Bikash Ch. Sadhukhan. M.Tech (CSE)

Lecturer. Dept of CSE/IT

Techno India College of Technology

Wireless network

� Roughly speaking there are two types of wireless networks:� Local Area Networks (LAN)

� Bluetooth, 802.11 Family, HiperLAN Family, HomeRF...

� Wide Area Networks (WAN)� Wide Area Networks (WAN)

� GSM, 3G, 4G, Iridium...

Mobile Communication Technology

according to IEEE (examples)

Wireless LANs

� A Wireless LAN or WLAN is a wireless local area network, which is the linking of two or more computers without using wires.

� WLAN utilizes spread-spectrum technology based on � WLAN utilizes spread-spectrum technology based on radio waves to enable communication between devices in a limited area, also known as the basic service set. This gives users the mobility to move around within a broad coverage area and still be connected to the network.

Characteristics of wireless LAN

� Advantages

� very flexible within the reception area

� Ad-hoc networks without previous planning possible

� (almost) no wiring difficulties

� more robust against disasters like, e.g., earthquakes, fire -or users pulling a plug...

� Disadvantages

� typically very low bandwidth compared to wired networks

� (1-10 Mbit/s) due to shared medium

� many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11n)

� products have to follow many national restrictions if working wireless, it takes a vary long time to establish global solutions like, e.g., IMT-2000

Design goals for wireless LANs

� Global, seamless operation

� Low power for battery use

� No special permissions or licenses needed to use the LAN

� robust transmission technology

� Simplified spontaneous cooperation at meetings � Simplified spontaneous cooperation at meetings

� Easy to use for everyone, simple management

� Protection of investment in wired networks

� Security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation)

� Transparency concerning applications and higher layer protocols, but also location awareness if necessary

Comparison: Infrared v/s Radio

transmission

Infrastructure network vs. Ad-hoc

networks

Infrastructure network vs. Ad-hoc

networks

� In Infrastructure network, the mobile stations(MS) are connected to a base stations or access points(AP). This is similar to a star network where all the mobile stations are attached to the base stations. Through a protocol the base attached to the base stations. Through a protocol the base station manages the dialogues between the AP and the MS.

� In an ad-hoc network, there is no access point or infrastructure. A number of mobile stations from a cluster communicate with each other. Actually there is no fixed physical topology defined for the ad-hoc network.

IEEE 802.11 Standards – Frequencies -Throughputs

IEEE has defined the specification for a wireless LAN, which is called as IEEE 802.11. The 802.11 family currently includes six over-the-air modulation techniques.

� 802.11b was the first widely accepted wireless networking standard, followed by 802.11a and 802.11g.

� 802.11b, is a standard for wireless LANs operating in the 2.4 GHz spectrum with a bandwidth of 11 Mbps.spectrum with a bandwidth of 11 Mbps.

� 802.11a is a different standard for wireless LANs operating in the 5 GHz frequency range with a maximum data rate of 54 Mbps.

� Another draft standard, 802.11g, is for WLANs operating in the 2.4 GHz frequency but with a maximum data rate of 54 Mbps.

2 Part ConceptStandards & Throughputs

•802.11b 11Mbps•802.11a 54Mbps•802.11g 54Mbps

Frequencies

•2.4 GHz•5.0 GHz•2.4 GHz

802.11 -Architecture of Wireless LAN

� Station (STA) - Each computer, mobile, portable or fixed, is referred to as a station.

� Basic Service Set (BSS) - When two or more stations come togetherto communicate with each other, they form a Basic Service Set (BSS).The minimum BSS consists of two stations. A BSS that stands aloneand is not connected to a base is called an Independent Basic ServiceSet (IBSS) or is referred to as an Ad-Hoc Network.Set (IBSS) or is referred to as an Ad-Hoc Network.

802.11 -Architecture of Wireless LAN� Extended Service Set (ESS) - Two or more BSS's are interconnected using

a Distribution System or DS. This concept of DS increases network coverage. Each BSS becomes a component of an extended, larger network. Several BSSs connected through APs form an ESS.

