Section A — 1 Mark Questions
1. Define unicast routing. [1 Mark]
Answer: Unicast routing is the process of forwarding data packets from a single source node to a single specific destination node in a network.
2. What is the primary purpose of a routing algorithm? [1 Mark]
Answer: The primary purpose is to determine the optimal path for a data packet from source to destination across a network.
3. What does a routing table store? [1 Mark]
Answer: A routing table stores information about network destinations and the next hop or interface to reach them.
4. Identify the main characteristic of static routing. [1 Mark]
Answer: Static routing requires manual configuration by an administrator and does not adapt automatically to changes in network topology.
5. Define dynamic routing. [1 Mark]
Answer: Dynamic routing uses protocols to automatically learn routes and update routing tables based on network changes.
6. What is broadcast routing? [1 Mark]
Answer: Broadcast routing is a method where a single packet is sent from one source to all other nodes in the network.
7. Define multicast routing. [1 Mark]
Answer: Multicast routing is the delivery of a packet to a specific group of destination nodes simultaneously.
8. What is an Adhoc network? [1 Mark]
Answer: An Adhoc network is a decentralized type of wireless network where nodes connect directly without pre-existing infrastructure.
9. What is a routing metric? [1 Mark]
Answer: A routing metric is a value used by a routing algorithm to compare and select the best path, such as hop count or latency.
10. State one advantage of distance-vector algorithms. [1 Mark]
Answer: They are relatively simple to implement and require less processing power than link-state algorithms.
11. State one advantage of link-state algorithms. [1 Mark]
Answer: They typically converge faster than distance-vector algorithms.
12. What is a flooding technique in routing? [1 Mark]
Answer: Flooding is a broadcasting method where a node sends incoming packets out on every outgoing link except the one it arrived on.
13. Name a common metric used in routing. [1 Mark]
Answer: Hop count.
14. What is meant by route convergence? [1 Mark]
Answer: Convergence is the state where all routers in a network have a consistent view of the network topology after a change.
15. What is a multicast group? [1 Mark]
Answer: A multicast group is a set of receivers identified by a single multicast address that wishes to receive the same data stream.
16. Why is Adhoc routing challenging? [1 Mark]
Answer: Because nodes are mobile, meaning the network topology changes frequently and unpredictably.
17. Define a 'Next Hop' in routing. [1 Mark]
Answer: It is the next router in the path that a packet must traverse to reach its destination.
18. What is load balancing in routing? [1 Mark]
Answer: It is the process of distributing network traffic across multiple paths to optimize resource usage and prevent congestion.
19. Define 'shortest path' routing. [1 Mark]
Answer: It is a routing strategy that selects the path with the minimum cost between the source and the destination.
20. What is a router? [1 Mark]
Answer: A router is a networking device that forwards data packets between different computer networks.
Section B — 2/3 Mark Questions
1. Briefly explain the difference between static and dynamic routing. [2 Marks]
Answer: Static routing involves manual entry of routes, which is stable but inflexible. Dynamic routing uses protocols to discover and update routes automatically, allowing the network to adapt to failures or topology changes.
2. List three essential characteristics of a good routing algorithm. [3 Marks]
Answer: 1. Correctness: The algorithm must deliver packets to the correct destination. 2. Simplicity: It should be easy to implement and maintain. 3. Robustness: It should handle network changes or hardware failures effectively.
3. What is the 'Count-to-Infinity' problem? [2 Marks]
Answer: It is a failure in distance-vector routing protocols where routers keep incrementing the hop count of an unreachable destination because they have stale information about the path, leading to routing loops.
4. Describe the role of a multicast address. [2 Marks]
Answer: A multicast address acts as an identifier for a group of interested hosts. Packets sent to this address are delivered to every host that has joined the group.
5. Why is flooding considered inefficient in broadcast routing? [3 Marks]
Answer: Flooding causes redundant traffic because every node receives multiple copies of the same packet. This leads to bandwidth wastage, potential network congestion, and increased packet processing overhead on routers.
6. Explain the concept of 'hop count' as a routing metric. [2 Marks]
Answer: Hop count is the number of routers (hops) a packet must traverse to reach the destination. A path with the lowest hop count is usually selected as the shortest path.
7. Differentiate between unicast and broadcast routing. [3 Marks]
Answer: Unicast involves communication from one sender to one specific receiver. Broadcast involves communication from one sender to all nodes in the network. Unicast is point-to-point, whereas broadcast is point-to-multipoint.
