP而建立的网关数据库。
3 Motivation and Problem Definition
3动机和问题定义
As IP telephony gateways grow in terms of numbers and usage, managing their operation will become increasingly complex. One of the difficult tasks is that of gateway location, also known as gateway selection, path selection, gateway discovery, and gateway routing. The problem occurs when a calling device (such as a telephony gateway or a PC with IP telephony software) on an IP network needs to complete a call to a phone number that represents a terminal on a circuit switched telephone network. Since the intended target of the call resides in a circuit switched network, and the caller is initiating the call from an IP host, a telephony gateway must be used. The gateway functions as a conversion point for media and signaling, converting between the protocols used on the IP network, and those used in the circuit switched network.
随着IP电话网关数量和使用量的增长，管理它们的操作将变得越来越复杂。其中一项困难的任务是网关定位，也称为网关选择、路径选择、网关发现和网关路由。当IP网络上的呼叫设备（如电话网关或带有IP电话软件的PC）需要完成对代表电路交换电话网络上终端的电话号码的呼叫时，就会出现问题。由于呼叫的预期目标位于电路交换网络中，并且呼叫者从IP主机发起呼叫，因此必须使用电话网关。网关作为媒体和信令的转换点，在IP网络上使用的协议和电路交换网络中使用的协议之间进行转换。
The gateway is, in essence, a relaying point for an application layer signaling protocol. There may be many gateways which could possibly complete the call from the calling device on the IP network to the called party on the circuit switched network. Choosing such a gateway is a non-trivial process. It is complicated because of the following issues:
网关本质上是应用层信令协议的中继点。可能有许多网关可以完成从IP网络上的呼叫设备到电路交换网络上的被叫方的呼叫。选择这样一个网关是一个非常重要的过程。这是复杂的，因为存在以下问题：
Number of Candidate Gateways: It is anticipated that as IP telephony becomes widely deployed, the number of telephony gateways connecting the Internet to the GSTN will become large. Attachment to the GSTN means that the gateway will have connectivity to the nearly one billion terminals reachable on this network. This means that every gateway could theoretically complete a call to any terminal on the GSTN. As such, the number of candidate gateways for completing a call may be very large.
候选网关数量：预计随着IP电话的广泛部署，将互联网连接到GSTN的电话网关数量将越来越多。连接到GSTN意味着网关将连接到该网络上可访问的近10亿个终端。这意味着理论上每个网关都可以完成对GSTN上任何终端的呼叫。因此，用于完成呼叫的候选网关的数量可能非常大。
Business Relationships: In reality, the owner of a gateway is unlikely to make the gateway available to any user who wishes to connect to it. The gateway provides a useful service, and incurs cost when completing calls towards the circuit switched network. As a result, providers of gateways will, in many cases, wish to
业务关系：实际上，网关的所有者不太可能将网关提供给任何希望连接到它的用户。网关提供了有用的服务，并且在完成对电路交换网络的呼叫时会产生成本。因此，在许多情况下，网关提供商希望
charge for use of these gateways. This may restrict usage of the gateway to those users who have, in some fashion, an established relationship with the gateway provider.
使用这些网关收费。这可能会将网关的使用限制为那些以某种方式与网关提供商建立了关系的用户。
Provider Policy: In all likelihood, an end user who wishes to make use of a gateway service will not compensate the gateway provider directly. The end user may have a relationship with an IP telephony service provider which acts as an intermediary to providers of gateways. The IP telephony service provider may have gateways of its own as well. In this case, the IP telephony service provider may have policies regarding the usage of various gateways from other providers by its customers. These policies must figure into the selection process.
提供商政策：希望使用网关服务的最终用户很可能不会直接向网关提供商进行补偿。最终用户可能与充当网关提供商中介的IP电话服务提供商有关系。IP电话服务提供商也可能有自己的网关。在这种情况下，IP电话服务提供商可能具有关于其客户使用来自其他提供商的各种网关的策略。这些政策必须纳入选择过程。
End User Policy: In some cases, the end user may have specific requirements regarding the gateway selection. The end user may need a specific feature, or have a preference for a certain provider. These need to be taken into account as well.
最终用户策略：在某些情况下，最终用户可能对网关选择有特定要求。最终用户可能需要特定功能，或者对某个提供商有偏好。这些也需要加以考虑。
Capacity: All gateways are not created equal. Some are large, capable of supporting hundreds or even thousands of simultaneous calls. Others, such as residential gateways, may only support one or two calls. The process for selecting gateways should allow gateway capacity to play a role. It is particularly desirable to support some form of load balancing across gateways based on their capacities.
容量：并非所有网关都是平等创建的。有些是大型的，能够同时支持数百甚至数千个电话。其他，如住宅网关，可能只支持一个或两个呼叫。选择网关的过程应允许网关容量发挥作用。基于网关的容量，支持网关间某种形式的负载平衡尤其可取。
Protocol and Feature Compatibilities: The calling party may be using a specific signaling or media protocol that is not supported by all gateways.
协议和功能兼容性：呼叫方可能正在使用并非所有网关都支持的特定信令或媒体协议。
From these issues, it becomes evident that the selection of a gateway is driven in large part by the policies of various parties, and by the relationships established between these parties. As such, there cannot be a global "directory of gateways" in which users look up phone numbers. Rather, information on availability of gateways must be exchanged by providers, and subject to policy, made available locally and then propagated to other providers. This would allow each provider to build up its own local database of available gateways - such a database being very different for each provider depending on policy.
从这些问题可以明显看出，网关的选择在很大程度上是由各方的政策以及各方之间建立的关系决定的。因此，不可能有一个全局“网关目录”，用户可以在其中查找电话号码。相反，有关网关可用性的信息必须由提供商交换，并根据政策在本地提供，然后传播给其他提供商。这将允许每个提供商建立其自己的可用网关本地数据库——根据策略，每个提供商的数据库都非常不同。
From this, we can conclude that a protocol is needed between administrative domains for exchange of gateway routing information. The protocol that provides these functions is Telephony Routing over IP (TRIP). TRIP provides a specific set of functions:
由此，我们可以得出结论，管理域之间需要一个协议来交换网关路由信息。提供这些功能的协议是IP电话路由（TRIP）。TRIP提供一组特定的功能：
o Establishment and maintenance of peering relationships between providers;
o 建立和维护提供商之间的对等关系；
o Exchange and synchronization of telephony gateway routing information between providers;
o 在提供商之间交换和同步电话网关路由信息；
o Prevention of stable routing loops for IP telephony signaling protocols;
o 防止IP电话信令协议的稳定路由环路；
o Propagation of learned gateway routing information to other providers in a timely and scalable fashion;
o 以及时且可扩展的方式将学到的网关路由信息传播给其他提供商；
o Definition of the syntax and semantics of the data which describe telephony gateway routes.
o 描述电话网关路由的数据语法和语义的定义。
TRIP can be generally summarized as an inter-domain IP telephony gateway routing protocol.
