One analyst suggests that the Verizon Wireless 4G Long Term Evolution (LTE) outage was caused by a Nokia Networks element in the IMS system that manages subscriber activity on the network. (See Verizon Investigating LTE Outage.)

Simon M. Leopold of Morgan Keegan & Company Inc. put out a research note Thursday afternoon that suggests that the daylong 4G outage was caused by a server that became unstable under heavy loads:

Our checks indicate that a team from Verizon and its key vendors including Alcatel-Lucent (NYSE: ALU), Ericsson AB (Nasdaq: ERIC) and Nokia Siemens Networks (NSN) pulled together and came up with a work around over night. Our checks suggest the problem resides deep in the network core and involves difficulties authenticating devices as they attempt to connect to the network. We suspect the overload relates to the HSS, the Home Subscriber Service, which is part of the IP Multimedia Subsystem (IMS). We believe the IMS solution comes from NSN. The infrastructure from Alcatel-Lucent and Ericsson seem as if they are functioning properly.

The HSS server holds all the user information related to preferences, subscriptions, location and authorization needed by the network to manage the subscribers as they move around on the 4G network. It is broadly similar to a Home Location Registrar (HLR) in a 3G network set-up.

Verizon Wireless had no comment when LR Mobile asked about the analyst note on Thursday.

— Dan Jones, Site Editor, Light Reading Mobile