Fast Reroute with Parallel OBS Activation

Figure 5: Parallel OBS activation architecture.

In the serial OBS activation architecture, route setup signaling messages flow serially starting at the node upstream to the failure and along the re-routed alternate path. However, this signaling scheme can be further improved by combining it with the parallel activation architecture introduced in [4]. Figure 5 illustrates our proposed scheme. In this hybrid signaling scheme, the egress node, multicasts separate OBS control packets to all the nodes on the alternate path over the DCN in parallel. Real internetworks are organized as transit-stub hierarchical structures [11]. As a result, the hop distance between a pair of nodes in an internetwork such as the DCN does not grow linearly with the geographical distance between them. Hence, the largest hop distance that an OBS control packet is required to travel before the data burst can be transmitted will always be smaller in case of the parallel OBS scheme than in the serial OBS activation architecture. This is reflected in the way $t_{setup}$ is estimated for the serial and parallel architectures. For this scheme $t_{detect}$ and $t_{FIS}$ remain same as in Eqn. (12) and Eqn. (13).

Figure 6: Calculating $t_{setup}$ for parallel OBS-based activation.

From Figure 5, following an argument similar to the one in the previous section, we arrive at the same⁷expression for $t_{restore}$ as Eqn. (15):

$$t_{restore} = t_{LOL} + {\rm max}(\forall~n \in \mathcal{P} : t_{n} - O_{n}) + t_{switch}$$ (16)

We now describe the experiments carried out in order to compare the performance of the four schemes discussed above.