Wireless Mobile & Multimedia Networking - Ad-hoc Networks 3
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What is a primary concern regarding route reply storms in wireless networks?

  • Increased contention from too many route replies. (correct)
  • Improper routing algorithms being used.
  • Too few nodes responding to route requests.
  • Inadequate network bandwidth available.

    • How can the route reply storm problem be eased?

  • By allowing all nodes to respond simultaneously.
  • By randomizing the delay time before sending route replies. (correct)
  • By using a central coordinator to manage responses.
  • By reducing the number of nodes in the network.

    • What action can a node take if it hears another RREP with a shorter route?

  • Ignore it and send its own RREP anyway.
  • Immediately propagate another route request.
  • Withdraw its previous route request.
  • Prevent itself from sending a RREP. (correct)

    • What is a consequence of inefficient usage of network bandwidth?

    <p>Higher likelihood of route reply storms.</p> Signup and view all the answers

    Which method is NOT mentioned as a way to prevent route reply storms?

    <p>Using shorter routes.</p> Signup and view all the answers

    What is the main characteristic of reactive routing protocols?

    <p>They only initiate routing processes when a path is needed.</p> Signup and view all the answers

    What is a feature of the Dynamic Source Routing (DSR) protocol?

    <p>The sender knows the complete path to the destination.</p> Signup and view all the answers

    Which process is initiated by the source node in DSR?

    <p>Route Discovery</p> Signup and view all the answers

    How does DSR minimize network overhead?

    <p>By eliminating periodic routing updates.</p> Signup and view all the answers

    What is one of the disadvantages of DSR?

    <p>Limited scalability in large networks.</p> Signup and view all the answers

    What does the 'route cache' feature in DSR facilitate?

    <p>Minimizing message exchanges by storing routes.</p> Signup and view all the answers

    What is a primary operation of the Dynamic Source Routing protocol?

    <p>Route Discovery</p> Signup and view all the answers

    What is the purpose of the Route Discovery phase in DSR?

    <p>To establish a route from the source node to the destination node</p> Signup and view all the answers

    Which of the following is NOT an existing on-demand routing protocol?

    <p>Static Route Algorithm (SRA)</p> Signup and view all the answers

    Which node performs the initial action in the Route Discovery process?

    <p>Source node</p> Signup and view all the answers

    What do intermediate nodes do upon receiving a RouteRequest (RREQ) packet?

    <p>Rebroadcast it to neighbouring nodes if conditions are met</p> Signup and view all the answers

    What is included in a RouteRequest (RREQ) packet?

    <p>A unique ID field generated by the source node</p> Signup and view all the answers

    When does a destination node respond with a RouteReply (RREP)?

    <p>When it receives a RouteRequest packet from the source node</p> Signup and view all the answers

    What feature is used in RouteRequest packets to prevent loop formation?

    <p>Unique ID field/sequence number</p> Signup and view all the answers

    What type of packet is sent by the destination node back to the source node?

    <p>RouteReply (RREP) packet</p> Signup and view all the answers

    Which of the following is NOT an operation of DSR?

    <p>Route Optimization</p> Signup and view all the answers

    What is the primary purpose of flooding RouteRequest messages in the DSR protocol?

    <p>To establish routes in a network</p> Signup and view all the answers

    In the example shown, which nodes are responsible for flooding the RouteRequest message in the first instance?

    <p>Intermediate nodes 2, 6, and 7</p> Signup and view all the answers

    What does the 'Seq No.' in the RREQ Packet represent?

    <p>The identifying number of the RouteRequest</p> Signup and view all the answers

    Which nodes are indicated in the path of the RREQ Packet from node 9?

    <p>1, 7, 9, 12</p> Signup and view all the answers

    What happens after intermediate nodes flood the RouteRequest message in a DSR protocol?

    <p>The destination node sends its route replies.</p> Signup and view all the answers

    Upon receiving multiple RouteRequest messages, how does the destination node typically respond?

