Server specifications for a robust Asterisk installation
A typical Quad-core motherboard based server running Asterisk PBX can handle in excess of 100 concurrent voice conversations with voice recording enabled. The capacity is determined by the load on the processor and the limitations of the bus on the motherboard. Transcoding (conversion from one CODEC to another) and TDM hardware interrupts can also be resource intensive. When you are running a full featured call center software, you will require more than one server. Most contact center applications today are web enabled and therefore require more than 1 server. Asterisk based contact center suite will probably run MySQL and Apache. When deploying Q-Suite, we require a minimum of 2 servers with one running MySQL/Apache and the second server running Asterisk and Q-Suite.
Legacy CTI boards have on-board DSP and use MVIP bus to move voice using TDM. Asterisk performs all these functions within the CPU. For any serious deployment, anything less than a Quad Core would be insufficient. Codec conversion and call recording are processor intensive. If there is any on-board TDM board, it will demand attention through interrupts. Lab load tests reveal that you can get 200 to 400 concurrent voice channels on high end servers. The limitation seems to come from Bus and not processor speed. Disk I/O access can become a serious bottleneck.
Higher RAM can alleviate some of the disk access bottlenecks in Asterisk. If call recording is shifted to a RAM disk, it makes a big difference. Anything upwards of 4GB is good. If you are running an ACD like Q-Suite, you are better of with 8 GB of RAM. This will allow the ACD as well as the dialer to run smoothly.