Troubleshooting a Mediation Server might become necessary in the event
that users are unable to make or receive calls to the PSTN. This
section discusses the key components of a Mediation Server to check
when issues arise. Common troubleshooting tools and tips are also
provided that should resolve many issues.
1. 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.
• 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.
2. Connectivity to Edge Servers
When Lync Edge Servers are deployed in the
environment, the Mediation Server service requires constant
communication with the Edge Server. The Mediation Server acts much like
a Lync client in regard to Edge Server connectivity. When the Mediation
Server is establishing any call, it must allocate Media Relay ports
with the Edge Server in the event that a remote user might be involved.
When the call is made from an internal user, this still happens, and
although the actual call might not fail, a delay in call setup time can
occur.
A common issue with call setup
delays is connectivity between Mediation Servers and Edge Servers.
Ensure that the Mediation Server can communicate with the Edge Server
on port 3478 UDP and 443 TCP for port allocation. If that network
connection is not available, a delay of several seconds might be
incurred during call setup time. Additionally, if remote Lync users are
not able to make calls to the PSTN, Edge Server connectivity is a key
component to analyze.
3. DNS Records
Lync Server 2013 Mediation Server
DNS requirements are fairly simple. However, because Mediation Server
Pools rely on DNS load balancing, it is important to validate the DNS
configuration. A Mediation Server Pool requires a DNS entry for each
server in that pool. For every Mediation Server in the pool, ensure
that there is an A record of the FQDN of the pool pointing to the IP of
the server.
4. Logs
A good source of information in
troubleshooting any server issue is the event logs. Lync Server 2013
creates a dedicated event log for informational activities, warnings,
and errors within the standard Windows Server Event Viewer console. To
view this event log, follow these steps:
1. Click Start.
2. Type eventvwr.msc and press Enter to open the Event Viewer Microsoft Management Console.
3. Expand the Applications and Services Logs folder.
4. Click the Lync Server log.
5. Examine the log for any warning or error events that might provide additional insight into any issues.
