How does eNB uses same source and destination port (36422) over X2 link using SCTP?

Question

Consider a case where eNB has only one IP address and it has to act as both SCTP server and SCTP client. Then, how can we do this using same port number as source and destination "36422" (as mention in 3GPP spec 36.422)?

Answer 1

Even though transport port is pre-defined for X2 interface but at a time one eNodeB will be act as sctp client and another another would become as server. It is operator network development choice. If you refer following client server program of sctp then you can understand .
http://simplestcodings.blogspot.in/2010/08/sctp-server-client-implementation-in-c.html

I would take example of S1 connection here . Enodeb and MME both uses 36412 port . MME should be active before S1 setup is triggered that's why MME acts as sctp server and enodeb acts as sctp client.

Comments

Hi Harshita, Thanks for the reply.
I agree the point on S1 interface. Because in S1 interface MME would always act as SCTP server and eNB as SCTP client. Hence it is clear that eNB would use destination port as 36412.However, it can use any random souce port for setting up SCTP connection. In addition to that, spec 36.412 for S1AP says "The eNB shall establish the SCTP association. The SCTP Destination Port number value assigned by IANA to be used for S1AP is 36412."
But for X2 interface, eNB would act as both client and server. Because any eNB can initiate a SCTP connection and all of the eNBs in network should be able to accept/connect from/to peer eNBs. And the spec says that all eNBs in network should use same port number for SCTP as 36422. As pwe spec 36.422 "An eNB shall use the Destination Port Number value 36422 assigned by IANA to be used for X2AP and this value shall also be used in Source Port Number by all eNBs within a network."
So the question is if eNB has only one ip address then how can we start both SCTP client and server on same IP and port(36422) combination?