Tham khảo tài liệu 'wireless mesh networks part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 114 Wireless Mesh Networks In a similar way the neighborhood between MRs and MCs are established exchanging HELLOs. Although the MCs only reacts to first HELLO sent by the MR. Usually as also illustrated in Fig. 3b the MR proactively sends a HELLO arrow 1 and in turn the MC reactively sends a HELLO as response arrow 2 . Fig. 3. MR-MR and MR-MC discovery process Beside of that the signaling approaches adopted by MRs and MCs have to integrate mechanisms to handle transmission problems that causes message loss. In MRs the proactive timer-based signaling approach just handles transmission errors by simply resending the HELLO message in the next time interval. In MCs the reactive event-based signaling approach deals with transmission errors by adopting a confirmed service in which MRs must acknowledge in their succeeding HELLO the reception of HELLOs sent by MC as illustrated in Fig. 4. Fig. 4. MR-MC discovery process with acknowledgement Thus in case of message loss the robustness of the process relies on immediately after detecting a neighbor MR an MC must reply with a HELLO message for each one received from that MR until it receives an acknowledgment sent by the MR. Note that the acknowledgement is indicated by just including the MC s address in the MR s HELLO message which contains the list of MCs from which the MR has received HELLOs during its last signaling interval around 2 seconds . Neighborhood loss When a node is declared as neighbor SNDP needs to monitor the neighbor node in order to detect the instant in which the neighborhood is lost. Once more SNDP adopts a hybrid strategy for detecting and managing neighborhood loss. On the one hand as MRs periodically sends HELLOs MCs adopt a timer-based approach. On the other hand as MCs reactively send HELLOs MRs adopts a notification-based approach. A Layered Routing Architecture for Infrastructure Wireless Mesh Networks 115 As MCs adopts the timer-based approach when an MC declares an MR as neighbor it also .
