Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

Figure 2.1 Basic SIP

Table 2.3 SIP Operations in a Nutshell

FUNCTION DESCRIPTION COMMENTS

Discovery of destina- Get SIP URI out of band: Basic SIP requires no SIP

tion address address book, business card, servers, as shown in Figure

e-mail, phone call. The URI 2.1.

requires several DNS lookups.

Query the DNS for the IP address. RFC 3261 specifies SIP

This allows the IP address to servers are optional.

change.

Single domain: Query a central This is the model for the IP

SIP proxy server to determine PBX or most public VoIP

the destination IP address. service providers (VISP).

This triangle model was first

used in RFC 2543.

Inter-domain: The query passes The trapezoid model will

to an outgoing SIP proxy and a support session setup

remote incoming SIP proxy. The between different Internet

trapezoid model is based on domains.

RFC 3261.

INVITE

Caller

1. Discovery of remote address


2. Setting up the session

Query another

SIP peer node in

P2P SIP.

Query chain of

SIP proxy

servers (service

providers).

Query one SIP

proxy server

(PBX).

Query DNS

for IP address.

Get URI of destination

out of band:

• Business card


• E-mail


• Phone call

Called

Caller IP/port for media and codec choices

200 OK

ACK

RTP media packets

Caller IP/port for media and selected codec

180 Ringing (or 183 Session Progress)

16 Chapter 2