615 PAPER 10  >From eyh5@ee.cornell.edu  Wed Sep 19 14:23:19 2001 Date: Wed, 19 Sep 2001 14:22:47 -0400 (EDT) From: Edward Hua  To: egs@CS.Cornell.EDU Subject: Summary of the ABR paper -------------------------------------------------       This paper presents a routing algorithm in which the selection of a suitable routh is based on the stability, or the associativity, of a route with respect to the nodes that comprise of the route. Unlikse many other routing algorithms for ad-hoc networks, this approach gives the destination node the authority to choose a suitable route for data transmission. In such a scenario, several routes may be available, some more stable (i.e., a higher degree of associativity) than the others The routing algorithm, executed at the destination node, will then choose the route with the best associativity. If more than one route has the same computed degree of associativity, the one that presents the minimal number of hops to the destination is chosen. It is clear that the ABR algorithm favors longevity of the route at the expense of added route acquisition overhead.          The proposed associativity-based routing algorithm seems suitable for an ad hoc network that does not experience drastic topological changes. Indeed, this design philosophy is based on the author's belief that "in an ad-hoc mobile network, fast adaptability at the expense of excessive radio bandwidth consumption is undesirable." This may also justify the author's choice of a conference-room size environment for his simulations.         ABR has a mechanism that is invoked when a link of the chosen route is severed. The Localized Query (LQ) is enabled to seek out an alternative partial route by the downstream pivoting node. This operation is possible because of the degree of associativity that is inherent in the chosen route. However, an issue that needs to be addressed here is a trade-off between the time-out period after which the pivoting node gives up searching for alternative partial node and the database of the upstream node of the broken link to queue the incoming packets from the source. One possible solution is to have the upstream node send a signal back to the source, temporarily halting the flow of the data packets until a certain amount of time has passed, after which the route is either re-established or a new route needs to be acquired.         One disadvantage of the ABR is its excessive use of the bandwidth in a BW-limited ad-hoc mobile environment. On the other hand, ABR may be a good candidate when we bring QoS into ad-hoc networks. Because it introduces a sense of stability in choosing a route, that may be desirable for many multimedia-intensive applications. However, in that regard, the classical question remains: how to effectively trade off between time delay, bandwidth utilization, and the guaranteed QoS level.