== Reducing Latency in Rendezvous-based systems: == 

  

 An architecture GeoRendezvous based on HERMES, SCRIBE and IniQoS, focus on minimizing the latency experienced by the clients. It runs on the top of Cell Hashing Routing and uses positon-based DHT to map the rendezvous nodes to the space on the basis of their geographical locations.Thus allowing the subscriber to take advantage of positional information of the nodes and hence reducing the signalling and latency. It is a topic-based publish-subscribe  
 middleware. 

 GeoRendezvous system uses Cell Hash Routing(CHR). It is a cluster-based DHT. Here the space is divided into cells and the nodes are mapped into these cells.Each cell has a virtual node which is responsible for the events related to the cell. The routing is done in CHR using the Greedy Perimeter Stateless Routing Algorithm. In this algorithm the sender assume itself as the virtual node and passes the message to any randomly picked node in the  populated neighbouring cells inorder to minimize the distance of the destination cell. If the node turns out to be the local minimum then it passes the message along the perimeter until the recieving cell is not the local minimum and then it re-assumes the greedy algorithm. If the message return to a cell twice then the destination cell is empty and it lies inside this perimeter(perimeter formed by the trace of the message called "home perimeter"). 
 As with other rendezvous systems, this also allows the sharing of the resources to reduce the traffic. Here the clients have to renew their advertisement and subscription to enable the system to react to the topological changes. The latency can be further reduced by replicting the rendezvous nodes as it allows the client to select from the group of the nodes based on the minimum hops. 

 Another important feature of position-based DHT is that the clients only have to send messages to the subset of nodes which are more close to it rather than to entire nodes. 

 References: 
           Reducing Latency in Rendezvous-Based Publish-Subscribe Systems for Wireless Ad Hoc Networks [Nuno Carvalho,Filipe Araujo, Luis Rodrigues]