4.5. Summary
Table 4-13 summarizes the survivability options discussed in this chapter. It can be seen from this table that network survivability techniques involve a multidimensional trade-off between restoration time, bandwidth efficiency, and failure robustness.
| Name | Restoration Time | Bandwidth Required | Failure Robustness |
|---|---|---|---|
| 1+1 Linear (SDH/SONET) | Typically under 50 ms | 2x | Only as good as the diversity of the alternative paths. Handles single failure. |
| 1:N Linear (SDH/SONET) | Typically under 50 ms | Only as good as the diversity of the paths, Handles single failure. | |
| Bi-directional Line Switched Ring (BLSR) Failures. | Typically under 100 ms | 2x | Diversity built in, one line out, except in 4F case which can handle multiple span. |
| Source Re-route Mesh Restoration | Depends on the number of circuits, the number of hops, and propagation delay | Network design consideration (less than 2x) As close as one can get to mesh limit | Can handle any recoverable situation, permits graceful degradation if desired. |
| Unidirectional Path Switched Ring (UPSR) | Typically under 50 ms | 2x | Diversity built in, can handle certain node failures. |
| Path Level (SNC) 1:N | Depends on the number of circuits, the number of hops, and propagation delay | Less than 2x, but above mesh limit. Dependent on sharing | The diversity of the paths determines robustness. Handles single failure. |
| P-cycle | Depends on propagation delay and the method for conveying protocol messages | Less than 2x but above mesh limit | Handles single failure. |
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