- Building Telephony Systems with OpenSIPS Second Edition
- SIP: Session Initiation Protocol
- Session Initiation Protocol (SIP) Basic Call Flow Examples
- Re-INVITE and Target-Refresh Request Handling in the Session Initiation Protocol (SIP)
- SDP: Session Description Protocol
- freeswitch权威指南
- SIP: Understanding the Session Initiation Protocol, Third Edition (Artech House Telecommunications)
- https://tools.ietf.org/html/rfc4028
- Hacking VoIP: Protocols, Attacks, and Countermeasures
