Difference between pre-plan and pre-configuration
For network protection, two aspects are important: (a) spare capacity pre-planned for restoration and (b) restoration speed for failure recovery. For the latter, the current protection or restoration techniques can be classified into two groups. One is pre-planned techniques and the other is pre-configured techniques. A pre-configured technique inherent embeds spare capacity pre-plan. The pre-planned protection technique include span restorable networks, shared backup path protection (SBPP), and path restoration (PR), while the pre-configured techniques include ring techniques, span-protecting p-cycles, segment-protecting p-cycles, and pre-cross-connected trails (PXT).
Fig. 1 Difference between preplan and preconfiguration
The key difference between pre-planned and pre-configured techniques is that the pre-configured techniques can achieve faster restoration speeds than the pre-planned techniques. In addition to pre-planning sufficient spare capacity for restoration upon a failure, the pre-configured techniques actually have set up protection path and cross-connected intermediate node switch states even before a failure. The benefit of this is that when a failure occurs, only the two end nodes of a working path or span need to perform switching-over operation to recover the failure. In contrast, under the pre-planned schemes, only sufficient protection capacity is reserved, but their connectivity on the intermediate nodes is not pre-cross-connected. When a failure occurs, a signaling session is required to activate the protection path and set up switch states on the traversed intermediate nodes. Thus, in general the pre-planned techniques require longer restoration time. In the aspect of spare capacity efficiency, these two types of techniques are essentially very close, although the pre-planned techniques can sometimes show a little bit better spare capacity efficiency. Fig. 1 shows an example for the difference between the concepts of pre-plan and pre-configuration. There is a preplanned protection path (dotted line), for which 3 units of protection capacity are reserved on all the three traversed links. Between the first and second links, the cross-connectivity between reserved protection capacity units on the two links are not preconfigured, which need to be activated through a later signaling process. In contrast, between the second and third links, the cross connectivity between protection capacity units are preconfigured, which do not need to be reconfigured in the future.