    <p>By sending a single RouteReply back</p> Signup and view all the answers

    What is the primary purpose of a route cache in DSR?

    <p>To store routes for destination nodes</p> Signup and view all the answers

    What does the 'Path' field in the RREQ Packet represent?

    <p>The sequence of nodes traversed</p> Signup and view all the answers

    Why might nodes 10 and 11 flood RouteRequest messages?

    <p>To find a route to the destination</p> Signup and view all the answers

    What effect can caching routes have on network performance?

    <p>It can lead to stale routes and increased route errors</p> Signup and view all the answers

    What happens when a wireless link is broken in DSR?

    <p>A RouteError (RERR) message is generated</p> Signup and view all the answers

    During route maintenance, what action is taken by intermediate nodes upon receiving a RouteError message?

    <p>They remove cached entries that are related to the broken link</p> Signup and view all the answers

    What does the source node do when it receives a RouteError message?

    <p>It starts the route discovery procedure again</p> Signup and view all the answers

    Which of the following is a potential issue caused by route caches in DSR?

    <p>Cached routes may become stale</p> Signup and view all the answers

    What role does the RouteRequest (RREQ) message play in DSR route discovery?

    <p>It floods the network with route discovery requests</p> Signup and view all the answers

    Which of the following is NOT a potential drawback of route caching in DSR?

    <p>Increased route discovery speed</p> Signup and view all the answers

    What does Node 14 do to initiate communication with Node 12?

    <p>It floods a RouteRequest message.</p> Signup and view all the answers

    What happens when the link between Node 8 and Node 11 is broken?

    <p>Node 8 sends a RouteError message to source Node 1.</p> Signup and view all the answers

    What is one advantage of using DSR routing protocol?

    <p>It reduces control overhead and route setting time.</p> Signup and view all the answers

    Which of the following is a disadvantage of the DSR routing protocol?

    <p>Route maintenance does not repair a broken link locally.</p> Signup and view all the answers

    What happens regarding routing overhead as the path length increases in DSR?

    <p>Routing overhead is proportional to the path length.</p> Signup and view all the answers

    What is a consequence of a stale route cache in DSR?

    <p>It may lead to incorrect routing decisions.</p> Signup and view all the answers

    What process does Node 1 undertake after receiving a RouteError message?

    <p>It re-discovers a route to the destination node.</p> Signup and view all the answers

    What effect does an increase in network size have on the path in a DSR protocol?

    <p>It increases the path length.</p> Signup and view all the answers

    Study Notes

    Wireless Mobile & Multimedia Networking

    • Course code: 7COM1076
    • Lecturer: Dr Tazeen Syed
    • Ad-hoc Networks 3

    Outline

    • Reactive Routing protocol
    • Dynamic Source Routing (DSR)
      • DSR Features
        • Basic operations
          • Route Discovery
          • Route Cache
          • Route Maintenance
      • DSR Routing Establishment
      • DSR Reply
      • DSR Route Maintenance
      • Advantages & Disadvantages
      • Further Improvement

    Reactive Routing Protocols

    • On-demand routing protocols, also known as on-demand routing protocols.
    • Execute the path-finding process and exchange routing information only when a path is required.
    • No periodic routing updates or exchange of routing information.
    • Examples include:
      • Dynamic Source Routing Protocol (DSR)
      • Ad hoc On-demand Distance-Vector Routing Protocol (AODV)
      • Temporally Ordered Routing Algorithm (TORA)
      • Location-Aided Routing (LAR)
      • Signal Stability-Based Adaptive Routing protocol (SSA)

    Dynamic Source (DSR) Routing Protocol

    • On-demand routing protocol
    • Designed to reduce bandwidth used by control packets by eliminating periodic routing updates.
    • Operation is based on Source Routing.
    • Route discovery begins at the source node.
    • The source node knows the full path to the destination.
    • Intermediate nodes are not required to know the full routing path.
    • Low network overhead due to the reduced message exchange between nodes.

