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This is an LA release that will only be provided to a select number of PLM-sanctioned customers (PDFs only). Contact PLM for details.

Note

The SBC supports, by default, 1,300 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.

The current TCP Fallback feature does the following:

  1. Enables the SBC to reject UDP INVITE with PDU size more than configured MTU value with “513 Message Too Large”.
  2. It is up to the far-end to recognize this “513 Message Too Large” and switch to TCP.
  3. This feature does not enable the SBC itself to fall back to TCP on receiving  “513 Message Too Large” from far-end.
  4. Once the transport protocol is determined by the application layer in SBC, if the size of the INVITE PDU is increased later (say through SMM rules), the SBC will NOT be able to change the transport protocol to TCP, instead the INVITE is sent using the already determined transport protocol irrespective of the MTU Size configured.
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