Modelling Ad Hoc Networks

1. Modelling Ad Hoc Networks Lecture 9

2. Use Cases

3. Possibilities • Telephones (cellular, cordless, other) • Cordless multimedia (headsets, speakers, mic.) • Portable computers (Laptops, desktop, other) • Cordless computer peripherals (keyboard, mouse) • LAN – Local Area Network peripherals (printer, fax) • PDAs - Personal Digital Assistants (palm top/pilot) • Digital cameras

4. Ad-…what? Ad-hoc network… …a LAN or other small network, …with wireless connections …devices are part of the network only for the duration of a communications session Or …while in close proximity to the network

5. Ad-hoc Networking Collection of wireless mobile nodes (devices) dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration

6. Properties • Requires devices to cooperate autonomously • Without user intervention • Rapid self-organizing wireless network • Independent of infrastructure • Heterogeneous & adaptive

7. Why? • Microprocessor embedding trend in: • cellular phones, car stereos, televisions, VCRs, watches, GPS (Global Positioning System) receivers, digital camera. • Ensembles of computational devices for: • environmental monitoring • personal area networks • geophysical measurement

8. How? • Transmission Standards: • Piconet • HomeRF (Radio Frequency) • IEEE 802.11 Wireless LAN WG (Working Group) • Bluetooth SIG (Special Interest Group) • These above use radio waves from licence-exempt • ISM (Industrial, Scientific and Medical) • frequency band - around 2.4 GHz • IrDA (InfraRed Data Association) • which uses infrared instead of radio waves

9. Piconet • A general purpose, low-powered, ad-hoc network • It allows two devices near each other to • inter-operate • These devices can be either mobile or fixed • The range is said to be reasonably short

10. HomeRF • Uses Shared Wireless Access Protocol (SWAP) system • carries both voice and data traffic • inter-operate with the PSTN • (Public Switched Telephone Network) • and the Internet • the range covers typical home and yard

11. IEEE 802.11 Wireless LAN • The principles of Wireless Local Area Network (WLAN) are defined in IEEE 802.11 standard • It defines two different topologies: • ad-hoc network and infrastructure network • This ad-hoc network is able to use only created wireless connection instead of fixed infrastructure

12. Bluetooth • The code name for an open specification for short-range wireless connectivity • Effortless, instant wireless connections between a wide range of communication devices in a small environment • The BT range restricts the environment to about 10 meters • Used in virtually any mobile device like that can have Bluetooth radios integrated into them

13. IrDA • based on technology similar to the remote control devices • high-speed short range, point-to-point cordless data transfer • in-room cordless peripherals to host-PC • maturity and standardization activities advantage over radio

14. Challenges Facing Ad Hoc • Security • scalability • load balancing / etiquette between hosts • QoS • CPU/memory overhead • effect on devices’ battery life

15. Issues in Protocol Design • Must run in distributed environment • must provide loop-free routes • must be able to find multiple routes • must establish routes quickly • must minimize overhead in its communication / reaction to topology change

16. Some Implementation Choices • Flat vs. hierarchical architecture • proactive vs. reactive to topology changes • table-based, demand-driven, associativity-driven • topology change dissemination methods • when/how often to exchange topology info • assumptions about rate of change of topology and/or quality of connections

17. Some Ad Hoc Protocols • DARPA (1970s military packet radio)used with SURAN (SURvivable Adaptive Network; an early ad hoc networking testbed) • CGSR (hierarchical) • TORA (time-based; uses link reversal) • DSR • AODV

18. CGSR: Hierarchical Routing • All nodes send their data to cluster head nodes • heads act as second-tier, high-power network • +: simpler routing -: poor load balancing, not secure

19. In-Depth: AODV (Ad-hoc On-demand Distance Vector routing) • purely on-demand(no routes determined until needed) • each node contains routing table of next-hop information for how to get to every other node

20. AODV Path Discovery • Source node broadcasts a path discovery • message continues until it reaches destination, or node with path in table • sequence nums • discovery response sent back along reverse path

