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Cognitive radio networks (CRNs) have emerged as a critical technique to solve spectrum shortage problem and enhance the utilization of licensed channels. To prevent from interfering with the co-locate incumbent networks, before data transmission, nodes in CRNs should rendezvous on an available channel (i.e., idle licensed channel) for establishing a link or exchanging control information. However, implementing rendezvous is challenging because the availability of channels is time-varying and position-varying. For reducing rendezvous failure and increasing throughput, a node pair in CRN should be able to rendezvous on every licensed channels (i.e., maximizing rendezvous diversity) and rendezvous on an available channel as soon as possible (i.e., minimizing maximum conditional time to rendezvous (MCTTR)). Besides, in order to take full advantage of the frequency diversity of multi-channel medium access, rendezvous should be spread out in time and channel (i.e., minimizing channel loading). In this paper, we proposed two rendezvous channel hopping algorithms, T-CH and D-CH, which can be used without time synchronization and role preassignment (each node has a pre-assigned role as either a sender or a receiver). D-CH requires that SUs in CRNs should have unique ID (identifier), while T-CH does not. Both of our T-CH and D-CH have maximum rendezvous diversity and minimum channel loading, and outperform in terms of MCTTR.

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Software defined networks (SDN) provide flexibility for developing new network protocols and policies in real networks. The SDN controller translates network policies into specific rules in the flow tables (which are usually implemented using ternary content addressable memory (TCAM)) of each network switch. However, due to the limitation of TCAM (e.g., high power consumption and high heat generation), flow tables cannot scale beyond a few hundred entries. Hence, switches usually reactively cache rules (i.e., installing rules on demand). However, reactively caching rules causes packet delay and large buffers, when cache misses happen. To improve the performance, in this paper, we propose a rule partition and allocation algorithm to distribute rules across network switches. Our algorithm not only is applicable to small TCAM switch scenario, but also guarantees semantically-invariant (i.e., the global action of the network is unchanged).

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