[asterisk-ss7] Redirection Counter and Number

Tuan Le tuan.le55 at gmail.com
Fri Jul 8 06:27:57 CDT 2011

Using Libss7/Dahdi and Asterisk 1.6.x, I want to be able to detect outbound
calls if it has been redirected and if so, how many times.  There are
standard fields in ISUP ITU Q.763 specs  (
https://staff.ti.bfh.ch/mdm1/Kursunterlagen/SS7/T-REC-Q.763.pdf) that stated
the information should be available.  This is for fraud prevention as we
have some very restricted numbers that cannot be forwarded.  For now, we
just need to be able to know if the call has been forwarded whether via
Asterisk log or writing some variable information back to the CDR for easier
looking up.  We don't need to cancel the call or take any action if a call
has been redirected.

We would like to perform some tests with the Redirection Counter increased
artificially (in Asterisk) to 4 or 5. We then look at the Release Cause,
which should give us some useful information. What we’re looking for is to
change bits KJI of section 3.45  in the attached ITU-T Q.763 document.

In our capture, we do see the following which shows the redirected number
down the line in the ACM message:

ACM: cwvoip1*CLI>    --OPTIONAL PARMS--
cwvoip1*CLI>    Generic Notification Indication:
cwvoip1*CLI>            [ 2c 01 fb ]
               Unknown Parameter (0xc):
cwvoip1*CLI>            [ 03 10 87 30 41 28 69 ]
               Unknown Parameter (0x36):
cwvoip1*CLI>            [ 19 ]

Can anyone clarify the “2c 01 fb” parameter please? I think we worked out
that ‘fb’ means “call is diverting”, which would be useful.  Unknown
Parameter 0xc appears to be the redirecting number.

We are also planning for an upgrade to Asterisk 1.8 to have access to the
redirection counters.(

Executing ... Set("SIP/447684527310-00000000", "REDIRECTING(count,i)=5") in
new stack
[Jul 6 17:02:29] ERROR[29662] pbx.c: Function REDIRECTING not registered

We're hoping to set this counter in Asterisk 1.8 and patch DAHDI to perform
pcap dump hoping maybe wireshark can help produce better analysis of the
field names instead of "Unknown" but for now, does anyone know what the
above means?
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