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