A SERVICE OF

logo

Basic SIP Operations
This section walks you through a basic communication
session — how it works, and how SIP supports it. Figure 2-2
illustrates the path of a typical session.
Figure 2-2: A typical SIP session’s ladder diagram.
The scenario in Figure 2-2 shows two users — Michael@
smallcompany.com and John@bigcompany.com
using SIP user agents, calling point-to-point through a proxy
server. Examples of UAs could be an Avaya SIP Phone, a
SIP softphone, or a PDA phone. The proxy server works
to connect the two UAs. The communication then follows
these steps:
1. Michael@smallcompany.com (the UAC) initiates a
session by inviting John@bigcompany.com.
Michael’s
softphone
Proxy
server
John’s
SIP phone
INVITE F1
100 Trying F3
200 OK F8
INVITE F2
100 Trying F4
180 Ringing F5
200 OK F7
ACK F9
180 Ringing F6
200 OK F11
BYE F10
Media Session
Dashboard
Profile:
Communications
Username:
Password:
Set Up:
Default
slp_user@avaya.com
*****
Login
History
Contacts
Part 2: SIP at a Glance
21
06_041498 ch02.qxp 3/16/06 5:52 PM Page 21
SIP guide