Vodafone were experiencing problems with their Home Location Registers (HLRs) which all got completely knocked out while Voda was trying to upgrade the way in which the software stores and shares text messages across the network.
HLRs are the main databases which hold all the subscriber information including address, account status, and preferences.
When a call is initiated out of the home area, the area Visting Location Register (VLR) sends out a request for information required to process the call. The Mobile Switching Centre (MSC) queries the HLR identified by the call for information, which it relays to the appropriate MSC, which in turn relays it to the VLR. The VLR sends routing information back to the MSC which allows it to find the station where the call originated, and, finally, the mobile device to connect.
So, quite important then.
Voda’s engineers couldn’t isolate the problem to any part of the network, only that there was a problem which clogged all the HLRs.
A Voda spokesperson said on Friday afternoon "We had a problem between 7 and 9am which affected around 50,000 customers. The majority have now been restored to the network. Some customers are still affected but we are working to fix that before the end of the day".