TRIP通常可以概括为域间IP电话网关路由协议。
4 Related Problems
4相关问题
At a high level, the problem TRIP solves appears to be a mapping problem: given an input telephone number, determine, based on some criteria, the address of a telephony gateway. For this reason, the gateway location problem is often called a "phone number to IP address translation problem". This is an over-simplification, however. There are at least three separate problems, all of which can be classified as a "phone number to IP address translation problem", and only one of which is addressed by TRIP:
从较高的层次上讲，TRIP解决的问题似乎是一个映射问题：给定一个输入电话号码，根据一些标准确定电话网关的地址。因此，网关位置问题通常被称为“电话号码到IP地址的转换问题”。然而，这是一种过度简化。至少有三个独立的问题，所有这些问题都可以归类为“电话号码到IP地址的转换问题”，其中只有一个通过TRIP解决：
o Given a phone number that corresponds to a terminal on a circuit switched network, determine the IP address of a gateway capable of completing a call to that phone number.
o 给定与电路交换网络上的终端相对应的电话号码，确定能够完成对该电话号码呼叫的网关的IP地址。
o Given a phone number that corresponds to a specific host on the Internet (this host may have a phone number in order to facilitate calls to it from the circuit switched network), determine the IP address of this host.
o 给定与Internet上特定主机对应的电话号码（此主机可能有电话号码，以便从电路交换网络呼叫），确定此主机的IP地址。
o Given a phone number that corresponds to a user of a terminal on a circuit switched network, determine the IP address of an IP terminal which is owned by the same user.
o 给定与电路交换网络上终端用户对应的电话号码，确定同一用户拥有的IP终端的IP地址。
The last of these three mapping functions is useful for services where the PC serves as an interface for the phone. One such service is the delivery of an instant message to a PC when the user's phone rings. To deliver this service, a switch in the GSTN is routing a call towards a phone number. It wishes to send an Instant Message to the PC for this user. This switch must somehow have access to the IP
这三个映射函数中的最后一个对于PC作为手机接口的服务非常有用。其中一项服务是当用户的电话铃响时向PC发送即时消息。为了提供这项服务，GSTN中的交换机将呼叫路由到电话号码。它希望为该用户向PC发送即时消息。此交换机必须以某种方式访问IP
network, in order to determine the IP address of the PC corresponding to the user with the given phone number. The mapping function is a name to address translation problem, where the name happens to be represented by a string of digits. Such a translation function is best supported by directory protocols. This problem is not addressed by TRIP.
网络，以确定与具有给定电话号码的用户对应的PC的IP地址。映射函数是一个名称到地址的转换问题，其中名称恰好由一个数字字符串表示。这样的翻译功能最好由目录协议支持。TRIP不能解决这个问题。
The second of these mappings is needed to facilitate calls from traditional phones to IP terminals. When a user on the GSTN wishes to call a user with a terminal on the IP network, they need to dial a number identifying that terminal. This number could be an IP address. However, IP addresses are often ephemeral, assigned on demand by DHCP [4] or by dialup network access servers using PPP [5]. The number could be a hostname, obtained through some translation of groups of numbers to letters. However, this is cumbersome. It has been proposed instead to assign phone numbers to IP telephony terminals. A caller on the GSTN would then dial this number as they would any other. This number serves as an alternate name for the IP terminal, in much the same way its hostname serves as a name. A switch in the GSTN must then access the IP network, and obtain the mapping from this number to an IP address for the PC. Like the previous case, this problem is a name to address translation problem, and is best handled by a directory protocol. It is not addressed by TRIP.
第二种映射需要方便从传统电话到IP终端的呼叫。当GSTN上的用户希望通过IP网络上的终端呼叫用户时，他们需要拨打识别该终端的号码。这个号码可能是IP地址。然而，IP地址通常是短暂的，由DHCP[4]或使用PPP的拨号网络访问服务器按需分配[5]。数字可以是主机名，通过将数字组转换为字母来获得。然而，这很麻烦。有人提议将电话号码分配给IP电话终端。然后，GSTN上的呼叫者会像拨打任何其他号码一样拨打该号码。此号码用作IP终端的备用名称，其主机名用作名称的方式大致相同。然后，GSTN中的交换机必须访问IP网络，并获取从该号码到PC的IP地址的映射。与前一种情况一样，此问题是名称到地址的转换问题，最好通过目录协议处理。它不是通过TRIP来解决的。
The first mapping function, however, is fundamentally an address to route translation problem. It is this problem which is considered by TRIP. As discussed in Section 3, this mapping depends on local factors such as policies and provider relationships. As a result, the database of available gateways is substantially different for each provider, and needs to be built up through specific inter-provider relationships. It is for this reason that a directory protocol is not appropriate for TRIP, whereas it is appropriate for the others.
然而，第一个映射函数基本上是一个地址到路由的转换问题。TRIP考虑的就是这个问题。如第3节所述，此映射取决于本地因素，如策略和提供者关系。因此，每个提供商的可用网关数据库都有很大不同，需要通过特定的提供商间关系来建立。正是由于这个原因，目录协议不适用于TRIP，而适用于其他协议。
5 Relationship with BGP
5与BGP的关系
TRIP can be classified as a close cousin of inter-domain IP routing protocols, such as BGP [6]. However, there are important differences between BGP and TRIP:
TRIP可以归类为域间IP路由协议的近亲，如BGP[6]。然而，BGP和TRIP之间存在重要区别：
o TRIP runs at the application layer, not the network layer, where BGP resides.
o TRIP运行在BGP所在的应用层，而不是网络层。
o TRIP runs between servers which may be separated by many intermediate networks and IP service providers. BGP runs between routers that are usually adjacent.
o TRIP在服务器之间运行，这些服务器可能由许多中间网络和IP服务提供商分隔开。BGP在通常相邻的路由器之间运行。
o The information exchanged between TRIP peers describes routes to application layer devices, not IP routers, as is done with BGP.
o TRIP对等方之间交换的信息描述了到应用层设备的路由，而不是像BGP那样的IP路由器。
o TRIP assumes the existence of an underlying IP transport network. This means that servers which exchange TRIP routing information need not act as forwarders of signaling messages that are routed based on this information. This is not true in BGP, where the peers must also act as forwarding points (or name an adjacent forwarding hop) for IP packets.
o TRIP假设存在一个底层IP传输网络。这意味着交换行程路由信息的服务器不需要充当基于此信息路由的信令消息的转发器。这在BGP中是不正确的，在BGP中，对等方还必须充当IP数据包的转发点（或命名相邻的转发跃点）。
o The purpose of TRIP is not to establish global connectivity across all ITADs. It is perfectly reasonable for there to be many small islands of TRIP connectivity. Each island represents a closed set of administrative relationships. Furthermore, each island can still have complete connectivity to the entire GSTN. This is in sharp contrast to BGP, where the goal is complete connectivity across the Internet. If a set of AS's are isolated from some other set because of a BGP disconnect, no IP network connectivity exists between them.
o TRIP的目的不是在所有ITAD之间建立全球连接。有许多旅游连接的小岛是完全合理的。每个岛代表一组封闭的管理关系。此外，每个岛仍然可以完全连接到整个GSTN。这与BGP形成了鲜明对比，BGP的目标是在互联网上实现完全连接。如果一组AS由于BGP断开而与其他AS隔离，则它们之间不存在IP网络连接。
o Gateway routes are far more complex than IP routes (since they reside at the application, not the network layer), with many more parameters which may describe them.
o 网关路由远比IP路由复杂（因为它们驻留在应用程序而不是网络层），有更多的参数可以描述它们。
o BGP exchanges prefixes which represent a portion of the IP name space. TRIP exchanges phone number ranges, representing a portion of the GSTN numbering space. The organization and hierarchies in these two namespaces are different.
o BGP交换表示IP名称空间一部分的前缀。TRIP交换电话号码范围，表示GSTN编号空间的一部分。这两个名称空间中的组织和层次结构是不同的。
These differences means that TRIP borrows many of the concepts from BGP, but that it is still a different protocol with its own specific set of functions.
这些差异意味着TRIP借用了BGP的许多概念，但它仍然是一个具有自己特定功能集的不同协议。
6 Example Applications of TRIP
TRIP的6个应用示例
TRIP is a general purpose tool for exchanging IP telephony routes between providers. TRIP does not, in any way, dictate the structure or nature of the relationships between those providers. As a result, TRIP has applications for a number of common cases for IP telephony.
TRIP是一种通用工具，用于在提供商之间交换IP电话路由。TRIP不以任何方式规定这些供应商之间关系的结构或性质。因此，TRIP应用于IP电话的许多常见情况。
A clearinghouse is a provider that serves as an exchange point between a number of other providers, called the members of the clearinghouse. Each member signs on with the clearinghouse. As part of the agreement, the member makes their gateways available to the other members of the clearinghouse. In exchange, the members have
票据交换所是一个提供者，它充当许多其他提供者（称为票据交换所成员）之间的交换点。每个成员都在票据交换所签字。作为协议的一部分，该成员向清算所的其他成员提供他们的网关。作为交换，成员们
access to the gateways owned by the other members of the clearinghouse. When a gateway belonging to one member makes a call, the clearinghouse plays a key role in determining which member terminates the call.
