Bill:
Thanks a million for the wonderful explanation! Much appreciated.
Cheers!
Reza.
- Original Message -
From: Bill Sandiford
To: Reza - Asterisk Enthusiast ; TAUG
Sent: Saturday, September 15, 2007 12:27 AM
Subject: Re: [on-asterisk] CNAM - Caller ID Name
1. Why dynamic CNAM issue is a big deal?
From a technical point of view it isn't usually a big deal at all. From a
liability point of view it could be. Some larger carriers are worried about
the implications if scam artists started setting their CNAM to things like
TORONTO POLICE and started calling people fraudlently. My argument to
the carriers has always been Well you let us set the number and nothing is
stopping the scam artists from setting the number to match the number of the
police, so whats the big deal? The usual answer I get is a confused look
and a shrug of the shoulders.
2. Why does the Name info have to be dug out each time from a shared
database (if its shared) based on the number (some carriers do this) by
the
carrier's lookup servers and then spit out to its subscribers?
Well, in Canada it isn't done that way at all. The CNAM database method is
how the CNAM info is looed up in the good old U S A. In the US carriers
access a shard CNAM database and query the database for the CNAM for every
call. In Canada we use a totally different method (described below)
3. Why can't the NAME be sent with the NUMBER info from one carrier to
the
other?
In Canada it is The CNAM in Canada is passed from carrier to carrier
as part of the messaging that take place when a call is initiated.
4. or Is transmitting NAME with the NUMBER simply a limitation on
the
switch the telcos carry?
Most of the time if its not working its as a result of interoperability
between varying switch types. If the trunks between carriers are SS7 then
the CNAM will most certainly work properly. However must people using
Asterisk don't have SS7, they have PRIs. The ISDN signalling between
different switches expect CNAM to be passed in different ways. For example,
a Nortel DMS (Bell Canada), expects the CNAM to be sent as part of the
initial Q.931 call setup message. Lucent 5ESS switches (Telus, Rogers)
expect it to be part of a subsequent progress message as a Facility IE. So,
in order to get CNAM to work on your PRI, its important to know what method
your carrier uses. I can tell you that Asterisk definately supports the
Facility IE message because I was the one that initiated the feature request
and did the testing for it back in April 2005.
http://bugs.digium.com/view.php?id=4046
To enable CNAM by Facility IE set facilityenable=yes in zapata.conf.
If you have SIP trunking, you are at the mercy of your carriers switch
capabilites and their PSTN connectivity arrangments.
Hope this helps clear things up for you !!!
Regards,
Bill Sandiford
Telnet Communications
905-674-2000 x100
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