In addition to Diameter client functionality where messages are originated and terminated, an SR node can also act as a transit node, routing messages between the peers. This functionality is primarily used in redundant Diameter multi-chassis configuration, where Diameter messages are sent between the two redundant SR nodes over inter-peer connection.
Transit Diameter request messages are never retransmitted. However, they are kept in a pending queue until a matching answer is received. If the answer to a request messages in the pending queue is not received within 10 seconds, the message is discarded. This 10 second timer is the same internal timer mentioned in section Retransmissions and message timers, which is also used for non-routable messages (such as CER/CEA, DPR/DPA).