handle telephone connections between the customer equipment and the central office.
lines. All users in the key system share up to four external lines for long-distance dialing. A key
system gives the user a choice of three or four external lines to use when dialing. While
punching a designated line, the user connects his phone to that line. The line lights up to indicate
to other users that it is unavailable. Key systems can include features such as hold, transfer, and
speed dial. Key systems are ideal for small office environments. Key systems are phone
switches with less-complex capabilities. Figure 16-4 shows a typical key system.
PBXs, each phone has a unique extension number. For interoffice communication, PBXs can
connect to other PBXs via a trunk connection. Many multisite businesses have trunk lines,
which are also known as tie-lines, between each office to allow users to use intercom dialing.
The trunk lines between offices create a private voice network within the enterprise. Using tie-
lines is cost-effective in that it allows the company to bypass the long-distance per-call charge.
A line connection refers to a connection between a telephone switch and a PBX.
toll bypass. Toll bypass lets businesses send their intraoffice voice and fax calls over their
existing data network.