Router line cards are partitioned, separating
packet forwarding from external or internal interfaces and enabling multiple line cards to access any set of external or internal data paths. Any failed working
line card can be switchably replaced by another
line card. In particular, a serial
bus structure on the interface side interconnects any interface port within a protection group with a protect
line card for that group. Incremental capacity allows the protect line card to perform packet forward functions. Logical mapping of line card addressing and identification provides locally managed protection switching of a line card that is transparent to other
router line cards and to all peer routers. One-for-N protection ratios, where N is some integer greater than two, can be achieved economically, yet provide sufficient capacity with acceptable protection switch time under 100 milliseconds. Alternatively, protect line cards can routinely carry low priority traffic that is interruptible, allowing the protect line card to
handle higher priority traffic previously carried by a failed working line card. This approach renders unnecessary
engineering a network for less than full capacity to allow rerouting in the event of individual line card failure. Consequently, all data paths can be fully utilized. If a particular interface module on one data
bus needs removal for maintenance, a duplicate data
bus is available intact, allowing hot replacement of any working or protect interface module, even while a line card protection switch is in effect.