� Access Point (AP) -Entry to the DS is accomplished with the use of Access Points (AP). An access point is a station, thus addressable. So, data moves between the BSS and the DS with the help of these access points.between the BSS and the DS with the help of these access points.

802.11 -Architecture of an ad-hoc network

� Direct communication within a limited range

� Station (STA):terminal with access mechanisms to the wireless medium

� Independent Basic Service Set (IBSS):group of stations using the same radio frequency using the same radio frequency

WLAN MAC Layer and Physical LayerWLAN MAC Layer and Physical Layer

Physical LayerWLAN uses different alternative signal generation methods for conversion of bits to a signal in the physical layer.

FHSS: FHSS: Frequency Hopping Spread Spectrum is a method in which a sender sends on one carrier frequency for a short amount of time, then hops to another carrier frequency for the same amount of time. Hops again to still another for the same amount of time, and so on. After N hopping the cycle is repeated. If the bandwidth of the original signal is B, the allocated spread spectrum bandwidth is N X B.

� Spreading makes it difficult for unauthorized persons to make sense of � Spreading makes it difficult for unauthorized persons to make sense of transmitted data.

� Maximum bit rate in this scheme is 2 Mbits/s.

� FHSS uses a 2.4 GHz ISM Band. The band is divided into 79 sub bands of 1 Mhz.

4 1 5 2 3 Frequency

Amplitude

Order of Transmission: 1,2,3,4,5

Physical LayerDSSS:Direct Sequence Spread Spectrum is a method in which each bit

sent by the sender is replaced by a sequence of bits called a chip code. Toavoid buffering, however, the time needed to send one chip code must bethe same as the time needed to send one original bit.

� Although this scheme is similar to CDMA, there is a major difference.DSSS is implemented at the physical layer. It is not a multiple accessmethodfor thedatalink layer.methodfor thedatalink layer.

� Maximum bit rate in this scheme is 11 Mbits/s.

� DSSS also uses 2.4 GHz ISM Band.

0 1 1 00

110011 110011 110011000111 000111

Chip code for 0: 110011 Chip code for 1: 000111

� OFDM: OFDM describes the ortogonal frequency division multiplexing method for signal generation in 5 Ghz ISM Band. OFDM is same as FDM, with one major difference all the subbands are used by one source at a given time and the bit rates are 6-54 Mbps.

� HR- DSSS: High Rate-Direct Sequence Spread Spectrum method for signal generation uses 2.4 Ghz ISM band with a maximum bit rate 11 Mbps.

Physical Layer

signal generation uses 2.4 Ghz ISM band with a maximum bit rate 11 Mbps. HR-DSSS is similar to DSSS except for the encoding method, which is called Complementary Code Keying (CCK). CCK encodes 4 or 8 bits to one CCK symbol.

� Infrared: It uses 850-950 nm wavelength with a maximum bitrate of 2 Mbps

Hidden station problem

� Stations A and C have a frame to transmit to station B. Station A cannot detect C’s transmission because it is outside the transmission range of C. Station C (resp. A) is therefore “hidden” to station A (resp. C). Since A and C transmission areas are not disjoint, there will be packet collisions at B. These collisions make the transmission from A and C toward B problematic.

Figure: Hidden terminal problem. Packet sent to B by A and C will collide at B

Exposed station problem

� The exposed station problem results from a situation where a transmission has to be delayed because of the transmission between two other stations within the sender’s transmission range.

� Let us assume that A and C are within B’s transmission range, and A is outside C’s transmission range. Let us also assume that B is transmitting to A, and C has a frame to be transmitted to D. According to the carrier sense mechanism, C senses a busy channel because of B’s transmission. Therefore, station C will refrain from transmitting to D, although this transmission station C will refrain from transmitting to D, although this transmission would not cause interference at A.

� The exposed station problem may thus result in a reduction of channel utilization.

