Chapter 4

112/04/22112/04/22 Prof. Huei-Wen FerngProf. Huei-Wen Ferng 11

Chapter 4Chapter 4

Wireless LAN Technologies Wireless LAN Technologies and Productsand Products


General DescriptionGeneral Description

Overview of TechnologiesOverview of Technologies


Technology TrendsTechnology Trends Physical layers of WLAN are based on Physical layers of WLAN are based on

SS (FHSS and DSSS) and IR SS (FHSS and DSSS) and IR technologiestechnologies

Frequency bands: ISM bandFrequency bands: ISM band Date rate:Date rate:

• Current products/standards: 1~54 MbpsCurrent products/standards: 1~54 Mbps• Future: 100 Mbps and aboveFuture: 100 Mbps and above


Wireless LAN Wish ListWireless LAN Wish List High speedHigh speed

• At least as fast as today’s EthernetAt least as fast as today’s Ethernet Low costLow cost

• Not much more than today’s EthernetNot much more than today’s Ethernet CoverageCoverage

• Throughout the building or campusThroughout the building or campus No use of the battery of the mobile computer, or at least No use of the battery of the mobile computer, or at least

minimal impactminimal impact No interference with other equipmentsNo interference with other equipments Easy installation, use, and managementEasy installation, use, and management Easy repair and upgradingEasy repair and upgrading PCMCIA form factorPCMCIA form factor No external antennaNo external antenna Co-operability of different wireless LAN systemsCo-operability of different wireless LAN systems


Effect of Multi-path Fading Effect of Multi-path Fading Multi-path: a number of different Multi-path: a number of different

paths of signals arrives at the paths of signals arrives at the receiverreceiver

Signals of different propagation Signals of different propagation delays can degrade performancedelays can degrade performance


Network ArchitectureNetwork Architecture


Network Architecture (Cont’d)Network Architecture (Cont’d) InfrastructureInfrastructure

• Connectivity is accomplished by access Connectivity is accomplished by access point (AP) between a station and other point (AP) between a station and other station or network station or network

Ad-hoc networkAd-hoc network• This network is set up temporarily to This network is set up temporarily to

meet some immediate needmeet some immediate need• It has no centralized server, like APIt has no centralized server, like AP


MAC ProtocolsMAC Protocols Three MAC protocols for wireless Three MAC protocols for wireless

LANsLANs• Listen Before You Talk MAC protocolListen Before You Talk MAC protocol• Integrated wireless LAN MAC protocolIntegrated wireless LAN MAC protocol• Polling MAC protocolPolling MAC protocol


Listen Before You Talk MAC Listen Before You Talk MAC protocolprotocol

LBT is basically a non-persistent CSMA LBT is basically a non-persistent CSMA protocolprotocol

It differs from CSMA in two waysIt differs from CSMA in two ways• An RTS packet is transmitted before data is An RTS packet is transmitted before data is

transmitted to the receiver, then the receiver transmitted to the receiver, then the receiver transmits a CTS packet to be heard by all transmits a CTS packet to be heard by all nodes to grant data transfer from the sending nodes to grant data transfer from the sending nodenode

• After RTS/CTS packets, the sending node After RTS/CTS packets, the sending node transmit the datatransmit the data

LBT or RTS/CTS scheme avoids the hidden LBT or RTS/CTS scheme avoids the hidden node problemnode problem


Integrated CSMA/TDMA MAC Integrated CSMA/TDMA MAC ProtocolProtocol

A hybrid of reservation and random accessA hybrid of reservation and random access The frame is segmented intoThe frame is segmented into

• Two reservation intervals for isochronous Two reservation intervals for isochronous TrafficTraffic

• One interval for random access trafficOne interval for random access traffic Movable boundary by a control functionMovable boundary by a control function

• Infrastructure: by APInfrastructure: by AP• Ah-hoc: the function is distributed among the Ah-hoc: the function is distributed among the

nodesnodes


Contents of HeadersContents of Headers Header AH:Header AH:

• Length of TA, TB, TCLength of TA, TB, TC• BSID: Unique ID of the APBSID: Unique ID of the AP• NET_ID: Network IDNET_ID: Network ID• NEXT_FREQ/NEXT_CODE/NEXT_CHNLNEXT_FREQ/NEXT_CODE/NEXT_CHNL• <Si, Wi>: AP transmit Si packets to user Wi<Si, Wi>: AP transmit Si packets to user Wi


Contents of Headers (Cont’d)Contents of Headers (Cont’d) Header BH:Header BH:

• The length of TB, TCThe length of TB, TC• <Si, Vi, Wi>: User Vi transmits Si packets to u<Si, Vi, Wi>: User Vi transmits Si packets to user Wiser Wi

Header CH:Header CH:• The length of TCThe length of TC• K: current estimate of users attempting tranK: current estimate of users attempting transmission in random access sectionsmission in random access section


Polling MAC ProtocolPolling MAC Protocol Incorporate the fairness issueIncorporate the fairness issue

• E.g., stock trading applicationE.g., stock trading application MechanismMechanism

• A node has a packet to send, it first A node has a packet to send, it first sends a request to the control pointsends a request to the control point

• The control point polls the users in turn The control point polls the users in turn by referencing the request queue by referencing the request queue

• Data needs ACK and goes through an Data needs ACK and goes through an AP, therefore, no ad-hoc networkingAP, therefore, no ad-hoc networking


