System information

better for each successive page to assign the next slot, since you will often have more
than one call parked at a time. Your users will get used to listening carefully to the
actual parking lot number (instead of just always dialing 701), and this will minimize
the chance of people accidentally retrieving the wrong call on a busy system.
If you are using parking, you are probably also going to need a way to announce the
parked calls so that the intended parties know how to retrieve them. While you could
just run down the hall yelling “Bob, there’s a call for you on 701!,” the more professional
method is to use a paging system (more formally known as a public address system),
which we will discuss in the next section.
Overhead and “Underchin” Paging (a.k.a. Public Address)
In many PBX systems, it is desirable to be able to allow a user to send his voice from a
telephone into a public address system. This normally involves dialing a feature code
or extension that makes a connection to a public address resource of some kind, and
then making an announcement through the handset of the telephone that is broadcast
to all devices associated with that paging resource. Often, this will be an external paging
system consisting of an amplifier connected to overhead speakers; however, paging
through the speakers of office telephones is also popular (mainly for cost reasons). If
you have the budget (or an existing overhead paging system), overhead paging is gen-
erally better, but set paging (a.k.a. “underchin” paging) can work well in many envi-
ronments. What is perhaps most common is to have a mix of set and overhead paging,
where, for example, set-based paging might be in use for offices, but overhead paging
would be used for warehouse, hallway, and public areas (cafeteria, reception, etc.).
In Asterisk, the Page() application is used for paging. This application simply takes a
list of channels as its argument, calls all of the listed channels simultaneously, and, as
they are answered, puts each one into a conference room. With this in mind, it becomes
obvious that one requirement for paging to work is that each destination channel must
be able to automatically answer the incoming connection and place the resultant audio
onto a speaker of some sort (in other words, Page() won’t work if all the phones just
ring).
So, while the Page() application itself is painless and simple to use, getting all the des-
tination channels to handle the incoming pages correctly is a bit trickier. We’ll get to
that shortly.
The Page() application takes three arguments, defining the group of channels the page
is to be connected to, the options, and the timeout:
exten => *724,1,Page(${ChannelsToPage},i,120)
The options (outlined in Table 11-3) give you some flexibility with respect to how
Page() works, but the majority of the configuration is going to have to do with how the
target devices handle the incoming connection. We’ll dive into the various ways you
can configure devices to receive pages in the next section.
Overhead and “Underchin” Paging (a.k.a. Public Address) | 229