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PART 4
Multimedia & Multimedia Networking
MSCEG442
Wireless networking
Contents
• 4.1 INTRODUCTION
• 4.2 WiFi 802.11a/b/g NETWORKS
• 4.3 MOBILE AD-HOC NETWORKS
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4.1 INTRODUCTION
• In this section we will present some history, future vision and some present wireless technologies
Is there a future for wireless?Some history
• Radio invented in the 1880s by Marconi
� Many sophisticated military radio systems were developed during and after WW2
� Cellular has enjoyed exponential growth since 1988, with almost 1 billion users worldwide today
� Ignited the recent wireless revolution� Growth rate tapering off� 3G (voice+data) roll-out disappointing
� Many spectacular failures recently� 1G Wireless LANs/Iridium/Metricom
RIP
Wireless
Revolution
1980-2003
� Ancient Systems: Smoke Signals, Carrier Pigeons, …
3
Glimmers of Hope
• Internet and laptop use exploding
• 2G/3G wireless LANs growing rapidly
• Low rate data demand is high
• Military and security needs require wireless
• Emerging interdisciplinary applications
Future Wireless Networks
Wireless Internet accessNth generation CellularWireless Ad Hoc NetworksSensor Networks Wireless EntertainmentSmart Homes/SpacesAutomated HighwaysAll these and more…
Ubiquitous Communication Among People and Devices
•Hard Delay Constraints
•Hard Energy Constraints
4
Design Challenges
• Wireless channels are a difficult and capacity-limited broadcast communications medium
• Traffic patterns, user locations, and network conditions are constantly changing
• Applications are heterogeneous with hard constraints that must be met by the network
• Energy and delay constraints change design principles across alllayers of the protocol stack
Multimedia Requirements
Voice VideoData
Delay
Packet Loss
BER
Data Rate
Traffic
<100ms - <100ms
<1% 0 <1%
10-3 10-6 10-6
8-32 Kbps 1-100 Mbps 1-20 Mbps
Continuous Bursty Continuous
One-size-fits-all protocols and design do not work well
Wired networks use this approach, with poor results
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Wireless Performance Gap
WIDE AREA CIRCUIT SWITCHING
User
Bit-Rate
(kbps)
14.4digitalcellular
28.8 modem
ISDN
ATM
9.6 modem
2.4 modem2.4 cellular
32 kbps
PCS
9.6 cellular
wired- wireless
bit-rate "gap"
1970 200019901980YEAR
LOCAL AREA PACKET SWITCHING
User
Bit-Rate
(kbps)
Ethernet
FDDI
ATM100 M
Ethernet
Polling
Packet
Radio
1st gen
WLAN
2nd gen
WLAN
wired- wirelessbit-rate "gap"
1970 200019901980.01
.1
1
10
100
1000
10,000
100,000
YEAR
.01
.1
1
10
100
1000
10,000
100,000
Evolution of Current Systems
• Wireless systems today— 2G Cellular: ~30-70 Kbps.— WLANs: ~10 Mbps.
• Next Generation— 3G Cellular: ~300 Kbps.— WLANs: ~70 Mbps.
• Technology Enhancements— Hardware: Better batteries. Better circuits/processors.— Link: Antennas, modulation, coding, adaptivity, DSP, BW.— Network: Dynamic resource allocation. Mobility support.— Application: Soft and adaptive QoS.
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Future Generations
Rate
Mobility
2G
3G
4G802.11b WLAN
2G Cellular
Other Tradeoffs:
Rate vs. Coverage
Rate vs. Delay
Rate vs. Cost
Rate vs. Energy
Fundamental Design Breakthroughs Needed
Crosslayer Design
• Hardware
• Link
• Access
• Network
• Application
Delay Constraints
Rate Constraints
Energy Constraints
Adapt across design layers
Reduce uncertainty through scheduling
Provide robustness via diversity
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Current Wireless Systems
• Cellular Systems
• Wireless LANs
• Satellite Systems
• Paging Systems
• Bluetooth
Cellular Systems:Reuse channels to maximize capacity
• Geographic region divided into cells• Frequencies/timeslots/codes reused at spatially-separated locations.• Co-channel interference between same color cells.• Base stations coordinate handoff and control functions• Shrinking cell size increases capacity, as well as networking burden
BASE
STATION
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Cellular Phone Networks
BSBS
Base
Station PSTNBase
Station
BS
Limassol
NicosiaInternet
3G Cellular Design: Voice and Data
• Data is bursty, whereas voice is continuous— Typically require different access and routing strategies
• 3G “widens the data pipe”:— 384 Kbps.— Standard based on wideband CDMA— Packet-based switching for both voice and data
• 3G cellular struggling in Europe and Asia
• Evolution of existing systems (2.5G,2.6798G):• GSM+EDGE• IS-95(CDMA)+HDR• 100 Kbps may be enough
• What is beyond 3G?
