Capacity planning for large call centers using Asterisk

Last updated: August 10, 2016

The architecture of a large call center setup shown below with Asterisk as telephony platform, includes web servers for serving agent web screens and a common database server. A high end Asterisk telephony server can handle over one hundred concurrent channels with compression and voice recording. High-end call center softwares are feature-rich and offer sophisticated agent screen scripting. The demand on the Web server will increase with increasing agent seats. The Web server will have to scale ahead of the Asterisk server.

The call center ACD software will scale to accommodate the size of the call center with additional web servers and Asterisk servers. The MySQL database size will eventually limit the maximum number of agents. The incoming ports are not as big a factor due to the availability of high quality Session Border Controllers (SBC) which will provide VoIP traffic to the Asterisk servers. It has been found that even with high-end servers, the number of PRI lines using Digium or Sangoma board per server should be restricted to 8 or less due to the interrupt demands of these hardware boards on the CPU. Redfone offers another option of bringing in PRI interface without loading the server. Converting the TDM traffic to VoIP through SBC reduced the load on the Asterisk servers.

As described in a newer post, leveraging Asterisk’s FastAGI is a more recent and sophisticated way to scale your large call center as the implementation of a FastAGI server removes a great deal of stress and strain to your Asterisk machines.