Restricting the number of simultaneous calls by incoming DID from ITSP

[peterk]

We're have a TA904e at a customer with SIP-based PSTN trunks on the network side and T1 to a NEC UX5000. The TA904e is running release 10.7.

There are several incoming DIDs mapped to the SIP-based PSTN trunk on the Adtran - the ISDN takes the last 4 digits of the DID and passes it to the PBX. The main line DID (e.g. 555-111-MAIN) typically has multiple incoming calls, which the Adtran processes without issue and sends to the PBX. So far so good.

One issue has surfaced - a particular user with a DID (e.g. 555-111-SHOP) has only one phone. In the previous configuration with the TDM carrier, only one call came through to the phone - if someone was on the SHOP line, the carrier busied out subsequent incoming calls to SHOP. With the SIP-based PSTN configuration, the call goes through and rings the extension. The user prefers the previous behavior.

Without touching the NEC UX5000 configuration, is there a way to build a policy that limits the number of simultaneous incoming calls for a particular DID to 1 - either on the SIP trunk side, or PRI to the NEC UX5000. In other words, allow certain DIDs such as 555-111-MAIN to process multiple incoming calls to the NEC while limiting other DIDs such as 555-111-SHOP to a single active call (multiple incoming calls are rejected with a busy signal).

Any insights appreciated - many thanks in advance.

[jayh]

I don't think so, with the "without touching the NEC" restriction.  Disabling call-waiting in the NEC should do it. 

This could also be a cause code mapping issue.  Debug ISDN l2-formatted and place a call to 111-SHOP.  With this call up place a second one.  You should see a cause code 17 user busy from the PBX.  The TA900 should map this to 486 busy here and the provider should return a busy signal. 

If the PBX is returning something other than 17 user busy for a busy extension, then you need to map that cause code to 486 busy here in the TA900.

There might be another way. I haven't tried it.  It's kind of an ugly hack, but it might work. 

• Create a second ISDN trunk referencing the same PRI to the NEC
• Set the maximum B-channels to "1"
• Create a grouped-trunk containing only 111-SHOP and include that trunk. Exclude 111-SHOP from the main ISDN trunk group.

[peterk · Accepted solution]

There are support issues on the customer NEC switch so we're being prudent in recommending changes unless absolutely needed. Clearly disabling call waiting should resolve the issue - we'll start there with the customer, and use the other two approaches as backup. We have access to other PBXs to test these changes with the Adtran ...

Many thanks for the response - this feedback helps us with next steps.

All the best

Peter