If you resolve the issue of e-mail playback using TTS by implementing two-factor authentication, you take care of limiting security issues surrounding authentication. However, there are other forms of access, such as eavesdropping on the over-the-wire phone session. Thus, phones are not secure if the call between the phone and the switch that it is connected to is not encrypted. If all phone calls were encrypted, you would not have to worry about any eavesdropping: If eavesdroppers accessed the audio portion of the call, they would hear only the noise of encrypted audio.

Encrypted calls are out of the scope of Unity’s capability. Nevertheless, they are always brought up as an issue when discussing message playback. Surprisingly, some organizations mention this issue during product evaluation more with message playback than with over-the-phone conversations.

The next question asked with any UM system such as Unity is, “Okay, so where are the voice messages stored, really?” The answer, of course, is that they are stored in the e-mail message store. This is actually a hard concept for people to accept. Are the voice messages stored somewhere on Unity? The answer is no. The voice messages are deposited in the Unity Messaging Repository (UMR); as long as the messaging system that Unity services is still online when the message is left there, it is delivered right away. A message stays on the Unity server only if the message system is unavailable. Should voice messages be stored on Unity or in both places, just in case? Possibly. They likely will be in the future—but not because Unity has to have any control over them. Unity eventually will need to consider its dependency on the messaging store to be essential but also behave in a benign way (that is, to minimize the impact the loss of this dependency on its normal operations) so that subscribers who simply want to dial in and check for new messages or manage old voice messages can do so, even if the message store is unavailable to them.

The important thing to note here is that Unity 3.1x and 4.0x can temporarily store messages (in the UMR) left by a subscriber or outside caller if the message cannot be delivered to an unavailable message store.

Another concern arises about storing voice messages with e-mail centers on the size of voice messages. Voice messages are created essentially as wave file attachments to an e-mail message. To play back the message, subscribers must use either the telephone or the VMO snap-in for Exchange or DUC client for Domino in the e-mail client. These snap-ins for the e-mail client recognize the voice message and enable subscribers to interface with the voice-messaging system so that they can record voice messages from their e-mail client (GUI) and send to others.

If voice messages are just wave file attachments to e-mail messages, then how big are the messages? That depends on two things: the codec or codecs used to encode the voice messages, and the average size of the message. Does this mean that voice messages have an impact on an e-mail system? Absolutely! You cannot migrate your entire legacy voice-messaging system onto your e-mail system without affecting it in at least three ways:

• An increase in the number of messages

• An increase in the average size of a message

     •  An increase in the overall disk storage

Any unified messaging system also affects the load of your messaging systems—some worse than others. Unity’s load on an existing messaging system varies, depending upon feature/function usage, the number of subscribers, and the number of messages submitted and retrieved. Be prepared to understand the effects that Unity has on your messaging systems. These effects are not a bad thing, but it is important to be realistic about the potential impact. They can become a bad thing if you are unprepared for them or don’t manage them.

To learn more about Unity’s use of codecs, see Chapter 7, “Components and Subsystems: Features;” Chapter 13, “Unity with Microsoft Exchange;” and Chapter 14, “Unity with Lotus Domino.” To learn about capacity planning for your message store, see Chapter 9.

This chapter is from Cisco Unity Deployment and Solutions Guide by Todd Stone (Addison-Wesley, 2004, ISBN: 1587051184). Check it out at your favorite bookstore today. Buy this book now.