Chapter 7.pdf

CCCN 422 Wireless Communication Networks Dr. Mohammed Balfaqih Assistant Professor [email protected] @modditto Lecture Outline ▪ Mobile Computing and Sensor Networks • • • • • • Mobile ad hoc networks (MANET) Link, Network and Transport Layers Considerations Routing in MANET. Location in ubiq...

CCCN 422 Wireless Communication Networks Dr. Mohammed Balfaqih Assistant Professor [email protected] @modditto Lecture Outline ▪ Mobile Computing and Sensor Networks • • • • • • Mobile ad hoc networks (MANET) Link, Network and Transport Layers Considerations Routing in MANET. Location in ubiquitous computing environments Security and privacy in ubiquitous computing environments Data collection in sensor networks Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Mobile ad hoc networks (MANET) ▪ Wireless Networks Access computing and communication services, on the move • Infrastructure-based Networks – traditional cellular systems (base station infrastructure) • Wireless LANs – Infrared (IrDA) or radio links (Wavelan) – very flexible within the reception area; ad-hoc networks possible – low bandwidth compared to wired networks (1-10 Mbit/s) • Ad hoc Networks – useful when infrastructure not available, impractical, or expensive – military applications, rescue, home networking Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Mobile ad hoc networks (MANET) ▪ Single-Hop Wireless • Single hop wireless connectivity to the wired world – – – – Space divided into cells A base station is responsible to communicate with hosts in its cell Mobile hosts can change cells while communicating Hand-off occurs when a mobile host starts communicating via a new base station Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Mobile ad hoc networks (MANET) ▪ Multi-Hop Wireless • May need to traverse multiple links to reach destination • Mobility causes route changes Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Mobile ad hoc networks (MANET) • Host movement frequent • Topology change frequent A B A B • No cellular infrastructure. Multi-hop wireless links. • Data must be routed via intermediate nodes. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Mobile ad hoc networks (MANET) ▪ Why Ad Hoc Networks ? • Setting up of fixed access points and backbone infrastructure is not always viable – Infrastructure may not be present in a disaster area or war zone – Infrastructure may not be practical for short-range radios; Bluetooth (range ~ 10m) • Ad hoc networks: – Do not need backbone infrastructure support – Are easy to deploy – Useful when infrastructure is absent, destroyed or impractical • Many Applications – – – – Personal area networking: cell phone, laptop, ear phone, wrist watch Military environments: soldiers, tanks, planes Civilian environments: taxi cab network, meeting rooms, sports stadiums, boats, small aircraft Emergency operations: search-and-rescue, policing and fire fighting Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations ▪ Effect of mobility on the protocol stack • Application – new applications and adaptations • Transport – congestion and flow control • Network – addressing and routing • Link – media access and handoff • Physical – transmission errors and interference Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations ▪ Medium Access Control in MANET • Can we apply media access methods from fixed networks? • Example CSMA/CD – Carrier Sense Multiple Access with Collision Detection – send as soon as the medium is free, listen into the medium if a collision occurs (original method in IEEE 802.3) • Medium access problems in wireless networks – – – – Dr. Mohammed Balfaqih signal strength decreases proportional to the square of the distance sender would apply CS and CD, but the collisions happen at the receiver sender may not “hear” the collision, i.e., CD does not work CS might not work, e.g. if a terminal is “hidden” CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Hidden terminals – – – – A sends to B, C cannot receive A C wants to send to B, C senses a “free” medium (CS fails) collision at B, A cannot receive the collision (CD fails) A is “hidden” for C • Exposed terminals – – – – Dr. Mohammed Balfaqih A B C B sends to A, C wants to send to another terminal (not A or B) C senses carrier, finds medium in use and has to wait A is outside the radio range of C, therefore waiting is not necessary C is “exposed” to B CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations ✓ Multiple Access with Collision Avoidance (MACA) [Karn90] • MACA uses signaling packets for collision avoidance – RTS (request to send) • sender request the right to send from a receiver with a short RTS packet before it sends a data packet – CTS (clear to send) • receiver grants the right to send as soon as it is ready to receive • Signaling packets contain – sender address – receiver address – packet size • Variants of this method are used in IEEE 802.11 Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • MACA avoids the problem of hidden terminals – A and C want to send to B – A sends RTS first – C waits after receiving CTS from