Page 74 of 378 ITG Engineering Guidelines
553-3001-202 Standard 1.00 April 2000
Network engineeri n g guidelines overvi ew
Traditionally Meridian 1 networks depende d on voice servi ces1 such as LEC
and IXC private lines. With ITG technology, the Mer idian 1 can selec t a new
delivery mechanism, one that uses packet-switching over a data network or
corporate intranet. The role of the ITG node is to convert steady-stream
digital voice into fixed-length IP packets, provide ISDN signalling, and
translate PSTN number s into IP addresses. The IP packets are transported
across the IP data network with a low latency that vari es with strict limits.
In the data world in the late 1960s, IP evolved from a protocol that allowed
multi-vendor hosts to communicate. The protocol adopted pac ket switching
technology, providing bandwidth efficiency for bursty data traffic that can
tolerate high latency and jitter (variation in latency). Since IP supported the
TCP transport layer, which provided connection-oriented and reliable
transport, IP took on the properties of being connectionless and a best-effort
delivery mechanism. The TCP/IP paradigm worked well in supporting data
applications at that time.
New considerations come into play now when the same corporate network is
expected to deliver voice traffic. The intra net int roduc es im pairm ents , dela y,
delay variation, and data packet loss, at levels that are higher than those
delivered by voice networks. Delay between talker and listener changes the
dynamics and reduces the efficiency of conversations, while delay variation
and packet errors causes introduces glitches in conversation. Connecting the
ITG nodes to the corporate intranet without preliminary assessments can
result in unacceptable degradation in the voice s ervice; ins tead correct des ign
procedures and principles must be considered.
1. For the sake of abbreviation, the term voice services also includes fax services.