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)
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”
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
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
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
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