B RTS A CTS B CTS C • MACA avoids the problem of exposed terminals – B wants to send to A, C to another terminal – now C does not have to wait, as it cannot receive CTS from A RTS A Dr. Mohammed Balfaqih CTS B RTS C CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations ✓ MAC: Reliability • Wireless links are prone to errors. High packet loss rate is detrimental to transport-layer performance. • Solution: Use of acknowledgements – When node B receives a data packet from node A, node B sends an Acknowledgement (Ack). – If node A fails to receive an Ack, it will retransmit the packet – This approach adopted in many protocols [Bharghavan94, IEEE 802.11] • IEEE 802.11 Wireless MAC – Distributed and centralized MAC components • Distributed Coordination Function (DCF) • Point Coordination Function (PCF) – DCF suitable for multi-hop ad hoc networking Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • IEEE 802.11 DCF – Uses RTS-CTS exchange to avoid hidden terminal problem Any node overhearing a CTS cannot transmit for the duration of the transfer – Uses ACK to achieve reliability – Any node receiving the RTS cannot transmit for the duration of the transfer To prevent collision with ACK when it arrives at the sender When B is sending data to C, node A will keep quiet A B C – IEEE 802.11 DCF Operation When transmitting a packet, choose a backoff interval in the range [0,cw]; cw is contention window Count down the backoff interval when medium is idle Count-down is suspended if medium becomes busy When backoff interval reaches 0, transmit RTS Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations – Time spent counting down backoff intervals is a part of MAC overhead – large cw leads to larger backoff intervals – small cw leads to larger number of collisions – MAC: Congestion Control IEEE 802.11 DCF achieves Congestion control by dynamically choosing the contention window cw – Binary Exponential Backoff in DCF: When a node fails to receive CTS in response to its RTS, it increases the contention window • cw is doubled (up to an upper bound) When a node successfully completes a data transfer, it restores cw to CWmin Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ✓ Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Finding a path from a source to a destination • Issues – Frequent route changes amount of data transferred between route changes may be much smaller than traditional networks – Route changes may be related to host movement – Low bandwidth links • Goal of routing protocols – decrease routing-related overhead – find short routes – find “stable” routes (despite mobility) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Unicast Routing Protocols – Many protocols have been proposed – Some specifically invented for MANET – Others adapted from protocols for wired networks – No single protocol works well in all environments some attempts made to develop adaptive/hybrid protocols – Standardization efforts in IETF MANET, MobileIP working groups http://www.ietf.org Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Routing Protocols - Proactive protocols Traditional distributed shortest-path protocols Maintain routes between every host pair at all times Based on periodic updates; High routing overhead Example: DSDV (destination sequenced distance vector) - Reactive protocols Determine route if and when needed Source initiates route discovery Example: DSR (dynamic source routing) - Hybrid protocols Adaptive; Combination of proactive and reactive Example : ZRP (zone routing protocol) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Protocol Trade-offs - Proactive protocols Always maintain routes Little or no delay for route determination Consume bandwidth to keep routes up-to-date Maintain routes which may never be used - Reactive protocols Lower overhead since routes are determined on demand Significant delay in route determination Employ flooding (global search) Control traffic may be bursty • Which approach achieves a better trade-off depends on the traffic and mobility patterns Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Reactive Routing Protocols - Dynamic Source Routing (DSR) [Johnson96] • When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery • Source node S floods Route Request (RREQ) • Each node appends own identifier when forwarding RREQ ▪ Route Discovery in DSR Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ Route Reply in DSR • Destination D on receiving the first RREQ, sends a Route Reply (RREP) • RREP is sent on a route obtained by reversing the route appended to received RREQ • RREP includes the route from S to D on which RREQ was received by node D Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ Data Delivery in DSR • Node S on receiving RREP, caches the route included in the RREP • When node S sends a data packet to D, the entire route is included in the packet header • hence the name source routing • Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ DSR Optimization: Route Caching • Each node caches a new route it learns by any means • When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F • When node K receives Route Request [S,C,G] destined for node, node K learns route [K,G,C,S] to node S • When node F forwards Route Reply RREP [S,E,F,J,D], node F learns route [F,J,D] to node D • When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D • A node may also learn a route when it overhears Data • Problem: Stale caches may increase overheads Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ DSR: Advantages • Routes maintained only between nodes who need to communicate • reduces overhead of route maintenance • Route caching can further reduce route discovery overhead • A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ DSR: Disadvantages • Packet header size grows with route length due to source routing • Flood of route requests may potentially reach all nodes in the network • Potential collisions between route requests propagated by neighboring nodes • insertion of random delays before forwarding RREQ • Increased contention if too many route replies come back due to nodes replying using their local cache • Route Reply Storm problem • Stale caches will lead to increased overhead Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Reactive Routing Protocols - Ad Hoc On-Demand Distance Vector Routing (AODV) [Perkins99Wmcsa] • DSR includes source routes in packet headers • Resulting large headers can sometimes degrade performance • particularly when data contents of a packet are small • AODV attempts to improve on DSR by maintaining routing tables at the nodes, so that data packets do not have to contain routes • AODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Route Requests (RREQ) are forwarded in a manner similar to DSR • When a node re-broadcasts a Route Request, it sets up a reverse path pointing towards the source • AODV assumes symmetric (bi-directional) links • When the intended destination receives a Route Request, it replies by sending a Route Reply (RREP) • Route Reply travels along the reverse path set-up when Route Request is forwarded Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ Route Requests in AODV Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ Reverse Path Setup in AODV Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ Forward Path Setup in AODV Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ Route Request and Route Reply • Route Request (RREQ) includes the last known sequence number for the destination • An intermediate node may also send a Route Reply (RREP) provided that it knows a more recent path than the one previously known to sender • Intermediate nodes that forward the RREP, also record the next hop to destination • A routing table entry maintaining a reverse path is purged after a timeout interval • A routing table entry maintaining a forward path is purged if not used for a active_route_timeout interval Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET ▪ Link Failure • A neighbor of node X is considered active for a routing table entry if the neighbor sent a packet within active_route_timeout interval which was forwarded using that entry • Neighboring nodes periodically exchange hello message • When the next hop link in a routing table entry breaks, all active neighbors are informed • Link failures are propagated by means of Route Error (RERR) messages, which also update destination sequence numbers • When node X is unable to forward packet P (from node S to node D) on link (X,Y), it generates a RERR message Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Node X increments the destination sequence number for D cached at node X • The incremented sequence number N is included in the RERR • When node S receives the RERR, it initiates a new route discovery for D using destination sequence number at least as large as N • When node D receives the route request with destination sequence number N, node D will set its sequence number to N, unless it is already larger than N Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Reactive Routing Protocols - Other Protocols • Many variations of using control packet flooding for route discovery • Power-Aware Routing [Singh98Mobicom] • Assign a weight to each link: function of energy consumed when transmitting a packet on that link, as well as the residual energy level • Modify DSR to incorporate weights and prefer a route with the smallest aggregate weight • Associativity-Based Routing (ABR) [Toh97] • Only links that have been stable for some minimum duration are utilized • Nodes increment the associativity ticks of neighbors by using periodic beacons • Signal Stability Based Adaptive Routing (SSA) [Dube97] • A node X re-broadcasts a Route Request received from Y only if the (X,Y) link has a strong signal stability • Signal stability is evaluated as a moving average of the signal strength of packets received on the link in recent past Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Proactive Routing Protocols - Destination-Sequenced Distance-Vector (DSDV) [Perkins94Sigcomm] • Each node maintains a routing table which stores • next hop, cost metric towards each destination • a sequence number that