SIP Requests(SIP协议中的请求类型)

SIP协议，请求命令描述如下：

SIP Request 

Description 

描述

INVITE

A client is being invited to participate in a call. 客户端发起邀请，邀请另一个客户端加入会话

ACK 

The client has confirmed the INVITE request.被邀请端确认接收邀请

BYE

The call has been terminated by either the caller or callee. 会话终止请求，可以是主叫方发出，也可以是被叫方发出

CANCEL 

Cancel any pending requests. 取消任何悬而未决的请求

OPTIONS 

Queries the server for its capabilities. 查询服务器的能力

REGISTER

Registers the client with the server according to the address in the To header. 在服务器端注册客户端的sip通信地址

PRACK

Similar to ACK, but a provisional confirmation. 

类似ACK，但只是一个临时的确认

SUBSCRIBE 

Subscribes the device for an event notification. 新客户端加入事件通知

NOTIFY 

Notifies all subscribers of an event. 通知所有用户事件

PUBLISH 

Publishes an event to a server. 发送事件到服务器

INFO 

Sends information in the middle of a session that doesn't modify the session's state. 在一个会话中发送消息，不会修改会话状态

REFER 

Asks the client to issue a SIP request, typically a call transfer. 要求客户端发出一请求，通常应用于一个呼叫转移

MESSAGE

Sends an instant message using SIP. 发送即时消息的方法

UPDATE

Modifies a session's state without altering the dialog state. 修改session的状态不改变dialog的状态