Answering machines are dwindling in American households these days, in favor of voice mail service provided by the local telephone company. If you're talking on your home phone and another call comes in (assuming you don't have call waiting), the other caller receives a busy signal and can't leave a message on your answering machine. However, if you've subscribed to a voice mail service, callers can leave you messages while you're on the phone.
Telephony designers for businesses recognized the benefits of voice mail long ago, and many existing PBX systems offer voice mail to PBX users. As businesses migrate from their PBX systems to VoIP systems, almost all designs require voice mail functionality.
Which Came First, the Voice Mail System or the CCM?
Fortunately, in many cases, companies don't need to throw out their existing voice mail system just because they replace their PBX with a Cisco CallManager (CCM). The CCM might still be able to leverage the business's existing investment in a voice mail system using the Simplified Messaging Desk Interface (SMDI) protocol.
Many legacy voice mail systems connect into PBX analog station ports. Similarly, businesses can connect many of these legacy voice mail systems into ports on some Cisco gateways. For example, the Cisco Catalyst 6000 and 6500 Series switches support a Communication Media Module, which can accommodate a 24-port Foreign Exchange Station (FXS) module, and the CCM can communicate with the Catalyst 6000/6500 Series switch via SMDI, allowing the legacy voice mail ports to be used by the CCM, as shown in Figure 7-1.
Figure 7-1. Legacy Voice Mail Integration
PBX users typically rely on their PBX voice mail system for voice messages, on their e-mail server for voice mail messages, and their fax machine for fax messages. Fortunately, Cisco offers a product called Cisco Unity that acts as a single repository for all these various message types.
Current versions of Cisco Unity run on a Windows Server 2003 platform and leverage Microsoft's Exchange software to store voice mail, e-mail, and fax messages. Unity can be configured such that users only need to check their single Unity mailbox to retrieve all their messages (that is, voice mail, e-mail, and fax messages). In order to retrieve their messages, Unity users don't need to be seated at a computer. Users can access their Unity message store via a phone and, for example, have their e-mail read to them, thanks to Unity's text-to-speech conversion feature.
Unity consists of three primary components:
Although all three components can reside on the same server, in larger environments, these components might be distributed across multiple servers for increased scalability. Although not required, a Unity messaging system can coexist with the CCM in an IP telephony environment, as shown in Figure 7-2.
Figure 7-2. Unity and CCM Integration
Consider a scenario. You're traveling, and you want to check your e-mail from a telephone. You call into your corporate messaging system (which uses Cisco Unity), and you can instruct the messaging system to read you your e-mail. Unity, using text-to-speech conversion technology, audibly reads you the text in your e-mails. Although it would be nice, Unity does not describe what the graphics in your e-mail look like. After you listen to your e-mails, Unity can let you listen to your voice mail. Perhaps later in the day, you're working on your laptop computer at the airport (using wireless network connectivity). You can log into your company's Unity system and retrieve your fax messages, including graphics.
Advanced Messaging with a PBX
As mentioned earlier, when a company migrates away from a PBX system to a CCM system, the company's IP telephony design doesn't immediately need to include Unity. Similarly, a company might migrate its voice mail solution to Unity, while retaining its existing PBX. The Cisco Unity PBX-IP Media Gateway (PIMG) offers one approach to making such integration possible. The PIMG contains eight ports, which connect back to the PBX, and a network connection, which allows the PIMG to communicate with Unity using the session initiation protocol (SIP), as discussed in Chapter 5, "Speaking the Gateways' Languages." Up to six PIMGs can be stacked, offering a total of 48 simultaneous conversations between the PBX and Unity, as shown in Figure 7-3. Unity supports several other integration options as well (for example, digital set emulation).
Figure 7-3. PBX and Unity Integration