1.会话发起协议(SIP)：
会话发起协议(SIP)是一种信令协议，它负责信号和控制手段连接、维护和断开交互通信会话。 SIP 建立实时多媒体会话意味着除了这种典型的语音呼叫外，它还建立了视频和音频组播会话以及即时消息应用程序和其他通信。但通常，如果我们会看到它用于通过 Internet/Internet 协议 (IP) 网络设置语音和视频呼叫。在 IPv4 和 IPv6 中支持会话发起协议。
会话发起协议适用于开放系统互连 (OSI) 模型的应用层。它接收来自客户端的请求并提供来自服务器的响应，因为它是一种请求响应协议。我们也可以将其视为客户端服务器架构。
例如，当我们进行任何互联网协议语音 (VoIP) 呼叫时，在两个设备之间建立会话发起协议期间。它是 VoIP 技术中最常用的协议。
2.综合业务数字网(ISDN)：
ISDN 代表综合业务数字网络，它是一种电信技术。它允许通过基于铜线对的数字线路传输语音和数字数据。同时，ISDN 通过一条电话线接收所有类型的流量。它提供了一组协议来建立、维护和完成呼叫。它在公共交换电话网 (PSTN) 的传统电路上工作。 ISDN 基本上是一个电路交换电话网络系统，但它也允许访问分组交换电话网络。
现在综合业务数字网络已被DSL、WAN等取代。它的设计目的是用数字技术取代传统的固定电话技术。现在，ISDN 仍在用于某些网络连接，但很少用于 Internet 访问。
SIP 和 ISDN 的区别：
| S.No. | SIP | ISDN |
|---|---|---|
| 01. | SIP stands for Session Initiation protocol. | ISDN stands for Integrated Service Digital Network. |
| 02. | It is a signalling protocol. | It is a telecommunication technology which is a set of communication standards/protocols. |
| 03. | It uses the Internet Protocol (IP) network/internet for communication. | It uses the traditional copper telephone network for communication. |
| 04. | It is based on packet switching. |
It is based on circuit switching but also allows access to packet switch. |
| 05. | It is likely to become next generation communication technology. | It is likely to become quickly out dated. |
| 06. | It makes instant changes. | It takes time for changes. |
| 07. | It cost effective and does not require installation and maintenance cost. | It requires expensive hardware and maintenance cost. |
| 08. | It allows to have many trunks depending upon our bandwidth support. | It is limited to 30 channels per line. |
| 09. | It offers as many numbers required with out any restrictions. | It allows geographically dependent numbers. |
| 10. | It provides more features than ISDN. | It provides limited features. |
| 11. | It provides flexibility in use. | It does not provide flexibility in usability point of view. |