Figure: Exposed Terminal problem: Because of B’s Transmission C refrains transmission to D

MAC layer

�MAC layer for medium access control has the following features

� CSMA/CD

� Point coordination support for time-bound applicationsapplications

� Acknowledged RTS/CTS (request to send/clear to send) mechanism before the data transmission

MAC layers in IEEE 802.11 standard

� IEEE 802.11 defines two MAC sub layer� Distributed coordination function (DCF): DCF uses CSMA/CA as the access method.

� Point Coordination function (PCF):The access method used in the point coordination function (PCF) MAC sub layer is polling.

CSMA/CA flowchart

Collision Avoidance: RTS-CTS

exchange

The network allocation vector (NAV) is a timer used for collision

avoidance

WLAN: IEEE 802.11b

WLAN: IEEE 802.11a

WLAN: IEEE 802.11-Current Developments

HIPER LAN

� Two main standards families for Wireless Lan:

� IEEE 802.11 (802.11b, 802.11a, 802.11g...)

� ETSI Hiperlan (Hiperlan Type 1, Type 2, HiperAccess, HiperLink...)HiperAccess, HiperLink...)

HIPER LAN

� HiperLAN is a set of wireless local area network (WLAN) communication standards primarily used in European countries.

� There are two specifications: HiperLAN/1 and HiperLAN/2. Both have been adopted by the European Telecommunications Standards Institute (ETSI).

� The HiperLAN standards provide features and capabilities similar to � The HiperLAN standards provide features and capabilities similar to those of the IEEE 802.11 wireless local area network standards, used in the U.S. and other adopting countries.

� HiperLAN/1 provides communications at up to 20 Mbps in the 5-GHz range of the radio frequency (RF) spectrum.

� HiperLAN/2 operates at up to 54 Mbps in the same RF band. HiperLAN/2 is compatible with 3G (third-generation) WLAN systems for sending and receiving data, images, and voice communications.

HiperLAN Family

Hiperlan 1 Hiperlan2 HiperAccess HiperLinkDescription Wireless

EthernetWireless ATM Wireless Local

LoopWireless Point-

to-PointFreq. Range 5GHz 5GHz 5GHz 17GHz

PHY Bit Rate 23.5Mbps 6~54Mbps ~25Mbps

(data rate)

~155Mbps

(data rate)

HiperLAN Type 1

� Developed by ETSI during 1991 to 1996

� Goal: to achieve higher data rate than IEEE 802.11 data rates: 1~2 Mbps, and to be used in ad hoc networking of portable devices

� Support asynchronous data transfer, carrier-sense � Support asynchronous data transfer, carrier-sense multiple access multiple access with collision avoidance (CSMA/CA), no QoS guaranteed.

� Products� Proxim's High Speed RangeLAN5 product family (24Mbps; 5GHz; QoS guaranteed)

� RadioLAN’s products for indoor wireless communication (10Mbps; 5GHz; Peer-to-Peer Topology)

HiperLAN Type 2

� Next generation of HiperLAN family: Proposed by

ETSI BRAN (Broadband Radio Access Networks) in

1999, and is still under development.

� Goal: Providing high-speed (raw bit rate ~54Mbps)

communications access to different broadband core communications access to different broadband core

networks and moving terminals

� Features: connection-oriented, QoS guaranteed,

security mechanism, highly flexibility

� Product: Prototypes are available now, and commercial

products are available at the end of 2001 (Ericsson).

Comparison with Peers

� Main competitor: IEEE 802.11 Family

� Pros

� High rate with QoS support: Suitable for data and multimedia app.

