Dialog-Based SIP Implementation

A Dialog-Based SIP Stack maintains session state across multiple transactions, allowing full session tracking. Unlike stateless and transaction-based SIP, it keeps a persistent dialog context, making it essential for VoIP, video calls, and long-lived SIP sessions.

How Dialog-Based SIP Operates

Unlike stateless SIP, which processes each request independently, and stateful SIP, which tracks individual transactions, dialog-based SIP extends state management to the entire session lifecycle. A dialog represents a long-lived relationship between user agents, grouping multiple transactions within the same session context. Instead of tracking only individual request-response cycles, the system maintains session state across multiple message exchanges, helping to ensure continuity throughout a call.
A single dialog consists of multiple transactions, including call setup (INVITE → 200 OK → ACK), session modifications (re-INVITE → 200 OK → ACK), and call termination (BYE → 200 OK). Unlike stateful SIP, which tracks transactions independently, dialog-based SIP associates multiple transactions within the same session, ensuring that session-related messages remain linked. This allows for reliable call state management, enabling the system to track call participants, process session modifications (e.g., hold, transfer), and ensure message delivery reliability.
Since dialogs persist beyond individual transactions, dialog-based SIP requires more memory and processing power. However, this trade-off is justified - while consuming more resources, it enables better call state management, reliable session modifications, and full control over the call lifecycle.