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Internet Networking recitation #6

Detailed overview of MANETs, TBRPF protocol, dynamic topology challenges, LSP dissemination, neighbor discovery, key modules & topology-based routing. Examples and in-depth explanations included.

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Internet Networking recitation #6

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  1. Internet Networkingrecitation #6 Mobile Ad-Hoc Networks TBRPF Spring Semester 2009, Dept. of Computer Science, Technion

  2. Mobile Ad-Hoc Networks (MANET) - Reminder • Wireless networks become an important part of the computers communication both globally and locally. • Ad-hoc networks are useful for providing communication support where no fixed infrastructure exists or the deployment of a fixed infrastructure is not economically profitable. • Ad-hoc networks consists of: • Mobile hosts • Non fixed communication infrastructure • No base station or any central entity which can follow the locations of the nodes. • Each host performs also the role of a router. • Multi-hop network. Internet Networking

  3. Main issues in MANET routing • Dynamic topology “by nature” of the network due to high mobility. • Changes in wired networks topology may happen every few hours while the mobility of Ad-Hoc networks cause topology changes much often. • No fixed infrastructure. • Lower bandwidth than in wired networks. This example shows that topology tables are changed often 2 2 After 10 seconds 3 1 1 3 s s D D 4 4 1 Km Internet Networking

  4. MANET Routing Protocols Demand-driven Vs. Table-driven Internet Networking

  5. The Link State Routing Problem • Based on a ‘Distributed Map’ concept • Each router builds a new LSP for every change in its neighbors group and send it to all of its neighbors. • Then – each of them builds a new LSP….. • In MANET – each node is a router • Changes occur very often • Bandwidth is limited • OSPF alike algorithm is not possible Internet Networking

  6. Topology-Based Reverse Path Forwarding (TBRPF) • A proactive, link-state routing protocol • Provides hop-by-hop routing along shortest paths to each destination. • Each node, using a Dijkstra's alike algorithm, computes a source tree that is based on partial topology information stored in a topology table • The Source Tree provides the shortest paths to all reachable nodes • LSP Dissemination is sent over ‘Source Trees’ • A combination of periodic and differential updates is used to keep all neighbors informed Internet Networking

  7. TBRPF (Cont.) • Consists of two modules • Neighbor Discovery Module • LSP Dissemination Module (“routing module”) • Neighbor Discovery • Done by using HELLO messages from all neighbors • Dissemination Module • performs topology discovery and route computation. Internet Networking

  8. Neighbor Discovery Module (I) • Allows each node i to quickly detect the neighbor nodes j, those with a bidirectional link between them (1-hop). • Quickly detects when a bidirectional link breaks or becomes unidirectional. • Uses small HELLO messages • reports only differential changes in the status of links. • results in much smaller HELLO messages • that can be sent more frequently • allows faster detection of topology changes. Internet Networking

  9. Neighbor Discovery Module (II) • Each MANET node can have multiple interfaces • both wireless and wired (e.g., Ethernet or point-to-point) • Nodes with multiple interfaces run Neighbor Discovery separately on each interface. • Thus, neighbor tables are maintained for each local interface • a HELLO sent on a particular interface contains only information regarding neighbors heard on that interface. • Each Topology Update message (used by the Routing Module over Hellos) is sent on all interfaces • Neighbor tables store state information for each link (i,j) between interface i and a neighbor interface j. • based on HELLO messages received on interface i (and possibly on link-layer notifications). Internet Networking

  10. Neighbor Discovery Module – HELLO Messages • Each TBRPF node must send at least one HELLO message per HELLO_INTERVAL. • A message contains a current HELLO sequence number (HSEQ) • incremented with each transmitted HELLO. • When link (i,j) status changes, typically 3 consecutive HELLOs are sent on its interface (i) • To ensure that node j will either receive one of them • Otherwise it declares this link as lost. • To avoid establishing a short-live link, node i must receive at least 2 of the last 3 HELLOs sent from a neighbor interface j. Internet Networking

  11. LSP Dissemination Module • Each node maintains a source tree (T) which provides shortest paths to all reachable nodes. • Each node computes and updates its source tree based on partial topology information stored in its topology table. Internet Networking

  12. Topology Graph Links • A link (u,v) is in the Topology Graph only if it is on the shortest path from next hop p(u) to node u. • Example: link (R2,R1) is on the shortest path from R2 to node S • Thus, R2 is included in R1 source tree of S • R1 is the Parent of R2 • It calculates that R2 is its child using neighbor discovery data U S D R1 v R3 Shortest Path from D to S u R2 P(U) Internet Networking

  13. The Reported Subtree • RT includes node i’s links to its neighbors • Example for R1 – R4,R5,R6,R7 • Also includes a branch rooted at neighbor j if node i is the next hop of some neighbor to reach j. • Example for R1 – the branch of S • When there are multiple min-hop paths, the one with the least node ID is used. • How R1 knows that it is not on the shortest path of R4? • R1 computes the shortest paths, up to 2 hops, from each neighbor to each other neighbor, using only neighbors (or itself) as an intermediate node S R4 D R1 R6 R3 R7 R5 Internet Networking Shortest Path from D to S

  14. Example of reportable subtrees Node 2and 6 have the same Min-Hop count to 7. Node 2 becomes a parent since it has the smallest ID. 9 6 7 8 5 4 2 3 1 13 12 11 Node 2’s reportable subtree (those it is on the shortest path from all to 7 + neighbors) 15 14 Node 6’s reportable subtree (only its neighbors) Internet Networking

  15. Example of a dissemination route of RT1 • Node 2 Receives information from nodes 1,6,7,3,11 • It stores and processes the information of nodes: 1,6,7,3,11 and 8,4,12,14 (up to 2 hops count) that it receives from it’s neighbors • It has a Min-Hop count to Node 7. • Node 2 becomes a parent of RT(7) for its neighbors • Send a message towards Nodes 3,6,1,7,11 9 6 7 8 5 4 2 3 1 13 12 11 15 14 Internet Networking

  16. Example (Cont.) • Now - Node 3 is on the shortest path to Node 1. • Node 3 becomes a parent of RT(7) for its neighbors • Send a message towards Nodes 8,4,12 • The message is not sent from Node 3 to Node 6 for example • Now - Node 4 is on the shortest path to Node 1. • Node 4 becomes a parent of RT(1) of its neighbors • Send a message towards Nodes 9,5,13 9 6 7 8 5 4 2 3 1 13 12 11 15 14 Internet Networking

  17. Example (Cont.) • Now - Node 5 knows that via node 4, it can reach Node 1 and that Node 4 is a neighbor of 9,3,13. • Note - Node 11 and Node 3 have the same Min-Hop count to Node 2. • Thus, Node 3 is chosen (lower ID) • Thus, Node 12 is reported by Node 3 and not Node 11 9 6 7 8 4 5 2 3 1 13 12 11 15 14 Internet Networking

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