7.2 Client-Side vs. Network-Side Protection

Client-side and network-side protection refers to where the protection mechanism is triggered; i.e., at the clients at the endpoints (client side) or in the optical layer (network side). From a cost perspective, the main impact of the two schemes is the amount of equipment required at the endpoints of protected demands. Either type of protection can be operated in a dedicated or shared mode; however, for illustrative purposes, the discussion in this section will center around dedicated protection.

First, consider client-side 1+1 dedicated protection, where the client is responsible for generating two copies of the signal, both of which are transmitted over the optical layer. A demand endpoint with this type of protection is illustrated in Fig. 7.3(a), where an IP router is serving as the client. The router sends two copies of the signal to the optical layer, which routes them over disjoint paths. In the reverse direction, the router receives two copies of the signal and is responsible for selecting the better of the two copies.

Figure 7.3: (a) Client-side protection where the client (here an IP router) delivers the working and protect signals to the optical layer in the transmit direction, and selects the better of the two signals in the receive direction. (b) Client-side protection where a splitter feeds the client signal into two transponders, and a selector chooses the better of the two paths in the receive direction. (b) Network-side protection where a two-way transponder generates the working and protect...