Sip Messages; Sip Fundamentals - 3Com MSR 50 Series Configuration Manual

2370 C 137: SIP O
HAPTER

SIP Messages

SIP Fundamentals

VERVIEW
Easy to install and maintain. Even unprofessional individuals can install and
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maintain SIP systems.
SIP messages, falling into SIP request messages and SIP response messages, are
encoded in text mode.
SIP request messages include INVITE, ACK, OPTIONS, BYE, CANCEL, and
REGISTER. An INVITE message is used to invite a subscriber to join a call. RFC 3261
defines the following five request messages:
ACK: Used to acknowledge the response to a request.
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OPTIONS: Used to query for the capabilities.
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BYE: Used to release an established call.
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CANCEL: Used to give up a call attempt.
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REGISTER: Used to register with the SIP registrar.
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SIP response messages, used to respond to SIP requests, indicate the status of a
call or registration, succeeded or failed. Response messages are distinguished by
status codes. Each status code is a 3-digit integer, where the first digit defines the
class of a response, and the last two digits describe the response message in more
detail.
Table 90 lists the status codes of response messages.
Table 90 Status codes of response messages
Code
100 - 199
200 - 299
300 - 399
400 - 499
Registration
In a complete SIP system, all SIP endpoints working as UAs should register with SIP
registrars, providing information such as location, session capabilities, and call
policy.
Normally, a SIP UA sends its registrar a REGISTER request at startup or in response
to an administratively registration operation, carrying all the information that must
be recorded. Upon receipt of the request, the registrar sends back a response
notifying receipt of the request and if the registration is accepted an OK
(SUCCESS) message as well. See
Description
The request is received and is being processed.
The action was successfully received, understood, and
accepted.
A further action needs to be taken in order to complete
the request.
The request contains bad syntax or cannot be fulfilled at
this server.
Figure 686.
Class
Provisional
Success
Redirection
Client error