Service Update: Intermittent One-Way Audio
Last updateresolvedOct 15 · 15:51 UTC
Description of Incident: On the 17/09/2026 Intermittent one-way audio issue affecting calls from 11.45 at its peak for about 30-45 minutes with a recurrence around at 15.15 for around 20 minutes. This was reported as silent calls, calls cutting off and calls not connecting but the reported incidents all led back to the one-way audio issue which was identified to be with the upstream provider (transit). The upstream provider was BT-IPEX (BTs IP Voice Exchange) and during the first issue an incident case was raised with them. After the second incident on the 17/09/2026 at 15.15 BT drained the calls down on the affected zone and pushed all traffic to our secondary zone. One the 23/07/2026 at around 15.30 the one-way audio issue surfaced again for around 25 minutes on the secondary zone. BT then distributed other affected service providers, government agencies and 999 services to other zones to spread the demand from our zone which temporarily fixed the one-way audio issue while they continued investigated. In subsequent conversations, BT confirmed this was a complex case and had the highest priority within BT and their vendor. They also explained they had a program of works throughout the summer to upgrade their network in readiness for the PSTN switch-off in January 2027, and the one-way audio was likely being caused by the network changes/upgrade. Resolution: After extensive investigation BT confirmed on the 02/10/2026 they believed they had fixed the issue and had released the drain on the primary route. They asked us to Monitor and report back our finding after 7 days. During this time, we had no one-way audio issues. On the 13/10/2026 BT released their Root Cause Analysis. The incident was caused by an unexpected network routing issue within the Orion Session Border Controller (SBC) environment. The Orion SBC is configured with media steering pools across two physical network interfaces. During the incident, the SBC issued a network update that incorrectly associated a media steering IP address with the wrong physical interface. As a result, network equipment updated its routing information and began directing media traffic to the incorrect interface. This led to media packets being delivered to the wrong location within the SBC, causing the loss of audio media experienced during the incident. Summary BT have over the summer caused several issue culminating in the one-way audio condition due to their program of works. BT have confirmed Callable’s traffic routes/zones have all been upgraded and there are no further planned works. They also report the Orion environment is now performing as expected, which is all good news. We thank you for your patience during this difficult time and on behalf of BT we apologies for the inconvenience caused. Chief Technology Officer Callable Limited.
Reported by Callable on their status page.