Tham khảo tài liệu 'mobil ad hoc networks protocol design part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 352 Mobile Ad-Hoc Networks Protocol Design networks with different sequence numbers. Based on the above consideration our synchronization mechanism is to send periodical sync message with sequence numbers which reaches only neighbor node. Also we prepare fields of a c and the generated time of links in link advertisement messages where the link generated time should be expressed by the sequence number based on the sending node s sync messages. Under the behavior above each node learns the timing to send sync messages so that the timing to send sync messages is synchronized in a network little by little. Thus finally all nodes send periodical sync messages almost simultaneously although some random factor should be considered to avoid interference among messages. Then if each node changes the metrics of all links in its database every time the node send a synchronization message the synchronization is done without problems. This mechanism is able to keep correct metrics even after loss of control packets. There is no problem in both case of division and join of networks although join process requires synchronization time to converge. Also additional message overhead is very low if we use existing messages such as hello messages as sync messages in LLD. Note that this mechanism is only an example to do synchronization. But it shows that we can perform required synchronization of LLD in low cost. 4. Theoretical analysis for loop-freeness Formulation of loop-freeness Here we give a condition of synchronization time interval to be loop-free. We start with formulation of loop-freeness. Let G V E be a network where V is a set of nodes and E is a set of links. For a pair of nodes 1 2 6 V we call they are adjacent if 1 2 6 E. A sequence of nodes p 1 2 . m where k k 1 6 E k 1 2 . m 1 are called path. The metric of link l at time t is denoted by Ỗ1 l aibt Cl where a b and c is a real value and 0 b 1. Note that the value of b must be common in a network but a and c is not.
