KNPRE table misdirecting valid DID calls

[kevin906]

Turning up a PRI circuit today ran into this issue.
Test calls from telco diverting to the ATC.
These trunks have only been used outbound up to now and have been in for some time.
The trace showed digits being redirected as 94801 when only 4801 was sent from telco.
Fooled around with DIDCR and set a table expecting 5 digits, stripping 1 off.
This got the calls to complete but I could not understand why.
Eventually found the KNPRE table configured to ISDN-SUBSCRIBER with 9 as EXIT.
Deleted the KNPRE entry for ISDN-SUBSCRIBER and calls now work with proper DIDCR of 4 digits, strip nothing.
I have not seen the KNPRE table in many systems and reading about in the design docs it
looked more like something to do with Cornet tandem calls.
I am guessing the KNPRE table has been in since installation and this issue never showed up before.
Since 4801 is a valid WABE entry with a working phone why would the inbound call reference the KNPRE table instead of looking to WABE first?

text file attached

Guess I don't understand why a PSTN circuit is referencing this table and misdirecting (adding 9) to the inbound number.

 

[sbcsu]

All that KNPRE does is to add before the incoming number the exit number, a long distance access or international access.
This is mostly for display - so if you get a missed call from a local number 5551234
Then 05551234 will show on the display and then as a missed call which you can then just dial because the access code (zero in this example) is included.
The KNPRE does not add digits before TDCSU or WABE it adds in those digits only when the call is presented to the phone

 

[Moriendi]

According to some documentation I have KNPRE can work on called not calling digits but I've never seen it do it (useful for transit calls maybe?), it's used as sbcsu says, to adjust incoming calling line ID so that the number can be dialled straight back. It works with private numbers and E.164 ISDN but I've only seen it configured for E.164 ISDN. Example, CO delivers an explicit calling line ID +212xxxx, national etc. KNPRE then makes that implicit - diallable - by adding exit code and prefix so the number makes sense in the phone display (and the call logging), and if you press SNR you can save the number and call it back. KNMAT could also do it by just adding a 9, but KNPRE understands the TON, subscriber, national, international etc. I've never seen it cause the problem you describe, I wonder if you haven't got KNDEF configured which could cause odd behaviour maybe with KNPRE.

 

[Moriendi]

I actually just had this problem - incoming call delivered to 4K was E.164 International (yours was subscrber) but dialled digits did not match in KNDEF. 4K prefixed 900 and bounced the call straight out again. Adding KNDEF correctly solved the problem. I'm sure it was your problem too. With correct KNDEF the 4K can strip the correct digits from the called party, leaving it with an internal number. If it can't get a match it assumes the call is for elsewhere and applies exit code etc from KNPRE.