进入票据交换所其他成员拥有的网关。当属于一个成员的网关发出呼叫时，清算所在确定哪个成员终止呼叫方面起着关键作用。
TRIP can be applied here as the tool for exchanging routes between the members and the clearinghouse. This is shown in Figure 1.
TRIP可以在这里作为成员和清算所之间交换路线的工具。这如图1所示。
There are 6 member companies, M1 through M6. Each uses TRIP to send and receive gateway routes with the clearinghouse provider.
有6家成员公司，M1至M6。每个协议都使用TRIP发送和接收清算所提供商的网关路由。
We refer to a confederation as a group of providers which all agree to share gateways with each other in a full mesh, without using a central clearinghouse. Such a configuration is shown in Figure 2. TRIP would run between each pair of providers.
我们将联盟称为一组提供者，它们都同意在一个完整的网格中彼此共享网关，而不使用中央清算所。这种配置如图2所示。TRIP将在每对提供者之间运行。
------ ------
| | | |
| M1 | TRIP TRIP | M2 |
| |\ | | /| |
------ \ | | / ------
\ \ / -------------- \ / /
------ \----| |----/ ------
| | | | | |
| M3 |--------| Clearinghouse|--------| M4 |
| | | | | |
------ /----| |----\ ------
/ -------------- \
------ / \ ------
| |/ \| |
| M5 | | M6 |
| | | |
------ ------
------ ------
| | | |
| M1 | TRIP TRIP | M2 |
| |\ | | /| |
------ \ | | / ------
\ \ / -------------- \ / /
------ \----| |----/ ------
| | | | | |
| M3 |--------| Clearinghouse|--------| M4 |
| | | | | |
------ /----| |----\ ------
/ -------------- \
------ / \ ------
| |/ \| |
| M5 | | M6 |
| | | |
------ ------
Figure 1: TRIP in the Clearinghouse Application
图1：票据交换所应用程序中的TRIP
------ ------
| |------| |
| M1 | | M2 |
| |\ /| |
------ \ / ------
| \/ |
| /\ |<-----TRIP
------ / \ ------
| |/ \| |
| M3 | | M4 |
| |------| |
------ ------
------ ------
| |------| |
| M1 | | M2 |
| |\ /| |
------ \ / ------
| \/ |
| /\ |<-----TRIP
------ / \ ------
| |/ \| |
| M3 | | M4 |
| |------| |
------ ------
Figure 2: TRIP for Confederations
图2：联合会的行程
In this application, there are a number of large providers of telephony gateways. Each of these resells its gateway services to medium sized providers. These, in turn, resell to local providers who sell directly to consumers. This is effectively a pyramidal relationship, as shown in Figure 3.
在此应用程序中，有许多大型电话网关提供商。每一家都将其网关服务转售给中型提供商。这些产品反过来转售给当地供应商，直接向消费者销售。这实际上是一种金字塔关系，如图3所示。
------
| |
| M1 |
| |
------
/ \ <------- TRIP
------ ------
| | | |
| M2 | | M3 |
| | | |
------ ------
/ \ / \
------ ------ ------
| | | | | |
| M4 | | M5 | | M6 |
| | | | | |
------ ------ ------
------
| |
| M1 |
| |
------
/ \ <------- TRIP
------ ------
| | | |
| M2 | | M3 |
| | | |
------ ------
/ \ / \
------ ------ ------
| | | | | |
| M4 | | M5 | | M6 |
| | | | | |
------ ------ ------
Figure 3: TRIP for Wholesalers
图3：批发商的旅行
Note that in this example, provider M5 resells gateways from both M2 and M3.
请注意，在本例中，提供商M5从M2和M3转售网关。
7 Architecture
7建筑
Figure 4 gives the overall architecture of TRIP.
图4给出了TRIP的总体架构。
ITAD1 ITAD2
----------------- ------------------
| | | |
| ---- | | ---- |
| | GW | | | | EU | |
| ---- \ ---- | | ---- / ---- |
| | LS | ---------------- | LS | |
| ---- ---- | / ---- \ ---- |
| | GW | / | /| | EU | |
| ---- | / | ---- |
| | / | |
------------------ / ------------------
/
/
--------- /----------
| | |
| ---- |
| | LS | |
| / ---- \ |
| ---- || ---- |
| | GW | || | EU | |
| ---- || ---- |
| ---- || ---- |
| | GW | / \ | EU | |
| ---- ---- |
| |
---------------------
ITAD3
ITAD1 ITAD2
----------------- ------------------
| | | |
| ---- | | ---- |
| | GW | | | | EU | |
| ---- \ ---- | | ---- / ---- |
| | LS | ---------------- | LS | |
| ---- ---- | / ---- \ ---- |
| | GW | / | /| | EU | |
| ---- | / | ---- |
| | / | |
------------------ / ------------------
/
/
--------- /----------
| | |
| ---- |
| | LS | |
| / ---- \ |
| ---- || ---- |
| | GW | || | EU | |
| ---- || ---- |
| ---- || ---- |
| | GW | / \ | EU | |
| ---- ---- |
| |
---------------------
ITAD3
Figure 4: TRIP Architecture
图4：TRIP架构
There are a number of Internet Telephony administrative domains (ITAD's), each of which has at least one Location Server (LS). The LS's, through an out-of-band means, called the intra-domain protocol, learn about the gateways in their domain. The intra-domain protocol is represented by the lines between the GW and LS elements in ITAD1 in the Figure. The LS's have associations with other LS's, over which they exchange gateway information. These associations are established administratively, and are set up when the IT administrative domains have some kind of agreements in place regarding exchange of gateway information. In the figure, the LS in ITAD1 is connected to the LS in ITAD2, which is in turn connected to the LS in ITAD3. Through Telephony Routing over IP (TRIP), the LS in ITAD2 learns about the two gateways in ITAD1. This information is accessed by end users
有许多Internet电话管理域（ITAD），每个域至少有一个位置服务器（LS）。LS通过带外方式（称为域内协议）了解其域中的网关。域内协议由图中ITAD1中GW和LS元素之间的线表示。LS与其他LS关联，通过这些关联交换网关信息。这些关联是以管理方式建立的，并且是在IT管理域就网关信息交换达成某种协议时建立的。在图中，ITAD1中的LS连接到ITAD2中的LS，后者又连接到ITAD3中的LS。通过IP电话路由（TRIP），ITAD2中的LS了解ITAD1中的两个网关。最终用户可以访问此信息
(EUs) in ITAD2 through the front-end. The front-end is a non-TRIP protocol or mechanism by which the LS databases are accessed. In ITAD3, there are both EUs and gateways. The LS in ITAD3 learns about the gateways in ITAD1 through a potentially aggregated advertisement from the LS in ITAD2.
（EUs）通过前端进入ITAD2。前端是访问LS数据库的非跳闸协议或机制。在ITAD3中，有EUs和网关。ITAD3中的LS通过来自ITAD2中LS的潜在聚合广告了解ITAD1中的网关。
8 Elements
8要素
The architecture in Figure 4 consists of a number of elements. These include the IT administrative domain, end user, gateway, and location server.
图4中的体系结构由许多元素组成。其中包括IT管理域、最终用户、网关和位置服务器。
An IT administrative domain consists of zero or more gateways, at least one Location Server, and zero or more end users. The gateways and LS's are those which are under the administrative control of a single authority. This means that there is one authority responsible for dictating the policies and configuration of the gateways and LS's.
IT管理域由零个或多个网关、至少一个位置服务器和零个或多个最终用户组成。网关和LS是由单一机构管理控制的。这意味着有一个机构负责指定网关和LS的策略和配置。
An IT administrative domain need not be the same as an autonomous system. While an AS represents a set of physically connected networks, an IT administrative domain may consist of elements on disparate networks, and even within disparate autonomous systems.
