Designing and Configuring Unified Messaging in Exchange Server 2010 : Unified Messaging Architecture (part 3)

2/24/2011 12:55:57 PM

Audio Codecs and Voice Message Sizes

Codec is a contraction of coding and decoding digital data. This is the format in which the audio stream is stored. It includes both the number of bit rate (bits/sec) and compression that is used.

The codec that is used by the Unified Messaging server to encode the messages is one of the following four:

  • Windows Media Audio (WMA)— 16-bit compressed

  • GSM 06.10 (GSM)— 8-bit compressed

  • G.711 PCM Linear (G711)— 16-bit uncompressed

  • Mpeg Audio Layer 3 (MP3)— 16-bit compressed

The Exchange Server 2010 unified messaging default is MP3. This is a change from Exchange Server 2007 in which the default was WMA. Although using WMA results in slightly smaller file sizes, most people prefer the universal nature of MP3. This enables a much larger number of mobile devices to play voice mail messages. The Audio Codec setting is configured on the UM dial plan on the Settings tab.


A dirty little secret is that the digital compression can result in loss of data. When the data is compressed and decompressed, information can be lost. That is, bits of the conversation or message can be lost. This is a trade-off that the codec makes to save space. This is why the G.711 codec is available, which doesn’t compress data and doesn’t lose data but at a heavy cost in storage.

These are stored in the message as attachments using the following formats:

  • Windows Media Audio Format (.wma)— For the WMA codec

  • RIFF/WAV Format (.wav)— For GSM or G.711 codecs

  • Mpeg Audio Layer 3 (.mp3)— For the MP3 codec

The choice of the audio codec impacts the audio quality and the size of the attached file. Table 1 shows the approximate size of data in the file attachment for each codec.

Table 1. Audio Size for Codec Options
Codec SettingApproximate Size of 10 Sec of Audio
WMA11,000 bytes
G.711160,000 bytes
GSM16,000 bytes
MP319,500 bytes

The G.711 audio codec setting results in a greater than 10:1 storage penalty when compared to the WMA audio codec setting. Although the GSM audio codec setting results in approximately the same storage as the WMA codec setting, this comes at a cost of a 50% reduction in audio quality. MP3 provides similar audio quality to WMA at an acceptable file size. The ubiquitous nature of the MP3 codec makes it the preferred choice for Exchange Server 2010.


The .wma file format has a larger header (about 7KB) than the .wav format (about 0.1KB). So for small messages, the GSM files will be smaller. However, after messages exceed 15 seconds, the WMA files will be smaller than the GSM files.

Operating System Requirements

This section discusses the recommended minimum hardware requirements for Exchange Server 2010 servers.

Exchange Server 2010 unified messaging supports the following processors:

  • x64 architecture-based Intel Xeon or Intel Pentium family processor that supports Intel Extended Memory 64 Technology

  • x64 architecture-based computer with AMD Opteron or AMD Athlon 64-bit processor that supports AMD64 platform

The Exchange Server 2010 unified messaging memory requirements are as follows:

  • 2GB of RAM minimum

  • 4GB of RAM recommended

The Exchange Server 2010 unified messaging disk space requirements are as follows:

  • A minimum of 1.2GB of available disk space

  • Plus 500MB of available disk space for each unified messaging language pack

  • 200MB of available disk space on the system drive

  • DVD drive

As features and complexity of the applications such as Exchange Server 2010 have grown, the installation code bases have grown proportionally. Luckily, so have the hardware specifications of the average new system, which now typically includes a DVD drive.

Exchange Server 2010 unified messaging supports the following operating system and Windows components:

  • Windows Server 2008, x64 Standard Edition with service pack 2

  • Windows Server 2008, x64 Enterprise Edition with service pack 2

  • Windows Server 2008, x64 R2 Standard Edition

  • Windows Server 2008, x64 R2 Enterprise Edition

Exchange Server 2010 unified messaging requires the following components to be installed:

  • Microsoft .NET Framework Version 3.5

  • Windows PowerShell 2.0

  • Windows Remote Management (WinRM) 2.0

  • Extensions for ASP.NET AJAX 1.0

  • Desktop Experience operating system feature

  • Microsoft Management Console (MMC) 3.0.

Out of the box, an Exchange Server 2010 Unified Messaging server is configured for a maximum of 100 concurrent calls. This is enough to support potentially thousands of users, given that the number of calls and voice messages per day is a fraction of the number of users and is spread out throughout the day.

Supported IP/VoIP Hardware

Exchange Server 2010 unified messaging relies on the ability of the IP/VoIP gateway to translate time-division multiplexing (TDM) or telephony circuit-switched based protocols, such as Integrated Services Digital Network (ISDN) or QSIG, from a PBX to protocols based on voice over IP (VoIP) or IP, such as Session Initiation Protocol (SIP), Real-Time Transport Protocol (RTP), or T.38 for real-time facsimile transport.