is created by the destination itself • Each node periodically forwards routing table to neighbors • Each node increments and appends its sequence number when sending its local routing table • Each route is tagged with a sequence number; routes with greater sequence numbers are preferred • Each node advertises a monotonically increasing even sequence number for itself • When a node decides that a route is broken, it increments the sequence number of the route and advertises it with infinite metric • Destination advertises new sequence number Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • When X receives information from Y about a route to Z • Let destination sequence number for Z at X be S(X), S(Y) is sent from Y X Y Z • If S(X) > S(Y), then X ignores the routing information received from Y • If S(X) = S(Y), and cost of going through Y is smaller than the route known to X, then X sets Y as the next hop to Z • If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is updated to equal S(Y) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Proactive Routing Protocols - Optimized Link State Routing (OLSR) [Jacquet00ietf] • Nodes C and E are multipoint relays of node A • Multipoint relays of A are its neighbors such that each two-hop neighbor of A is a onehop neighbor of one multipoint relay of A • Nodes exchange neighbor lists to know their 2-hop neighbors and choose the multipoint relays Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Nodes C and E forward information received from A • Nodes E and K are multipoint relays for node H • Node K forwards information received from H Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Hybrid Routing Protocols - Zone Routing Protocol (ZRP) [Haas98] • ZRP combines proactive and reactive approaches • All nodes within hop distance at most d from a node X are said to be in the routing zone of node X • All nodes at hop distance exactly d are said to be peripheral nodes of node X’s routing zone • Intra-zone routing: Proactively maintain routes to all nodes within the source node’s own zone. • Inter-zone routing: Use an on-demand protocol (similar to DSR or AODV) to determine routes to outside zone. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET Radius of routing zone = 2 Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Routing in MANET • Routing Summary • Protocols • Typically divided into proactive, reactive and hybrid • Plenty of routing protocols. Discussion here is far from exhaustive • Performance Studies • Typically studied by simulations using ns, discrete event simulator • Nodes (10-30) remains stationary for pause time seconds (0-900s) and then move to a random destination (1500m X300m space) at a uniform speed (0-20m/s). CBR traffic sources (4-30 packets/sec, 64-1024 bytes/packet) • Attempt to estimate latency of route discovery, routing overhead … • Actual trade-off depends a lot on traffic and mobility patterns • Higher traffic diversity (more source-destination pairs) increases overhead in ondemand protocols • Higher mobility will always increase overhead in all protocols Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • User Datagram Protocol (UDP) Studies comparing different routing protocols for MANET typically measure UDP performance Several performance metrics are used routing overhead per data packet packet delivery delay throughput/loss Many variables affect performance Traffic characteristics Mobility characteristics Node capabilities Difficult to identify a single scheme that will perform well in all environments Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Transmission Control Protocol (TCP) - Reliable ordered delivery Reliability achieved by means of retransmissions if necessary - End-to-end semantics Receiver sends cumulative acknowledgements for in-sequence packets Receiver sends duplicate acknowledgements for out-of-sequence packets - Implements congestion avoidance and control using sliding-window Window size is minimum of receiver’s advertised window - determined by available buffer space at the receiver congestion window - determined by the sender, based on feedback from the network Congestion window size bounds the amount of data that can be sent per round-trip time Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations - Detection of packet loss in TCP • Retransmission timeout (RTO) • sender sets retransmission timer for only one packet • if Ack not received before timer expiry, the packet is assumed lost • RTO dynamically calculated, doubles on each timeout • Duplicate acks • sender assumes packet loss if it receives three consecutive duplicate acknowledgements (dupacks) • On detecting a packet loss, TCP sender assumes that network congestion has occurred and drastically reduces the congestion window Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • TCP in MANET Several factors affect TCP performance in MANET: • Wireless transmission errors • may cause fast retransmit, which results in • retransmission of lost packet • reduction in congestion window • reducing congestion window in response to errors is unnecessary • Multi-hop