IT管理域不必与自治系统相同。虽然AS代表一组物理连接的网络，但IT管理域可能由不同网络上的元素组成，甚至在不同的自治系统内。
The end users within an IT administrative domain are effectively the customers of that IT administrative domain. They are interested in completing calls towards the telephone network, and thus need access to gateways. An end user may be a customer of one IT administrative domain for one call, and then a customer of a different one for the next call.
IT管理域中的最终用户实际上是该IT管理域的客户。他们对完成电话网络的呼叫感兴趣，因此需要访问网关。最终用户可能在一次呼叫中是一个IT管理域的客户，然后在下一次呼叫中是另一个IT管理域的客户。
An IT administrative domain need not have any gateways. In this case, its LS learns about gateways in other domains, and makes these available to the end users within its domain. In this case, the IT administrative domain is effectively a virtual IP telephony gateway provider. This is because it provides gateway service, but may not actually own or administer any gateways.
IT管理域不需要任何网关。在这种情况下，其LS将了解其他域中的网关，并将这些网关提供给其域中的最终用户。在这种情况下，IT管理域实际上是一个虚拟IP电话网关提供商。这是因为它提供网关服务，但实际上可能不拥有或管理任何网关。
An IT administrative domain need not have any end users. In this case, it provides "wholesale" gateway service, making its gateways available to customers in other IT administrative domains.
IT管理域不需要有任何最终用户。在这种情况下，它提供“批发”网关服务，使其网关可供其他it管理域的客户使用。
An IT administrative domain need not have gateways nor end users. In this case, the ITAD only has LS's. The ITAD acts as a reseller, learning about other gateways, and then aggregating and propagating this information to other ITAD's which do have customers.
IT管理域不需要网关或最终用户。在这种情况下，ITAD只有LS。ITAD充当转售商，了解其他网关，然后将此信息聚合并传播给其他拥有客户的ITAD。
A gateway is a logical device which has both IP connectivity and connectivity to some other network, usually a public or private telephone network. The function of the gateway is to translate the media and signaling protocols from one network technology to the other, achieving a transparent connection for the users of the system.
网关是一种逻辑设备，它既具有IP连接，又具有与其他网络（通常是公用或专用电话网络）的连接。网关的功能是将媒体和信令协议从一种网络技术转换为另一种网络技术，从而实现系统用户的透明连接。
A gateway has a number of attributes which characterize the service it provides. Most fundamental among these are the range of phone numbers to which it is willing to provide service. This range may be broken into subranges, and associated with each, some cost metric or cost token. This token indicates some notion of cost or preference for completing calls for this part of the telephone number range.
网关具有许多属性，这些属性描述了它所提供的服务的特征。其中最基本的是它愿意提供服务的电话号码范围。该范围可分为若干子范围，并与每个子范围、某些成本度量或成本令牌相关联。此令牌表示完成电话号码范围这一部分的呼叫的成本或偏好。
A gateway has attributes which characterize the volume of service which it can provide. These include the number of ports it has (i.e., the number of simultaneous phone calls it can support), and the access link speed. These two together represent some notion of the capacity of the gateway. The metric is useful for allowing Location Servers to decide to route calls to gateways in proportion to the value of the metric, thus achieving a simple form of load balancing.
网关具有表征其可以提供的服务量的属性。这些包括它拥有的端口数（即它可以支持的同时电话呼叫数）和接入链路速度。这两者一起代表了网关容量的一些概念。该度量对于允许位置服务器根据该度量的值决定将调用路由到网关非常有用，从而实现简单的负载平衡。
A gateway also has attributes which characterize the type of service it provides. This includes, but is not limited to, signaling protocols supported, telephony features provided, speech codecs understood, and encryption algorithms which are implemented. These attributes may be important in selecting a gateway. In the absence of baseline required features across all gateways (an admirable, but difficult goal), such a set of attributes is required in order to select a gateway with which communications can be established. End users which have specific requirements for the call (such as a user requesting a business class call, in which case certain call features may need to be supported) may wish to make use of such information as well.
网关还具有表征其提供的服务类型的属性。这包括但不限于支持的信令协议、提供的电话功能、理解的语音编解码器以及实现的加密算法。这些属性在选择网关时可能很重要。在所有网关都没有基线要求的特性（这是一个令人钦佩但困难的目标）的情况下，需要这样一组属性来选择可以建立通信的网关。对呼叫有特定要求的最终用户（例如请求业务类呼叫的用户，在这种情况下可能需要支持某些呼叫功能）也可能希望使用此类信息。
Some of these attributes are transported in TRIP to describe gateways, and others are not. This depends on whether the metric can be reasonably aggregated, and whether it is something which must be conveyed in TRIP before the call is set up (as opposed to negotiated or exchanged by the signaling protocols themselves). The philosophy of TRIP is to keep it simple, and to favor scalability above abundance of information. TRIP's attribute set is readily extensible. Flags provide information that allow unknown attributes to be reasonably processed by an LS.
其中一些属性在TRIP中传输以描述网关，而其他属性则不是。这取决于是否可以合理地聚合度量，以及它是否是在建立呼叫之前必须在TRIP中传输的内容（与信令协议本身协商或交换的内容相反）。TRIP的理念是保持它的简单性，并支持可伸缩性而不是丰富的信息。TRIP的属性集易于扩展。标志提供允许LS合理处理未知属性的信息。
An end user is an entity (usually a human being) which wishes to complete a call through a gateway from an IP network to a terminal on a telephone network. An end user may be a user logged on at a PC with some Internet telephony software. The end user may also be connected to the IP network through an ingress telephone gateway, which the user accessed from telephone handset. This is the case for what is referred to as "phone to phone" service with the IP network used for interexchange transport.
最终用户是希望通过网关完成从IP网络到电话网络终端的呼叫的实体（通常是人）。最终用户可能是使用某些Internet电话软件在PC上登录的用户。最终用户还可以通过入口电话网关连接到IP网络，用户可以从电话听筒访问入口电话网关。这就是所谓的“电话对电话”服务，其IP网络用于交换间传输。
End users may, or may not be aware that there is a telephony routing service running when they complete a call towards the telephone network. In cases where they are aware, end users may have preferences for how a call is completed. These preferences might include call features which must be supported, quality metrics, owner or administrator, and cost preferences.
最终用户在完成对电话网络的呼叫时，可能知道，也可能不知道正在运行电话路由服务。在他们知道的情况下，最终用户可能对如何完成呼叫有偏好。这些首选项可能包括必须支持的呼叫功能、质量指标、所有者或管理员以及成本首选项。
TRIP does not dictate how these preferences are combined with those of the provider to yield the final gateway selection. Nor does TRIP support the transport of these preferences to the LS. This transport can be accomplished using the front end, or by some non-protocol means.
TRIP不规定如何将这些首选项与提供者的首选项组合以产生最终网关选择。TRIP也不支持将这些首选项传输到LS。这种传输可以使用前端或通过一些非协议方式来完成。
The Location Server (LS) is the main functional entity of TRIP. It is a logical device which has access to a database of gateways, called the Telephony Routing Information Base (TRIB). This database of gateways is constructed by combining the set of locally available gateways and the set of remote gateways (learned through TRIP) based on policy. The LS also exports a set of gateways to its peer LS's in other ITAD's. The set of exported gateways is constructed from the set of local gateways and the set of remote gateways (learned through TRIP) based on policy. As such, policy plays a central role in the LS operation. This flow of information is shown in Figure 5.
