Stateful SIP Implementation (Transaction-Based)

A Stateful SIP Stack maintains transaction state, ensuring reliable message handling. It tracks SIP requests and responses within the scope of a single transaction, allowing for retransmission management and improved reliability while remaining more efficient than a full dialog-based stack.

How Stateful SIP Operates

Unlike stateless SIP, where each request is processed independently and discarded immediately, stateful SIP keeps track of each transaction. This means that every SIP request (e.g., INVITE, BYE, REGISTER, OPTIONS) is tracked separately, ensuring that responses are correctly linked to the corresponding transaction.
A transaction in SIP consists of a request and all the responses associated with it. The SIP stack stores information about transactions until they are completed, which allows it to handle retransmissions. This is important for ensuring that SIP messages reach their intended destination without duplication or loss.
Stateful SIP tracks transactions. When a request (e.g., INVITE) is received, a transaction is created. This transaction persists until the final response is sent or received. In unreliable transport protocols like UDP, message delivery is not guaranteed. So the SIP stack resends responses if no acknowledgment is received. This ensures that call setup and termination messages are properly exchanged.
Transaction tracking is also important for associating requests with their corresponding responses. Each SIP response is linked to an active transaction, preventing misrouting. Unlike stateless SIP, where responses are processed independently, stateful SIP ensures that each response is directed to the correct request.
And of course, there are consequential effects - since transactions are stored, stateful SIP consumes more memory compared to stateless SIP. However, this trade-off improves reliability and ensures proper sequencing of messages.