The trillion dollar question
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� WLANs connect “local” computers (100m range)
� Breaks data into packets
� Channel access is shared (random access)
� Backbone Internet provides best-effort service
� Poor performance in some apps (e.g. video)
01011011
Internet
Access
Point
0101 1011
Wireless Local Area Networks (WLANs)
Wireless LAN Standards
• 802.11b (Current Generation)— Standard for 2.4GHz ISM band (80 MHz)— Frequency hopped spread spectrum— 1.6-10 Mbps, 500 ft range
• 802.11a (Emerging Generation)— Standard for 5GHz NII band (300 MHz)— OFDM with time division— 20-70 Mbps, variable range— Similar to HiperLAN in Europe
• 802.11g (New Standard)— Standard in 2.4 GHz and 5 GHz bands— OFDM — Speeds up to 54 Mbps
In 200?,
all WLAN
cards will
have all 3
standards
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Satellite Systems
• Cover very large areas
• Different orbit heights— GEOs (39000 Km) versus LEOs (2000 Km)
• Optimized for one-way transmission— Radio (XM, DAB) and movie (SatTV) broadcasting
• Most two-way systems struggling or bankrupt— Expensive alternative to terrestrial system
— A few ambitious systems on the horizon
Paging Systems
• Broad coverage for short messaging
• Message broadcast from all base stations
• Simple terminals
• Optimized for 1-way transmission
• Answer-back hard
• Overtaken by cellular
11
8C32810.61-Cimini-7/98
Bluetooth
• Cable replacement RF technology (low cost)
• Short range (10m, extendable to 100m)
• 2.4 GHz band (crowded)
• 1 Data (700 Kbps) and 3 voice channels
• Widely supported by telecommunications, PC, and consumer electronics companies
• Few applications beyond cable replacement
Ad-Hoc Networks
• Peer-to-peer communications.
• No backbone infrastructure.
• Routing can be multihop.
• Topology is dynamic.
• Fully connected with different link SINRs
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Design Issues
• Ad-hoc networks provide a flexible network infrastructure for many emerging applications.
• The capacity of such networks is generally unknown.
• Transmission, access, and routing strategies for ad-hoc networks are generally ad-hoc.
• Crosslayer design critical and very challenging.
• Energy constraints impose interesting design tradeoffs for communication and networking.
Sensor NetworksEnergy is the driving constraint
— Nodes powered by nonrechargeable batteries— Data flows to centralized location.— Low per-node rates but up to 100,000 nodes.— Data highly correlated in time and space.— Nodes can cooperate in transmission, reception, compression, and
signal processing.
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Energy-Constrained Nodes
• Each node can only send a finite number of bits.
— Transmit energy minimized by maximizing bit time
— Circuit energy consumption increases with bit time
— Introduces a delay versus energy tradeoff for each bit
• Short-range networks must consider transmit, circuit, and processing energy.
— Sophisticated techniques not necessarily energy-efficient.
— Sleep modes save energy but complicate networking.
• Changes everything about the network design:
— Bit allocation must be optimized across all protocols.
— Delay vs. throughput vs. node/network lifetime tradeoffs.
— Optimization of node cooperation.
Distributed Control over Wireless Links
• Packet loss and/or delays impacts controller performance.
• Controller design should be robust to network faults.
• Joint application and communication network design.
Automated Vehicles- Cars- UAVs- Insect flyers
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Joint Design Challenges
• There is no methodology to incorporate random delays or packet losses into control system designs.
• The best rate/delay tradeoff for a communication system in distributed control cannot be determined.
• Current autonomous vehicle platoon controllers are not string stable with any communication delay
Can we make distributed control robust to the network?
Yes, by a radical redesign of the controller and the network.
