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While both projects require a fair amount of knowlege and effort on your part, they
                  also share a huge coolness factor, are extrememly popular, and are of excellent quality.


               Medium systems

               Medium-sized systems (from 10 to 50 phones) are where performance considerations
               will be the most challenging to resolve. Generally, these systems will be deployed on
               one or two servers only and, thus, each machine will be required to handle more than
               one specific task. As loads increase, the limits of the platform will become increasingly
               stressed. Users may begin to perceive quality problems without realizing that the system
               is not faulty in any way, but simply exceeding its capacity. These problems will get
               progressively worse as more and more load is placed on the system, with the user ex-
               perience degrading accordingly. It is critical that performance problems be identified
               and addressed before they are noticed by users.
               Monitoring performance on these systems and quickly acting on any developing trends
               is key to ensuring that a quality telephony platform is provided.

               Large systems
               Large systems (more than 120 channels) can be distributed across multiple systems and
               sites and, thus, performance concerns can be managed through the addition of ma-
               chines. Very large Asterisk systems have been created in this way.
               Building a large system requires an advanced level of knowledge in many different
               disciplines. We will not discuss it in detail in this book, other than to say that the issues
               you’ll encounter will be similar to those encountered during any deployment of mul-
               tiple servers handling a single, distributed task.

               Choosing a Motherboard

               Just to get any anticipation out of the way, we also cannot recommend specific moth-
               erboards in this book. With new motherboards coming out on a weekly basis, any
               recommendations we could make would be rendered moot by obsolescence before the
               published copy hit the shelves. Not only that, but motherboards are like automobiles:
               while they are all very similar in principle, the difference is in the details. And as Asterisk
               is a performance application, the details matter.
               What we will do, therefore, is give you some idea of the kinds of motherboards that
               can be expected to work well with Asterisk, and the features that will make for a good
               motherboard. The key is to have both stability and high performance. Here are some
               guidelines to follow:
                 • The various system buses must provide the minimum possible latency. If you are
                   planning a PSTN connection using analog or PRI interfaces (discussed later in this
                   chapter), having Zaptel cards in the system will generate 1,000 interrupt requests


               18 | Chapter 2: Preparing a System for Asterisk
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