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

their entire content. Replay control is exercised by moving the cursor to the
desired message part marked by timestamps.
PC retrieval of voicemail can be a valuable component of a package of desk-
top and laptop PC applications for IP communications.
Figure 12.2 shows an example of a complete unified messaging system.
The UM system in Figure 12.2 supports Web, e-mail, IM, and phone clients,
and uses only the core protocols for the transport and control of these applica-
tions (HTTP, SMTP, SIP, and RTSP). Media (voice, fax, and video) is carried in
RTP packets. Application programming interfaces are notrequired for interop-
erability in the open, standards-based unified message system. This unified
message system is built entirely along the lines of the component server archi-
tecture described in more detail in Chapter 19, “SIP Component Services,”
where the only parameter the individual servers have to know about each
other are the respective URIs. Each server can be developed independently,
without any knowledge of the internal working of the other corresponding
servers.
We will exemplify in the following discussions some relevant message
exchanges for unified messaging.

Figure 12.2 Complete unified messaging system

SIP Clients

PSTN or PBX

Network

SIP Server

Subscriber Data

Subscriber
Data

Subscriber Data

Voice Mail Server

Subscriber Data

SIP

SIP SIP

SMTP

IMAP4

HTTP

Web Client

E-mail Client

Messages SMTP, POP3, IMAP4

Voice/

RTP

Registration and

Account Maintenance

LDAP

Directory

Unified

Message

Store

Unified

Message

Server

GWY

Voicemail and Universal Messaging 213