Spectrum Regulation
• Spectral Allocation in US controlled by FCC (commercial) or OSM (defense)
• FCC auctions spectral blocks for set applications.
• Some spectrum set aside for universal use
• Worldwide spectrum controlled by ITU-R
Regulation can stunt innovation, cause economic
disasters, and delay system rollout
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Standards
• Interacting systems require standardization
• Companies want their systems adopted as standard
— Alternatively try for de-facto standards
• Standards determined by TIA/CTIA in US
— IEEE standards often adopted
• Worldwide standards determined by ITU-T— In Europe, ETSI is equivalent of IEEE
Standards process fraught with
inefficiencies and conflicts of interest
Spring 2008 MSCEG442
Wireless Spectrum(LAN vs. WAN)
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Wireless MAP
• Where do we spend our time?
— office (wireless LAN and wireless PBX)
— residential, public area (PHS, CT-2)
— mobile (GSM, GPRS, 3G)
Wireless WAN vs. LAN
• Wireless WAN:
— transmission speed: 10K-1M
— real-time voice supported: circuit-switching
— ubiquitous coverage
— roaming speed: vehicular
• Wireless LAN:
— transmission speed: > 1Mbps
— packet-switching
— coverage: a few hundred meters
— roaming speed: pedestrian
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Wireless WAN Examples
• cellular: now moving from analog to digital
• paging: one-way alerting
• packet-radio: data service (RAM, Mobitex)
• satellite: low earth-orbit system
— Motorola’s Iridium system: 66 satellites
— Qualcomm and Microsoft: > 800 satellites
• cordless: smaller cells (DECT)
• PCS: voice + data
The Radio Spectrum
103
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Radio Spectrum (cont.)
• We separate frequencies as “extremely low”, “very low”, “medium”, “high”, “very high”, “ultra high”, “microwave region”, “infrared region”, “visible light region”, and “X-ray”.
• Audio:
— 20 Hz to 20 KHz
• AM radio station: 1 MHz
• FM and TV: 100 MHz
• Paging: 50~500 MHz
• Mobile Radio: < 1 GHz
• Cordless and PCS: about 2GHz
— Why most wireless networking services are crowded around 1~2 GHz? availability (but is becoming full in recent years)
• To move to higher frequency:
— need to use Gallium Arsenide (GaAs): more expensive
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Cell Size vs. Throughput
• Cell sizes can vary from tens of meters to thousands of kilometers.
• Data rates may range from 0.1 K to 50 Mbps
• Examples:
— LAN: high rate (11 M), small range (50 m)
— Satellite: low rate (10 K), extremely large range (1000 Km)
— Paging: very low rate (1 Kbps), large cell (10s of Km)
Contents
• 4.1 INTRODUCTION
• 4.2 WiFi 802.11a/b/g NETWORKS
• 4.3 MOBILE AD-HOC NETWORKS
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4.2 Wi-Fi 802.11a/b/g Networks
• In this section we will present the 802.11a/b/g infrastructure, operation and problems associated with it as well as mobile ad-hoc networks
802.11a/b/g
• Operates in 2 different modes:
— Infrastructure mode
• Associates with an access point
• All communication goes through the access point
• Used for wireless access at a company or campus
— Peer-to-Peer Ad Hoc Mode
• If two nodes are within range of each other they can communicatedirectly with no access point
• A few users in a room could quickly exchange files with no access point required
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Infrastructure Access
• Access Points:
— Provide infrastructure access to mobile users
— Cover a fixed area
— Wired into LAN
Peer to Peer Ad Hoc Mode
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Infrastructure Access
Infrastructure Access
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1 Mbps
2 Mbps
5.5 Mbps
11 Mbps
802.11a/b/g are multi-rate devices
MAC Layer Fairness Models
• Per Packet Fairness: If two adjacent senders continuously are attempting to send packets, they should each send the same number of packets.
• Temporal Fairness: If two adjacent senders are continuously attempting to send packets, they should each be able to send forthe same amount of medium time.
• In single rate networks these are the SAME!
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Temporal Fairness Example
3.9831.609Total
Throughput
0.4500.7131 Mbps Link
3.5330.89611 Mbps
Link
OAR
Temporal Fairness
802.11
Packet Fairness
1 Mbps
11 Mbps
1 Mbps
11 Mbps
Per Packet Fairness
Temporal Fairness
802.11b Channels
• 11 available channels (in US)
• Only 3 are non-overlapping!
