How PBX Installation Differs from Router Installation
Most readers of this book are likely entering into the world of PBX systems
from the data world. In fact, many of you may never have installed
a PBX or voice system. However, whether you approach data from a
voice background or voice from a data background, the reality is that at
a high level the two differ less than you might imagine.
It would be inappropriate to enter into the commands and syntax
of PBX configuration here—for one, which system would we use as a
reference? There are many PBX systems, each with different software
versions and hardware options, and each revision of code introduces
new commands and syntax. This is not unlike an academic conversation
on router configuration—Cisco or Nortel, Multilayer Switch Feature Card
(MSFC) or Route Switch Module (RSM) or Route Switch Processor (RSP)-
2. In fact, this is the first of the ways in which the systems parallel one
another. PBXs and routers both have their own unique features and
commands based on the vendor and the version of code.
Configuring & Implementing…
Continued
12 Chapter 1 • Old World Technologies
Interpreting PBX Terminology
The world of telecommunications and PBX systems includes a vocabulary unique
unto itself.You may find that many of the words and acronyms are familiar and
common if your background is based in the data world. Nevertheless, there are a
number of new terms and concepts that need to be understood before tackling the
integration of voice and data systems. In addition, some acronyms have multiple
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In the previous sidebar, “What Voice Designers Do,” we discussed
the design and deployment considerations of a modern PBX. We also
saw the similarities between data systems and voice PBXs. These similarities
include redundancy, cost/performance, and design limitations.
PBX systems augment these similarities with a few distinct differences,
including:
Power Electrical requirements in PBX systems are frequently
48 volt DC. Data network devices are often 120 volt AC.
Wiring It is rare that a PBX system will require Category 5
cabling for connectivity, unlike Ethernet. In addition, it is
uncommon to terminate voice grade wiring on patch panels.
Rather, voice wiring uses punch-down blocks that hold each
bare wire onto a clip. Requirements such as maintaining
twists and staying under 100 meters are not part of the typical
voice installation.
Dial Plan Unlike IP routers, voice systems rely on static
routing tables when forwarding calls. Calls are routed based
on a match with the destination number—unlike data networks,
the source address is rarely used for call routing. The
static route map will define a preferred path, an alternate
path, and, sometimes, tertiary paths for each number within
the environment.
Circuits In the data world, most circuits are billed at a flatrate
per month. These charges can be distance insensitive (as
in the case in Frame Relay), or distance sensitive (common in
leased line connections). In voice, it is common to use leased
line connections and the associated tariffs, which can allow
for significant savings when traffic is carried on alternative
paths. These paths may be the connection to the long-distance
provider, or may be a private leased line between
PBX systems.