Tham khảo tài liệu 'mobile ad hoc networks applications part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Impact of the Mobility Model on a Cooperative Caching Scheme for Mobile Ad Hoc Networks 271 through nodes 5 4 and 2 which will annotate that node 6 will probably store the document B in its local cache in the local cache. As node 2 receives the request it will reply to node 6 intercepting the request. The reply will pass through nodes 4 and 5 to node 6 that will annotate that the document B is stored in node 2 and they will also update the TTL information of the request. Under this situation if node 4 requests the document B it will realize that DS node 2 and node 6 are located 3 1 and 2 hops away respectively and hence node 4 will request the document directly to node 2 which is the closer node that is known to have a valid copy of the document B. We have to remark that if the TTL of the information about the document location is not set the redirection is not allowed. This constraint prevents from redirecting a request to a node that has not received a certain requested document as the TTL is obtained from the reply and not from the request. Unfortunately although the TTL assigned to the redirection information prevents from redirecting requests to nodes that have an obsolete copy of the document this mechanism does not avoid the requests redirection to a node that has evicted the document because of the replacement policy. To cope with this situation we propose that the node that receives a redirected request and it has not a valid copy of the document in its local cache sends a special error message to the requester in order to send the request again. This message will pass through the redirecting node that will update the information about the incorrect redirection. Let us suppose that after the situation described previously in the Figure 1 node 6 deletes the document B from its local cache and then node 5 requests the document B. Node 5 has stored that nodes 6 and 2 have the document B and they are located at 2 and 1 hops away respectively. As node 6 is .