routes on shared wireless medium • Longer connections are at a disadvantage compared to shorter connections, because they have to contend for wireless access at each hop • Route failures due to mobility Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Impact of Multi-hop Wireless Paths TCP throughput degrades with increase in number of hops • Packet transmission can occur on at most one hop among three consecutive hops • Increasing the number of hops from 1 to 2, 3 results in increased delay, and decreased throughput • Increasing number of hops beyond 3 allows simultaneous transmissions on more than one link, however, degradation continues due to contention between TCP Data and Acks traveling in opposite directions • When number of hops is large enough (>6), throughput stabilizes. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Impact of Node Mobility TCP throughput degrades with increase in mobility but not always mobility causes link breakage, resulting in route failure Route is repaired TCP sender times out. Starts sending packets again No throughput No throughput despite route repair TCP data and acks discarded Dr. Mohammed Balfaqih Larger route repair delays are especially harmful CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Improved Throughput with Increased Mobility C B D C D B A C B D A A ▪ Low speed: (Route from A to D is broken for ~1.5 seconds) • When TCP sender times after 1 second, route still broken. • TCP times out after another 2 seconds, and only then resumes ▪ High speed: (Route from A to D is broken for ~0.75 seconds) • When TCP sender times out after 1 second, route is repaired ▪ TCP timeout interval somewhat (not entirely) independent of speed ▪ Network state at higher speed may sometimes be more favorable than lower speed Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Impact of Route Caching TCP performance typically degrades when caches are used for route repair • When a route is broken, route discovery returns a cached route from local cache or from a nearby node • After a time-out, TCP sender transmits a packet on the new route. However, typically the cached route has also broken after it was cached timeout due to route failure timeout, cached timeout, second cached route is broken route also broken • Another route discovery, and TCP time-out interval • Process repeats until a good route is found Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Caching and TCP performance • Caching can result in faster route repair • Faster does not necessarily mean correct • If incorrect repairs occur often enough, caching performs poorly • If cache accuracy is not high enough, gains in routing overhead may be offset by loss of TCP performance due to multiple time-outs • Need mechanisms for determining when cached routes are stale Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Impact of Acknowledgements • TCP Acks (and link layer acks) share the wireless bandwidth with TCP data packets • Data and Acks travel in opposite directions • In addition to bandwidth usage, acks require additional receive-send turnarounds, which also incur time penalty • Reduction of contention between data and acks, and frequency of send-receive turnaround • Mitigation [Balakrishnan97] • Piggybacking link layer acks with data • Sending fewer TCP acks - ack every d-th packet (d may be chosen dynamically) • Ack filtering - Gateway may drop an older ack in the queue, if a new ack arrives Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • TCP Parameters after Route Repair • Window Size after route repair • • • • Same as before route break: may be too optimistic Same as startup: may be too conservative Better be conservative than overly optimistic Reset window to small value; let TCP learn the window size • Retransmission Timeout (RTO) after route repair • Same as before route break: may be too small for long routes • Same as TCP start-up: may be too large and respond slowly to packet loss • new RTO could be made a function of old RTO and route lengths Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Link, Network and Transport Layers Considerations • Improving TCP Throughput • Network feedback • Network knows best (why packets are lost) • Need to modify transport & network layer to receive/send feedback - Need mechanisms for information exchange between layers • Inform TCP of route failure by explicit message • Let TCP know when route is repaired • Probing • Explicit notification • Better route caching mechanisms • Reduces repeated TCP timeouts and backoff Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Ubiquitous computing • Computing is the process of using computer technology to complete a given goal-oriented task. Computing may encompass the design and development of software and hardware systems for a broad range of purposes. • Computing Generations • The first era of computing is known as the Mainframe era – many people to one computer. This computer was the central system from which entire offices, and sometimes, companies called their computing infrastructure. • The second era of computing is known as the PC era – one computer to one person. • The third era of computing is known as the Ubiquitous computing - one person using many computers. