Here we are discussing what shall happen when both nodes shall send the CER at the same time to each other.
First message that is exchanged as soon as Transport Connection is established is CER, In general Node acting as a client shall send the CER message toward server. But it is not hard and fast that only client can send the CER; Node acting as a server can also send the CER. Moreover some time it is difficult to judge which is server and which is client; Because both are intermediate nodes. So server can also trigger the CER message.
Now if both nodes shall trigger the CER message at the same time; then two diameter connection shall be established but there is no way to make two diameter connection between two nodes. In this case one diameter connection MUST be dropped. Which connection to be dropped shall be identified by Election Process.
In Election Process; each node lexicographically [Dictionary Order] compares the Origin-Host Id of its own with the Origin-Host Id received in CER message. Node that has Higher Origin host wins ELECTION and terminates the connection initiated by it. The connection on which winner shall send CEA shall be used for further message communication.
In Dictionary Order 'b' succeeds 'a' and 'c' succeeds 'b' so Node with Diameter identity 'b' wins election if node 'a' is peer; then node 'b' shall terminate the DIAMETER connection initiated by it. Identity comparison is case insensitive.