7. Session Management

USSD is primarily a dialog-based service: the subscriber and the service exchange one or more messages within a bounded interaction window. A USSD Gateway therefore must maintain runtime session context that correlates:

• network-side dialog identifiers (TCAP/MAP),
• subscriber identity (MSISDN/IMSI as available),
• the selected backend destination (routing “stickiness”),
• timers and state (waiting for application vs waiting for user),
• termination reason (normal end, user cancel, timeout, error).

While USSD sessions are short-lived and do not usually require persistent storage, the gateway cannot be “stateless” during execution—at minimum, it must track correlation and enforce timeouts for every active dialog.