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You have to choose your hardware configuration to meet your network's needs. You can decide on the performance you need your sever to be capable of by considering the maximum number of concurrent calls you expect to have made on the said server. The general formula is that for every concurrent call, you server will use up
33MHz CPU + 8 Mb of RAM memory memory + 86 Kb of your network's bandwidth
How do the extensions affect the servers?
Another way of figuring out what you server will have to stand up against is the total number of extensions on it. For example, if your server will provide VoIP for residential clients, most extensions will probably be phone terminals that do not require plenty of resources. On the other hand, if you resell towards businesses, IVRs, Queues and other costly extensions will need a more powerful hardware configuration.
How does the server handle PSTN?
Another issue that needs to be addressed is that of connecting your server to a public telephony telephone network. This becomes of your concern especially when your server is in-house. To connect to such a network you will need a gateway that routes and translates calls between the two networks for the VoIP user. The telephone company provides one or more trunk lines to the customer for connection to the customer's PBX.
What about codecs?
Codecs are designed to enhance VoIP calling sound quality. However, these codecs influence your server’s or your network’s performance.
As an example, G711u and G711a do not compress packages upon sending them. This means that your call quality will improve, but they consume bandwidth. On the other hade, if you use G729 – which is one of the most used codecs – the packages will be compressed and you call quality amplified, but this action consumes a greater amount of CPU.
A fair conclusion is that you should always calculate your system to have at least 30% resources free most of the time, so that you won't have to worry about peaks.
ne company provides one or more trunk lines to the customer for connection to the customer's PBX.
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