R2511-HP MSR Router Series Voice Configuration Guide(V5)

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• Scalable system—Allows expansion as enterprises grow.
• Support to remote users—With SIP, an enterprise network can extend to all its users, wherever they
are.
• Competitive advantage potentials—More SIP-based services are emerging.
• Consistent communication method—Management becomes easier as the result of consistency in
dialup mode and system access method used by branches, SOHOs, and traveling personnel.
• Quick launch—The system can be updated quickly to accommodate new branches and personnel,
as well as changes resulting from job rotation or relocation.
• Easy to install and maintain—Even non-professional individuals can install and maintain SIP
systems.
SIP messages
SIP messages, consisting of SIP request messages and SIP response messages, are encoded in text mode.
SIP request messages include INVITE, ACK, OPTIONS, BYE, CANCEL, REGISTER. RFC 3261 defines the
following six request messages:
• INVITE—Used to invite a user to join a call.
• ACK—Used to acknowledge the response to a request.
• OPTIONS—Used to query for the capabilities.
• BYE—Used to release an established call.
• CANCEL—Used to give up a call attempt.
• REGISTER—Used to register with the SIP registrar.
SIP response messages, used to respond to SIP requests, indicate the status of a call or registration,
whether succeeded or failed. Response messages are distinguished by status codes. As shown in Table
13 , eac
h 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 13 Status codes of response messages
Code Descri
p
tion Class
100–199 The request is received and is being processed. Provisional
200–299 The request is successfully received, understood, and accepted. Success
300–399 A further action needs to be taken in order to process the request. Redirection
400–499 The request contains bad syntax and thus cannot be processed. Client error
500–599 The request cannot be processed due to UAS or server error. Server error
600–699 The request cannot be processed by any UAS or server. Global error
SIP fundamentals
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.