1.会话发起协议(SIP)：
会话发起协议(SIP)是一种信令协议，它负责信号和控制装置连接，维护和断开交互式通信会话。 SIP可以建立实时多媒体会话，并与典型的语音呼叫一起建立视频和音频多播会话以及即时消息传递应用程序和其他通信。但是通常情况下，如果我们将看到它用于通过Internet / Internet协议(IP)网络建立语音和视频呼叫。在IPv4和IPv6中，支持会话发起协议。
会话启动协议在开放系统互连(OSI)模型的应用程序层上工作。它接收来自客户端的请求，并提供来自服务器的响应，因为它是一个请求响应协议。我们也可以将其视为客户端服务器体系结构。
例如，当我们拨打Internet语音(VoIP)呼叫时，在两个设备之间建立了会话初始协议。它是VoIP技术中最常用的协议。
2.综合业务数字网(ISDN)：
ISDN代表综合服务数字网络，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通过一条电话线处理所有类型的流量。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。
如今，集成服务数字网络已被DSL，WAN等取代。其设计目的是用数字技术替代传统的固定电话技术。如今，ISDN仍用于某些网络连接，但很少用于Internet访问。
SIP和ISDN之间的区别：
| 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. |