System information

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 users notice them.
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 performance concerns can be managed through the addition of machines.
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
appendix), having DAHDI cards in the system will generate 1,000 interrupt re-
quests per second. Having devices on the bus that interfere with this process will
result in degradation of call quality. Chipsets from Intel (for Intel CPUs) and nVidia
nForce (for AMD CPUs) seem to score the best marks in this area. Review the
specific chipset of any motherboard you are evaluating to ensure that it does not
have known problems with IRQ latency.
• If you are running DAHDI cards in your system, you will want to ensure that your
BIOS allows you maximum control over IRQ assignment. As a rule, high-end
motherboards will offer far greater flexibility with respect to BIOS tweaking; value-
priced boards will generally offer very little control. This may be a moot point,
646 | Appendix C: Preparing a System for Asterisk