Installation manual

77
Appendices
Network Requirements IP\H.323
The network requirements for point-point connections between videoconferencing terminals are as
follows.
The complete network path connecting two H.323 terminals must have a constant available
bandwidth for the whole duration of the connection. The effective bandwidth used on LAN/WAN
Full-Duplex network connections is equal to the sum of the Audio Rate and Video Rate, plus
approximately 20% for TCP/IP overhead.
In the case of Half-Duplex LAN/WAN networks, the aforementioned bandwidth is doubled. For
example, if it is necessary to guarantee a 384K connection for the video and a 64K for the audio, the
bandwidth allocated must be at least (384+64) *1.2 ≈ 540K for each Half-Duplex connection. In
case of dial-up WAN links, it should be underlined that their efficiency in terms of “useful”
bandwidth is approximately half the total available bandwidth.
It is always preferable to use mechanisms such as QoS for WANs because they take into account
the total bandwidth required for a videoconference, rather than relying exclusively on over-
dimensioning the network. This is necessary for the handling of increasing numbers of simultaneous
connections or a network that is already loaded.
The network needs to be set up so that latency and jitter are as low as possible. Extended times for
latency and variable jitter can create serious problems, especially in video quality.
It is always preferable for H.323 terminals to be connected to switched type LAN connections to
avoid the traffic generated by terminals being superposed on the normal traffic present on the
network.
It is preferable to avoid using NAT-type protocols on router interfaces that route H.323 packets,
since NAT protocols often do not allow the correct routing of connections.
If NAT, firewall or access list implementations are to be used, they must be H.323 compatible.
Network Requirements for Multivideoconferences H.323 (MCU)
The same requirements indicated above apply to multipoint connections between more H.323
videoconference terminals.
In this case, more H.323 streams converge in the network, increasing the local network-load. The
consequence is that the bandwidth allocated must be the sum of the bandwidths required for each of
the individual connections, calculated according to the description given in the previous section.
The network requirements previously described are also valid for connections between H.323 and
H.320 terminals via gateways. In this case, more than one H.323 stream converges on the gateway
increasing local network traffic. As such, the necessary bandwidth, at the point where the
H.323/H.320 gateway is to be installed, must be the sum of the bandwidths required for each
individual connection, calculated as shown in the previous section.