An IP PBX is a telephone switching system inside an enterprise that switches calls between Voice over IP (VoIP) users on local lines and lets all users share a certain number of external telephone lines. The typical IP PBX can also switch calls between a VoIP user and a traditional telephone user, or between two traditional telephone users much like a conventional PBX does. With a conventional PBX, you must have separate networks for voice and data communications. One of the main advantages of an IP PBX is that it uses converged data and voice networks. This means that network access, in addition to VoIP communications and traditional telephone communications, are all possible by using a single line to each user. Like a traditional PBX, an IP PBX is typically owned by an organization.

There are many manufacturers of IP PBXs. However, for an IP PBX to interoperate with Exchange 2007 Unified Messaging, the IP PBX generally must support the following:

• Session Initiation Protocol (SIP) over Transmission Control Protocol (TCP)
  
• T.38 for fax
  
• For a list of supported IP PBXs, see Telephony Advisor for Exchange Server 2007.
  

However, even if a specific IP PBX supports these protocols, there is no guarantee that the IP PBX will successfully interoperate with Exchange 2007 Unified Messaging.

Correctly configuring your organization's IP PBXs is a difficult deployment task that must be completed to successfully deploy Exchange 2007 Unified Messaging. To help answer questions and give you the most up-to-date IP PBX configuration information, see Telephony Advisor for Exchange Server 2007. That toic gives you IP PBX configuration notes and files that are required to correctly configure your organization's IP PBXs to work with Exchange 2007 Unified Messaging.

Cisco CallManager

Cisco CallManager tracks all active VoIP network components. These components include telephones, gateways, conference bridges, voice mail boxes, and other components. Cisco CallManager frequently uses the Skinny Client Control Protocol (SCCP) as a communications protocol for signaling the hardware endpoints of the system, such as IP-based telephones, or it uses SIP to pass call signaling to IP gateways. Cisco CallManager evaluates numbers that are dialed and activates IP gateway events to receive or send calls to the public switched telephone network (PSTN).

Exchange 2007 Unified Messaging has been tested for use with Cisco CallManager version 5.x. If you have Cisco CallManager 5.x on your network, you will be able to connect Exchange 2007 Unified Messaging servers directly to CallManager without the requirement of an IP gateway. Many of the features that are included with Exchange 2007 Unified Messaging are fully functional with Cisco CallManager 5.x. However, the Message Waiting Indicator (MWI) feature does not work and faxing does not work because the T.38 faxing protocol is not supported by Cisco CallManager.

Important:
Cisco CallManager 4.x is only appropriate for a test environment. There are various limitations for this version of Cisco CallManager. Therefore, we recommend that you use it only for test or lab environments.

Cisco CallManager version 5.0 has been tested for direct IP interoperability with Exchange 2007 Unified Messaging. For a listing of the PBXs that are supported, see Telephony Advisor for Exchange Server 2007.

New in Exchange SP1

A PBX, sometimes known as a telephone switch or telephone switching device, is a device that connects office telephones in a business to the public telephone network. The central functions of a PBX are to route incoming calls to the appropriate extension in an office, and to share telephone lines between extensions. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX.

Most medium-size and larger organizations use a PBX because it is much less expensive than connecting an external telephone line to every telephone in the organization. In addition, it is easier to call someone that has an extension number within the same PBX because the number that you dial is typically merely three or four digits.

Correctly configuring your organization's PBXs is frequently one of the more difficult deployment tasks because PBXs are very different and their functionality depends on the PBX model and software that is installed. To help answer questions and give you the most up-to-date PBX configuration information, see Telephony Advisor for Exchange Server 2007. That topic gives you PBX configuration notes and files that are required to correctly configure your organization's PBXs to work with Exchange 2007 Unified Messaging.

For more information about the IP gateways that are supported for Exchange 2007 Unified Messaging, see Supported IP Gateways.