什么是 IP 多媒体子系统？
我读到，IMS 定义了一个完整的体系结构和框架，可以在基于 IP 的基础设施上集成语音、视频、数据和移动网络技术。 SIP 网络元素（如注册服务器、位置服务器和代理服务器）提供的框架是否不足以支持 VOIP 电话？那么这个IMS是必需的吗？我无法理解 SIP 网络和 IMS 之间的区别。
I have read that IMS defines a complete architecture and framework that enables the integration of voice, video, data and mobile network technology over an IP-based infrastructure.
Does the framework provided by the SIP network elements like Registrar Server, Location Server and Proxy Server is not sufficient for VOIP telephony? So this IMS is required? I am not able to understand the difference between SIP network and IMS.
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IMS 是电信行业向全 IP 网络过渡蓝图的一部分（长期演进 (LTE) 项目的核心组成部分）。它使用 SIP 作为在控制平面中进行会话设置的骨干协议。
每个 IMS 安装都会有两个网络元素，类似于通常的 SIP 注册器和代理服务器。然而，除了简单的注册器和代理功能之外，计费、认证和授权（通常称为 AAA）以及管理移动性和进出不同网络类型的访问都增加了 IMS 核心的职责。
例如，IMS 核心中的服务呼叫会话控制功能服务器 (S-CSCF) 是 SIP 服务器，它非常类似于注册器，执行用户注册、管理会话控制、与服务层交互，并负责计费。用户从不直接与S-CSCF交互，而是仅通过代理CSCF服务器(P-CSCF)进行通信，顾名思义，代理CSCF服务器本质上是SIP代理服务器。
IMS 安装的核心还有另一个 CSCF，即询问 CSCF (I-CSCF)，但它不太适合与通常的 SIP 服务器进行比较。
总之，当与 IMS 安装交互时，您应该能够以与典型的 SIP 注册器和基于代理服务器的网络大致相同的方式对待它，但是，IMS 需要在上面完成更多工作。
IMS is part of the telecom industry's blueprint for the transition to an all-IP network (a core component of the Long Term Evolution (LTE) project). It uses SIP as the backbone protocol for session setup in what is refered to as the Control Plane.
Each IMS installation will have two network elements which are similar to the usual SIP Registrar and Proxy servers. However, Accounting, Authentication and Authorization (usually refered to as AAA) as well as managing mobility and access to and from different network types all add to the responsibilities of the IMS core over and above the simple Registrar and Proxy functions.
For example, the Serving Call Session Control Function server (S-CSCF) in the IMS-core is the SIP server that closely resembles the Registrar performing user registration, managing session control, interacting with the services layer, and is charged with accounting for usage. Users never interact directly with the S-CSCF, instead, they communicate only via the Proxy CSCF server (P-CSCF), which as its name suggests is essentially a SIP proxy server.
There is another CSCF at the heart of an IMS installation, the Interrogating CSCF (I-CSCF), but doesn't lend itself to comparision with the usual SIP servers as much.
So in summary, when interacting with an IMS installation you should be able to treat it in much the same way as a typical SIP Registrar and Proxy server-based network, however, IMS need to accomplish much more on top.
总的来说，SIP（以及其他协议）适合 VoIP。正如您所说，IMS 定义了 VoIP 以外的服务组合。 IMS 是一个定义 VoIP、视频通话、状态、即时消息等的架构。因此您可以看到 IMS 是 IP 媒体的下一个演进。它不仅仅是 VoIP。
这里可能需要一些有关定义的词：
等级。它的部分功能使用 SIP 和许多其他协议
建筑学。
SIP (with other protocols) is, overall, suitable for VoIP. As you said, IMS defines a combination of services other than VoIP. IMS is an architecture that defines VoIP, video calls, presence, instant messaging, etc. So you can see IMS being the next evolution of medias on IP. It is much more than just VoIP.
Some words on definitions may be good here:
level. It uses SIP and many other protocols for parts of its
architecture.
我喜欢 jwri 的答案，但我想提出一个不太技术性的答案:-)
IMS 是一种架构，SIP（和 Diameter）是使用的协议。
它应该允许移动服务提供商构建异构（多供应商）网络。
这实际上起作用并且有意义的是应用程序服务器（AS）：
您应该能够从任何供应商将语音邮件等独立服务添加到您的 IMS 核心。 IMS 定义了一种将 AS 连接到呼叫流程、计费等的标准方法。
因此，为了回答您的问题，IMS 只是设置 SIP 代理 (CSCF) 注册器（由 HSS 支持）、计费的一种特定方法等等。
就像您是 2G 移动提供商一样，理论上您可以部署一堆 BSS 塔，将它们连接到您自己的 A 接口实现，并以您喜欢的任何方式在它们之间进行切换。或者构建您自己的无线电并仅实现 GSM 无线电接口，这足以进行无线电话，您不需要所有 BSC、MSC、HLR 等:-)
I like the answer by jwri, but I'd like to pitch in a less technical one :-)
IMS is an architecture, SIP (and Diameter) are the protocols used.
It should allow mobile service providers to build heterogeneous (multi-vendor) networks.
Where this actually works and makes sense is the Application Servers (AS):
You should be able to add independent services like Voice Mail to your IMS core from any vendor. IMS defines a standard way to hook an AS up to the call flow, billing, etc.
So to answer your question, the IMS is just one specific way to set up your SIP Proxies (CSCF) registrar (backed by the HSS), billing, etc.
Just like if you were a 2G mobile provider, you could theoretically deploy a bunch of BSS towers, hook them up to your own implementation of the A interface, and do the switching between them any way you like. Or build your own radios and implement the GSM radio interface only, it's enough to do radio telephony, you don't need all the BSCs, MSCs, HLRs, and so on :-)