Setting the Maximum Transmission Unit (MTU) Size for Communications Server Instances

When a Communications Server instance is sending a Session Initiation Protocol (SIP) message over User Datagram Protocol (UDP), the packet size might exceed the MTU size. In this situation, Communications Server switches from UDP to Transmission Control Protocol (TCP). To prevent Communications Server from switching from UDP, set the MTU size to a value that will not be exceeded by the packet size. Set the MTU size for each Communications Server instance that you want to prevent from switching from UDP.

To set the MTU size for Communications Server instances, set the com.ericsson.ssa.sip.dns.MAX_MTU_SIZE Java system property to the required MTU size in bytes:

asadmin> create-jvm-options --target=target -Dcom.ericsson.ssa.sip.dns.MAX_MTU_SIZE=mtu-size

target

One of the following targets, which specifies the instances for which the MTU size is set:

• server (default). The MTU size is set for the domain administration server (DAS).

• The name of a Communications Server instance. The MTU size is set for only the specified instance.

• The name of a Communications Server cluster. The MTU size is set for all instances in the cluster.

• The name of a Communications Server configuration. The MTU size is set for all instances that reference the configuration.

mtu-size

An integer that specifies the MTU size in bytes. The default value is 1300.

The operating system must support the MTU size that you set.