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Use this object to configure TCP Fallback settings.

To View and Edit TCP Fallback

On SBC main screen, go to Configuration > System Provisioning > Category: SIP Carrier Peering > Signaling > TCP Fallback. The TCP Fallback window is displayed.

The TCP Fallback can be checked for each Address Context, for each Zone, for each Sip Trunk Group created or for all the Address Contexts, Zones and Sip Trunk Groups created. Use the drop-down box to select the desired Address Context, Zone and Sip Trunk Group.

The Edit TCP Fallback window is displayed.

Figure : SIP Carrier Peering - Signaling - TCP Fallback

The following fields are displayed:

Table : Sip Trunk Group - Signaling - TCP Fallback parameters



Max MTU Supported Over UDP Control

 Maximum MTU Size accepted over UDP.

  • disabled (default)
  • enabled

Max MTU Supported Over UDP Value

Maximum size of the SIP Invite accepted over UDP. The value ranges from 1 to 5000 and the default value is 1300.

Make the required changes and click Save at the right hand bottom of the panel to save the changes made.


The SBC supports, by default, 1300 Maximum Transmission Unit (MTU) bytes, and the MTU size used by the SBC is configurable. If the initial INVITE message size exceeds the default MTU value, the SBC sends the data over the TCP transport protocol. The TCP transport protocol is used if it is allowed by the transport profile, irrespective of its preference order.


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