位置服务器（LS）是TRIP的主要功能实体。它是一种逻辑设备，可以访问网关数据库，称为电话路由信息库（TRIB）。该网关数据库是根据策略将本地可用网关集和远程网关集（通过TRIP学习）结合起来构建的。LS还将一组网关导出到其他ITAD中的对等LS。导出的网关集由本地网关集和基于策略的远程网关集（通过TRIP学习）构成。因此，策略在LS操作中起着核心作用。此信息流如图5所示。
|
|Intra-domain protocol
\ /
Local
Gateways
|
|Intra-domain protocol
\ /
Local
Gateways
TRIP--> Gateways POLICY Gateways -->TRIP
IN Out
|
\ /
Telephony Routing
Information Base
TRIP--> Gateways POLICY Gateways -->TRIP
IN Out
|
\ /
Telephony Routing
Information Base
Figure 5: Flow of Information in TRIP
图5:TRIP中的信息流
The TRIB built up in the LS allows it to make decisions about IP telephony call routing. When a signaling message arrives at a signaling server, destined for a telephone network address, the LS's database can provide information which is useful for determining a gateway or an additional signaling server to forward the signaling message to. For this reason, an LS may be coresident with a signaling server. When they are not coresident, some means of communication between the LS and the signaling server is needed. This communication is not specifically addressed by TRIP, although it is possible that TRIP might meet the needs of such a protocol.
LS中建立的TRIB允许它决定IP电话呼叫路由。当信令消息到达以电话网络地址为目的地的信令服务器时，LS的数据库可以提供有助于确定将信令消息转发到的网关或附加信令服务器的信息。因此，LS可以与信令服务器协同工作。当它们不相互关联时，LS和信令服务器之间需要某种通信方式。TRIP并没有专门处理这种通信，尽管TRIP可能满足此类协议的需要。
An ITAD must have at least one LS in order to participate in TRIP. An ITAD may have more than one LS, for purposes of load balancing, ease of management, or any other reason. In that case, communications between these LS's may need to take place in order to synchronize databases and share information learned from external peers. This is often referred to as the interior component of an inter-domain protocol. TRIP includes such a function.
ITAD必须至少有一个LS才能参与TRIP。出于负载平衡、易于管理或任何其他原因，ITAD可能有多个LS。在这种情况下，可能需要在这些LS之间进行通信，以便同步数据库并共享从外部对等方获取的信息。这通常被称为域间协议的内部组件。TRIP包括这样一个功能。
Figure 5 shows an LS learning about gateways within the ITAD by means of an intra-domain protocol. There need not be an intra-domain protocol. An LS may operate without knowledge of any locally run gateways. Or, it may know of locally run gateways, but through static configuration. An LS may also be co-resident with a gateway, in which case it would know about the gateway that it is co-resident with.
图5显示了LS通过域内协议了解ITAD内网关的情况。不需要有域内协议。LS可以在不知道任何本地运行网关的情况下运行。或者，它可以通过静态配置知道本地运行的网关。LS还可以与网关共存，在这种情况下，LS将知道与其共存的网关。
9 Element Interactions
9元素相互作用
Gateways must somehow propagate information about their characteristics to an LS within the same ITAD. This LS may, in turn, further propagate this information outside of the ITAD by means of TRIP. This LS is called an originating LS for that gateway. When an LS nis not coresident with the gateway, the means by which the information gets propagated is not within the scope of TRIP. The protocol used to accomplish this is generally called an intra-domain protocol.
网关必须以某种方式将有关其特性的信息传播到同一ITAD中的LS。反过来，该LS可通过TRIP在ITAD之外进一步传播该信息。此LS称为该网关的原始LS。当LS与网关不相关时，传播信息的方式不在TRIP范围内。用于实现这一点的协议通常称为域内协议。
One way in which the information can be propagated is with the Service Location Protocol (SLP) [7]. The gateway can contain a Service Agent (SA), and the LS can act as a Directory Agent (DA). SLP defines procedures by which service information is automatically propagated to DA's from SA's. In this fashion, an LS can learn about gateways in the ITAD.
信息传播的一种方式是使用服务位置协议（SLP）[7]。网关可以包含服务代理（SA），LS可以充当目录代理（DA）。SLP定义了服务信息从SA自动传播到DA的过程。通过这种方式，LS可以在ITAD中了解网关。
An alternate mechanism for the intra-domain protocol is via the registration procedures of SIP or H.323. The registration procedures provide a means by which users inform a gatekeeper or SIP server about their address. Such a registration procedure could be extended to allow a gateway to effectively register as well.
域内协议的替代机制是通过SIP或H.323的注册过程。注册过程提供了一种方法，用户可以通过该方法将其地址通知网守或SIP服务器。这样的注册程序可以扩展到允许网关也有效注册。
LDAP [8] might also be used for the intra-domain protocol. A gateway can use LDAP to add an entry for itself into the database. If the LS also plays the role of the LDAP server, it will be able to learn about all those gateways in its ITAD.
LDAP[8]也可用于域内协议。网关可以使用LDAP将自己的条目添加到数据库中。如果LS还扮演LDAP服务器的角色，它将能够在ITAD中了解所有这些网关。
The intra-domain protocol which is used may be different from IT administrative domain to IT administrative domain, and is a matter of local configuration. There may also be more than one intra-domain protocol in a particular ITAD. An LS can also function without an intra-domain protocol. It may learn about gateways through static configuration, or may not know of any local gateways.
所使用的域内协议可能因IT管理域的不同而不同，并且是本地配置的问题。在特定的ITAD中也可能有多个域内协议。LS也可以在没有域内协议的情况下运行。它可能通过静态配置了解网关，也可能不知道任何本地网关。
The interaction between LS's is what is defined by TRIP. LS's within the same ITAD use TRIP to synchronize information amongst themselves. LS's within different ITADs use TRIP to exchange gateway information according to policy. In the former case the LS's are referred to as internal peers, and in the latter case, external peers.
LS之间的相互作用由TRIP定义。同一ITAD中的LS使用TRIP在它们之间同步信息。不同ITAD中的LS使用TRIP根据策略交换网关信息。在前一种情况下，LS被称为内部对等点，在后一种情况下，LS被称为外部对等点。
LS's communicate with each other through persistent associations. An LS may be connected to one or more other LS's. LS's need not be physically adjacent or part of the same autonomous system. The association between a pair of LS's is normally set up administratively. Two LS's are configured to communicate with each other when their administrators have an agreement in place to exchange gateway information. While TRIP does not provide an autodiscovery procedure for peer LS's to discover each other, one could possibly be used. Such a procedure might be useful for finding a backup peer LS when a crash occurs. Alternatively, in an environment where the business relationships between peers become more standardized, peers might be allowed to discover each other through protocols like the Service Location Protocol (SLP) [9]. Determination about whether autodiscovery should or should not be used is at the discretion of the administrator.
LS通过持久关联相互通信。LS可以连接到一个或多个其他LS。LS不需要物理上相邻或属于同一自治系统。一对LS之间的关联通常是通过管理方式建立的。两个LS被配置为在其管理员有交换网关信息的协议时相互通信。虽然TRIP没有为对等LS提供自动发现过程来发现彼此，但也可以使用一个。这样的过程可能有助于在崩溃发生时查找备份对等LS。或者，在对等点之间的业务关系变得更加标准化的环境中，可能允许对等点通过服务位置协议（SLP）[9]等协议相互发现。管理员可自行决定是否应使用自动发现。
The syntax and semantics of the messages exchanged over the association between LS's are dictated by TRIP. The protocol does not dictate the nature of the agreements which must be in place. TRIP merely provides a transport means to exchange whatever gateway routing information is deemed appropriate by the administrators of the system. Details are provided in the TRIP protocol specification itself.
通过LS之间的关联交换的消息的语法和语义由TRIP决定。议定书没有规定必须订立的协议的性质。TRIP仅提供一种传输方式，用于交换系统管理员认为合适的网关路由信息。详细信息见TRIP协议规范本身。
The rules which govern which gateway information is generated, propagated, and accepted by a gateway is called a location server policy. TRIP does not dictate or mandate any specific policy.
