Instant Messaging | SIP Architecture

In different variations, instant messaging has been around longer than the Internet has been popular. In the 1970s, the TALK command was implemented on UNIX machines, which invoked a split screen that allowed users of the system to see the messages they typed in individual screens. In the 1980s, Bulletin Board Systems (BBSes) became popular, where people would use a modem to dial into another person’s computer to access various resources, such as message boards, games, and file downloads. On BBSes, the system operator (SYSOP) could invoke a chat feature that allowed the SYSOP to send messages back and forth with the caller on a similar split-screen. If the BBS had multiple phone lines, then the callers could Instant message with each other while they were online. As the Internet gained popularity, the ability to exchange messages with other users became a feature that was desired and expected.

Today there are a large number of IM applications that can be used to exchange text messages over the Internet and other IP networks. Although this is nowhere near a complete list, some of the more popular ones include:

• AIM, America Online Instant Messenger
• ICQ
• Yahoo Messenger
• MSN Messenger

In addition to these, there are also applications that allow communication using VoIP or other multimedia that also provide the ability to communicate using text messages. As seen in Figure 1, Skype provides a chat feature that allows two or more users to communicate in a private chat room. Each message between the participants appears on a different line, indicating who submitted which line of text and optionally the time that each message was sent. This allows participants to scroll back in the conversation to identify previously mentioned statements or topics of discussion. Although the figure depicts instant messaging in Skype, it is a common format that is used in modern IM software.

 

Figure 1: Instant Messaging through Skype

One of the important features of any IM application is the ability to keep a contact list of those with whom you routinely communicate. In many programs the contact list is also known as a Buddy List. However, even with this listing, it would be impossible to contact anyone if you didn’t know when each contact was available. If a person had a high-speed connection and was always connected to the Internet, then they might always appear online. As such, they would need a way of indicating that they were online but not available, or whether the person was available for one form of communication but not another. The ability to display each contact’s availability in a Buddy List when someone opens an IM application is called presence.

Deploying Instant Messaging for OWA

A new feature in Exchange 2010 is the integration of Instant Messaging (IM) into Outlook Web App, so your OWA users can see who is online and directly chat with the users without the requirement of installing Office Communicator on their client computer.

Note

IM integration for OWA does not require a UM server role to be installed in your environment; it just requires OCS 2007 R2 to be available. For that reason the feature also does not require an Exchange E-CAL like UM does.

To deploy this functionality, you need to install the OCS 2007 R2 Web Service Provider on all Client Access servers, enable IM on the Client Access server, and configure the OCS 2007 R2 Server to be able to access the Client Access server.

For IM integration you need the following:

• The Firewall configuration between the OCS 2007 R2 and Client Access server needs to allow the following TCP ports: 5061 (SIP), 5075, 5076, and 5077.
• The Client Access server requires a digital certificate that includes the FQDN or Client Access server array name as Subject Name and is from the same CA as the certificate of the OCS server. Certificates from different CAs—even if the CAs are trusted—might cause problems.

You must perform the following steps on every Client Access Server role where users access OWA and want to use IM:

1. Download the Microsoft Office Communications Server 2007 R2 Web Service Provider at http://go.microsoft.com/fwlink/?LinkID=135129 and run CWAOWASSPMain.msi to extract the package:
   1. Run vcredist_x64.exe to install Microsoft Visual C++ 2008 Redistributable.
   2. Run Ucmaredist.msi to install the OCS 2007 R2 Unified Communication Managed API 2.0 Core Redistributable.
   3. Run CWAOWASSP.msi to install the OCS 2007 R2 Web Service Provider.
2. Download and install the API 2.0 Core update for Windows Server 2008 R2 with the file name UcmaRedist.msp at http://www.microsoft.com/downloads/details.aspx?FamilyID=b3b02475-150c-41fa-844a-c10a517040f4.
3. Identify the Client Access server's certificate subject name and thumbprint using the Get-ExchangeCertificate |flcmdlet.
4. Configure the OWA Virtual Directory of the Client Access server to enable IM by running the Get-OwaVirtualDirectory -Server | Set-OWAVirtualDirectory -InstantMessagingServerName - InstantM essagingCertificateThumbprint -InstantMessagingEnabled $true - InstantMessagingType OCS cmdlet, as shown in Figure 1.

   Note

   In Exchange 2010 RTM this task required modifying web.config file located in the \ClientAccess\Owa folder. If you have not installed Exchange 2010 SP1 yet, please follow the instructions to configure the web.config file at http://technet.microsoft.com/en-us/library/ee633458.aspx.

5. Restart World Wide Web Publishing Service to apply the changes. Remember, restarting the service will disconnect all active users.

 

Figure 1: Enabling IM on Client Access server

After you have configured the Client Access Server role, you need to perform the following steps on your OCS 2007 R2 Server:

1. In the Office Server 2007 R2 Management Console, on your OCS 2007 R2 pool, open Front-End properties.
2. On the Host Authorization tab, click Add Authorized Host and configure the Client Access Server or the Client Access Server namespace. In Settings, select Throttle As Server and Treat As Authenticated, as shown in Figure 2.

   Note

   The Server name must be exactly the same as the Subject name of the certificate you have configured on your Client Access server(s).

3. For the settings to take effect immediately, you need to restart Office Communication Server Front-End service. Be aware that this will disconnect any active users.

 

Figure 2: Adding an authorized host in OCS 2007 R2

After you've configured your OCS 2007 R2 and Client Access Server role, your users should see their presence information and should be able to chat with their contacts using OWA as shown in Figure 3.

 

Figure 3: Instant Messaging integration in OWA