Elastic interface buses, abbreviated as EI bus connections, can be generalized as bus connections which are high speed interfaces that send clock signals with data.
EI bus connections require that the net topology and timing characteristics for each net on the bus are at least similar to each other in order to make lining up the edges of the data to the clock signals possible.
Elastic Interface repair involves a spare wire that is built into the bus interface in the connection module that has the same topology and characteristics of the rest of the nets in the bus.
It includes hardware that is able to switch from the bad net in the interface to the spare net (as of now, this operation must be supported by the original manufacturer of the EI bus connector).
In the original design specification for the EI spare, the wire was driven with a constant zero when not used.