1. By Ioannis Chatzigiannakis, Elena Kaltsa, Sotiris Nikoletseas
On the Effect of User Mobility and Density on the Performance of Routing Protocols for Ad-hoc Mobile Networks
By Ioannis Chatzigiannakis, Elena Kaltsa, Sotiris Nikoletseas
An Overview, by Frank McCown
Mobile Computing CS Old Dominion University
November 12, 2004

2. Protocol Overview Flooding should be avoided Approaches
Construct and dynamically update paths
Take advantage of host movement and accidental meetings

3. AODV Overview Ad-hoc On Demand Distance Vector routing protocol
University of California – MOMENT Laboratory
Path maintenance algorithm
Supports unicast and multicast routing
Builds routes on demand

4. AODV in Action Source S D Destination I need to send “ABC” to D.
Do I know where D is? D
Destination

5. AODV Path Discovery Process
Source S
RREQ
RREQ
RREQ
RREQ
RREQ – route request
That message is for me! D
Destination

6. AODV Path Discovery Process
Remember where D is.
Remember where D is.
Source S
RREP
RREP
Remember where D is and send my message.
RREP
RREP – route reply
Route replies are sent back the reverse path from which the RREQ were sent. D
Destination

7. AODV Overview cont. Nodes maintain routes
Routes timeout after certain period
Sequence numbers used to keep routes fresh and ensure no loops
Destination sequence numbers used to ensure routes are loop-free and contain the most recent route information.
AODV builds routes using a route request / route reply query cycle. When a source node desires a route to a destination for which it does not already have a route, it broadcasts a route request (RREQ) packet across the network. Nodes receiving this packet update their information for the source node and set up backwards pointers to the source node in the route tables. In addition to the source node's IP address, current sequence number, and broadcast ID, the RREQ also contains the most recent sequence number for the destination of which the source node is aware. A node receiving the RREQ may send a route reply (RREP) if it is either the destination or if it has a route to the destination with corresponding sequence number greater than or equal to that contained in the RREQ. If this is the case, it unicasts a RREP back to the source. Otherwise, it rebroadcasts the RREQ. Nodes keep track of the RREQ's source IP address and broadcast ID. If they receive a RREQ which they have already processed, they discard the RREQ and do not forward it.
AODV uses the following fields with each route table entry: - Destination IP Address - Destination Sequence Number - Valid Destination Sequence Number flag - Other state and routing flags (e.g., valid, invalid, repairable, being repaired) - Network Interface - Hop Count (number of hops needed to reach destination) - Next Hop - List of Precursors (described in Section 6.2) - Lifetime (expiration or deletion time of the route)
A destination node increments its own sequence number in two circumstances:
Immediately before a node originates a route discovery, it MUST increment its own sequence number. This prevents conflicts with previously established reverse routes towards the originator of a RREQ.
Immediately before a destination node originates a RREP in response to a RREQ, it MUST update its own sequence number to the maximum of its current sequence number and the destination sequence number in the RREQ packet.

8. AODV Route Maintenance
My neighbor has moved! Tell everyone the route is no longer valid.
Source S
RERR
RERR – route error
Route error sent if an active route has been broken because a downstream node has moved and is no longer available. D
Destination

9. RUNNERS Overview Developed by Chatzigiannakis, et. al.
Semi-compulsory protocol
Select the support Σ (runners) during setup phase
Runners quickly traverse entire network
Runners relay messages between communicating nodes
Developed at Univ of Patras.
The support Σ of the network is formed during the setup phase. This can be done either by a randomized process, that randomly selects a number of mobile users or alternatively, the implementer may provide a specific number of mobile hosts (with specialized specifications, such as fast moving and versatile vehicles) that will form the support Σ. This small team
of k = |Σ| mobile hosts to move fast enough so that they cover (in sufficiently short time) the entire network area.
The support serves as a set of mobile relay hosts, that temporarily buffer messages (and delivery receipts) until they get delivered. Since Σ moves randomly around the area of the ad-hoc network, it will cover the entire area in sufficiently short time, thus servicing effectively all messages.
Semi-compulsory protocol – some nodes must move as per the needs of the protocol.
Compulsory protocol – all nodes most move as per the needs of the protocol. S D Σ

10. RUNNERS Overview
Runners store list of all undelivered messages and list of receipts to be given to originating senders
Nodes must wait until running into runner to send and receive messages
Runners synchronize when meeting
Synchronization protocol – runners remove already delivered messages, add any new messages yet to be delivered, and remove/add response receipts
synch Σ

11. Evaluation
Host density
vs.
Mobility rate
vs.

12. Modeling Motion Graph G = (V, E)
Any node that broadcasts a message will be heard if the listening node is within the radius of the transmitting node.