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Ubiquitous computing • Ubiquitous computing: The method of enhancing computing use by making many devices (services) available throughout the physical environment but making them effectively invisible to the user “Mark Weiser”. • The information processing has been thoroughly integrated into everyday objects and activities . • Goal: any device, from clothing to tools to appliances to cars to homes to the human body to your coffee mug, can be imbedded with chips to connect the device to an infinite network of other devices. • Physical space with embedded computing/sensing power creates an heretofore unseen fusion. • It is also called pervasive computing. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Ubiquitous computing Example • A corridor or room automatically adjusts heating, cooling and lighting levels based on the occupant’s profile. • “Smartness” may extend to individual objects [e.g. moldable handles that reshape themselves, cars that automatically adjust steering wheel and seat placement] regardless of the space they are in. • Smart” software. [Simple example: “vacation/out of office” messages] Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Ubiquitous computing • In order to do this, nodes must: 1. 2. 3. 4. 5. self-organize themselves into ad hoc networks divide the task of monitoring among themselves perform tasks in an energy-efficient manner adapt sensing quality only to the available resources reorganize upon failure or addition of nodes. • Location is one of the most important components of user context. It can be also used to infer additional pieces of context, such as user activity, mode of transportation, and social relationship. • Location technologies is a major part of the ubiqutious systems. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Determining location • Specific location • Context information • Context aware applications Trade-offs: accuracy, range and cost [Ranging accuracy from one milimeter(magnetic fields) to tens of kilomters (radio frequency)] Examples Entertainment, Navigation, Asset tracking, Healthcare monitoring, Emergency response Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Location Representation Forms • Absolute • Relative • Symbolic Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Three Classes of Location Systems • Client-based: device computes it own location by using signals that comes from the satellite or a network. ✓ Gps • Network-based: network infrastructure will calculate the device’s location. It is commonly used in the buildings to detect where is the user. ✓ Active Badge • Network-network assisted location: both device and the infrastructure take place in calculating the position. • LOCATION PRIVACY X • Battery Life • Processing and Store Capability ✓ aGps Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Approaches to Determining Location • Proximity • Trilateration - Time of Flight - Signal Strength Attenuation • Hyperbolic Lateration • Triangulation • Dead Reckoning • Some of these techniques requires one or more reference points whose precise location is known in advance. Dr. Mohammed Balfaqih reference points ➢GPS satellite ➢WiFi access point ➢Cellular Tower CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Proximity • NFC in cms • device vs reference point • closeness of a device • more RP -> more accuracy examples • Bluetooth 10ms • WiFi 100ms • Cellular phone kms Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Trilateration • distance between a device and a number of reference points • intersections of reference point circles • types: ➢ time of flight of signal ➢ attenuation of the strength of the signal Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Trilateration / Time of Flight KNOWN • Speed of Sound : 344 meters per second in 21° C • Speed of Light : NEEDS • precise clock synchronization • instead round trip delay 299,792,458 meters per second EASY TO CALCULATE! X = V.t Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Trilateration / Signal Strength Attenuation -decrease of the signal’s strength by factor of 1/r² -r:distance from source Challenges -signal propagation medium -reflaction, diffraction,changing direction Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Hyperbolic Lateration • CALCULATION time difference between signal arrival times to more 3 rp. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Triangulation the angle of arrival (AOA) of signals to reference points !angle measurement errors. