Tuning Asterisk PBXs
By: Phil Lam

Performance of SoftPBXs is usually measured by 3 people. These 3 people include a user, a technical specialist and a financial specialist. A user does not measure performance; instead, they expect a dial tone with no echo and lost calls. They will ask where their features are. A technical person has already planned the system – peak period dial tone, system loads, ease of configuration, uptime and downtime. The financial person will analyze the expenditure, value, features and tolls.

The scale reliability in a Performance Tuning Asterisk-based PBX depends on managing the faxing, transcoding and echo cancellation. Traditional or Legacy PBX systems have a sizable upfront purchase, set features which can be unlocked and have a price point, proprietary hardware, proprietary interfaces, and proprietary endpoints. The Open Source PBX costs only a fraction of traditional systems. The feature sets are almost overwhelming, allowing for more customization. It is built on standard PC-based hardware and is open and available for a normal fee. IP phones differ mostly by feature sets.

Host Media Processing (HMP) is the movement away from specialized hardware. The CPU manages voice calls including applications such as transcoding, echo cancellation and protocol conversion. Host CPU’s have challenges scaling to properly manage call switching while managing TDM transcoding and echo cancellation. The PCI bus can manage call switching although specialized DSPs are still required. Asterisk is the first viable HMP application. There are many Open Source Applications, and to name a few are Asterisk, YATE, FreeSwitch, OpenPBX. Asterisk clearly started the revolutions and continues to leading it.

There are considerations for the size of your PBX system. How many concurrent users at peak times, is TDM and IP required, what type of compression: G. 729, G. 723, G. 711, GSM, AMR? With TDM, will echo be an issue, and how much faxing is required? How to maximize PBX hardware performance? During heavy use, the application becomes less stable if you are using TDM. The best would be to distribute tasks using specific DSP resources.

The features of Hardware Based Echo cancellation comes with background comfort noise, ability to configure to 128ms echo tails, adaptive noise reduction, tone detection and re-generation, field upgradeable channels and eliminates double talk. The best solution will be the G. 729 Transcoding Solutions. Software G.729 comes with dual xeon, hyper threading 4 gig. Transcoding 7.11 to 7.29 in software with hardware echo cancellation will process 100 concurrent calls. Hardware G. 729 comes with dual xeon, hyper threading 4 gig. Transcoding 7.11 to 7.29 in hardware with hardware echo cancellation will process 240 concurrent calls. Hardware based G. 729 lightens system load considerably. The upfront cost of G. 729 in hardware is negligible over the life of the systems and savings in bandwidth cost.

Gateway with TDM access functions with an internal and external device. External gateways off load TDM and DSP processes from the PC entirely. Additional devices, cables and rules to manage, and you can select your features upfront. Internal gateways have lower cost expandability, adds features as you grow, have dual capabilities with voice and data and the configuration for least cost routing is either IP or TDM.

Article Source: http://www.ArticleJoe.com

Article contributed by Phil Lam who is a VoIP consultant at Lantone Information Systems. Led by a team of experienced IT developers, Lantone Information Systems is one of the leading www.voip.com.sg“>VoIP Provider in Singapore. Please visit their official website for the latest information on VoIP. This article may be reprinted in its original form as long as the resource box is left intact and the links live and the article is not to be modified in any way.

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