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Wireless Networks Routing. 國立屏東教育大學 資訊科學系 王朱福 教授. Outlines. Wireless networks architectures Routing protocols for wireless networks Mobile ad-hoc Networks (MANETs) Wireless Sensor Networks (WSNs) Vehicle ad-hoc networks (VANETs). Wireless Communications.

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Wireless Networks Routing


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    1. Wireless Networks Routing 國立屏東教育大學 資訊科學系 王朱福 教授

    2. Outlines • Wireless networks architectures • Routing protocols for wireless networks • Mobile ad-hoc Networks (MANETs) • Wireless Sensor Networks (WSNs) • Vehicle ad-hoc networks (VANETs)

    3. Wireless Communications • Wireless networks use radio frequency channels as their physical medium for communications. • Each node in the network broadcast information which can be received by all nodes within its direct transmission range.

    4. Wireless network architectures • Infrastructure-based wireless networks • Fixed base stations / access points are used. • Infrastructure-less wireless networks (Ad-hoc networks) • No fixed infrastructure support are available. • Hybrid wireless networking architecture

    5. Wireless network architectures (cont.) • Infrastructure-based wireless networks • Uses fixed base stations / access points which are responsible for coordinating communication between the hosts. • Single-hop communication

    6. Wireless network architectures (cont.) • Ad-hoc networks • Consists of nodes which communicate with each other through wireless medium without any fixed infrastructure. • Multi-hop communications

    7. Properties of ad-hoc networks • No pre-build infrastructure • All nodes are wireless capable • Base stations are not necessary • Ease of deployment • Quickly deploy

    8. Some emerging types of wireless networks • MANETs (Mobile Ad-hoc Networks) • WSNs (Wireless Sensor Networks) • VANET (Vehicle Ad-hoc Networks) • WMN (Wireless Mesh Networks) • …

    9. Routing protocols for wireless networks – MANETs • A dynamically reconfigurable ad-hoc network. • Main issues in the design and operation of MANETs. • (1) MANETs are more unstable than wired-networks because of the lack of a centralized entity.

    10. Routing protocols for wireless networks – MANETs (cont.) (2) Mobility will cause network topology to change, which results in a great change in connection between two hosts. (3) The connectivity between network nodes is not guaranteed, so intermittent connectivity is common.

    11. The main routing problems for MANETs 8 10 9 7 4 6 Node mobility  Routing path broken frequently 2 3 5 1

    12. Traditional ad-hoc routing protocols

    13. Routing protocols for MANETs • Flooding-type routing protocol (flooding) • Table-driven routing protocol (proactive) • On-demand routing protocol (reactive) • Hybrid routing protocol

    14. 11 1 4 3 2 7 16 6 15 12 10 9 8 20 19 18 17 14 13 Flooding-type routing protocol (Flooding)

    15. Flooding-type routing protocol (Flooding) • Advantage: They do not need to maintain network topology, or is looking for data transmission path, so they can quickly transfer information. • Disadvantage: Node receives information after, must repeat broadcast, making it fast consumes its battery energy, and produces broadcast storm.

    16. Routing protocols for MANETs (cont.) • Table-driven routing protocol (proactive): • They maintain the global topology information in the form of tables at every node. • These tables are updated frequently in order to maintain consistent and accurate network state information. • For example, DSDV, WRP, and STAR.

    17. Table-driven routing protocol—Destination Sequenced Distance Vector routing (DSDV) • The DSDV routing protocol is an enhanced version of the distributed Bellman-Ford algorithm where each node maintain a table that contain the shortest distance and the first node on the shortest path to every other node in the network.

    18. Table-driven routing protocol – DSDV (cont.) Example: Routing table for Node 1 15 14 13 11 12 9 10 8 6 4 7 5 3 1 2

    19. Table-driven routing protocol – DSDV (cont.) • Each node, upon receiving an update, quickly disseminates it to its neighbors in order to propagate the broken-link information to the whole network. Thus a single link break leads to the propagation of table update information to the whole network.

    20. Table-driven routing protocol – DSDV (cont.) Routing table for Node 1 15 14 13 11 12 10 8 9 6 4 7 5 3 1 2

    21. Table-driven routing protocol – DSDV (cont.) • Advantage: It can be applied to MANETs with few modifications. The updates are propagated throughout the network in order to maintain an up-to-date view of the network topology at all the nodes.

    22. Table-driven routing protocol – DSDV (cont.) • Disadvantage: • (1) The DSDV suffers from excessive control overhead that is proportional to the number of nodes in the network and therefore is not scalable in MANETs, which have limited bandwidth and whose topologies are highly dynamic.

    23. Table-driven routing protocol – DSDV (cont.) • (2) In order to obtain information about a particular destination node, a node has to wait for a table update message initiated by the same destination node. This delay could result in stale routing information at nodes.

    24. Routing protocols for MANETs (cont.) • On-demand routing protocol (reactive): • They execute the path-finding process and exchange routing information only when a path is required by a node to communicate with a destination. • For example, AODV and DSR.

    25. On-demand routing protocol – Ah-hoc On-demand Distance-Vector Routing Protocol (AODV) • AODV, a route is established only when it is required by a source node for transmitting data packets. • In AODV, the source node and intermediate nodes store the next-hop information corresponding to each flow for data packet transmission.

    26. On-demand routing protocol – AODV (cont.) • The major difference between AODV and other on-demand routing protocol is that it uses a destination sequence number ( DestSeqNum) to determine an up-to-date path to the destination. • A node updates its path information only if the DestSeqNum of the current packet received is greater than the last DestSeqNum stored at the node.

