Скачать презентацию Modelling Ad Hoc Networks Lecture 9 Use Скачать презентацию Modelling Ad Hoc Networks Lecture 9 Use

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Modelling Ad Hoc Networks Lecture 9 Modelling Ad Hoc Networks Lecture 9

Use Cases 2 Use Cases 2

Possibilities • Telephones (cellular, cordless, other) • Cordless multimedia (headsets, speakers, mic. ) • 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 3

Ad-…what? Ad-hoc network… …a LAN or other small network, …with wireless connections …devices are 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 4

Ad-hoc Networking Collection of wireless mobile nodes (devices) dynamically forming a temporary network without 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 5

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

Why? Microprocessor embedding trend in: • cellular phones, car stereos, televisions, VCRs, watches, GPS 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 7

How? Transmission Standards: 1. Piconet 2. Home. RF (Radio Frequency) 3. IEEE 802. 11 How? Transmission Standards: 1. Piconet 2. Home. RF (Radio Frequency) 3. IEEE 802. 11 Wireless LAN WG (Working Group) 4. Bluetooth SIG (Special Interest Group) • 5. These above use radio waves from licence-exempt ISM (Industrial, Scientific and Medical) frequency band - around 2. 4 GHz Ir. DA (Infra. Red Data Association) • which uses infrared instead of radio waves 8

Piconet • A general purpose, low-powered, ad-hoc network • It allows two devices near 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 9

Home. RF Uses Shared Wireless Access Protocol (SWAP) system • carries both voice and Home. RF 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 10

IEEE 802. 11 Wireless LAN The principles of Wireless Local Area Network (WLAN) are 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 11

Bluetooth • The code name for an open specification for short-range wireless connectivity • 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 12

Ir. DA • based on technology similar to the remote control devices • high-speed Ir. DA • 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 13

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

Issues in Protocol Design • • • Must run in distributed environment must provide 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 15

Some Implementation Choices • • • Flat vs. hierarchical architecture proactive vs. reactive to 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 16

Some Ad Hoc Protocols • DARPA (1970 s military packet radio) used with SURAN Some Ad Hoc Protocols • DARPA (1970 s 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 17

CGSR: Hierarchical Routing • All nodes send their data to cluster head nodes • 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 18

In-Depth: AODV (Ad-hoc On-demand Distance Vector routing) • purely on-demand (no routes determined until 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 19

AODV Path Discovery • Source node broadcasts a path discovery • message continues until 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 20

AODV Path/Connection Maintenance • Nodes ‘ping’ with hello messages to test links • timeouts 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 21

Contrast: DSR (Dynamic Source Routing) • resides in kernel IP layer (based on IPv Contrast: DSR (Dynamic Source Routing) • resides in kernel IP layer (based on IPv 6 format) • nodes contain tables of full paths to other nodes • messages: Route Request, Route Reply, Route Error, ACK • Send, Retransmit buffers • passive ACK 22

Mobility models classification • Entity MMs A node’s movement does not influence in anyhow Mobility models classification • 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 • 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

Random Walk (1) It wants represent the movement of the entities in an unpredictable Random Walk (1) 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, 2 pi] — Speed between [Min. Speed, Max. Speed] — 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. 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.

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

Random Waypoint (1) It is a variation of Random Walk. It introduces the concept Random Waypoint (1) 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, 2 pi] — Speed [Minvel, Maxvel] — Destination point (x, y) to reach. . 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] = [Min. Speed, Max. Speed]) 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.

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

Random Direction (1) Designed to overcame the concentration of the nodes of which R. Random Direction (1) Designed to overcame the concentration of the nodes of which R. Waypoint suffers. Nodes start moving by choosing — Direction between [0, 2 pi] — Speed between [Min. Speed, Max. Speed] • 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]. 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).

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

Questions 30 Questions 30