Kamailio

This guide explains how to configure Kamailio as a stateful SIP proxy and high-performance load balancer using the TM (Transaction Management) and Dispatcher modules. You will learn how to define destination sets, select load balancing algorithms, handle automatic downstream failover, and manage destination health checks. By the end of this guide, you will be able to deploy a robust entry point for distributing SIP traffic across media servers or PSTN gateways.

Outbound SIP INVITE requests sent across carrier peering interconnects fail with 'SIP 408 Request Timeout'. The local Session Border Controller (SBC) repeatedly retransmits the INVITE without receiving a 100 Trying or 180 Ringing response from the carrier endpoint, resulting in call setup failures and high Post-Dial Delay (PDD).

SIP endpoints located behind routers with aggressive Symmetric NAT UDP aging timers successfully register initially but become unreachable for inbound INVITE and OPTIONS requests after 30 to 60 seconds of inactivity.

Inbound SIP INVITE requests time out at the HA SBC cluster boundary, generating a '504 Server Timeout' back to upstream carriers during active-standby switchover or when downstream media gateways fail to respond within default transaction timers.