We recently had an interesting troubleshooting experience with a customer where we provide a PRI via an Adtran TA900 to a PBX maintained by a different vendor. Both the new PBX and the SIP based PRI were turned up at the same time.
Everything went smoothly from a configuration and installation perspective, no issues to report. Shortly after turn-up, we started getting reports of random dropped calls on transfer. The PBX vendor claimed that everything there was fine, and we saw no errors on our side.
Numerous site visits and attempts by both vendors were inconclusive, we couldn’t duplicate the problem.
Eventually, we turned on full logging and asked the customer to keep track of problem calls. After some time we got call examples. The IAD showed normal clearing from the PRI so we asked the PBX vendor to get involved. They insisted everything was fine on their end, although they didn’t have the capability to debug and log calls. The reports came from the attendant, which makes sense as that’s where most transferred calls originate.
The PBX vendor swapped the phone, swapped the card in the PBX, and moved the phone to a different port. No improvement from the customer, yet we couldn’t duplicate the problem ourselves in testing. Stumped.
Eventually, we all camped out in the office and watched and waited for a call failure on transfer. Patience paid off. The problem?
The layout of this particular phone has the RELEASE button directly above the TRANSFER button. The receptionist had long fingernails and was occasionally tapping RELEASE before TRANSFER. A quick trim and no further problems.