1.3.4. SIP Messages

In SIP, there are two types of messages:

• SIP Request Messages
• SIP Response Messages

SIP Request Messages

The most commonly used SIP request messages are:

• INVITE
• ACK
• BYE
• REGISTER
• CANCEL
• OPTIONS

For more information see RFC 3261 at http://www.ietf.org/rfc/rfc3261.txt?number=3261.

SIP Response Messages

SIP response messages are numbered. The first digit in each response number indicates the type of response. The response types are as follows:

• 1xx - Information responses, for example, 180 Ringing
• 2xx - Successful responses, for example, 200 OK
• 3xx - Redirection responses, for example, 302 Moved Temporarily
• 4xx - Request failure responses, for example, 402, Forbidden
• 5xx - Server failure responses, for example, 504, Gateway Timeout
• 6xx - Global failure responses, for example, 600, Busy Everywhere

For more information see RFC 3261.

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