One of the bottlenecks in using Asterisk is the system resource load when using PSTN connections. This has always been pretty much a constant and has limited systems from having large numbers of concurrent calls or for trying to run T1/E1 connections on minimal hardware platforms.
Thanks to a new feature in Zaptel/Dahdi that enables you to change the chunk size, it is now possible to optimize a system for particular hardware configurations, especially important when your interface devices use hardware echo cancellation.
The results below are for a machine with an Intel® Core™2 Quad CPU Q9550 @ 2.83GHz with 4 Gbytes of RAM. Two A108D (8-port digital card with hardware echo cancellation) cards provided a 496 call capacity (31 channels per span x 16 E1 spans).
The reductions are quite dramatic. At 496 calls, the system load was reduced from 26% to 7%, as the chunk size goes from 8 bytes (1 ms) to 80 bytes (10 ms). That’s a decrease of over 70%. At idle, the reduction went from 15% down to a negligible 1%.
To read the complete white paper, download their PDF file here.