In a keyswitch
system, you can set up most of your phones to have a nearly identical
configuration, in which each phone is able to answer any incoming PSTN call on
any line. Phone users are generally close to each other and seldom need to use
the telephone to contact each other.
For example, a 3x3
keyswitch system has three PSTN lines shared across three telephones, such that
all three PSTN lines appear on each of the three telephones. This permits an
incoming call on any PSTN line to be directly answered by any telephone—without
the aid of a receptionist, an auto-attendant service, or the use of (expensive)
DID lines. Also, the lines act as shared lines—a call can be put on hold on one
phone and resumed on another phone without invoking call transfer.
In the keyswitch
model, the same directory numbers are assigned to all IP phones. When an
incoming call arrives, it rings all available IP phones. When multiple calls
are present within the system at the same time, each individual call (ringing
or waiting on hold) is visible and can be directly selected by pressing the
corresponding line button on an IP phone. In this model, calls can be moved
between phones simply by putting the call on hold at one phone and selecting
the call using the line button on another phone. In a keyswitch model, the
dual-line option is rarely appropriate because the PSTN lines to which the
directory numbers correspond do not themselves support dual-line configuration.
Using the dual-line option also makes configuration of call-coverage (hunting)
behaviors more complex.
You configure the
keyswitch model by creating a set of directory numbers that correspond
one-to-one with your PSTN lines. Then you configure your PSTN ports to route
incoming calls to those ephone-dns. The maximum number of PSTN lines that you
can assign in this model can be limited by the number of available buttons on
your IP phones. If so, the overlay option may be useful for extending the
number of lines that can be accessed by a phone.
shows an incoming call from the PSTN (1), which is routed to extension 1001 on
all three phones (2).
Figure 4. Incoming PSTN
Call Using Keyswitch Model
Configure Phones for a Key System.