控制网关生成、传播和接受哪些网关信息的规则称为位置服务器策略。TRIP不规定或强制执行任何具体政策。
The information exchanged by the LS's is a set of routing objects. Each routing object minimally consists of a range of telephone numbers which are reachable, and an IP address or host name which is the application-layer "next hop" towards a gateway which can reach that range. Routing objects are learned from the intra-domain protocol, static configuration, or from LS's in remote ITAD's. An LS may aggregate these routing objects together (merging ranges of telephone numbers, and replacing the IP address with its own IP address, or with the IP address of a signaling server with which the LS is communicating) and then propagate them to another LS. The decision about which objects to aggregate and propagate is known as a route selection operation. The administrator has great latitude in selecting which objects to aggregate and propagate, so long as they are within the bounds of correct protocol operation (i.e., no loops are formed). The selection can be made based on information learned through TRIP, or through any out of band means.
LS交换的信息是一组路由对象。每个路由对象至少由一系列可访问的电话号码和一个IP地址或主机名组成，该IP地址或主机名是通向可到达该范围的网关的应用层“下一跳”。路由对象从域内协议、静态配置或远程ITAD中的LS中学习。LS可以将这些路由对象聚合在一起（合并电话号码的范围，并用其自己的IP地址或LS与之通信的信令服务器的IP地址替换IP地址），然后将它们传播到另一个LS。关于聚合和传播哪些对象的决定称为路由选择操作。管理员在选择要聚合和传播的对象时有很大的自由度，只要它们在正确的协议操作范围内（即，不形成循环）。可根据通过TRIP或任何带外方式获得的信息进行选择。
A routing object may have additional information which characterizes the service at the gateway. These attributes include things like protocols, features supported, and capacity. Greater numbers of attributes can provide useful information, however, they come at a cost. Aggregation becomes difficult with more and more information, impacting the scalability of the protocol.
路由对象可能具有表征网关处服务的附加信息。这些属性包括协议、支持的功能和容量。更多的属性可以提供有用的信息，但是，它们是有代价的。随着信息越来越多，聚合变得越来越困难，从而影响了协议的可伸缩性。
Aggregation plays a central role in TRIP. In order to facilitate scalability, routing objects can be combined into larger aggregates before being propagated. The mechanisms by which this is done are specified in TRIP. Aggregation of application layer routes to gateways is a non-trivial problem. There is a fundamental tradeoff between aggregatability and verbosity. The more information that is present in a TRIP routing object, the more difficult it is to aggregate.
聚合在TRIP中起着核心作用。为了促进可伸缩性，路由对象可以在传播之前组合成更大的聚合。TRIP中指定了执行此操作的机制。将应用层路由聚合到网关是一个非常重要的问题。在可聚合性和冗长性之间有一个基本的折衷。出行路线对象中存在的信息越多，聚合起来就越困难。
Consider a simple example of two gateways, A and B, capable of reaching some set of telephone numbers, X and Y, respectively. C is an LS for the ITAD in which A and B are resident. C learns of A and B through some other means. As it turns out, X and Y can be combined into a single address range, Z. C has several options. It can propagate just the advertisement for A, just the advertisement for B, propagate both, or combine them and propagate the aggregate advertisement. In this case C chooses the latter approach, and sends a single routing object to one of its peers, D, containing address range Z and its own address, since it is also a signaling server. D is also a signaling server.
考虑一个简单的例子，两个网关A和B，分别能够达到一些电话号码，X和Y。C是A和B所在ITAD的LS。C通过其他方式学习A和B。事实证明，X和Y可以组合成一个地址范围，Z.C有几个选项。它可以只传播A的广告，只传播B的广告，传播两者，或者将它们结合起来传播聚合广告。在这种情况下，C选择后一种方法，并将一个路由对象发送到它的一个对等方D，其中包含地址范围Z和它自己的地址，因为它也是一个信令服务器。D也是一个信令服务器。
Some calling device, E, wishes to place a phone call to telephone number T, which happens to be in the address range X. E is configured to use D as its default H.323 gatekeeper. So, E sends a call setup message to D, containing destination address T. D determines that the address T is within the range Z. As D had received a routing object from C containing address range Z, it forwards the call setup message to C. C, in turn, sees that T is within range X, and so it forwards the call setup to A, which terminates the call signaling and initiates a call towards the telephone network.
一些呼叫设备E希望拨打电话到电话号码T，电话号码T恰好在地址范围X内。E被配置为使用D作为其默认的H.323网守。因此，E向D发送包含目标地址T的呼叫设置消息。D确定地址T在Z范围内。由于D从C接收到包含地址范围Z的路由对象，它将呼叫设置消息转发给C。C依次看到T在X范围内，因此将呼叫设置转发给a，它终止呼叫信令并向电话网络发起呼叫。
One of the factors which is useful to consider when selecting a gateway is "QoS" - will a call through this gateway suffer sufficiently low loss, delay, and jitter? The quality of a call depends on two components - the QoS on the path between the caller and gateway, and the capacity of the gateway itself (measured in terms of number of circuits available, link capacity, DSP resources, etc.). Determination of the latter requires intricate knowledge of
选择网关时有用的因素之一是“QoS”——通过这个网关的呼叫会遭受足够低的丢失、延迟和抖动吗？呼叫的质量取决于两个部分：呼叫方和网关之间路径上的QoS，以及网关本身的容量（根据可用电路数量、链路容量、DSP资源等衡量）。确定后者需要复杂的知识
underlying network topologies, and of where the caller is located. This is something handled by QoS routing protocols, and is outside the scope of TRIP.
基础网络拓扑，以及调用方所在的位置。这是由QoS路由协议处理的，超出了TRIP的范围。
However, gateway capacity is not dependent on the caller location or path characteristics. For this reason, a capacity metric of some form is supported by TRIP. This metric represents the static capacity of the gateway, not the dynamic available capacity which varies continuously during the gateways operation. LS's can use this metric as a means of load balancing of calls among gateways. It can also be used as an input to any other policy decision.
但是，网关容量不取决于呼叫方位置或路径特征。因此，TRIP支持某种形式的容量指标。此指标表示网关的静态容量，而不是在网关运行期间不断变化的动态可用容量。LS可以使用此指标作为网关间呼叫负载平衡的一种手段。它还可以用作任何其他政策决策的输入。
Another useful attribute to propagate is a pricing metric. This might represent the amount a particular gateway might charge for a call. The metric can be an index into a table that defines a pricing structure according to a pre-existing business arrangement, or it can contain a representation of the price itself. TRIP itself does not define a pricing metric, but one can and should be defined as an extension. Using an extension for pricing means more than one such metric can be defined.
要传播的另一个有用属性是定价指标。这可能表示特定网关可能对呼叫收取的费用。该指标可以是根据预先存在的业务安排定义定价结构的表的索引，也可以包含价格本身的表示。TRIP本身并没有定义定价指标，但可以而且应该定义为一个扩展。使用扩展进行定价意味着可以定义多个这样的度量。
10 The Front End
10前端
As a result of TRIP, the LS builds up a database (the TRIB) of gateway routes. This information is made available to various entities within the ITAD. The way in which this information is made available is called the front end. It is the visible means by which TRIP services are exposed outside of the protocol.
作为TRIP的结果，LS建立网关路由的数据库（TRIB）。该信息可供ITAD内的各个实体使用。提供这些信息的方式称为前端。它是在协议之外公开跳闸服务的可见方式。
There are several entities which might use the front end to access the TRIB. These include, but are not limited to:
有几个实体可能使用前端访问TRIB。这些包括但不限于：
Signaling Servers: Signaling servers receive signaling messages (such as H.323 or SIP messages) whose purpose is the initiation of IP telephony calls. The destination address of these calls may be a phone number corresponding to a terminal on the GSTN. In order to route these calls to an appropriate gateway, the signaling server will need access to the database built up in the LS.
信令服务器：信令服务器接收信令消息（如H.323或SIP消息），其目的是启动IP电话呼叫。这些呼叫的目的地地址可以是与GSTN上的终端相对应的电话号码。为了将这些呼叫路由到适当的网关，信令服务器将需要访问LS中建立的数据库。
End Users: End users can directly query the LS to get routing information. This allows them to provide detailed information on their requirements. They can then go and contact the next hop signaling server or gateway towards that phone number.
