Appendix A: X25 Communications

X25 connectivity will be made over permanently connected SVCs. The Elavon host system can establish multiple connections to one partner. Two is considered the minimum to achieve resilience and load sharing. An SVC is connected and maintained as follows:

  1. Make an X25 call to the appropriate NUA
  2. If the call is accepted, check the status of the SVC, otherwise go back to 1
  3. If the SVC is connected, go to data transfer mode (start sending and receiving) otherwise clear the SVC and go back to 1.
  4. Should the SVC disconnect, clear it and go back to 1.

TCP/IP Communications

Establishing and maintaining a TCP/IP connection uses a similar logic flow to that for X25.