A term commonly used to describe the gradual 'filling up' of a lot of telecom operators optical networks. Many of these fibre optic system were designed in the pre-Internet days when the average PSTN call time (in the UK anyway) was around 6 minutes. This figure has now increased to around 45 minutes and is rapidly climbing, with the longest current call on the public network standing at just over 40 hours.

The upshot of this is that many of the current networks are running at 70-80% of capacity, and the day is approaching when the system will be full (i.e. all the fibre will be exhausted) unless some way of improving on the current TDM system is found. One current suggestion is the implementation of DWDM.