Applies to: Exchange Server 2010 SP3, Exchange Server 2010 SP2

Topic Last Modified: 2011-04-28

Call processing is a term that describes how incoming calls are answered and handled by a Microsoft Exchange Server 2010 Unified Messaging server in different incoming call scenarios.

Unified Messaging handles the following sorts of incoming calls:

Incoming Calls Overview

When an incoming call is received by a Unified Messaging server, the call is answered and then routed using a message transport, for example, SMTP, MAPI, remote procedure call (RPC), or LDAP. The message transport protocol used to route messages depends on the type of incoming call the Unified Messaging server answers.

Unified Messaging depends on the Active Directory directory service to route incoming calls. Each UM-enabled recipient must have a telephone extension number listed in Active Directory for call answering to function correctly. The extension number for the recipient is listed in Active Directory and is mapped to the extension number that's configured on the user's UM-enabled Exchange mailbox. When a Unified Messaging server answers a call, an Active Directory lookup is performed to locate the appropriate UM-enabled recipient and the message is routed to the recipient's mailbox.

Message Flow

Message flow in Unified Messaging is the process by which a message received by a Unified Messaging server is routed in an Exchange 2010 organization.

In earlier versions of Exchange, routing groups were used to route messages between bridgehead servers—known in Exchange 2007 and Exchange 2010 as Hub Transport servers. There are no routing groups in Exchange 2010.

For example, in an incoming call scenario that includes incoming voice messages, a Hub Transport server uses the SMTP transport protocol to submit the voice mail message to the Mailbox server. In a routing scenario that includes multiple Hub Transport servers, the incoming voice mail message is first submitted to the closest Hub Transport server and is then routed to the Mailbox server that contains the UM-enabled mailbox.

The Unified Messaging servers use a spooling or retry algorithm to make sure all incoming messages are transmitted and delivered to UM-enabled recipients. They try to connect to a Hub Transport server every 30 seconds to submit all messages stored on the Unified Messaging server.

For more information about how the Unified Messaging server handles incoming calls and how messages flow in Unified Messaging, see the following topics: