Intercom to a large number of phones

We would like to use our Linksys/Cisco IP phones as intercom endpoints. I know we can use the Page Pro module for this, but I have several questions:

  1. The documentation says that the recommended limit for number of extensions in a page group is 25. Is there any reliable way to overcome this limitation?
  2. I saw a reference to RTP multicast. Is this incoming or outgoing? We already have several Algo announcers that use multicast; if it were possible to have the phones respond to the multicast transmission from these units, that would be ideal.


Multicast paging is indeed how you would overcome this. Have you read through the Multicast paging wiki?

Multicast paging is indeed how you would overcome this. Have you read through the Multicast paging wiki?

Thanks! I have read through it. Unfortunately I don’t know how to configure my phones (mostly SPA962 and similar) to auto-answer a multicast page. I’ve tried to hire someone who could set it up, but haven’t had any luck finding someone who could do it.

If you or anyone else can give me some guidance either on finding someone to set this up for me, or in how to set it up on these specific devices, I’d be most appreciative.

You need to first figure out if those old phones even support multicast. Google is your friend here.

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They do all support multicast in some way, but I’m not sure exactly in what way. That is to say, you can have all of them listen on a multicast address, but I can’t find any documentation on how these are used except with Cisco phone managers.

Multicast is exactly how we do it here (on Yealink T46G phones)

The bottom line is, you set up the Multicast listener IP and port on the phones. The phones don’t “answer the call” in a traditional sense… they just listen on that address.

When you broadcast on that address (whether it be as a multicast page from another phone, an RTP stream from VLC, whatever) the phones see the activity and play the stream through the speaker. This is outside of the normal calls… nothing is answered… calls do take precedence over the streams, so it doesn’t interrupt calls or prevent you from answering in the middle of a page.

The phone just sits there, listening on that address, and if a compatible (right bitrate/etc) stream comes along, it plays it.

Simple as that.


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