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图省略 Figure 1. Two mobile and IP integration scenarios. This article describes the iGSM architecture and the protocols for location update and call delivery. We discuss how the tromboning effect in a standard GSM system can be avoided when accessing the IP network. Then we investi­gate the misrouting problem caused by user mobility.	图省略 图1  移动网和IP网的两种集成方案 这一节介绍了iGSM的体系结构以及位置更新和呼叫传递所使用的协议，探讨了在接入IP网络时如何避免在标准GSM系统中产生拉长号效应以及由用户移动性导致的错打问题。
THE IGSM ARCHITECTURE The iGSM system consists of GSM and H.323 (IP) networks. Although we consider H.323 as the VoIP protocol, our results can be general­ized to accommodate other protocols such as Media Gateway Control Protocol. We briefly introduce H.323 as follows. Inter­national Telecommunication Union — Telecom­munication Standardization Sector (ITU-T) H.323 covers the technical requirements for multimedia communications over packet-based networks that may not provide a guaranteed quality of service. Figure 2 illustrates an H.323 system. In this figure the terminal, gateway, gatekeeper, and multipoint control unit are called endpoints.	iGSM体系结构 iGSM系统由GSM和H.323（IP）网络组成。尽管我们将H.323看作VoIP协议，但我们的结果也会被普化，以适应其他协议（如“媒体网关控制协议”）。 我们简单介绍H.323如下。国际电信联盟——电信标准化部门（ITU-T） H.323包括在无QoS保证的分组网络中进行多媒体通信所需的技术要求。图 2是H.323系统的体系结构图。在该图中，终端、网关、网守和多点控制单元都被称作“endpoint（端点）”。
The terminal is customer premises equipment that provides audio, video, and data communica­tions capability in point-to-point or multipoint conferences in the H.323 network. The gateway performs call control functions (setup and release) and provides communication protocol translation mechanism between an H.323 endpoint and an endpoint of an external network such as PSTN, ISDN, or LAN. It also translates the transmitted media from one for­mat to another between the IP and circuit-switched networks. Two H.323 endpoints in the same network can communicate without involving the gateway.	“终端”是用户设备，在H.323网络中的点到点或点到多点会议中提供音频、视频和数据通信功能。 “网关”执行呼叫控制功能（通信建立和通信释放）以及在H.323端点和外部网络（像PSTN、ISDN或LAN）的端点之间提供通信协议转换机制。此外，它还负责在IP网和电路交换网络之间将被发送媒体从一种格式转变成另一种格式。同一网络中的两个H.323端点无需通过网关就可以相互通信。
Figure 2. The H.323 architecture. Figure 3. The iGSM architecture. The gatekeeper is optional in an H.323 net­work, which may be physically collocated with a terminal, gateway, or multipoint control unit. A gatekeeper provides call control services to the H.323 endpoints. The functions of the gatekeep­er include address translation, admission control, bandwidth control, and zone management. The gatekeeper may also perform optional functions such as call control signaling, call authorization, and call management.	图 2  H.323的体系结构 图 3  iGSM体系结构 “网守”是H.323网络的一个可选组件，在物理实现时可以包含在终端、网关或多点控制单元中。网守的功能是向H.323端点提供呼叫控制服务，其功能包括地址翻译、许可控制、带宽控制和区域（zone）管理。此外，它还提供像呼叫控制信令、呼叫鉴权（call authorization）和呼叫管理等可选功能。
The multipoint control unit (MCU) utilizes multipoint controllers (and optionally multipoint processors)to support multipoint conferences. The multipoint controller (MC) provides con­trol functions to support conferences between three or more endpoints in a multipoint confer­ence. Every MCU contains an MC. Terminals, gateways, and gatekeepers may or may not con­tain MCs.	“多点控制单元（MCU）”利用多点控制器（和可选的多点处理器）支持多个端点设备的会议。 “多点控制器（MC）”为支持三个以上端点设备的会议提供控制功能。每个MCU包含一个MC。终端、网关和网守中可以包含MC也可以不含。
The multipoint processor (MP) receives audio, video, and/or data streams from the endpoints involved in a multipoint conference. An MP is optionally included in a gateway, gatekeeper, or MCU. Figure 3 illustrates the iGSM architecture. In this architecture the GSM network is not modi­fied. In the IP network an iGSM gateway is implemented to perform two major functions besides the standard H.323 mechanisms: GSM MAP and H.225 Registration, Admission, and Status (RAS) protocol translation.	“多点处理器（MP）”从多方会议中的端点那里接收音频、视频和/或数据流。网关、网守或MCU中可以包含MP也可以不含。 图3是iGSM的体系结构图。在该体系结构中没有修改GSM网络。在IP网络中，iGSM网关用于实现除标准H.323机制之外的两项主要功能： GSM MAP和H.225注册、接入和状态（RAS）协议转换
Note that in TIPHON, the signaling gateway (which manages signaling protocols such as SS7 ISUP/TACP, GSM MAP, and ISDN) is separat­ed from the media gateway. To simplify our dis­cussion, we assume that both signaling and media gateways are integrated into an iGSM gateway.	注意，在TIPHON中，信令网关（管理像SS7 ISUP/TACP、GSM MAP和ISDN之类的信令协议）从媒体网关那里分离了出来。为了简化讨论，我们假定信令网关和媒体网关都被并入到iGSM网关。
An iGSM gatekeeper is implemented to serve as the VLR for iGSM subscribers who visit the IP network. Thus, every iGSM gatekeeper is assigned an ISDN number that can be recog­nized by the HLR. The iGSM gatekeeper also maintains a list of all iGSM subscribers (whether they visit the IP network or not). Based on this list, the gatekeeper performs MSISDN to trans­port address translation (using the standard H.323 alias address into transport address trans­lation mechanism) and GSM roaming manage­ment procedures for the iGSM subscribers. Note that the iGSM architecture is scalable. We can add iGSM gateways and gatekeepers into the system just like the multiple VLRs and MSCs in a GSM network.	iGSM网守用作访问IP网络的iGSM用户的VLR。这样一来，每个iGSM网守都被分配了一个可被HLR识别的ISDN号码。此外，IGSM网守还保存了一个存有所有iGSM用户信息的表（他们是否访问IP网络）。网守根据这个表为iGSM用户（使用标准H.323别名地址转变成传输地址的翻译机制）将MSISDN翻译成传输地址，以及执行GSM漫游管理流程。 注意，iGSM的体系结构是可伸缩的。我们可以往系统内添加iGSM网关和网守，就像在GSM网络中添加几个VLR和MCS一样。