209We will show in this chapter how SIP-based voicemail, presence, and e-mail
can support unified messaging on the same Internet infrastructure at much
reduced complexity, while at the same time providing enhanced functionality.
The integration of e-mail and IM is beyond our scope here, since this can be
done in a text-based message gateway in a straightforward manner. Fax and
video messages can be treated in a similar manner to voice as shown here.
After presenting an example for the overall messaging architecture, we will
discuss the major steps in the life cycle of a voice message: Depositing a mes-
sage, notification of message waiting, and message retrieval.
Problem Statement for Unified Messaging
On the positive side, rich messaging choices (such as the venerable voicemail
and the various text-based messaging services), especially Internet-based
e-mail, can accommodate the preferences of users for one or another mode of
communications. Some users hate voicemail and prefer e-mail only, while
other users prefer to have voicemail as well.