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Channel 1 Channel 6
Channel 11
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Problems
• Access Point placement depends on wired network availability
• Obstructions make it difficult to provide total coverage of an area
• Site surveys are performed to determine coverage areas
• Security Concerns: rogue access points in companies etc..
• Each Access Point has limited range
Peer to Peer Ad Hoc Mode
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Peer to Peer Ad Hoc Mode
X
XX
Problems
• Communication is only possible between nodes which are directly in range of each other
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Problems for both Infrastructure and Ad hoc Mode
• If nodes move out of range of the access point (Infrastructure Mode)
• OR nodes are not in direct range of each other (Ad Hoc Mode)
• Then communication is not possible!!
What if ??
OR
Multi-hop Infrastructure AccessMulti-hop Ad Hoc Network
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Multi-hop Infrastructure Access
• Nodes might be out of range of the access point, BUT in range of other nodes.
• The nodes in range of the access point could relay packets to allow out of range nodes to communicate.
• NOT part of 802.11
Multi-hop Ad Hoc Network
• If communication is required between two nodes which are out of range of each other, intermediary nodes can forward the packets.
• NOT part of 802.11
Source Destination
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How can this be done?
• ROUTING!!
— Wired Networks:
• Hierarchical Routing
– Network is divided into subnets
– Nodes look at netmask and determine if the address is directly reachable. If not, just forward to the default gateway.
– Different protocols for different levels of the hierarchy
• RIP, OSPF, BGP
Wireless Routing
• Flat routing
— You can’t assume that since a node is in your subnet that it is directly accessible
— Node must maintain or discover routes to the destination
— All nodes are routers
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Contents
• 4.1 INTRODUCTION
• 4.2 WiFi 802.11a/b/g NETWORKS
• 4.3 MOBILE AD-HOC NETWORKS
Mobile Ad Hoc Networks
• Formed by wireless hosts which may be mobile
• Without (necessarily) using a pre-existing infrastructure
• Routes between nodes may potentially contain multiple hops
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Mobile Ad Hoc Networks
• May need to traverse multiple links to reach a destination
Mobile Ad Hoc Networks (MANET)
• Mobility causes route changes
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Why Ad Hoc Networks ?
• Ease of deployment
• Speed of deployment
• Decreased dependence on infrastructure
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
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Challenges
• Limited wireless transmission range
• Broadcast nature of the wireless medium
• Packet losses due to transmission errors
• Mobility-induced route changes
• Mobility-induced packet losses
• Battery constraints
• Potentially frequent network partitions
• Ease of snooping on wireless transmissions (security hazard)
Spring 2008 MSCEG442
Unicast RoutinginMobile Ad Hoc Networks
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Why is Routing in MANET different ?
• Host mobility
— link failure/repair due to mobility may have different characteristics than those due to other causes
• Rate of link failure/repair may be high when nodes move fast
• New performance criteria may be used
— route stability despite mobility
— energy consumption
Unicast Routing Protocols
• Many protocols have been proposed
• Some have been invented specifically for MANET
• Others are adapted from previously proposed protocols for wired networks
• No single protocol works well in all environments
— some attempts made to develop adaptive protocols
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Routing Protocols
• Proactive protocols
— Determine routes independent of traffic pattern
— Traditional link-state and distance-vector routing protocols are proactive
• Reactive protocols
— Maintain routes only if needed
• Hybrid protocols
Trade-Off
• Latency of route discovery
— Proactive protocols may have lower latency since routes are maintained at all times
— Reactive protocols may have higher latency because a route from X to Y will be found only when X attempts to send to Y
• Overhead of route discovery/maintenance
— Reactive protocols may have lower overhead since routes are determined only if needed
— Proactive protocols can (but not necessarily) result in higher overhead due to continuous route updating
• Which approach achieves a better trade-off depends on the traffic and mobility patterns
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References
• W. Stalling, Local and Metropolitan Area Networks, 6th
edition, Prentice Hall, 2000
• F. Halsall, Data Communications, Computer Networks and Open Systems, 4th edition, Addison Wesley, 1995
• B.A. Forouzan, Data Communications and Networking, 4th edition, McGraw-Hill, 2007
• W. Stallings, Data and Computer Communications, 7th edition, Prentice Hall, 2004