    27. On-demand routing protocol – AODV (cont.) • AODV utilizes routing tables to store routing information. • The routing table stores:

    28. The AODV routing procedure 1. If a node wants to send a packet to some destination. At first, it checks its routing table to determine whether it has a current route to the destination or not. =>If yes, it forwards the packet to next hop node of the route. =>If no, it initiates a route discovery process.

    29. The AODV routing procedure (cont.) • The Route discovery process: • It begins with the creation of a RouteRequest (RREQ) packet. Broadcasting is done via flooding. • Broadcast ID gets incremented each time a source node uses RREQ. • Broadcast ID and source IP address form a unique identifier for the RREQ. RREQ packet format

    30. The AODV routing procedure (cont.) 2. Sender S broadcasts a RREQ to all its neighbors, each node receiving RREQ forwards RREQ to its neighbors. *Sequence numbers help to avoid the possibility of forwarding the same packet more than once. 3. An intermediate node (not the destination) may also send a RouteReply (RREP) packetprovided that it knows a more recent path than the one previously known to sender S. RREP packet format

    31. The AODV routing procedure (cont.) • 4. As an intermediate node receives the RREP packet, it sets up a forward path entry to the destination in its routing table. • 5. The source node can begin data transmission upon receiving the first RREP.

    32. Illustration of route establishment in AODV • 1. Node S needs a routing path to node D. • 2. Node S creates a RREQ packet RREQ [D’s IP addr, seq#, S’s IP addr, seq#, hopcount] • Node S broadcasts RREQ to its neighbors. B RREQ{D, D’seq, S, S’seq, 0} S A D C

    33. Illustration of route establishment in AODV (cont.) • 2. Node A rebroadcasts RREQ to all its neighbors. B RREQ{D, D’seq, S, S’seq, 1} S A D RREQ{D, D’seq, S, S’seq, 1} C

    34. Illustration of route establishment in AODV (cont.) • 3. Since, node C known a route to D. • Node C creates a RREP packet and unicasts RREP to A. • Set forward path in node C’s routing table. B S A RREP{D, D’seq, S, S’seq, 1} D C

    35. Illustration of route establishment in AODV (cont.) • 3. Node A creates a RREP packet and unicasts RREP to S. • 4. Set forward path in node A’s routing table. B S A D RREP{D, D’seq, S, S’seq, 2} C

    36. Illustration of route establishment in AODV (cont.) • 4. Set forward path in node S’s routing table. B S A D C

    37. Route maintenance in AODV (Path broken due to host mobility) 1. If intermediate nodes or the destination move. The next hop links break. Routing tables are updated for the link failures. All active neighbors are informed by RouteError (RRER) packet. 2. When a source node receives an RRER, it can reinitiate the route discovery process. 3. It can be also dealt with by a local fix scheme.

    38. Illustration of route maintenance in AODV • Assume link between C and D breaks. • Node C invalidates route to D in route table. • Node C creates RRER packet and sends to its upstream neighbors. • Node A sends RRER to S. • Node S rediscovers route if still needed. B RRER S A RRER D C

    39. On-demand routing protocol – AODV (cont.) • Advantage: • The routes are established on demand and the destination sequence number can find the latest route to the destination. • Disadvantage: • The intermediate nodes can lead to inconsistent routes if the source sequence number is very old. • The periodic beaconing leads to unnecessary bandwidth consumption.

    40. On-demand routing protocol – Dynamic Source Routing Protocol (DSR) • DSR designed to restrict the bandwidth consumed by control packets in ad hoc wireless networks by eliminating the periodic table-update messages required in the table-driven approach.

    41. 7 2 5 8 1 3 6 4 Route Discovery (broadcasting the RREQ packets) <1,2> <1,3,5,7> <1,3,5> <1> Destination <1> <1,3> Source <1,4,6> <1> <1,4>

    42. 7 2 5 8 1 3 6 4 Route Discovery (cont.) (propagating the RREP packets back to source) <1,3,5, 7> <1,3,5, 7> <1,3,5, 7> <1,3,5, 7> <1,3,5, 7> Destination <1,3,5, 7> Source <1,4,6> <1,4,6> <1,4,6>

    43. Hybrid routing protocol –Zone Routing Protocol (ZRP) • A hybrid routing protocol which effectively combines the best features of both proactive and reactive routing protocols. • The key concept employed in ZRP is to use a proactive routing scheme within a limited zone in the γ-hop neighborhood of every node, and use a reactive routing scheme for nodes beyond this zone.

    44. Routing zone for node 8 in ZRP 15 14 13 11 12 10 8 9 6 7 4 5 Routing Zone with Radius = 1 3 1 2 Routing Zone with Radius = 2 Routing Zone for Node 8

    45. Performing the Proactive Routing for node 8 (destination=node 16) 15 14 13 11 12 16 8 10 9 4 6 RouteRequest 7 5 RouteReply 3 2 1 Routing Zone with Radius = 2 Routing Zone for Node8

    46. Hybrid routing protocol – ZRP (cont.) • Advantage: • By combining the best features of proactive and reactive routing schemes, ZRP reduces the control overhead. • Disadvantage: • But in the absence of a query control, ZRP tends to produce higher control overhead than the previously schemes.

    47. Other routing issue for MANET –The Intermittent connected routing problem • In case of the nodes density of a MANET is sparse, it will cause the intermittent connected routing problem, and consequently the traditional routing protocols will be no longer fit.

    48. Intermittent connected routing problem

    49. Epidemic routing protocol • Epidemic is a simple routing protocol to resolve the intermittent connected routing problem. • The nodes adopt store-carry-forward communication scheme. • A node can carry the messages in its cache if no any direct routing path to the destination is available. • If a node moves into the node’s transmission range, they will exchange the carried messages between them.

    50. S 3 5 2 4 1 (Epidemic routing)