ased systems. Low-energy efficiency. 4 SIP Trunking Comparing VolP Signaling Protocols Any protocol that communicates messages can be used for IP Telephony. However, hav- ing a standard protocol that many people use has the following great benefits: Interoperability between vendors is easily accomplished. A wider base of training for talent exists in the field. A guideline for tools expected to work with these protocols exists. The primary protocols used for VoIP are the following: H.323: This is the longest running VoIP standard. Implemented to help solve the problem of mapping traditional telephony features from TDM signaling that had ex- listed for years to IP based signaling. This standard was implemented and ratified by the Internal Telecommunications Union (ITU). One of the major objectives to the early version of this protocol was to minimize signaling overhead. To accomplish this, it mandated that the signaling messages be encoded in a binary format called ASN.1 encoding. This required the messages be decoded in a specific order to be read and could not be read without running the packet trace of a call through a decoder. This encoding requirement was relaxed in subsequent versions of the protocol but is still the primary method used for encapsulating H.323 messages in most networks today. H.323 is currently on Version 6 of the standard protocol, but the most widely de- ployed versions are H.323v2 and H.323v6. SIP: SIP was first proposed as RFC-2543 in 1999 to the International Engineering Task Force (IETF) by E. Scholler and Jonathan Rosenberg and has since been updated to RFC-3261. You can view the current draft recommendation at http://www.ietf.org/ rfc/rfc3261.txt. This protocol, because it is authored and standardized at the IEFT, is more similar to other protocols that have built the Internet, such as HTTP and SMTP, and less similar to the protocols that built the large TDM-based networks, such as ISDN that were standard- ized in the ITU. One of the major differences between the protocols developed 