Use the chart below to select a base system size. The chart is based on concurrent calls, which is the most important metric in sizing an Asterisk PBX system. Concurrent calls means: “How many people will be on the phone at the same time?”

For instance:

• If you have a T1 with 23 channels of voice and 1 channel of data, then your max concurrent calls is 23 channels.
• If you have a 5-line SIP trunk from your ITSP or SIP service provider, then the max number of calls you’ll be able to place concurrently is 5, so that’s 5 channels.
• If you have 8 copper phone lines from the telephone company, the max number of calls you can max is 8, so that’s 8 channels. 

Find your concurrent calls in the first column, and view your recommended system requirements.

- Source: Total Ticket Systems