On the negative side, the proliferation of messaging services, such as voice-
mail on PBXs, for PSTN phones, for mobile phones, e-mail, fax, instant mes-
saging, and paging, creates challenges for:
■■ End users—To manage and keep track of their messages on multiple
devices, systems, and networks
■■ Service providers and network administrators—To manage multiple mes-
sage systemsThis challenge has prompted vendors and service providers to offer various
solutions for unified messaging, but a closer look will reveal these systems to
be proprietary. Service integration is accomplished by “brute force” with its
resulting high complexity.
There are incompatible PBX voicemail systems, PSTN voicemail, mobile voice-
mail, fax, and pagers. There are different e-mail clients and Web clients, includ-
ing multiple media (text, voice, fax, video) and individual user preferences.
A very short summary of key system properties would look like the
following:
■■ Full user control of messaging features and personalization
■■ Full user control of recording and playback
■■ Options for receiving notifications: e-mail, IM, pager, Web browser
■■ Scalability for very large systems and multiple accounts
■■ Media-agnostic (text, voice, fax, video, whiteboard, and so on)
■■ Device-agnostic (PC, phones, fax, pager)
■■ Use existing infrastructure, including:
■■ Data types and records
■■ Network protocols between network elements
■■ Network elements
■■ IP telephony gateways
■■ SIP servers: registrar, redirect, proxy, forking
■■ Component servers: media servers, voice portal, or IVR
■■ Directory
■■ Security infrastructureThe main new network element in the design of a unified message system is
the universal message store, under control of a unified message server. The
unified message server and store can be implemented in various ways to meet210 Chapter 12