1. Recommendation H.323, H.323: packet-based multimedia communications systems by ITU-T. Article No. E35738 (2010)
2. J. Rosenberg et al., SIP: Session Initiation Protocol. IETF RFC 3261, June 2002
3. CISCO, Understanding H.323 Gatekeepers. Document ID 5244, Sept 2014
4. K. Wallace, Implementing Cisco Unified Communications Voice Over IP and QoS (Cvoice) Foundation Learning Guide (Cisco Press, 2011)
5. H.323 FORUM. Available: http://www.h.323forum.org