1:N – This protection scheme allows up to N working lines to be protected by 1 protection line. When not used for protection purposes, the protection line can either be left idle or can be used to carry low priority extra traffic. In case the protection line is carrying extra traffic, this traffic is ignored when one of the working line goes down and protection line has to protect that working line.
1:1 is a special case of 1:N with N=1. In 1:1 protection scheme one working line is protected by one protection line and at any given point of time, traffic is transmitted only on one line.
1:N or 1:1 are examples of revertive protection scheme.
1+1 – This protection scheme allows one working line to be protected by one protection line and at any given point of time, traffic is transmitted on both working as well as protection line. Thus, unlike 1:N protection scheme, 1+1 protection scheme does not allow protection line to carry any extra traffic.
1+1 is an example of non-revertive protection scheme.