Appendix A: Keys to a Successful Mission-Critical VoIP Installation
Solutions for Shared VoIP & Non-VoIP IP Traffic
When there is no choice but to put your VoIP application on the same network as other
applications, there are some things you can do to help ensure that the VoIP packets are
not lost. The solution is to use a priority scheme that gives VoIP packets higher priority
than other traffic. This can be done by proper setup of configurable routers and switches;
by giving priority to the switch & router jacks to which VoIP equipment is connected, or
by giving priority to IP addresses and ports numbers used by VoIP traffic. Some VoIP
equipment also allows you to append priority bits (called QOS bits) to VoIP packets
themselves so that intelligent routers in the network deliver the VoIP packet with priority
end-to-end. But beware that you can only provide such priority on the private portion of
the network you control – not on traffic which flows through a public network such as
the internet.
The Right Knowledge
This brings us to the other key to success, and that is the right knowledge. By this we
mean the knowledge of the technical staff planning and installing the system. The
planning staff needs to know how to calculate, measure, and/or control traffic on the
target network, so that they can determine the peak payload being used. And they need to
know the end-to-end bandwidth capability of the target IP network. Then they need to
compare this against the payload, delay, and jitter requirements of the VoIP system
(which can generally be found on the product specification sheet). This information will
then tell the technical staff whether or not the VoIP system is compatible with the target
network.
The installation staff will need to know to configure equipment to work on the IP
network; they must be familiar with IP addresses, IP ports, routers, switches, and the like.
Basic computer networking skills may be sufficient if the installation is occurring only
within a dedicated LAN, but if an IP network includes shared traffic or multiple
subnets or a WAN, then the installation staff should be qualified IT professionals.
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