21. AODV Path/Connection Maintenance • Nodes ‘ping’ with hello messages to test links • timeouts assumed to be broken links • (only) recent active nodes notified of topology changes--propogated to neighbors

22. Contrast: DSR (Dynamic Source Routing) • resides in kernel IP layer (based on IPv6 format) • nodes contain tables of full paths to other nodes • messages: Route Request, Route Reply, Route Error, ACK • Send, Retransmit buffers • passive ACK

23. Entity MMs • A node’s movement does not influence in anyhow other nodes’ movements. Nodes move independently from each other. • Random Walk ( & its probabilistic version) • Random Waypoint • Random Direction • Gauss-Markov • City section mobility models Mobility models classification • Group MMs • represent MNs whose movements are dependent. Used when MNs collaborate together to accomplish a common goal. Typical situations do exist in military environments (soldiers move together)… • Column MM • Nomadic Community • Pursue • Reference Point Group MM

24. It wants represent the movement of the entities in an unpredictable way. In particular, a node moves from its current location to a new one by randomly choosing: • Direction between [0,2pi] • Speed between [MinSpeed, MaxSpeed] • Either duration of movement tm OR distance d • Direction and speed are both uniformly distributed • A node which “crashes” against the boundary keeps on moving on an opposite direction between [0,pi] depending on the incoming one. Random Walk (1) OBSERVATIONS: 1) Nodes start moving at t=0. Choosing a DURATION implies that all the nodes change directions at the same time and travel for different distances. In contrast, choosing a DISTANCE implies same distances but different duration. 2) The pattern is memory-less i.e. current speed and direction do not depend upon the previous ones. Therefore, there will be sharp and sudden turns. 3) Short tm or d lead the nodes to move around their current location. Unless it is necessary to study a semi-static network, they MUST be chosen large.

25. Example of a travelling pattern of a mobile node using the 2D Random Walk MM Random Walk (2) Surface size 300 x 600 m, tm = 60s

26. It is a variation of Random Walk. It introduces the concept of pause time. A node randomly chooses (Parameters uniformly distributed): • Pause Time (to wait before resuming the movement) [Pmin,Pmax] • Direction [0,2pi] • Speed [Minvel,Maxvel] • Destination point (x,y) to reach.. Random Waypoint (1) • OBSERVATIONS: • 1) the duration of the movement depends on the destination point chosen. • 2) nodes do not start roaming all together unless Pmin = Pmax = 0. • 3) the pattern becomes a Random Walk when (Pmin = Pmax = 0 ) AND ([Minvel,Maxvel] = [MinSpeed, MaxSpeed]) • 4) it is the most commonly used MM in ad-hoc network simulation studies (often times is modified). • It needs particular attention to choose the initial locations. Discard the initial part of the simulation OR save the node’s location OR do not place the nodes randomly. • The choice of Pauses and Speeds is relevant. Fast nodes and long pauses produces a more stable network than slow nodes and short pauses. • The most argued issue is that nodes are more likely to be in the central part of the topology rather than close to the bounds.

27. Example of a travelling pattern of a mobile node using the Random Waypoint MM • Clearly the motion is centrally happening • Nodes appear to converge, disperse and converge again • Nodes tend to have many neighbors when in the center and almost none when they disperse. Random Waypoint (2) Surface size 300 x 600 m

28. Designed to overcame the concentration of the nodes of which R. Waypoint suffers. Nodes start moving by choosing • Direction between [0,2pi] • Speed between [MinSpeed, MaxSpeed] • Nodes will travel till the bound is reached. On this position they’ll stand for a pause time before leaving to a New-Direction [0,pi]. Random Direction (1) • OBSERVATIONS: • 1) Nodes are forced to basically stay away from the center for the most of the time. In fact, they ALL pause somewhere on the perimeter. • Implications: • Average Hop count for Data-packets will be much higher than in R. Waypoint or R Walk. (nodes are on average far from each others) • Higher probability to have Network partition (especially with few MNs).

29. Example of a travelling pattern of a mobile node using the Random Direction MM Random Direction (2) Surface size 300 x 600 m

30. Questions