� Security mechanism

� Flexibility: different fixed network support, link adaptation, dynamic frequency selection…

� Cons� High cost

� Tedious protocol specification

� Limited outdoor mobility

� No commercial products in market till now

WATM

Some history: Why wireless ATM?� Seamless connection to wired ATM, a integrated services high performance network supporting different types a traffic streams

� ATM networks scale well: private and corporate LANs, WAN

� B-ISDN uses ATM as backbone infrastructure and integrates several different services in one universal systemseveral different services in one universal system

� Mobile phones and mobile communications have increasing importance in everyday life current wireless LANs do not offer adequate support for multimedia data streams

� Merging mobile communication and ATM leads to wireless ATM from a telecommunication provider point of view

� Goal: seamless integration of mobility into B-ISDN

� Problem: very high complexity of the system – never reached products

WATM services

� Office environment� multimedia conferencing, online multimedia database access

� Universities, schools, training centers� distance learning, teaching

� Industry� database connection, surveillance, real-time factory management� database connection, surveillance, real-time factory management

� Hospitals� reliable, high-bandwidth network, medical images, remote monitoring

� Home� high-bandwidth interconnect of devices (TV, CD, PC, ...)

� Networked vehicles� trucks, aircraft etc. interconnect, platooning, intelligent roads

WATM Reference model

WATM components

� WMT (Wireless Mobile ATM Terminal)

� RAS (Radio Access System)

� EMAS-E (End-user Mobility-supporting ATM Switch - Edge)

� EMAS-N (End-user Mobility-supporting ATM Switch - Network)

� M-NNI (Network-to-Network Interface with Mobility support)

� LS (Location Server)

� AUS (Authentication Server)

BRAN – Broadband Radio Access Networks

� Motivation

� deregulation, privatization, new companies, new services

� How to reach the customer?

� alternatives: xDSL, cable, satellite, radio

� Radio access

� flexible (supports traffic mix, multiplexing for higher efficiency, can be asymmetrical)asymmetrical)

� quick installation

� economic (incremental growth possible)

� Market

� private customers (Internet access, tele-xy...)

� small and medium sized business (Internet, MM conferencing, VPN)

� Scope of standardization

� access networks, indoor/campus mobility, 25-155 Mbit/s, 50 m-5 km

� coordination with ATM Forum, IETF, ETSI, IEEE, ....

Bluetooth

� Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephone, notebook, computers, printers and so on

� Universal radio interface for ad-hoc wireless connectivity

� Short range (10 m), low power consumption, license-free 2.45 GHz ISM

Voice and data transmission, approx. 1 Mbit/s gross data rate� Voice and data transmission, approx. 1 Mbit/s gross data rate

Bluetooth Architecture: Piconet

� Collection of devices connected in an ad hoc fashion

� One unit acts as master and the others as slaves for the lifetime of the piconet

� Any device can function as master or slave, first establishing device in a piconet becomes mastermaster

� Master determines hopping pattern, slaves have to synchronize

� Each piconet has a unique hopping pattern

� Each piconet has one master and up to 7 simultaneous slaves (> 200 could be parked)

� There can be a maximum of eight devices with a master in piconet and a maximum of 79 channels in Bluetooth networks

State of devices in a piconet� Standby:

� Waiting to discover the master and thus the piconet

� No RF signal communication is taking place)

� Device is yet to be assigned an address in the piconet

� Active:� Inquiring─ (carrying out discovery broadcasting in all neighbourhood and listening to the

response for finding out a radio channel to connect

� Paging ─ sending a page specifying the relationship with master after discovering the channelchannel

� Connected and performing data transactions─3 bit address called AMA (active member address) assigned by the master device

� Park� Device already discovered the piconet But not communicating at present

� Is held in power-saving mode

� Assigned a 3 bit address called PMA (parked member address) after being released of the AMA

� Hold

� Hold state retains the AMA but suspends asynchronous connectionless link (ACL)

� Reduces power dissipation for communication in this piconet when there are no packet exchanges with the master

Scatternet� An ad-hoc network formed by various piconets within 100 m through a Bluetooth-enabled bridging device

� Any Bluetooth device can function as a bridge in order to form the ad-hoc network

� In such a network, two devices in two piconets communicate as in a peer-to-peer communication

� Each piconet uses FH-CDMA so that there is a distinct hopping sequence � Each piconet uses FH-CDMA so that there is a distinct hopping sequence with respect to other piconets in the scatternet