8. What are the primary constraints of Adhoc network routing? [2 Marks]
Answer: Primary constraints include limited battery power of mobile nodes and the frequent, unpredictable changes in network topology due to node mobility.
9. What is a link-state advertisement? [3 Marks]
Answer: A link-state advertisement is a packet that contains the status of a router's direct connections. It is flooded to all routers in the network so that every router can independently construct an accurate map of the network topology.
10. Explain the 'Split Horizon' technique. [2 Marks]
Answer: Split horizon is a method used to prevent routing loops by ensuring a router does not advertise a route back out of the same interface from which it originally learned that route.
Section C — 5 Mark Questions
1. Compare distance-vector and link-state routing algorithms. [5 Marks]
Answer:
Comparison
| Feature | Distance-Vector | Link-State |
|---|---|---|
| Information Shared | Entire routing table | Only local link status |
| Knowledge of Topology | Only knows next hop | Knows full topology |
| Convergence Speed | Slow | Fast |
| Bandwidth Usage | Low | High |
Explanation
- Distance-vector algorithms (like RIP) distribute routing information to neighbors only. This is bandwidth-efficient but leads to slower convergence and potential loops.
- Link-state algorithms (like OSPF) share information about neighbors with all routers in the area. This allows each router to calculate the shortest path independently using Dijkstra's algorithm, leading to faster convergence but higher memory and CPU usage.
2. Explain the mechanism of broadcast routing in computer networks. [5 Marks]
Answer:
Introduction
Broadcast routing is the technique of sending a packet to every destination node in the network. It is typically used for address resolution or network discovery.
Methods of Broadcasting
- Flooding: Each node forwards incoming broadcast packets out of every connected link. While simple, it generates heavy traffic.
- Multi-destination routing: The source sends a separate copy of the packet to each destination. This is efficient for small groups but becomes unmanageable as the number of nodes grows.
- Spanning Tree: A tree structure is built that covers all nodes. Broadcast packets follow the edges of this tree, ensuring each node receives the packet exactly once without loops.
3. Describe the challenges and unique requirements of routing in Adhoc networks. [5 Marks]
Answer:
Introduction
Adhoc networks are decentralized wireless networks where nodes act as both hosts and routers. Routing is complex due to the absence of centralized infrastructure.
Key Challenges
- Dynamic Topology: Nodes move constantly, causing links to break and form frequently. Routing tables must be updated rapidly.
- Resource Constraints: Devices are often battery-powered. Routing protocols must be energy-efficient to prolong node lifespan.
- Limited Bandwidth: Wireless media has lower capacity; therefore, routing control packets should be minimized to avoid congestion.
Routing Strategies
Adhoc protocols like AODV (Ad hoc On-Demand Distance Vector) perform route discovery only when needed to save energy and bandwidth, rather than maintaining constant path tables.
4. Discuss the importance of routing metrics in path selection. [5 Marks]
Answer:
Introduction
Routing metrics are quantitative values used by algorithms to determine the 'cost' of a path. They are the primary criteria for path selection when multiple routes to a destination exist.
Common Metrics
- Hop Count: Measures the number of routers. Simple but ignores link speed.
- Latency (Delay): Measures the time taken for a packet to traverse a path. Critical for real-time applications like VoIP.
- Bandwidth: Measures the data transmission capacity. High-bandwidth links are preferred for large file transfers.
- Reliability: Refers to the error rate of the link. Higher reliability reduces retransmissions.
- Load: Reflects the current utilization of a link. Routing traffic away from congested links improves overall network performance.
Conclusion: Choosing the right metric depends on the application requirement, balancing factors like speed, cost, and reliability.
5. Explain the role and functioning of multicast routing. [5 Marks]
Answer:
Introduction
Multicast routing enables efficient data delivery from a source to a specific group of subscribers, rather than broadcasting to all nodes or unicasting to each individual.
How it Works
- Group Membership: Hosts send join requests to become members of a multicast group identified by a multicast IP address.
- Tree Construction: Routers maintain a distribution tree (often a spanning tree) to manage how multicast traffic flows to group members.
- Efficient Replication: Routers replicate packets only when necessary (at branching points in the tree), ensuring a single stream reaches all members without saturating the source's bandwidth.
Applications
Multicast is extensively used in live video streaming, IPTV, and software updates, where large groups of receivers need the same information simultaneously.