Although there are many types and manufacturers of PBXs, IP/VoIP gateways, and IP/PBXs, there are essentially two types of IP/VoIP gateway component configurations:

  • IP/VoIP Gateway— A legacy PBX and an IP/VoIP gateway provisioned as two separate devices. The Unified Messaging server communicates with the IP/VoIP gateway.

  • IP/PBX— A modern IP-based or hybrid PBX such as a Cisco CallManager. The Unified Messaging server communicates directly with the PBX.

Table 2 lists the currently supported IP/VoIP gateways.

Table 2. Supported IP/VoIP Gateways for Exchange Server 2010 UM
ManufacturerModelSupported Protocols
AudioCodesMediaPack 114, MediaPack 118Analog with In-Band or SMDI
AudioCodesMediant 1000/2000T1/ or E1 with CAS—In-Band or SMDI, T1/E1 with Primary Rate Interface (PRI) and Q.SIG or Analog PSTN
Dialogic1000/2000T1/ or E1 with CAS—In-Band or SMDI, T1/E1 with Primary Rate Interface (PRI) and Q.SIG or Analog PSTN
Ferrari AGOfficeMaster 3.2PSTN Analog
NetVX1200T1/ or E1 with CAS—In-Band or SMDI, T1/E1 with Primary Rate Interface (PRI) and Q.SIG or Analog PSTN
NortelCS1000Direct SIP
QuintumTenor-seriesAnalog PSTN

To support Exchange Server 2010 unified messaging, one or both types of IP/VoIP device configurations are used when connecting a telephony network infrastructure to a data network infrastructure.

All these solutions must communicate with the unified messenger via SIP over TCP (TLS encrypted) and SRTP.

Telephony Components and Terminology

With the integration of Exchange Server 2010 into the telephony world, it is important for the Exchange Server administrator to understand the various components and terminology of a modern telephone system.

The following are some of the common components and terms that are critical to understand:

  • Circuit— A circuit is a connection between two end-to-end devices. This allows the device to communicate. A common example of this is a telephone call where two people are talking, in which a circuit is established between the two telephones.

  • Circuit-switched networks— Circuit-switched networks consist of dedicated end-to-end connections through the network that support sessions between end devices. The circuits are set up end-to-end through a series of switches as needed and torn down when done. While the circuit is set up, the entire circuit is dedicated to the devices. A common example of a circuit-switched network is the PSTN.

  • DTMF— The Dual Tone Multiple frequency (DTMF) signaling protocol is used for telephony signaling and call setup. The most common use is for telephone tone dialing and is known as Touch-Tone. This is used to convey phone button key presses to devices on the network.

  • IP/PBX— With the advent of high-speed ubiquitous packet-switched networks, many corporations have moved from legacy PBXs to modern IP-based PBXs known as Internet Protocol/Private Branch Exchange (IP/PBX). These devices come in a myriad of forms, including true IP/PBXs that only support IP protocols to hybrid devices that support both circuit-switched and packet-switched devices. A major advantage of the IP/PBXs is that they are typically much easier to provision and administer. Rather than having to add a separate physical line to plug a phone into, IP phones are simply plugged into the Ethernet jack. Rather than being provisioned by the physical line they are plugged into, the IP phones are provisioned by their own internal characteristics such as the MAC address. This allows for more flexibility.

  • IP/VoIP gateways— Connecting legacy circuit-switched networks to packet-switched networks, IP/VoIP gateways provide connections between the new packet-switched VoIP protocols and the circuit-switched protocols. These gateways can connect the PSTN to an IP/PBX or a legacy PBX to VoIP devices. In the case of Exchange Server 2010 unified messaging, the IP/VoIP gateway connects the Unified Messaging server to the legacy PBX. This is not typically needed if the PBX that the Unified Messaging server is connecting to is an IP/PBX.

  • Packet-switched networks— In packet-switched networks, there is no dedicated end-to-end circuit. Instead, the sessions between devices are disassembled into packets and transmitted individually over the network, then reassembled when they reach their destination. All sessions travel over the shared network. A common example of a packet-switched network is the Internet.

  • PBX— In all but the smallest companies, there is a device that takes incoming calls from the circuit-switched telephone network and routes them within the company. This device is called a Private Branch Exchange or PBX. In the old days, this was done by an operator who plugged in the lines manually. The PBX also routes internal outgoing calls, calls between internal phones, and calls to other devices such as the voice mail system.

