Connectivity to Next-Hop Gateways

Given the Mediation Server’s role of providing PSTN connectivity through a next-hop gateway, ensuring that connectivity to those next-hop services is healthy is important in all troubleshooting scenarios. Lync Server 2013 maintains health monitoring of these connections by default, and it does so in two ways:

• SIP OPTIONS Requests—The Mediation Server continuously communicates with the next-hop gateway through SIP OPTIONS requests. These exchanges are a method of validating a healthy connection between the two services. If these messages fail to be exchanged, Lync Server 2013 will alert administrators through the Lync Server Event Log. For information on checking this log, see the “Logs” section.

• Routing Timeouts—Lync Server 2013 identifies issues with a Mediation Server and next-hop gateway after a number of failed calls. If a Mediation Server is not able to route calls, it is marked as down. When this occurs, Lync Server routes calls through alternative routes if available; if not, users receive errors when making outbound calls and Event Logs are recorded identifying the error.

Whenever troubleshooting PSTN call issues, always ensure that a healthy connection between the Mediation Server and the Gateway is active. Look for the errors described previously, and also validate connectivity between the two servers utilizing tools such as Ping and Telnet.