Using Exchange Server 2007 for Unified Messaging

From the year 2000 until Exchange Server 2007, Microsoft IT used a combination of traditional voice mail systems and a third-party UM solution to provide employees with voice mail capabilities. Microsoft IT supported 46,000 users in the unified messaging environment, 79 percent of whom accessed the UM servers from the headquarters in Redmond. Microsoft IT maintained 25 servers (including six tracing servers) for UM in eight sites located in North America, Asia, and South America. These servers answered approximately 280,000 calls per week, with 40 percent of the calls resulting in voice mail messages. The remaining 60 percent of calls resulted in answered calls or callers not leaving voice mail messages.

With the third-party UM system, Microsoft IT maintained a database for user administration of UM-enabled users. This database existed separately from the Active Directory user database. Therefore, UM user management for Microsoft IT entailed additional tasks outside managing users and user attributes through Active Directory.

Telephony and Network Infrastructure

Microsoft IT’s UM environment before Exchange Server 2007 included third-party UM servers, e-mail servers, PBXs, and telephony and IP connectivity. The combination and setup of these components varied to support the user capacity needs of each UM server location. Although Microsoft IT supports over 500 office locations worldwide, only eight sites (Redmond, Silicon Valley, Shinjuku, Mexico City, Bangalore, Singapore, Sao Paulo, and Austin) housed third-party UM servers. Most of these sites were small, requiring only 16 digital phone lines each to provide UM services to regional users. The sites with more users, such as Redmond and Silicon Valley, relied on T1 connectivity.

Table 1 shows the locations that housed the third-party UM servers. The UM servers required connectivity to Microsoft Exchange Server 2003 Mailbox servers and the PBX system. Whereas Exchange Mailbox servers communicated with UM servers through the IP network, the PBXs communicated with UM servers through telephony connections, such as T1 or digital set emulation. Telephony connection runs are expensive to implement over long distances. As a result, Microsoft IT deployed the third-party UM servers in the same physical site as the PBX.

Some of these sites have multiple forests and multiple PBXs. For instance, the Redmond site has one main logical layout to support the entire Redmond area. Yet, there are five Active Directory forests within Redmond for different purposes, such as legacy product support and future product testing. Multiple PBXs service these forests.


Connectivity in a UM system includes the telephony TDM connections between PSTNs and PBXs, the IP-based SIP/T.38 connections between VoIP gateways and UM servers, and IP network connections such as MAPI and LDAP between UM servers and the rest of the network. For its third-party UM system, Microsoft IT relied on the following types of connectivity:

  • Telephony The type of telephony connection that Microsoft IT used varied depending on the capacity needs of the area and the connectivity available. Sites that supported a lower call volume relied on a digital set emulation connection between the PBX and third-party UM servers. Larger sites required a T1 connection between the PBX and third-party UM servers to support a higher call volume. Microsoft IT used T1 Channel Associated Signaling (CAS) for connectivity. For T1 CAS SMDI call integration, Microsoft IT used RS232 integration links.
  • Local area network (LAN) Before Exchange Server 2007 UM, Microsoft IT placed third-party UM servers on the LAN that is located in the same geographical site as the PBX. Microsoft IT made this decision based on costs: Running long-distance PBX telephony connections is expensive.
  • WAN As explained in the “E-Mail Messaging Infrastructure” section later in this document, Microsoft IT consolidated mailbox servers to just four sites by using  Exchange Server 2003. The third-party UM servers communicated with the Exchange Mailbox servers in these sites through WAN connections. The sites that housed UM servers had low-latency connections to the locations that housed Exchange Server 2003 Mailbox servers.

In this environment, the telephony connectivity type and number of ports, which are based on the number of UM users and call load, determine the PBX and number of third-party UM servers necessary for a particular location. Microsoft IT used the following site models:

  • Small site   Most of the UM sites provided services to fewer than 2,000 users. In these sites, eight phone lines per UM server supported incoming calls. Each of these small sites contained two third-party UM servers. The third-party UM servers accepted voice mail messages received by the PBX and transferred messages to the Exchange Mailbox servers.
  • Medium site   Shinjuku in Tokyo was the only medium site in the third-party UM solution, with 32 digital set emulation ports dedicated to voice mail to support a higher call volume. Shinjuku used two third-party UM servers with 16 digital lines per server, instead of the eight lines per server used in smaller configurations.
  • Large site   Redmond and Silicon Valley were the largest sites, designed to support a high volume of calls. They used T1 CAS connections between the PBXs and UM servers. Each T1 line carried 24 channels of voice, and a single RS232 integration link carried the SMDI call integration information.