  • POTS— The Plain Old Telephone System (POTS) is the original analog version of the PSTN. The term originally referred to Post Office Telephone Service, but morphed into the current definition when control of the telephone systems was removed from national post offices.

  • PSTN— The Public Switched Telephone Network (PSTN) is the circuit-switched network to which most telephones connect. It can be either analog, digital, or a combination of the two.

  • TDM— Time-division multiplexing (TDM) is a digital, multiplexing technique for placing multiple simultaneous calls over a circuit-switched network such as the PSTN.

  • VoIP— Voice over Internet Protocol (VoIP) is the use of voice technologies over packet-switched networks using TCP/IP transport protocols rather than circuit-switched networks like the PSTN. This takes advantage of and reflects the trend toward a single, ubiquitous packet-switched network. The local area network (LAN) and wide area network (WAN) are used not only for data traffic, but also for voice traffic. VoIP is not a single technology, but rather a collection of different technologies, protocols, hardware, and software.

Unified Messaging Protocols

The Exchange Server 2010 Unified Messaging servers use several telephony-related protocols to integrate and communicate with telephony devices. These protocols are listed and discussed in the following list:

  • SIP— Session Initiation Protocol (SIP) is the signaling protocol that is used to set up and tear down VoIP calls. These calls include voice, video, instant messaging, and a variety of other services. The SIP protocol is specified in RFC 3261 produced by the Internet Engineering Task Force (IETF) SIP Working Group. SIP is only a signaling protocol and does not transmit data per se. After the call is set up, the actual communications take place using the RTP for voice and video or T.38 for faxes.


    Exchange Server 2010 only supports SIP over TCP. SIP can be configured to run over User Datagram Protocol (UDP) or Transmission Control Protocol (TCP). UDP is connectionless and does not provide reliability guarantees over the network. TCP is connection-oriented and provides reliability guarantees for its packets.

  • RTP— Real-Time Transport Protocol (RTP) is a protocol for sending the voice and video data over the TCP/IP network. The protocol relies on other protocols, such as SIP or H.323, to perform call setup and teardown. It was developed by the IETF Audio-Video Transport Working Group and is specified in RFC 3550. There is not a defined port for the RTP protocol, but it is normally configured to use ports in the range 16384–32767. The protocol uses a dynamic port range, so it is not ideally suited to traversing firewalls.

  • T.38— The Real-Time Facsimile Transport (T.38) protocol is an International Telecommunication Union (ITU) standard for transmitting faxes over TCP/IP. The protocol is described in RFC 3362. Although it can support call setup and teardown, it is normally used in conjunction with a signaling protocol such as SIP.

It is important to note that the Exchange Server 2010 Unified Messaging server is also a Windows server, a web server, and a member of the Active Directory domain. There are a myriad of protocols, including domain name system (DNS), Hypertext Transfer Protocol (HTTP), Lightweight Directory Access Protocol (LDAP), remote procedure calls (RPC), and Simple Mail Transfer Protocol (SMTP) among others, that the servers use to communicate with other servers in addition to the telephony communications.

Unified Messaging Port Assignments

Table 3 shows the IP ports that unified messaging uses for each protocol. The table also shows if the ports can be changed and where.

Table 3. Ports Used for Unified Messaging Protocols
ProtocolTCP PortUDP PortCan Ports Be Changed?
SIP-UM Service5060 Ports are hard-coded.
SIP-Worker Process5061 and 5062 Ports are set by using the Extensible Markup Language (XML) configuration file.
RTP Port range above 1024The range of ports can be changed in the Registry.
T.38 Dynamic port above 1024Ports are defined by the system.
UM Web ServiceDynamic port above 1024 Ports are defined by the system.

  •  Designing and Configuring Unified Messaging in Exchange Server 2010 : Unified Messaging Features
  •  Exploring Sample Virtualized SharePoint 2010 Architecture
  •  Virtualizing SharePoint Components : Virtualization of SharePoint Roles
  •  Monitoring a SharePoint 2010 Environment : Establishing Maintenance Schedules for SharePoint
  •  Using System Center Operations Manager to Simplify Management of SharePoint 2010
  •  Designing and Implementing Mobility in Exchange Server 2010 : Working with Windows Mobile Pocket PC and Smartphone Editions
  •  Designing and Implementing Mobility in Exchange Server 2010 : Working with ActiveSync Policies
  •  Designing and Implementing Mobility in Exchange Server 2010 : Securing Access to ActiveSync Using Internet Security and Acceleration (ISA) Server 2006
  •  Monitoring a SharePoint 2010 Environment : Understanding Timer Jobs for SharePoint 2010
  •  Monitoring a SharePoint 2010 Environment : Using SharePoint’s Native Reporting Capabilities
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