System information

Beyond a certain size, your Asterisk system will be unable to page mul-

tiple sets. For example, in an office with 200 telephones, using SIP to

page every set would not be possible; the traffic and CPU load on your

Asterisk server would simply be too much. In cases like this, you should

be looking at either multicast paging or external paging.

Perhaps the trickiest part of SIP-based paging is the fact that you usually have to tell

each set that it must auto-answer, but different manufacturers of SIP telephones use

different SIP messages for this purpose. So, depending on the telephone model you are

using, the commands needed to accomplish SIP-based set paging will be different. Here

are some examples:

• For Aastra:

exten => *724,1,Verbose(2,Paging to Aastra sets)

same => n,SIPAddHeader(Alert-Info: info=alert-autoanswer)

same => n,Set(PageDevice=SIP/00085D000000)

same => n,Page(${PageDevice},i)

• For Polycom:

exten => *724,1,Verbose(2,Paging to Polycom sets)

same => n,SIPAddHeader(Alert-Info: Ring Answer)

same => n,Set(PageDevice=SIP/0004F2000000)

same => n,Page(${PageDevice},i)

• For Snom:

exten => *724,1,Verbose(2,Paging to Snom sets)

same => n,Set(VXML_URL=intercom=true)

; replace 'domain.com' with the domain of your system

same => n,SIPAddHeader(Call-Info: sip:domain.com\;answer-after=0)

same => n,Set(PageDevice=SIP/000413000000)

same => n,Page(${PageDevice},i)

• For Cisco SPA (the former Linksys phones, not the 79XX series):

exten => *724,1,Verbose(2,Paging to Cisco SPA sets -- but not Cisco 79XX sets)

same => n,SIPAddHeader(Call-Info:\;answer-after=0) ; Cisco SPA phones

same => n,Set(PageDevice=SIP/0004F2000000)

same => n,Page(${PageDevice},i)

Assuming you’ve figured that out, what happens if you have a mix of phones in your

environment? How do you control which headers to send to which phones?

Any way you slice it, it’s not pretty.

#Hint: the local channel will be your friend here.

232 | Chapter 11: Parking and Paging