| The integrated voice features, for example unified | | | | of transporting same sequenced audio patterns to |
| messaging and "click-to-dial", became available with | | | | effectively reduce the number of packets |
| circuit-switched PBX systems. Complex | | | | transmitted. |
| coordination of voice and data networking | | | | H.323 |
| environments are required. IP network level | | | | H.323 - a set of related ITU recommendations |
| however, eliminates much of this complexity, | | | | that describe the architecture for multimedia |
| attaining results which are lower costs from | | | | communication over a packet-switched network. |
| consolidating equipment and rapid integration with | | | | Key factors: |
| business applications. The requirements necessary | | | | -H. 323, defining the multimedia infrastructure, |
| for IP PBX systems to successfully integrate with | | | | including the role of devices, gateways and gate |
| a packet network are: | | | | keepers. |
| -Reliability to minimize the loss of voice packets | | | | -H. 245, specifying the call control processes for |
| and control network delay. | | | | establishing and terminating a multimedia session, |
| -Quality of Service (QoS) to ensure that voice | | | | which includes the exchange of the capabilities |
| packets are transmitted through each network | | | | supported by client devices. |
| element with the correct priority relative to other | | | | -H. 450, specifying a set of supplementary |
| types of packets. | | | | devices, like call transfer, hold, message waiting |
| Real Time Protocol (RTP) | | | | etc. This protocol is useful communication |
| RTP uses a set of Internet Engineering Task | | | | between clients without the aid of a switch. |
| Force (IETF) standard protocols for reliably | | | | Session Initiation Protocol (SIP) |
| transporting voice, video, and data among | | | | SIP is an IETF standard protocol helpful for |
| participating parties across a packet network. | | | | initiating an interactive user session that carries |
| Comments requests include: | | | | multimedia subjects. The SIP architecture comes |
| -The RTP protocol (RFC 2550), carrying voice | | | | with a method for delivering connections for users |
| that has been encoded using ITU G.711 or an | | | | at any location where he/she is registered. In |
| alternative codec system. The protocol includes | | | | contrast to the H.323, SIP uses an extensible |
| time stamps and sequence numbers, "jitter | | | | text-based format, similar to HTTP. SIP, being the |
| management". | | | | basis for multi applicable programs including instant |
| -RTP for dual tone multi-frequency digits carries | | | | messaging and gaming. It can function as a |
| encoded tones used in interactive voice response | | | | standalone call control protocol or together with H. |
| (IVR) applications. | | | | 323. |
| -RTP for redundant audio data specifies a mode | | | | |