Why is ISDN
Video Conferencing better than Internet based VC?
Infrastructure choices and its disadvantages
PSTN/POTS Plain Old telephone System - audio and video has to
fit into 56 kbps. Poor quality.
LAN/WAN - calling within your own organization only.
IP ( Internet ) - poor quality and long latency. Dialogue
difficult.
ISP's will not call your dial-up line open for incoming calls.
IP video telephony needs gatekeepers, name servers and cracks to
firewalls.
IP video telephony might take off only long after VoIP ( voice
over Internet ) has done so first.
XDSLs are not switched networks.
ATM H.321 is not widely available.
ISDN H.320 videoconferencing is THE BIGGEST market.
ISDN
Over one million ISDN H.320 videoconferencing end-points.
There are 10 Million ISDN cards in European PCs.
ISDN is THE ONLY media over which video telephony really works
today.
ISDN is the fastest growing telecommunications segment in Europe
and Japan.
ISDN gives a switched circuit at 128kbps per line 2 x 64k bearer
channels and a D channel. This bandwidth is locked in for the
duration of the connection. Quality of Service or QoS is
guaranteed. When you have an Internet connection regardless if
its 128kbps or 1mbps to your ISP, you are dependant on all of
the routers between the endpoints to provide you with
through-put. There is no readily available QoS. Currently the
Internet is user heavy and bandwidth light! A call that you
attempt to originate for video over IP at 400kbps may only find
56kbps worth of through-put due to routing restriction on the
network. There are protocols like RSVP a resource reservation
protocol that enable you to request a QoS (a specific
bandwidth), but it requires that all routers and endpoints
involved in the data transfer support the protocol, therein lies
the problem of RSVP and its limited use currently.
