Every GTP node maintains two restart counter.
1. Local restart counter.
2. Remote restart counter.
Remote restart counter is just to track the maintain the peer restart counter. Similarly, each GTP node maintains its own restart counter. remote restart counter is maintain in volatile memory and local restart counter is maintained in non-volatile memory.
GTP protocol runs over UDP protocol which is a connection less protocol.
Echo Request and Echo Response messages are being used for path management purposes.
Periodicity for these messages can be configured. So there may possibility that peer node has been already restarted before the echo request message gets triggered from other end.
That's why Echo Request and Echo Response both have "Recovery" information element.
In Echo Request message, sender sends its local restart counter hand in response message it receives remote restart counter.
