Recently we had a call from one of our new customers with Telstra SIP Connect lines saying that they had noisy lines at one site but only on incoming calls. The first call was fine but when a second call came in it was noisy and very hard to hear the person at the other end. What could it be? Some issue in the Telstra network? Some issue with the Avaya phone system all of a sudden or something else? Outgoing calls were perfect. SIP trunks can manifest all sorts of odd faults so it would be a case of investigating that first. Curly cords on the phones can also be an issue. Perhaps the second call was always answered on a particular phone that had a damaged curly cord that was inducing noise.
Fortunately the tech who was allocated the job was the same tech who attended site a couple of weeks ago to tidy up the programming after multiple other companies had had a go at it and he knew that out of the 7 sites, this particular site still had some analogue lines that had been taking incoming calls with only the outgoing calls going over the SIP Connect. A little investigation revealed that not only had the call forward dropped off the main number, perhaps because of a Telstra exchange restart over the weekend, but Line 2 was locked up to the voicemail and Line 3 was actually the noisy line that was getting picked for the second inbound call. A 3rd call would have got a good Line 4 and a 4th call would have got busy.
A little local knowledge and a methodical approach to testing are key factors for the speedy resolution of this fault. The temporary call forward was reapplied to the SIP trunk until an order to permamanently call forward the number takes effect.