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Ad Hoc Networks Routing. Addendum . Instructor: Carlos Pomalaza-Ráez Fall 2003 University of Oulu, Finland. Hierarchical Routing Protocols. Traditional option when the network has a large number of nodes

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Ad Hoc Networks Routing


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    1. Ad Hoc Networks Routing Addendum Instructor: Carlos Pomalaza-RáezFall 2003University of Oulu, Finland

    2. Hierarchical Routing Protocols • Traditional option when the network has a large number of nodes • Common table-driven protocols and on-demand protocols are for flat topologies and thus have a scalability problem when the network is large • For table-driven protocols there is high volume of overhead transmissions • For on-demand protocols there is large discovery latency • The experience gained in wired networks suggests the use of a hierarchical structure to address the scalability problem • The use of hierarchical routing protocol in ad-hoc networks reduces overhead traffic and discovery latency but it has drawbacks such as: • Suboptimal routes • Complex management of the network hierarchical structure due to its dynamic nature

    3. Basic Hierarchical Approach The basic idea is to divide the network into cluster or domains

    4. Basic Hierarchical Approach • The mobile nodes are grouped into regions • Regions are grouped into super-regions, and so on. • A specific mobile host is chosen as the clusterhead for each region. • Hierarchical routing • Mobile nodes know how to route packets to their destination within its own region, but do not know the route outside of its own region • Clusterheads know how to reach other regions

    5. Fisheye State Routing (FSR) • The “eye” of the fish captures with high detail the points near the focal point • As the distance from the focal point increases less details are captured • For routing this approach translates into an accurate information in the immediate neighborhood of a node and less detail as the distance increases • FSR is similar to link state (LS) routing in that each node maintains a view of the network topology with a cost for each link • In LS routing link state packets are flooded into the network whenever a node detects a topology change • In FSR nodes maintain a link state table based on the up-to-date information received from neighboring nodes and periodically exchange it with their local neighbors • For large networks in order to reduce the size of the routing update messages the FSR technique uses different exchange periods for different entries in the routing table • Relative to each node the network is divided in different scopes

    6. Scopes of FSR 33 3 8 9 5 1 2 4 10 7 13 18 12 14 19 6 21 11 22 15 36 23 16 17 20 29 35 24 27 25 26 28 34 30 32 1 hop 31 2 hops 3 or more hops

    7. Message Reduction in FSR LST HOP 0 LST HOP 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 1 0 1 1 2 2 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 1 2 0 1 2 1 3 LST HOP Entries in black are exchanged more frequently 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 2 1 1 0 1 2 4 5

    8. FSR - Summary • Routing table entries for a given destination are updated, i.e. exchanged with the neighbors, with progressively lower frequency as distance to destination increases • The further away the destination, the less accurate the route • As a packet approaches destination, the route becomes progressively more accurate • Benefits • Scales well to large network sizes • Control traffic overhead is manageable • Problems • Route table size still grows linearly with network size • As mobility increases routes to remote destinations become less accurate