Forming a piconet

� All devices in a piconet hop together

� Master gives slaves its clock and device ID� Hopping pattern: determined by device ID (48 bit, unique worldwide)

� Phase in hopping pattern determined by clock

� Addressing

� Active Member Address (AMA, 3 bit)

� Parked Member Address (PMA, 8 bit)� Parked Member Address (PMA, 8 bit)

Bluetooth Layers

Bluetooth uses several layers that do not exactly match those of the Internet

model

Radio Layer

� Transmits packets received from baseband layer

� At the other end of the link, it receives

� Operate at the least required power levels so that the transactions may not be detected by a distant receiver of transactions may not be detected by a distant receiver of signals, thus maintaining confidentiality

� Blue tooth uses Frequency hopping spread spectrum which ensures negligible interference and least risk of jamming by distant sources.

Radio layer characteristics

� Frequency band─ 2.4 GHz

� Maximum power levels for devices ─ 1, 2, or 3 corresponding to 100 mW, 2.5 mW, or 1 mW

� Bluetooth radio ─ FHSS with each carrier separated by 1 MHz, 1600 frequency hops per second among 79 carriers, and frequency changing after every 1/1600 s or 625 µs (also known as dwell time)changing after every 1/1600 s or 625 µs (also known as dwell time)

� Transceiver modulation─ GFSK

� Data transfer rates ─ 1 Mbps or less

� Range ─ 10 m in a piconet and 100 m in a scatternet

� Baseband─ uses a fast frequency hopping algorithm and after 625 µs, the frequency of a channel changes according to a code which defines the sequence in which the carrier frequency has to change

Base band Layer

� The Baseband layer is roughly equivalent to the MAC sublayer in LANs.

� The master and the slave communicate with each other using timeslots. The length of the time slotsis exactly the same as the dwell time, 625 µs.

� Note that the communication is only between the master and a slave; slaves can not directly communicate with one another.slaves can not directly communicate with one another.

� Bluetooth uses a form of TDMA that is called TDD-TDMA ( Time Division Duplex TDMA), which is a kind of half duplex communication.

Multiple-slave communication

Single-slave communication

Multiple-slave communication

Baseband Physical links

Baseband uses Two types of links between two Bluetooth devices

� ACL (asynchronous connectionless link): ACL link provides best effort traffic providing high data integrityintegrity

� SCO (synchronous connection oriented link): SCO links provide real-time voice traffic using reserved bandwidth avoiding latency.

Base band Frame format

Link Manager

� Baseband and radio provide a link between master and slave

� The functions of the link manager─

(i) supervision

(ii) monitoring of power, synchronization, state, and mode of transmission,transmission,

(iii) exchange of QoS parameters (for example, packet flow latency, peak data rate, average data rate, and maximum burst size) for L2CAP and higher layers and capability information exchange

(iv) handling device pairing

(v) handling data encryption and device authentication

L2CAP layer

� The Logical Link Control and Adaptation Protocol is roughly equivalent to the LLC sublayer in LANs

� Facilitates segmentation of packets while transmitting and reassembling of packets on reception

� Multiplexes the data between different higher layer protocols and manages forward transmission from a Bluetooth device to other manages forward transmission from a Bluetooth device to other devices

� Does QoS management for higher layer data

� [A program file needs error free transfer. A picture being transferred can contain errors but still look good. It means ensuring the expected level of service.]

� Provides connection-establishment based communication after a host ACL is established

Bluetooth Security

� As the Bluetooth is a wireless network where every bit is on air, security concerns are also embedded in this technology.

� Bluetooth offers security infrastructure starting from authentication key exchange to encryption.

� In addition to encryption, a frequency hopping scheme with 1600 hops/second is employed. It makes the system difficult to hops/second is employed. It makes the system difficult to eavesdrop.

� At the lowest level of the protocol stack, bluetooth uses the publicly available cipher algorithm known as SAFER+ to authenticate a device’s identity.

� In addition to these basic security functions, different application verticals use their own security infrastructure at the application layers