Diameter Connections Degraded, Egress Transport Congestion, While At Only 4K MPS

Asset ID:	1-71-2388412.1
Update Date:	2018-04-18
Keywords:

Solution Type Technical Instruction Sure

Solution 2388412.1 : Diameter Connections Degraded, Egress Transport Congestion, While At Only 4K MPS

Applies to:

Oracle Communications Diameter Signaling Router (DSR) - Version DSR 7.0.1 and later
Information in this document applies to any platform.

Goal

During testing, with two MPs, there were multiple occurrences of the connection going into a Degraded state, CPL2 or CPL1, showing Operational Reason 'Egress Transport Congestion'.
The servers under test should be capable of 40K Ingress MPS, the test scenario didn't approach this rate on any single server throughout the testing.
Why was Egress Transport Congestion seen?

Solution

While an MP may have a total of about 40K MPS, Egress Transport Congestion is assessed on a per connection basis. The maximum ingress MPS for a single connection is 10K and therefore lower values can be configured.

But even if the 10K is configured for the connection, congestion can be seen with low traffic. Virtually all of the congestion cases we have seen have been with nominal traffic since as mentioned before congestion is often seen due to delays in the network or processing speeds at the peer.

Egress Transport Congestion is the result of exhausting the connection's send buffer and is often the result of delays in the network or inability of the far end to handle the offered traffic at the current rate. Delays in the network or slowness on the part of the far end causes the DSR to hold the message longer (because acknowledgments take longer) and this eventually can cause the buffer to start filling up.

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