615 PAPER 19 >From linga@CS.Cornell.EDU Tue Sep 24 11:59:20 2002 >Date: Tue, 24 Sep 2002 11:59:19 -0400 (EDT) >From: Prakash Linga  >To: Emin Gun Sirer  >Subject: PAPER #19 > > > >CEDAR > >The goal of this paper is provide quality of service (QoS) routing in MANET. >Here bandwidth is used as the QoS metric. So the goal is to find a route from >source to destionation satisfying the b/w requirements with high probability, >given that there is one. Concentration here is on coming up with a robust >algorithm which may be way off from the optimal. >Main idea is to work with the core (a dominating set of the network which >approximates the minimum dominating set). Core is formed using only local >computation and local state using constant time (each node does a small amount >of work in parallel.) Each core node performs route computation for the nodes >in its domain and also maintains the local topology. Core broadcast is >achieved using a reliable unicast mechanism while avoiding redundant message >transfers by monitoring RTS/CTS packets. >Only b/w information of stable links is propagated through the core network >(info about dynamic or low b/w links is kept local). This is done using slow- >moving increase waves and fast-moving decrease waves. When the b/w of a link >(ab) changes (increases/decreases beyond a threshold) either node a or b will >inform its dominator about the change and that will propage the change across >the core n/w using increase/decrease waves. The maximum distance a link state >can travel is proportional to the b/w of that link so that a lot of nodes know >about the good links. >QoS routing has three key steps: >-discover the location of destination and establish a ccore path to the same. >-now by finding the shortest-widest furthest admissible path along the core >path and iterating, we find a short stable admissible QoS route from source to >destination. >-in face of link failures or topology changes dynamically reestablish the >routes for ongoing connections. >Performance evaluation: Three main kinds of results: characteristics of the >basic routing algorithm, performance of QoS routing and performance in case of >failures/mobility. >Pros: One of the first to talk about QoS routing in adhoc networks. They give >a list of goals for QoS routing in adhoc networks. Results show the proof of >concept and satisfactory performance numbers. >Cons: Only QoS metric used here is b/w. Other metrics like delay, jitter etc >have not been considered. It is not clear why robustness is much more important >than optimality (finding close to the best possible). Experiment/Simulation >results are not complete; try out with larger number of nodes and more >realistic topologies. Here they state that their goal is robustness and not >optimality. There are many details which need to worked out (like how good an >idea is caching RTS/CTS, how often do we send information about b/w updates, >how does using reliable unicast to simulate core broadcast compare to naive >broadcasting and hoping redundancy would take care of transmission failures or > have some other scheme to take care of failures). Future work would include >addressing the issues discussed above. > >