终端用户：终端用户可以直接查询LS获取路由信息。这使他们能够提供有关其需求的详细信息。然后，他们可以去联系下一跳信令服务器或网关，找到该电话号码。
Administrators: Administrators may need to access the TRIB for maintenance and management functions.
管理员：管理员可能需要访问TRIB以实现维护和管理功能。
When a signaling server contacts the LS to route a phone number, it is usually doing so because a calling device (on behalf of an end user) has attempted to set up a call. As a result, signaling servers effectively act as proxies for end users when accessing the LS database. The communication between the calling devices and their proxies (the signaling servers) is through the signaling protocol.
当信令服务器联系LS以路由电话号码时，它通常这样做是因为呼叫设备（代表最终用户）已尝试建立呼叫。因此，在访问LS数据库时，信令服务器有效地充当最终用户的代理。呼叫设备与其代理（信令服务器）之间的通信通过信令协议进行。
The advantage of this proxy approach is that the actual LS interaction is hidden from the calling device. Therefore, whether the call is to a phone number or IP address is irrelevant. The routing in the case of phone numbers takes place transparently. Proxy mode is also advantageous for thin clients (such as standalone IP telephones) which do not have the interfaces or processing power for a direct query of the LS.
这种代理方法的优点是对调用设备隐藏了实际的LS交互。因此，无论是打电话给电话号码还是IP地址都无关紧要。电话号码的路由是透明的。代理模式也有利于瘦客户机（如独立IP电话），因为瘦客户机没有接口或处理能力来直接查询LS。
The disadvantage of the proxy approach is the same as its advantage - the LS interaction is hidden from the calling device (and thus the end user). In some cases, the end user may have requirements as to how they would like the call to be routed. These include preferences about cost, quality, administrator, or call services and protocols. These requirements are called the end user policy. In the proxy approach, the user effectively accesses the service through the signaling protocol. The signaling protocol is not likely to be able to support expression of complex call routing preferences from end users (note however, that SIP does support some forms of caller preferences for call routing [10]). Therefore, direct access from the end user to the LS can provide much richer call routing services.
代理方法的缺点与优点相同——LS交互对调用设备（以及最终用户）是隐藏的。在某些情况下，最终用户可能会要求如何路由呼叫。其中包括有关成本、质量、管理员或呼叫服务和协议的首选项。这些要求称为最终用户策略。在代理方法中，用户通过信令协议有效地访问服务。信令协议不可能支持终端用户复杂呼叫路由偏好的表达（然而，请注意，SIP确实支持呼叫路由的某些形式的呼叫方偏好[10]）。因此，从最终用户到LS的直接访问可以提供更丰富的呼叫路由服务。
When the end user policy is presented to the LS (either directly or through the signaling protocol), it is at the discretion of the LS how to make use of it. The location server may have its own policies regarding how end user preferences are handled.
当终端用户策略（直接或通过信令协议）呈现给LS时，LS可自行决定如何使用该策略。对于如何处理最终用户首选项，位置服务器可能有自己的策略。
There are numerous protocols that can be used in the front end to access the LS database. TRIP does not specify or restrict the possibilities for the front end. It is not clear that it is necessary or even desirable for there to be a single standard for the front end. The various protocols have their strengths and weaknesses. One may be the right solution in some cases, and another in different cases.
前端可以使用许多协议来访问LS数据库。TRIP未指定或限制前端的可能性。目前尚不清楚是否有必要或甚至希望为前端制定一个单一的标准。各种协议各有优缺点。在某些情况下，一种可能是正确的解决方案，在不同的情况下，另一种可能是正确的解决方案。
Some of the possible protocols for the front end are:
前端的一些可能协议包括：
Service Location Protocol (SLP): SLP has been designed to fit exactly this kind of function. SLP is ideal for locating servers described by a set of attributes. In this case, the server is a gateway (or next hop towards the gateway), and the attributes are the end user policy. The end user is an SLP UA, and the LS is an SLP DA. The Service Query is used to ask for a gateway with a particular set of attributes.
服务定位协议（SLP）：SLP的设计正好适合这种功能。SLP非常适合定位由一组属性描述的服务器。在这种情况下，服务器是网关（或向网关的下一跳），属性是最终用户策略。最终用户是SLP UA，LS是SLP DA。服务查询用于请求具有特定属性集的网关。
Open Settlements Protocol (OSP): OSP [11] is a client server protocol. It allows the client to query a server with a phone number, and get back the address of a next hop, along with authorization tokens to use for the call. In this case, the server can be an LS. The routing table it uses to respond to OSP queries is the one built up using TRIP.
开放结算协议（OSP）：OSP[11]是一种客户机-服务器协议。它允许客户端使用电话号码查询服务器，并返回下一个跃点的地址，以及用于呼叫的授权令牌。在这种情况下，服务器可以是LS。它用来响应OSP查询的路由表是使用TRIP建立的。
Lightweight Directory Access Protocol (LDAP): LDAP is used for accessing distributed databases. Since the LS server contains a database, LDAP could be used to query it.
轻量级目录访问协议（LDAP）：LDAP用于访问分布式数据库。由于LS服务器包含一个数据库，因此可以使用LDAP来查询它。
Web Page: The LS could have a web front end. Users could enter queries into a form, and the matching gateways returned in the response. This access mechanism is more appropriate for human access, however. A signaling server would not likely access the front end through a web page.
网页：LS可以有一个Web前端。用户可以在表单中输入查询，并在响应中返回匹配的网关。然而，这种访问机制更适合于人工访问。信令服务器不可能通过网页访问前端。
TRIP: The protocols discussed above are all of the query-response type. There is no reason why the LS access must be of this form. It is perfectly acceptable for the access to be through complete database synchronization, so that the entity accessing the LS database effectively has a full copy of it. If this approach were desired, TRIP itself is an appropriate mechanism. This approach has obvious drawbacks, but nothing precludes it from being done.
TRIP：上面讨论的协议都是查询响应类型。没有理由说明LS访问必须是这种形式。通过完全的数据库同步进行访问是完全可以接受的，这样访问LS数据库的实体就可以有效地拥有数据库的完整副本。如果需要这种方法，TRIP本身就是一种合适的机制。这种方法有明显的缺点，但没有什么能阻止它。
11 Number Translations
11个数字翻译
The model for TRIP is that of many gateways, each of which is willing to terminate calls towards some set of phone numbers. Often, this set will be based on the set of telephone numbers which are in close geographic proximity to the gateway. For example, a gateway in New York might be willing to terminate calls to the 212 and 718 area codes. Of course, it is up to the administrator to decide on what phone numbers the gateway is willing to call.
TRIP的模式是多个网关，每个网关都愿意终止对某组电话号码的呼叫。通常，这组电话号码基于地理位置靠近网关的一组电话号码。例如，纽约的网关可能愿意终止对212和718区号的呼叫。当然，由管理员决定网关愿意拨打的电话号码。
However, certain phone numbers don't represent GSTN terminals at all, but rather they represent services or virtual addresses. An example of such numbers are freephone and LNP numbers. In the telephone network, these are actually mapped to routable telephone numbers, often based on complex formulae. A classic example is time-of-day-based translation.
