Wireless Mobile & Multimedia Networking

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Questions and Answers

In a DSR route discovery process, what event triggers the flooding of a RouteRequest message?

When a source node wants to establish a route (correct)

When a source node updates its routing table

When a destination node receives a data packet

When an intermediate node detects a broken link

Which nodes are responsible for flooding the RouteRequest message in this example?

Only the source node and its immediate neighbors

All intermediate nodes in the network (correct)

Intermediate nodes surrounding the destination node

Only the source and destination nodes

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

A unique identifier for each RouteRequest packet (correct)

The order of the RouteRequests sent

The sequence of data packets received

The number of nodes that forwarded the RREQ

What is indicated by the 'Path' in the RREQ Packet structure?

The sequence of nodes visited during the route discovery Signup and view all the answers

What could cause a delay in the route discovery process in DSR?

Heavy network traffic and collisions Signup and view all the answers

Which of the following is NOT a benefit of the DSR routing protocol?

Complex route management Signup and view all the answers

During the route establishment phase, what role do intermediate nodes play?

They forward RouteRequest messages to other nodes Signup and view all the answers

What is a possible outcome if the RouteRequest message is not successfully flooded?

The discovery process may fail to establish a route Signup and view all the answers

What is a key characteristic of reactive routing protocols?

They only exchange routing information when required. Signup and view all the answers

Which of the following is a feature of Dynamic Source Routing (DSR)?

It eliminates the need for intermediary nodes to know the path. Signup and view all the answers

What initiates the route discovery process in DSR?

The source node. Signup and view all the answers

Which of the following routing protocols is NOT part of the reactive routing protocols listed?

Distance Vector Routing Protocol (DVR) Signup and view all the answers

How does DSR reduce network overhead?

By removing the need for periodic routing. Signup and view all the answers

What is the primary advantage of using source routing in DSR?

The sender knows the complete path without extra overhead. Signup and view all the answers

What is a disadvantage of on-demand routing protocols like DSR?

Latency in discovering routes. Signup and view all the answers

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

To facilitate route discovery for future transmissions. Signup and view all the answers

What issue arises when too many nodes respond to route requests using their local cache?

Route Reply Storm problem Signup and view all the answers

Which method can help mitigate the effects of a route reply storm?

Preventing nodes from sending RREP if another RREP is heard with a shorter route Signup and view all the answers

What can be implemented to further reduce route reply storms?

Randomized delay before sending route replies Signup and view all the answers

What issue does inefficient usage of network bandwidth commonly lead to?

Reduced network throughput Signup and view all the answers

What is a notable consequence of increased contention in network routing?

Collisions between route requests and replies Signup and view all the answers

Study Notes

Wireless Mobile & Multimedia Networking - 7COM1076

Course title: Wireless Mobile & Multimedia Networking
Course code: 7COM1076
Lecturer: Dr Tazeen Syed
Email: [email protected]
Module: Ad-hoc Networks 3

Outline of Dynamic Source Routing (DSR)

Reactive Routing protocol: On-demand routing protocols, implementing path-finding and routing information exchange only when needed.
Dynamic Source Routing (DSR): A reactive routing protocol designed to reduce bandwidth consumption by eliminating periodic updates, instead operating on a source routing basis.
DSR Features:
- On-demand routing protocol
- Designed to restrict bandwidth used by control packets by eliminating periodic updates.
- Operation based on Source Routing.
- Route discovery initiated by the source node.
- Source node knows complete path to the destination.
- Intermediate nodes not required to know full routing path.
- Less network overhead as message exchange is low.
Basic Operations (DSR):
- Route Discovery:
  - Source node initiates by sending RouteRequest (RREQ) packets.
  - Intermediate nodes forward RREQ packets by flooding.
  - Destination node replies with RouteReply (RREP) along the reverse path.
  - RouteRequest (RREQ) packet: a broadcast packet, includes unique ID, source & destination addresses.
  - RouteReply (RREP) packet: a unicast packet from destination containing full path to source.
- Route Cache:
  - Each node maintains a route cache for destination nodes.
  - Route cache used during route construction phase.
  - Intermediate nodes reply to source sending a RouteReply (RREP).
  - Caching routes can impact network performance, especially in dynamic, large, highly mobile environments, with potential for stale routes, increased errors, cache overflow, security vulnerabilities.
- Route Maintenance:
  - When wireless link breaks, a RouteError (RERR) message is sent from the adjacent node to the source.
  - Source node reinitializes route discovery.
  - Nodes remove cached entries receiving the RouteError message.
DSR Route Established: Examples illustrated using diagrams showcasing route discovery and other operations.

DSR Advantages & Disadvantages

Advantages:
- No periodical routing table exchanges.
- Finds routes to only the destination — not all nodes.
- Route cache reduces control overhead & setting up time.
Disadvantages:
- Route maintenance can't locally fix broken links.
- Route cache can become stale.
- Higher route setup delay.
- Routing overhead increases proportionally with path length.
- Packet header size increases with path length.

Further Improvements

Care needed to avoid collisions between route requests & replies from neighbors.
Possible increase in contention if too many replies come back due to nodes replying from their local cache ("reply storm").
Preventing reply storm via:
- A node not sending RREP if it receives another RREP with a shorter route.
- Randomizing reply delay times.

References

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

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Description

This quiz covers the Dynamic Source Routing (DSR) protocol within the context of Wireless Mobile & Multimedia Networking. You will explore key features, benefits, and the operational mechanics of DSR as a reactive routing protocol. Ideal for students studying ad-hoc networks, this quiz will test your understanding of source routing and its impact on bandwidth consumption.