原创 1224 Structure of the Protocol
SIP is structured as a layered protocol, which means that its behavior is described in terms of a set of fairly
原创 1223 REGISTER01
No ACK is sent - an ACK is only sent in response to a response to an INVITE request Registration is another common ope
原创 1222 sending a re-INVITE to change the session
The other party sends a 200 (OK) to accept the change. The requestor responds to the 200 (OK) with an ACK. If the
原创 1228 Generating the Request
A valid SIP request formulated by a UAC MUST, at a minimum, contain the following header fields: To, From, CSeq,
原创 1220 SIP is not a vertically integrated communications system.
SIP is rather a component that can be used with other IETF protocols to build a complete multimedia architecture.
原创 1225 TU layer
saction layer is called the transaction user (TU). Each of the SIP entities, except the stateless proxy, is a t
原创 1231 Sending the Request
Local policy MAY specify an alternate set of destinations to attempt. If the Request-URI contains a SIPS URI, any a
原创 1226 SIP Messages
Both types of messages consist of a start-line, one or more header fields, an empty line indicating the end of the
原创 1221 Additional Via
Before forwarding the request, the atlanta.com proxy server adds an additional Via header field value that cont
原创 1219 Response Codes 01
486 忙 The callee's end system was contacted successfully, but the callee is currently not willing or able to take a
原创 1229 Call-ID
The Call-ID header field acts as a unique identifier to group together a series of messages. It MUST be the same f
原创 0107 UAS Applying Extensions
A UAS that wishes to apply some extension when generating the response MUST NOT do so unless support for that ex
原创 1227 Status-Line,Header
Status-Line = SIP-Version SP Status-Code SP Reason-Phrase CRLF 例如: SIP/2.0 200 OK header =
原创 1230 Via
x The Via header field indicates the transport used for the transaction and identifies the location where the respon
原创 0101 Processing Responses
Responses are first processed by the transport layer and then passed up to the transaction layer. The transaction