然而，某些电话号码根本不代表GSTN终端，而是代表服务或虚拟地址。例如freephone和LNP号码。在电话网络中，这些号码实际上被映射到可路由的电话号码，通常基于复杂的公式。一个典型的例子是基于时间的翻译。
While nothing prevents a gateway from advertising reachability to these kinds of numbers, this usage is highly discouraged. Since TRIP is a routing protocol, the routes it propagates should be to routable numbers, not to names which are eventually translated to routable numbers. Numerous problems arise when TRIP is used to propagate routes to these numbers:
虽然没有任何东西可以阻止网关宣传这些类型的数字的可达性，但这种使用是非常不鼓励的。由于TRIP是一种路由协议，它传播的路由应该是可路由的编号，而不是最终转换为可路由编号的名称。当TRIP用于将路线传播到这些数字时，会出现许多问题：
o Often, these numbers have only local significance. Calls to a freephone number made from New York might terminate in a New York office of a company, while calls made from California will terminate in a California branch. If this freephone number is injected into TRIP by a gateway in New York, it could be propagated to other LS's with end users in California. If this route is used, calls may be not be routed as intended.
o 通常，这些数字只具有局部意义。从纽约拨打的免费电话号码可能会在公司的纽约办事处终止，而从加利福尼亚拨打的电话则会在加利福尼亚分公司终止。如果这个免费电话号码被纽约的一个网关注入到TRIP中，它可能会被传播到其他LS，最终用户在加利福尼亚州。如果使用此路由，则可能无法按预期路由呼叫。
o The call signaling paths might be very suboptimal. Consider a gateway in New York that advertises a ported number that maps to a phone in California. This number is propagated by TRIP, eventually being learned by an LS with end users in California. When one of them dials this number, the call is routed over the IP network towards New York, where it hits the gateway, and then is routed over the GSTN back to California. This is a waste of resources. Had the ported number been translated before the gateway routing function was invoked, a California gateway could have been accessed directly.
o 呼叫信令路径可能非常不理想。考虑一下纽约的一个网关，它把在加利福尼亚的电话号码映射到一个电话号码。这个数字通过TRIP传播，最终由一个LS和加利福尼亚的终端用户一起学习。当其中一人拨这个号码时，电话会通过IP网络路由到纽约，在那里它会到达网关，然后通过GSTN路由回到加利福尼亚。这是浪费资源。如果在调用网关路由功能之前翻译了端口号，则可以直接访问加利福尼亚网关。
As a result, it is more efficient to perform translations of these special numbers before the LS routing databases are accessed. How this translation is done is outside the scope of TRIP. It can be accomplished by the calling device before making the call, or by a signaling server before it accesses the LS database.
因此，在访问LS路由数据库之前执行这些特殊编号的翻译更为有效。如何翻译不在TRIP的范围之内。它可以在呼叫之前由呼叫设备完成，或者在访问LS数据库之前由信令服务器完成。
12 Security Considerations
12安全考虑
Security is an important component in TRIP. The TRIP model assumes a level of trust between peer LS's that exchange information. This information is used to propagate information which determines where calls will be routed. If this information were incorrect, it could cause complete misrouting of calls. This enables a significant denial of service attack. The information might also be propagated to other
安全是TRIP的重要组成部分。TRIP模型假设交换信息的对等LS之间存在一定程度的信任。此信息用于传播确定呼叫路由位置的信息。如果此信息不正确，可能会导致呼叫完全错误路由。这会导致严重的拒绝服务攻击。该信息也可能传播到其他用户
ITADs, causing the problem to potentially spread. As a result, mutual authentication of peer LS's is critical. Furthermore, message integrity is required.
ITADs，导致问题可能蔓延。因此，对等LS的相互认证至关重要。此外，还需要消息完整性。
TRIP messages may contain potentially sensitive information. They represent the routing capabilities of an ITAD. Such information might be used by corporate competitors to determine the network topology and capacity of the ITAD. As a result, encryption of messages is also supported in TRIP.
跳闸信息可能包含潜在的敏感信息。它们表示ITAD的路由功能。公司竞争对手可能会使用这些信息来确定ITAD的网络拓扑和容量。因此，TRIP中也支持消息加密。
As routing objects can be passed via one LS to another, there is a need for some sort of end to end authentication as well. However, aggregation will cause the routing objects to be modified, and therefore authentication can only take place from the point of last aggregation to the receiving LS's.
由于路由对象可以通过一个LS传递到另一个LS，因此也需要某种端到端身份验证。但是，聚合将导致路由对象被修改，因此身份验证只能从最后一次聚合点到接收LS发生。
13 Acknowledgments
13致谢
The authors would like to thank Randy Bush, Mark Foster, Dave Oran, Hussein Salama, and Matt Squire for their useful comments on this document.
作者要感谢Randy Bush、Mark Foster、Dave Oran、Hussein Salama和Matt Squire对本文件的有用评论。
14 Bibliography
14参考书目
[1] International Telecommunication Union, "Visual telephone systems and equipment for local area networks which provide a non-guaranteed quality of service," Recommendation H.323, Telecommunication Standardization Sector of ITU, Geneva, Switzerland, May 1996.
[1] 国际电信联盟，“提供非保证服务质量的局域网可视电话系统和设备”，建议H.323，国际电联电信标准化部门，瑞士日内瓦，1996年5月。
[2] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg, "SIP: Session Initiation Protocol", RFC 2543, March 1999.
[2] Handley，M.，Schulzrinne，H.，Schooler，E.和J.Rosenberg，“SIP：会话启动协议”，RFC 25431999年3月。
[3] Arango, M., Dugan, A., Elliott, I., Huitema, C. and S. Pickett, "Media Gateway Control Protocol (MGCP) Version 1.0", RFC 2705, October 1999.
[3] Arango，M.，Dugan，A.，Elliott，I.，Huitema，C.和S.Pickett，“媒体网关控制协议（MGCP）1.0版”，RFC 27052999年10月。
[4] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.
[4] Droms，R.，“动态主机配置协议”，RFC 2131，1997年3月。
[5] Simpson, W., "The Point-to-Point Protocol (PPP)," STD 51, RFC 1661, July 1994.
[5] 辛普森，W.，“点对点协议（PPP）”，标准51，RFC16611994年7月。
[6] Rekhter Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC 1771, March 1995.
[6] Rekhter Y.和T.Li，“边境网关协议4（BGP-4）”，RFC 1771，1995年3月。
[7] Veizades, J., Guttman, E., Perkins, C. and S. Kaplan, "Service Location Protocol", RFC 2165, June 1997.
[7] Veizades，J.，Guttman，E.，Perkins，C.和S.Kaplan，“服务位置协议”，RFC 21651997年6月。
[8] Yeong, W., Howes, T. and S. Kille, "Lightweight Directory Access Protocol", RFC 1777, March 1995.
[8] Yeong，W.，Howes，T.和S.Kille，“轻量级目录访问协议”，RFC 17771995年3月。
[9] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service Location Protocol, Version 2", RFC 2608, June 1999.
[9] Guttman，E.，Perkins，C.，Veizades，J.和M.Day，“服务位置协议，版本2”，RFC 26081999年6月。
[10] Schulzrinne H. and J. Rosenberg, "SIP caller preferences and callee capabilities", Work in progress.
[10] Schulzrinne H.和J.Rosenberg，“SIP呼叫方偏好和被呼叫方能力”，正在进行中。
[11] European Telecommunications Standards Institute (ETSI), Telecommunications and Internet Protocol Harmonization Over Networks (TIPHON), "Inter-domain pricing, authorization, and usage exchange," Technical Specification 101 321 version 1.4.2, ETSI, 1998.
[11] 欧洲电信标准协会（ETSI），网络上的电信和互联网协议协调（TIPHON），“域间定价、授权和使用交换”，技术规范101 321版本1.4.2，ETSI，1998年。
15 Authors' Addresses
15作者地址
Jonathan Rosenberg dynamicsoft 72 Eagle Rock Avenue First Floor East Hanover, NJ 07936
Jonathan Rosenberg dynamicsoft 72 Eagle Rock大道一楼东汉诺威，NJ 07936
Email: jdrosen@dynamicsoft.com
Email: jdrosen@dynamicsoft.com
Henning Schulzrinne Columbia University M/S 0401 1214 Amsterdam Ave. New York, NY 10027-7003
亨宁·舒尔兹林内哥伦比亚大学M/S 0401 1214纽约州纽约市阿姆斯特丹大道10027-7003
Email: schulzrinne@cs.columbia.edu
Email: schulzrinne@cs.columbia.edu
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Acknowledgement
确认
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