Page 47 - Asterisk™: The Future of Telephony

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 Zaptel 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,
however, as APIC-enabled motherboards turn IRQ control over to the operating
system.
• Server-class motherboards generally implement a different PCI standard than
workstation-class motherboards. While there are many differences, the most ob-
vious and well known is that the two versions have different voltages. Depending
on which cards you purchase, you will need to know if you require 3.3V or 5V PCI
‖
slots. Figure 2-1 shows the visual differences between 3.3V and 5V slots. Most
server motherboards will have both types, but workstations will typically have only
the 5V version.

There is some evidence that suggests connecting together two com-
pletely separate, single-CPU systems may provide far more benefits
than simply using two processors in the same machine. You not
only double your CPU power, but you also achieve a much better
level of redundancy at a similar cost to a single-chassis, dual-CPU
machine. Keep in mind, though, that a dual-server Asterisk solu-
tion will be more complex to design than a single-machine solution.
• Consider using multiple processors, or processors with multiple cores. This will
provide an improvement in the system’s ability to handle multiple tasks. For As-
terisk, this will be of special benefit in the area of floating-point operations.
• If you need a modem, install an external unit that connects to a serial port. If you
must have an internal modem, you will need to ensure that it is not a so-called
“Win-modem”—it must be a completely self-sufficient unit (note that these are
very difficult, if not impossible, to find).
• Consider that with built-in networking, if you have a network component failure,
the entire motherboard will need to be replaced. On the other hand, if you install
a peripheral Network Interface Card (NIC), there may be an increased chance of

‖ With the advent of PCI-X and PCI-Express, it is becoming harder and harder to select a motherboard with
the correct type of slots. Be very certain that the motherboard you select has the correct type and quantity of
card slots for your hardware. Keep in mind that most companies that produce hardware cards for Asterisk
offer PCI and PCI-Express versions, but it’s still up to you to make sure they make sense in whatever
motherboard and chassis combination you choose.

Server Hardware Selection | 19