An internal telephony user can connect to another internal telephony user by using the Office Communicator 2007 client. A user can initiate a call to another user by either selecting the user from a contacts lookup list or dialing that user’s contact number. When the user initiates a call using a SIP (Session Initiation Protocol (News - Alert)) client, the client sends an SIP “Invite” message along with the SIP URI (Uniform Resource Indicator) of the call recipient to the Front End Server. After receiving the SIP Invite, the Front End Server queries the SQL Server 2005 database to check if the SIP URI for the call recipient is present in the database. If the SIP URI is available, the Front End Server applies client rules on the Invite, and then routes the Invite to all active SIP clients corresponding to the URI of the call recipient. If the Front End Server receives a busy or does not receive an acknowledgement from any one of the SIP clients of the call recipient, the Front End Server then routes the call to the Exchange Server 2007 voice mail service.

 

The pictutorial is available at: http://blog.tmcnet.com/cross-talk/

 

The voice mail service generates an e-mail to the call recipient along with the voice mail attachment as an audio file. However, if an acknowledgement is received from any one of the SIP clients of the call recipient, the Front End Server responds with a Ringing message to that client. The Front End Server also sends a Cancel Invite message to all the other registered clients of the call recipient. A call session is established when the call recipient answers the call by using the SIP client. The Front End Server then opens a media stream between the clients of both users. After the conversation, either of the clients can send a Bye message and the Front End Server terminates the call session.

 

The Front End Server also indexes the SQL Server 2005 database to translate (map-resolve) the normalized (canonical) number to a user URI-Uniform Resource Indicator. Note: URI refers to the complete SIP telephone address not just the mail URL-Uniform Resource Locator. If the Front End Server does not receive an acknowledgement from any one of the SIP clients of the call recipient, the configured InfoAgent or Outbound Router logic running on the Front End Server detects that the call recipient is not answering the call.

 

For those unfamiliar with SQL, SQL (Structured Query Language), which is an ANSI (American National Standards Institute) standard computer language for accessing and manipulating database systems. SQL statements are used to retrieve and update data in a database. SQL Statements contain “same type” information (e.g., store address, SKU, shelf count) sometimes referred to as columns. The DML (Data Manipulation Language) is used to retrieve, add/insert and change/modify database information. For a detailed animated tutorial on SQL, go to http://www.techtionary.com