    Basic Operations – DSR

    • The basic operations of DSR include:
      • Route Discovery
      • Route Cache
      • Route Maintenance

    Basic operation – DSR (cont.)

    • Route Discovery starts when a source node wishes to send data to a destination node.
      • Source Node:
        • Initializes and sends RouteRequest (RREQ) packets to the network as it has no prior route information.
      • Intermediate Nodes:
        • Forward RouteRequest packets to the network by flooding.
        • Upon receiving the RouteRequest packet, intermediate nodes rebroadcast only to neighboring nodes if the packet has not already been forwarded and the receiving node is not the destination node and the time to live has not expired.
        • Use a source-sequenced number in the RouteRequest to prevent loop formation and avoid redundant forwarding.
      • Destination Node:
        • Sends a RouteReply (RREP) back to the source node using the reverse path of the RouteRequest packet.

    Basic Operation - DSR (cont.) - Route Discovery

    • Route Request (RREQ) Packet
      • Broadcast packet throughout the network
      • Includes unique ID field/sequence number from the source node.
      • Contains source and destination addresses.
    • Route Reply (RREP) Packet
      • Unicast packet sent by the destination node to the source node.
      • Contains the complete path from source to destination.

    Basic operation – DSR (cont.) - Route Caches

    • Each node maintains a route cache that stores routes for destination nodes.
    • The route cache is used during the route construction phase.
    • Intermediate nodes can reply to the source node by sending a RouteReply (RREP) packet containing the cached route information.
    • Benefits:
    • Disadvantages:

    Basic operation – DSR (cont.) - Route Maintenance

    • If a wireless link is broken, a RouteError (RERR) message is generated by the adjacent node.
    • The source node re-initializes the route discovery procedure, and cache entries are removed upon receiving the RouteError.

    DSR Route Established – Route Discovery

    • Examples are shown of the route discovery process unfolding over multiple steps as RouteRequest (RREP) packets are flooded throughout the network until a RouteReply (RREP) reaches the source node.

    DSR Route Established – Route Reply

    • Destination node sending back a RouteReply (RREP)
      • RouteReply includes the route.
      • It is sent in the reverse direction of the original RouteRequest.
      • Unidirectional links need a route discovery from the destination to the source (piggybacking RouteRequest on RouteReply).

    DSR Route Establishment – Route Cache

    • Example of a node sending a RouteRequest message.

    DSR Route Maintenance (cont.)

    • Examples of the route maintenance process where a link is broken, and a RouteError message is sent back to the source.
    • Steps taken by node 1 to rediscover the route to destination node 12

    DSR Advantages & Disadvantages

    • Advantages
      • No need for periodic exchange of routing tables.
      • Finds routes only to the destination.
      • Route caching reduces overhead and setup time.
    • Disadvantages
      • Route maintenance does not repair broken links locally.
      • Route cache may become stale.
      • High route setup delay; routing overhead is proportional to path length
      • Packet header size increases with path length.

    Further Improvements

    • Care must be taken to avoid collisions between route requests and route replies.
    • Increased contention if too many route replies come back due to nodes replying using their local cache
    • Route Reply Storm Problem
      • Reply storm may be mitigated by preventing a node from sending RREP if an identically shorter route packet is received.
      • Route reply storms are also avoided by randomizing delay time before sending route replies.

    References

    • Ad Hoc Wireless Networks, architectures and protocols. C. Siva Ram Murthy and B. S. Manoj, 1st edition. Sections 7.5.1

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    Ad-Hoc Networks 3 PDF

    Description

    This quiz covers Ad-hoc Networks focusing on Reactive Routing Protocols, particularly the Dynamic Source Routing (DSR) protocol. Participants will explore DSR features, operations, routing establishment, and its advantages and disadvantages. Test your understanding of on-demand routing protocols and their applicability in mobile and multimedia networking.

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