Routing Protocol Evaluation

1. Routing Protocol Evaluation David Holmer dholmer@jhu.edu

2. Mobility Models

3. Random Waypoint Mobility • Two parameters • Pause Time (Pt) • Max Speed (Vmax) • Each node starts at a random location • Executes loop • Pause for Pt seconds • Select a random destination (waypoint) • Move to that destination at a random speed (0,Vmax) • Repeat upon arrival

4. Random Waypoint Properties • Advantages • Easy to implement • Allows heterogeneous speeds and temporarily stationary nodes • Disadvantages • Non-uniform node distribution (tend towards center) • Un-stable instantaneous mobility (tends towards zero and oscillates)

5. Random Waypoint Properties (cont)

6. Random Waypoint Properties (cont)

7. Modified Random Waypoint • Narrow the random speed range • (.1 Vmax, .9 Vmax) instead of ( 0, Vmax ) • Pre-simulation mobility • Mobility properties stabilize before routing and data commences • Doesn’t fix non-uniform node distribution

8. Other Mobility Models • Billiard Model • Node selects a random direction, speed, and time • Moves in that direction at that speed for that time and then repeats (may have pause time as well) • Bounces off simulation boundary like a “billiard ball” • Maintains uniform node distribution, and uniform average speed (due to time selection) • Group mobility patterns • Node mobility is sum of group mobility and individual mobility • Used by clustering based routing protocols (well suited for certain applications like the military) • Trace based mobility patterns • Record real life people/vehicle/etc. motion patterns • Requires location hardware such as GPS • Difficult to try variations or change “parameters”

9. Routing Performance Metrics

10. Routing Protocol Evaluation Metrics • Four most common metrics • Delivery Ratio • Latency • Path Length Optimality • Control Overhead

11. Delivery Ratio • Number of packets successfully received by the destination / number sent by the source • Evaluated by setting up a number of “test” flows in the network • Commonly a number of constant bit rate (CBR) flows with a specified number of packets per second • Uses UDP so every dropped packet results in a reduction of the delivery ratio (no end-to-end retransmissions) • Congestion Sensitive • A large enough test load will result in reduced delivery ratio for ANY protocol due to congestion • Mobility Sensitive • If the routing protocol does not respond quickly to topology change, then packets sent on links that no longer exist will be lost

12. Delivery Ratio Examples Delivery Ratio vs. Test Load Delivery Ratio vs. Mobility

13. Latency • The time between the creation of a packet and its delivery to the destination • Usually measured using the same setup as delivery ratio • Congestion sensitive • Latency will drastically increase as the congestion limit is reached (due to waiting in large buffers) • Retransmission sensitive • Protocols that locally recover packets will achieve higher delivery ratio but will increase latency • On-demand sensitive • Protocols that setup routes after data is sent will have higher latency on the initial packets of a flow

14. Latency Example

15. Path Length Optimality • The difference between the length of the path used for sending packets in the protocol and the length of the best possible path • Measurement • Protocol path length observed for each packet using test flows • Best possible path computed offline using same mobility pattern • Measure of protocol’s ability to track good routes • Extra hops from non-optimal routes will result in increased congestion and medium utilization

16. Path Length Optimality Example

17. Control Overhead • Number/size of routing control packets sent by the protocol • Calculated using counters while simulating with test flows • Sometimes expressed as a ratio of control to data • Indication of how efficiently a routing protocol operates • High control overhead may adversely affect delivery ratio and latency under higher loads

18. Control Overhead Example