User's Manual

Chapter 15 VoIP
B222s User’s Guide
137
Aft er successful registrat ion, t he SI P server know s t hat t he users ( ident ified by t heir dedicat ed SI P
URI s) are represent ed by t he UA, and knows t he I P address to which t he SI P request s and
responses should be sent .
Registration is initiat ed by t he User Agent Client ( UAC) running in the VoI P gat eway ( t he LTE
Device) . The gat eway m ust be configur ed with inform at ion lett ing it know where to send t he
REGI STER m essage, as well as t he relevant user and authorization dat a.
A SI P registrat ion has a lim ited lifespan. The User Agent Client m ust renew it s regist rat ion wit hin
this lifespan. I f it does not do so, the registrat ion dat a w ill be delet ed from t he SI P regist rar's
dat abase and the connection broken.
The LTE Device at t em pts t o register all enabled subscriber port s w hen it is swit ched on. When you
enable a subscriber port t hat was previously disabled, t he LTE Device at tem pt s to register t he por t
im m ediately.
Authorization Requirements
SI P registrat ions ( and subsequent SI P requests) requir e a usernam e and password for
authorization. These credent ials ar e validat ed via a challenge / response system using t he HTTP
digest m echanism ( as det ailed in RFC3261, "SI P: Session I nit iation Prot ocol") .
SIP Servers
SI P is a client- server prot ocol. A SI P client is an applicat ion program or device t hat sends SI P
requests. A SI P server responds t o t he SI P requests.
When you use SI P to m ake a VoI P call, it originates at a client and t erm inates at a server. A SI P
client could be a com put er or a SI P phone. One device can act as bot h a SI P client and a SI P server.
SIP User Agent
A SI P user agent can m ake and receive VoI P telephone calls. This m eans t hat SI P can be used for
peer- to-peer com m unications even t hough it is a client- server protocol. I n the following figure,
eit her A or B can act as a SI P user agent client t o initiat e a call. A and B can also both act as a SI P
user agent t o receive t he call.
Figure 76 SI P User Agent
SIP Proxy Server
A SI P proxy server receives requests from client s and forwards t hem to anot her server.
I n t he following exam ple, you want t o use client device A to call som eone w ho is using client device
C.
1 The client device ( A in the figure) sends a call invit at ion t o t he SI P pr oxy ser ver B.
A
B