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In this article we describe how to configure the Sonus SBC Edge to use a server pool to accomplish DNS load balancing using a pool of Lync Mediation Servers.

For the purpose of this article, we assume that the the PBX - SBC Edge - Microsoft Lync 2010 topology is in place and employs multiple front end servers, as shown below. 

Perform a Name Server (NS) Lookup on of the Lync 2010 Pool (cspool.mylync.com) with three front end servers.

NS Lookup


The FQDN cspool.mylync.com resolves to three separate IP Addresses:

  • Front End Server 1:
  • Front End Server 2:
  • Front End Server 3:

On this page:


Configuration for this functionality is straight-forward and relatively simple. It involves two basic steps"

  • Creating SIP Server Table and/or entry.
  • Assigning that SIP Server Table and specifying the Load Balancing Method in a Signaling Group.

SIP Server Table

Create a new SIP Server Table and entry as shown below.
(warning) Use the FQDN of the Lync pool as shown.

SIP Server Table


Signaling Group

Create a new, or modify an existing, SIP Signaling Group and configure the SIP Server Table and Load Balancing options as shown below.

Configure SIP Server Table and Load Balancing



Example of Round Robin Load Balancing

In the Sonus SBC 1000/2000 to Lync direction call scenarios in this setup, Sonus SBC 1000/2000 load balances outbound calls among the multiple IP addresses to which the FQDN resolves. The following screenshot depicts the multiple calls received by the Sonus SBC 1000/2000 and how they are sent to different Front End Servers in a round robin fashion.

Calls Received by Sonus SBC 1000/2000



the load balancing also works if the multiple IP addresses are configured in same SIP Server Table instead of a FQDN. In other words, if IP addresses of,, and are listed in the server table instead of cspool.mylync.com, the load balancing still occurs in the outbound SIP Signaling Groups that use this server table.