Wireless Mobile Networking - Ad-hoc Networks 2

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Questions and Answers

What is the main disadvantage of DSDV in terms of route updates?

It necessitates a full dump update periodically. (correct)

It requires a constant connection to function properly.

It can only operate in small static networks.

It relies on a single node for updating routes.

How does DSDV handle link breakage in a network?

By broadcasting the link breakage to neighboring nodes. (correct)

By assuming that the link is still active.

By establishing a new route immediately.

By ignoring the link breakage until the next update cycle.

In what type of network is DSDV most effective?

Network environments with high bandwidth requirements.

Static wireless networks without mobility.

Ad-hoc networks with small populations of mobile nodes. (correct)

Large-scale enterprise networks with fixed nodes.

What happens when the topology of a network changes in DSDV?

The network becomes unstable until updates propagate. Signup and view all the answers

What is a characteristic of DSDV's approach to connectivity information?

It requires periodic updates throughout the network. Signup and view all the answers

What is a key characteristic of Table Driven/Proactive Routing protocols?

They maintain the global topology information in the form of tables in every node. Signup and view all the answers

What problem is associated with the DSDV routing protocol?

Count to infinity problem. Signup and view all the answers

How are routing tables established in the DSDV protocol?

They are populated through a sequence of route advertisement messages. Signup and view all the answers

What occurs during DSDV route maintenance?

Link breakages are managed by sending immediate update messages. Signup and view all the answers

Which statement best describes DSDV's use of sequence numbers?

They are utilized to prevent routing loops and ensure fresh routes. Signup and view all the answers

What action does node D take upon its arrival in the network?

Node D broadcasts its existence. Signup and view all the answers

How does node C respond when it detects the link breakage involving node D?

It sets the distance to node D as infinity. Signup and view all the answers

What should node C do when it receives an out-of-date full dump from node B?

Ignore node B's dump and keep its current sequence number. Signup and view all the answers

Which node initiates the full dump process upon learning of the new node D?

Node C broadcasts the full dump immediately. Signup and view all the answers

Which of the following statements accurately describes the sequence number function in DSDV?

Higher sequence numbers indicate more recent information. Signup and view all the answers

Study Notes

Wireless Mobile & Multimedia Networking

Course code: 7COM1076
Lecturer: Dr Tazeen Syed
Email: [email protected]
Institution: University of Hertfordshire

Ad-hoc Networks 2 - Outline

Table Driven Routing protocol (DSDV)
- Count to infinity Problem
- Basic operations
- Routing table Structure
- Sequence Number
- Route Advertisement
- Route Updating
- DSDV Routing Establishment
  - Building routing tables
  - Adding new node
- DSDV Route Maintenance
  - Link Breakage
- Stability and Scalability

Table Driven/Proactive Routing Protocols

Extensions of wired network routing protocols
Maintain global topology information in tables in each node
Tables updated frequently to maintain network state
Examples:
- Destination Sequenced Distance-Vector (DSDV)
- Wireless Routing protocol (WRP)
- Source-tree Adaptive Routing Protocol (STAR)
- Cluster-Head Gateway Switch Routing Protocol (CGSR)

DSDV Routing Protocol

Enhanced version of Bellman-Ford routing protocol
Loop-free
Tags each routing table entry with a destination sequence number
Faster convergence
Makes immediate route advertisement on significant changes in routing tables, but waits with advertising unstable routes.
Counters the count-to-infinity problem

Basic Operation - DSDV

Each node maintains routing information for all known destinations
Routing information must be updated periodically
Traffic overhead remains even if network topology doesn't change
Routes are exchanged between neighbors to keep updated view of network topology
Routes available to all destinations on all nodes
Updates are initiated by a destination
Sequence number is always greater than previous one

Count-to-Infinity Problem

A network issue where routing loops can occur
A temporary loss of connectivity can lead to incorrect route information
Routing tables adjust incorrect values of distance

Routing Table Structure

Contains destination, next node, distance, and sequence number entries
Dest: Destination node
NextNode: Node to reach the destination
Dist: Distance to reach destination
SeqNo: Sequence number from destination node

Use of Sequence Number

Destination sequenced
Sender increases its destination sequence number (even numbers only) on each advertisement
If a node is not reachable (timeout), increase the sequence number by 1 (odd number) and set metric to ∞
Ensures efficient, fresh, & accurate routing

Route Advertisement

Routing information in tables is transmitted by broadcast
Route advertisement is performed periodically or immediately if topology change detected
Two types of advertisement:
- Full dump: all changed information since the last full dump
- Incremental update: all changes since the last dump

Route Updating

Rules:
- Choose the route entry with the highest sequence number
- If sequence numbers are equal, choose the route with the smaller metric

DSDV Route Establishment & Maintenance

Example of building routing tables (1-4)
- Illustrates initial states and updates as nodes are added/removed and routes change

DSDV Route Establishment & Maintenance - New Node (1-3)

Examples illustrating updating routing tables when new nodes enter the network

DSDV Route Establishment & Maintenance - Example of Link Breakage (1-3)

Shows how routing tables are updated with link failure/breakage

DSDV Route Establishment & Maintenance - Example of Link Breakage (4)

Shows updates when link breakage occurs that are advertised to a node

Stability and Scalability

DSDV requires full dump updates, inefficient in route updates
Unstable when network topology changes
Effective in small-scale mobile ad-hoc networks
A brute-force approach with connection information requiring frequent updates

References

"Ad Hoc Wireless Networks" by C. Siva Ram Murthy and B. S. Manoj (1st edition)
Sections 7.1, 7.2, 7.3, 7.4.1
RFC 2501
Online RFC

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Description

This quiz covers the fundamental aspects of Ad-hoc Networks, focusing on the Table Driven Routing protocol (DSDV). It explores key concepts such as routing table structure, route maintenance, and the stability and scalability of the protocol. Ideal for students studying Wireless Mobile & Multimedia Networking.