R0106-HP MSR Router Series Voice Configuration Guide(V7)

SIP messages

SIP is a text-based protocol. A SIP message is either a request from a client to a server, or a response from

a server to a client.

SIP requests include INVITE, ACK, OPTIONS, BYE, CANCEL, and REGISTER.

• INVITE—Invites a user to join a call.

• ACK—Acknowledges the response to a request.

• OPTIONS—Queries for the capabilities.

• BYE—Releases an established call.

• CANCEL—Gives up a call attempt.

• REGISTER—Registers with the SIP registrar.

SIP responses indicate the status of a call or registration. Responses are distinguished by status codes. As

shown in Table 8, eac

status code is a 3-digit integer, where the first digit defines the class of the

response, and the last two digits describe the response message in more detail.

Table 8 Status codes of responses

Code Descri

tion Class

100–199 The request was received and is being processed. Provisional

200–299 The request was successfully received, understood, and accepted. Success

300–399 A further action must be taken to complete the request. Redirection

400–499 The request contains bad syntax or cannot be fulfilled at this server. Client failure

500–599 The server failed to fulfill an apparently valid request. Server failure

600–699 The request cannot be fulfilled at any server. Global failure

Transport protocols supported by SIP

SIP supports the following transport protocols:

• UDP—Connectionless and unreliable. SIP connections over UDP are unreliable.

• TCP—Connection-oriented and reliable. TCP solves packet loss and retransmission issues for SIP

messages and voice packets. SIP also supports Transport Layer Security (TLS) over TCP. TLS over TCP

provides security for SIP messages. For more information, see "Signaling authentication and

encr

yption."

When active calls are present, switching transport protocols is not supported.

SIP security

Signaling authentication and encryption

TLS over TCP provides a security solution for mutual authentication and encryption. The two

communication parties authenticate each other by using digital certificates before establishing a TLS

connection. SIP messages are encrypted over the TLS connection. For more information about TLS, see

"Configuring TLS as the transport protocol.

To use TLS for SIP, you must also configure TLS security

policies (see Security Configuration Guide).