1

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

2

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

5

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.

6

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

7

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

8

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

9

� 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

10

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

12

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.

13

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

14

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

15

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)

16

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

17

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

18

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

19

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

20

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

21

Infrastructure Access

• Access Points:

— Provide infrastructure access to mobile users

— Cover a fixed area

— Wired into LAN

Peer to Peer Ad Hoc Mode

22

Infrastructure Access

Infrastructure Access

23

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!

24

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!

25

Channel 1 Channel 6

Channel 11

26

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

27

Peer to Peer Ad Hoc Mode

X

XX

Problems

• Communication is only possible between nodes which are directly in range of each other

28

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

29

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

30

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

31

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

32

Mobile Ad Hoc Networks

• May need to traverse multiple links to reach a destination

Mobile Ad Hoc Networks (MANET)

• Mobility causes route changes

33

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

34

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

35

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

36

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

37

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