We have been advised by our upstream carrier for VoIP calls they will be conducting maintenance during the above window. This will affect call flow for a short duration. Below is the official notification sent to us:
Will be migrating some infrastructure configuration from a core router to a higher capacity device on Saturday 25 May 2013. The outage window will be between 0400 and 0500 UTC. The outage duration is not expected to be more than 5 minutes. During this time calls in progress may be cut off. This activity is part of our ongoing capacity improvement programme. We apologise for any inconvenience that may be caused.