praekelt/vumi — pull request #753 by smn (2014-03-27 15:11:20+00:00)
Title: Mica's USSD over SMPP implementation details have changed

A bit cryptic but this:

```
1. user_message_reference is used as the identifier with (and only with!) source
number. to identify session with timeout based identification.
user_message_reference type is Short -- it can't be used as a global identifier.

2. If you need global identifier, you can implement global session as source +
user_msg_ref internally on your side (as per docs) and it will identify session.
if somehow old session not cleared, value of user_msg_ref will be incremented by
ussdc until clearing time of obsolete sessions.

3. destination_addr contains shortCode used, short_message contains actual
ussdString from the network (handset).
```