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Adjacency Persistency in OSPF MANET

5 th China-Ireland International Conference on Information and Communication Technologies CIICT 2010 Wuhan (China), 10-11 October 2010. Adjacency Persistency in OSPF MANET. Juan Antonio Cordero Équipe Hipercom -- INRIA Saclay (France). Adjacency Persistency in OSPF MANET CIICT 2010.

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Adjacency Persistency in OSPF MANET

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  1. 5th China-Ireland International Conference on Information and Communication Technologies CIICT 2010 Wuhan (China), 10-11 October 2010 Adjacency Persistency in OSPF MANET Juan Antonio Cordero Équipe Hipercom -- INRIA Saclay (France)

  2. Adjacency Persistency in OSPF MANET CIICT 2010 Motivation (1) • Link State Routing in Mobile Ad hoc Networks • Same link-state database (LDSB)  Database Synchronization • Distribution of the network topology Topology Flooding • Each node announces (part of) its links Topology Selection  These operations are very costly in MANETs, so they have to be optimized to reduce the set of involved links while preserving the overall routing quality.

  3. Adjacency Persistency in OSPF MANET CIICT 2010 Motivation (and 2) • Open Shortest Path First (OSPF) • Adjacency: links declared as adjacent • synchronize the databases of the endpoints • participate in the flooding of topology information • are advertised in the topology information packets • Three OSPF MANET extensions (standardized by IETF): • MPR-OSPF Multi-Point Relays RFC 5449 • OSPF-MDR MANET Designated Routers RFC 5614 • OR/SP Overlapping Relays / Smart Peering RFC 5820

  4. Adjacency Persistency in OSPF MANET CIICT 2010 MPR - OSPF Multi-Point Relays (MPR) • Idea: Only a subset of 1-hop neighbors of a source (multi-point relays of the source) are necessary to relay a message to every 2-hop neighbor • Different relay selection heuristics are possible, as long as they respect the MPR coverage criterion MPR coverage criterion Every 2-hop neighbor of the source is covered by (at least) one relay

  5. Adjacency Persistency in OSPF MANET CIICT 2010 MPR - OSPF Multi-Point Relays (MPR) • MPR selection depends on the 2-hop neighborhood of the computing source •  • Changes in 2-hop neighbors have an impact on the MPRs •  • MPRs are significantly less stable than average (bidirectional) neighbors

  6. Adjacency Persistency in OSPF MANET CIICT 2010 adjacent (adj. rule) bidirectional (!adj. rule)(bidir.) (bidir.) (!bidir.) non-bidirectional (!bidir.) Adjacency Persistency (1) Non-Persistent Adjacency State Machine • non-persistent adjacencies: • the condition for upgrading a link to the adjacent status is symmetric of the condition for degrading an adjacent link.

  7. Adjacency Persistency in OSPF MANET CIICT 2010 adjacent (!adj. rule)  (bidir.) (adj. rule) bidirectional (bidir.) (!bidir.) (!bidir.) non-bidirectional Adjacency Persistency (and 2) Persistent Adjacency State Machine • persistent adjacencies: • the condition for degrading an adjacent link is stronger than the condition for uploading a link into the adjacent status.

  8. Adjacency Persistency in OSPF MANET CIICT 2010 Configurations Adjacencies Flooding Topology PPM PersistentPersistent Path MPRs PMP Persistent MPR Selectors Persistent PMM Persistent MPR Selectors Path MPRs (RFC 5449) MMM MPRs MPR Selectors Path MPRs (Non-pers.)

  9. Adjacency Persistency in OSPF MANET CIICT 2010 Results (1) Data Delivery Ratio • The non-persistent configuration (MMM) performs significantly worse than the other (partially persistent) configurations • The delivery achieved by current standard RFC 5449 can be improved by implementing persistency also in flooding (PPM) or in topology selection (PMP)

  10. Adjacency Persistency in OSPF MANET CIICT 2010 Results (2) Adjacencies • Persistent adjacencies are far more stable, but persistency increases the size of the adjacent links set.

  11. Adjacency Persistency in OSPF MANET CIICT 2010 Results (and 3) Control Traffic Overhead • Overall, the cost (in overhead) of implementing persistency in flooding (PPM) is more significant than implementing it for topology selection (PMP) • The benefits of flooding persistency are roughly equivalent as those of topology selection persistency • Non-persistent configuration (MMM) generates more overhead than other persistent confs. (PMM and PMP) due to adjacency unstability

  12. Adjacency Persistency in OSPF MANET CIICT 2010 Conclusions • Persistency is an interesting technique for the management of synchronized links (adjacencies, in OSPF terminology) in a link-state routing protocol over an ad hoc network. • This paper analyzes the impact of persistency in 4 different configurations of OSPF based in RFC 5449, each of them implementing persistent approaches for (1) LSDB synchronization, (2) topology information flooding and (3) link advertisement for Shortest Paths computation. • In the OSPF MANET standard RFC 5449, persistent adjacencies improve significantly the overall performance with respect to a non-persistent configuration. • Our results also show that the persistency technique is also beneficial in other operations related to link-state routing, in particular for selection of advertised links for computation of Shortest Paths.

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