One of the biggest worries of network managers deploying IP Telephony is whether or not the network can handle the traffic. This is such a concern because there are so many potential bottlenecks, any one of which could cause the entire system to be non-functional.
An obvious point of concern is raw bandwidth and throughput. Can switch and router packet buffers handle the anticipated volume without introducing too much delay or jitter? What about WAN links? You've tuned your QoS parameters to compensate, but how do you really know they're going to work? Perhaps there are other choke points like firewalls or LAN server segment with heavy utilization. Are your trunks sized appropriately?
Next, there are the control protocols. Do your gateways have sufficient DSP resources to process the codecs? Can your H.323 gatekeepers or SIP proxies keep up with the demand? If your system is integrated into DNS or LDAP to map phone numbers to names, will that system do lookups fast enough?
With careful planning, you can be reasonably sure your network will hold up, but the only way to really answer the question "How many calls can this network support?" is to test it. Generating a large number of real calls is difficult, but there is software available to assist you.
If you're interested in stress testing your network, some of these packages may appeal to you:
If you're looking for something a little easier on the wallet and less-full-featured, consider the open source CallGen323 for Windows or Linux, which you can find at openh323.org.
Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.