System information

Multicast Paging on Cisco SPA Telephones
The multicast paging feature on Cisco SPA phones is a bit strange, but once configured
it works fine. The trick of it is that the address you put into the phone is not the multicast
address that the page is sent across, but rather a sort of signaling channel.
What we have found is that you can make this address the same as the multicast address,
but simply use a different port number.
The dialplan looks like this:
exten => *724,1,Page(MulticastRTP/linksys/239.0.0.1:1234/239.0.0.1:6061)
In the SPA phone, you need to log into the Administration interface and navigate to
the SIP tab. At the very bottom of the page you will find the section called Linksys Key
System Parameters. You need to set the following parameters:
• Linksys Key System: Yes
• Multicast Address: 239.0.0.1:6061
Note that the multicast address you assign to the phone is the one that comes second
in the channel definition (in our example, the one using port 6061).
Note that you can write the Page() command in this format in an environment where
there is a mix of SPA phones (FKA Linksys, now Cisco) phones and other types of
phones. The other phones will use the first address and will work the same as if you
had used basic instead of linksys.
VoIP paging adaptors
Recently, there have been some VoIP-based paging speakers introduced to the market.
These devices are addressed in the dialplan in the exact same way as a SIP ATA con-
nected to a UTI1, but they can be installed in the same manner as overhead speakers
would be. Since they auto-answer, there is no need to pass them any extra information,
the way you would need to with a SIP telephone set.
For smaller installations (where no more than perhaps half a dozen speakers are re-
quired), these devices may be cost-effective. However, for anything larger than that,
(or installation in a complex environment such as a warehouse or parking lot), you will
get better performance at far less cost with a traditional analog paging system connected
to the phone system by an analog (FXS) interface.
We don’t know if these devices support multicast. Keep this in mind if you are planning
to use a large number of them.
Combination paging
In many organizations, there may be a need for both set-based and external paging. As
an example, a manufacturing facility might want to use set-based paging for the office
area but overhead paging for the plant and warehouse. From Asterisk’s perspective,
234 | Chapter 11: Parking and Paging