13. Experiments
Nodes start at random locations and move in random directions at random speeds
Nodes must stay within motion graph
Nodes never breakdown or fail
Nodes can communicate if located on the same vertex or within transmission range
Each node has identical communication and computing capabilities
10,000 rounds per experiment with at least 200,000 messages
Simulation time measured in rounds.

14. Parameters n = |V| u = total number of mobile hosts
µ = rate of movement
λ = message generation rate
Σ size = 10, 15, D: n = 121, 529, D: n = 125, 512, 1000
Σ moves at rate µ = 1
n = size of motion graph
If µ = 0.05 then node moves roughly every 20 rounds. If = 1, it moves every round.
λ (lamda)

15. Part I – Study of Host Density
n = size of motion graph
If µ = 0.05 then node moves roughly every 20 rounds. If = 1, it moves every round.
λ (lamda)

16. Message Delivery Rate Average message delivery rate n = 121 µ = 0.01
λ = 0.02
n = size of motion graph
If µ = 0.05 then node moves roughly every 20 rounds. If = 1, it moves every round.
λ (lamda) = message generation rate

17. Message Delay Average message delay n = 121 µ = 0.01 λ = 0.02
AODV is much more efficient. Remember that in AODV we are only taking into account those messages that were actually delivered.
RUNNERS and AODV delay is unaffected by the number of users.

18. AODV – Hops per Message Average number of hops per message n = 121
µ = 0.01
λ = 0.02
Not applicable to RUNNERS because no control messages are used and no paths are constructed.
When there are few users, few of the messages are being properly delivered.

19. AODV – Control Messages
Average number of control messages per data message
n = 121
µ = 0.01
λ = 0.02
Not applicable to RUNNERS because no control messages are used and no paths are constructed.
Linear growth implies significant protocol overhead for large number of users.

20. Density - Second Approach
Keep number of users same
Modify size of motion graph
Protocol’s performance might depend on both number of uses and area size separately. We need to evaluate these parameters separately.

21. AODV – Message Delivery Rate
Average message delivery rate
µ = 0.01
u = 50
The rate of sending messages does not affect performance.
As size of motion graph increases (n), performance of network drops.

22. AODV – Message Delay Average message delay µ = 0.01 u = 50
The rate of sending messages does not affect performance.
As size of motion graph increases (n), performance of network drops.

23. Density Results High density Low density AODV
+ delivery rates + message delays
- delivery rates - message delays
RUNNERS
+ delivery rates - message delays
AODV works best in high density networks.
RUNNERS works best in sparse networks.

24. Part II – Study of User Mobility
n = size of motion graph
If µ = 0.05 then node moves roughly every 20 rounds. If = 1, it moves every round.
λ (lamda)

25. Message Delivery Rate Average message delivery rate n = 125 λ = 0.02
u = 50
Motion rate of users has little impact in RUNNERS.
AODV performs horribly as nodes begin to move faster.

26. Message Delay Average message delay n = 125 λ = 0.02 u = 50
RUNNERS messages will be delivered more quickly as speed increases because runners run into nodes more often.

27. AODV – Hops per Message Average number of hops per message n = 125
λ = 0.02
u = 50

28. AODV - Control Messages
Control messages per data message
n = 125
λ = 0.02
u = 50

29. Mobility Results High mobility Low mobility AODV
- delivery rates - message delays
+ delivery rates + message delays
RUNNERS
+ delivery rates - message delays
AODV works best in high density networks.
RUNNERS works best in sparse networks.

30. Conclusion
Path maintenance algorithms (like AODV) are well suited for highly dense, low mobility MANETs
Semi-compulsory algorithms (like RUNNERS) are well suited for highly mobile MANETs and succeed in delivering messages even in low density networks
There is no protocol that is suitable for all cases.