Asterisk can run up to forty-eight spans of Digital Telephony (1,440 simultaneous calls) without concern for overloading the CPU.
Even with the most powerful CPU, Asterisk systems can often show significant CPU load related problems when running anything more than eight spans of Digital Telephony (T1/E1/J1) Boards.
By using hardware-based echo cancellation and properly implementing a little know feature called Adjustable Chunk Size, single-chassis systems can have dramatic reductions in CPU load.
At 496 calls, the system load is reduced by over 70% – from 26% to 7% – as the chunk size goes from 8 bytes (1 ms) to 80 bytes (10 ms). At idle, the reduction is from 15%, down to a negligible 1%.