User manual

100
Appendices
IP Network Requirements for Videocommunication
The network requirements for point-point connections between IP videoconferencing
terminals are as follows.
The complete network path connecting two IP 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 IP 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 IP
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 IP
compatible.
NAT – FIREWALL Interoperability
Introduction
There are many strategic advantages for companies that succeed in making all traffic
converge from voice applications, video and data to one IP network infrastructure.
Unfortunately, the drive to concentrate all IP communications onto one single network
has reduced. The connection between a company’s corporate network and the Internet
world is accomplished with firewalls and devices using NAT (Network Address
Translation), which block voice and video calls via IP. Firewalls block IP traffic for
video and voice by preventing any unsolicited communication from the outside.
Devices implementing NAT block IP traffic because all equipment on the internal
network uses private IP addresses, and can therefore not be contacted from outside
the local domain.
There are several solutions to the problem of getting IP communications past NAT and
firewalls: bypassing the firewall or NAT device, upgrading the network infrastructure
with an Application Level Gateway (ALG), and going out through the firewall or NAT
using semi-tunneling connections.