Understanding the SIP Protocol

contains a number of header fields. Header fields are named attributes that provide additional information about a message. The ones present in an INVITE include the following:

„Unique identifier for the call

„Destination address

„Caller A's address

„Information about the type of session that Caller A wishes to establish with Caller B.

The INVITE (message F1 in Figure 20) might look like this:

 

atlanta.com . . . biloxi.com

 

 

.

proxy

 

proxy

.

 

A's

.

 

 

 

 

.

 

. . . . . . . . . . . . . . . . . . . . . . b's

 

softphone

 

 

SIP Phone

INVITE F1

 

 

 

 

INVITE F2

 

---------------

100 Trying F3

>

INVITE F4

---------------

100 Trying F5

>

<---------------

 

---------------

>

 

 

<--------------

180 Ringing F6

 

 

180 Ringing F7

<---------------

200 OK F9

180 Ringing F8

<---------------

200 OK F10

<---------------

200 OK F11

 

<---------------

 

<---------------

 

<---------------

 

ACK F12

 

 

 

 

 

 

-------------------------------------------------

 

 

Media Session

 

 

>

 

 

 

 

 

<================================================>

 

 

 

BYE F13

 

 

<-------------------------------------------------

 

 

200 OK F14

 

 

 

 

 

 

 

-------------------------------------------------

 

 

 

 

 

>

 

 

 

 

 

 

Figure 20. SIP Session Setup Example With Sip Trapezoid

November 2009

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Image 248
Dialogic 6.2 manual SIP Session Setup Example With Sip Trapezoid, November 248