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Dead Reckoning • USES - previously known location - elapsed time - direction - average speed • DEPENDS ON - accuracy of speed and direction, - use of accelemators for acceleration, odometers for distance, gyroscope for direction Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Error Sources • AIM - produce accurate location estimates • Sources of Errors - Incorrect reference point coordinates - Delay in signal - Clock synchronization - Multipath - Geometry Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Location in ubiquitous computing environments Characteristics • Metrics for Evaluation - Scalability - Resolution - Active vs. Passive - Centralization - Infrastructure • Dr. Mohammed Balfaqih Properties - Scalability Resolution Active vs. Passive Centralization Infrastructure • Concerns - Indoor/Outdoor, Pervasiveness - Accuracy, Performance - Initiating, Tag Carrying - Privacy Concerns - Multiple Deployment, Cost Security and privacy in ubiquitous computing environments • Two types of security and privacy issues: location and trust • Location 1. Don’t want to store location information in a centralized location because a hack would reveal all information 2. Instead, store information about each person at a local PC or workstation. (Still, there are serious consequences to accumulating information about individuals over long periods of time. Implication arises that there is never a purely technological solution to privacy, but by giving more power to individual helps move society towards a more private technological world.) Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Security and privacy in ubiquitous computing environments • Trust 1. As a user becomes more dependent on a pervasive computing system, it becomes more knowledgeable about that user’s movements, behavior patterns and habits. 2. Information must be strictly controlled in order to protect it from being used in unsavory situations (ie. targeted spam or blackmail). 3. Greater reliance on infrastructure means a user must trust that infrastructure and the infrastructure needs to be confident of the user’s identity and authorization level. 4. Difficult challenge to establish trust between both the infrastructure and the user in a manner that is minimally intrusive and preserves the goal of ubiquitous computing: invisibility. Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Data collection in sensor networks • Sensor – A device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument • Sensor sensitivity – How much the sensor's output changes when the measured quantity changes Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Data collection in sensor networks Sensor Types • Thermal: Temperature/heat sensors • Electromagnetic: Electrical resistance/voltage/power sensors, magnetism sensors, metal detectors, RADAR • Mechanical: Acceleration, position, pressure, switch, liquid sensors • Chemical: Odor (smell) sensor, oxygen sensors • Optical radiation: Light sensors, infra-red sensor, proximity sensor • Acoustic: Sound sensors • Motion sensors: Radar gun, speedometer, tachometer, odometer • Orientation sensors: Gyroscope Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Data collection in sensor networks Sensors in Ubiquitous Environment • Information processing has been thoroughly integrated into everyday objects and activities → Ubiquitous environments • Paradigm change – Ordinary: a single user consciously engages a single device for a specialized purpose – New: engages many computational devices and systems simultaneously, in the course of ordinary activities, and may not necessarily even be aware that they are doing so • Related technologies – Ubiquitous computing, pervasive computing, ambient intelligence – Haptic computing, things that think Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks Data collection in sensor networks Sensors in Ubiquitous Environments • Body Sensor – Physiological sensor – Biosensor: Identity, emotion, facial expression, behavior, gait – Location sensor (GPS) • Environment Sensor – Video camera – Light – Noise & sound – Temperature & humidity – Pressure – Movement – Acceleration • Object Sensor – Position & status of object Data collection in sensor networks Service & Applications • Application model • Services Data collection in sensor networks Object Sensors Dr. Mohammed Balfaqih Smart Bag - MIT bYOB Project Data collection in sensor networks Body Sensors (1) Microsoft’s SenseCam Microsoft’s Spot Watch Body Media’s ArmBand Adias’ Intelligent Shoes Dr. Mohammed Balfaqih Data collection in sensor networks Body Sensors (2) Dr. Mohammed Balfaqih Olympus Optical Co., Ltd. is pleased to announce its new wearable user interface technologies. Employing gestures and other hand movements for input, the system is an ideal match for new wearable PCs. Data collection in sensor networks Body Sensors (3) eSleeve of Univ. of Bristol, UK Dr. Mohammed Balfaqih http://www.redwoodhouse.com/wearable/index.html http://wearables.cs.bris.ac.uk/public/wearables/esleeve.htm http://www.ices.cmu.edu/design/streetware/ Data collection in sensor networks Environment Sensors Smart Dust of UC Berkeley Dr. Mohammed Balfaqih Data collection in sensor networks Integrated Sensors (1) Dr. Mohammed Balfaqih Data collection in sensor networks Integrated Sensors (2) Dr. Mohammed Balfaqih Data collection in sensor networks Integrated Sensors (3) Dr. Mohammed Balfaqih Thank you Dr. Mohammed Balfaqih CCCN 422: Wireless Communication Networks