Power ManagementPower Management In order to achieve low power budgets, the In order to achieve low power budgets, the

WLAN adaptor must sleep as much as WLAN adaptor must sleep as much as possiblepossible

Three States are defined for WLAN Three States are defined for WLAN adapter:adapter:• Transmit stateTransmit state

Transmitter is turned onTransmitter is turned on• Awake stateAwake state

Receiver is powered on and ready to receiveReceiver is powered on and ready to receive• Doze stateDoze state

Transceiver dozingTransceiver dozing


Power Management (Cont’d)Power Management (Cont’d) The power savings scheme is with the help The power savings scheme is with the help

of APof AP The AP buffers traffic for dozing nodesThe AP buffers traffic for dozing nodes The AP informs nodes of traffic in The AP informs nodes of traffic in

broadcast packets called Traffic Delivery broadcast packets called Traffic Delivery Information Messages (TDIM)Information Messages (TDIM)• The frame header include: which stations have The frame header include: which stations have

data to receive, how much data to receive, and data to receive, how much data to receive, and when it will be deliveredwhen it will be delivered


Power Management (Cont’d)Power Management (Cont’d) The node will wake up when The node will wake up when

• they are transmittingthey are transmitting• they have data to receive in the specify timethey have data to receive in the specify time• during the frame header to check the TDIMduring the frame header to check the TDIM

The node periodically check the frame The node periodically check the frame headerheader

Palm-top computer do not wake up every Palm-top computer do not wake up every frame. They remain sleep as long as they frame. They remain sleep as long as they wishwish


Interconnection with Backbone Interconnection with Backbone NetworksNetworks

Connecting with the same networkConnecting with the same network• Done below the network layer using Done below the network layer using

MAC layer bridgesMAC layer bridges Mobility between different networksMobility between different networks

• Done at the network layer via new Done at the network layer via new protocols such as Mobile IPprotocols such as Mobile IP


Mobility within the Same NetworkMobility within the Same Network

Mobile nodes are roaming in the same arMobile nodes are roaming in the same area that are covered by different APs in thea that are covered by different APs in the same networke same network Each AP contains three componentsEach AP contains three components

• A WLAN interface card (AP<->Node)A WLAN interface card (AP<->Node)• A wired LAN interface card (AP<->Network)A wired LAN interface card (AP<->Network)• A MAC layer bridge to filter the traffic betweA MAC layer bridge to filter the traffic between the wireless subnet and the backboneen the wireless subnet and the backbone


BridgesBridges Bridging is used to filter traffic from Bridging is used to filter traffic from

different wired segments of a large different wired segments of a large LANLAN

Differences among repeater, bridge, Differences among repeater, bridge, and router?and router?


Mechanism of BridgesMechanism of Bridges When a bridge is first installed, it When a bridge is first installed, it

acts as a repeateracts as a repeater Then as a traffic goes through it, it Then as a traffic goes through it, it

learns which nodes are on which LAN learns which nodes are on which LAN segment and forms a tablesegment and forms a table

Next time it receives a packet, it Next time it receives a packet, it forwards it only on the LAN segment forwards it only on the LAN segment destined; otherwise, it broadcasts on destined; otherwise, it broadcasts on all LAN segments all LAN segments


TimersTimers The entries in the table are not kept The entries in the table are not kept

foreverforever Bridges have a timer for each nodeBridges have a timer for each node The age-out timers in wired LANs are on The age-out timers in wired LANs are on

the order of hoursthe order of hours The age-out timers in wireless LANs are on The age-out timers in wireless LANs are on

the order of minutesthe order of minutes What happen if the age-out timer is too What happen if the age-out timer is too

short?short? What happen if the age-out timer is too What happen if the age-out timer is too

long?long?


Additional Functions of BridgesAdditional Functions of Bridges Buffering between different speed Buffering between different speed

LANsLANs Changing frame formats between Changing frame formats between

incompatible LANsincompatible LANs Adding and deleting fields within the Adding and deleting fields within the

frame, e.g., 802.3 has a data length frame, e.g., 802.3 has a data length field but 820.4 doesn’tfield but 820.4 doesn’t


MAC Layer Bridging ProtocolsMAC Layer Bridging Protocols Spanning tree bridgesSpanning tree bridges

• Need a distributed database of where all the nodes are Need a distributed database of where all the nodes are and the best way to reach any nodeand the best way to reach any node

• The network topology takes shape using multiple The network topology takes shape using multiple bridgesbridges

• The way to form the topologyThe way to form the topology Using a distributed algorithm for selecting a root bridge and Using a distributed algorithm for selecting a root bridge and

a tree that reaches every other bridgea tree that reaches every other bridge Source routing bridgesSource routing bridges

• Rely on the source node, which keeps a table of where Rely on the source node, which keeps a table of where other nodes areother nodes are

• It includes the route the packet is to take in the headerIt includes the route the packet is to take in the header• Places greater burden on the nodesPlaces greater burden on the nodes


Mobility among Different Networks Mobility among Different Networks (Mobile IP)(Mobile IP)

The goals of mobile IP are:The goals of mobile IP are:• Mobility is handled at the network layerMobility is handled at the network layer• Transport and higher layers are unaffectedTransport and higher layers are unaffected• Applications do not need to changeApplications do not need to change• The infrastructure of non-mobile routers are The infrastructure of non-mobile routers are

unaffectedunaffected• Non-mobile hosts are unaffectedNon-mobile hosts are unaffected• Continuous operation occurs across multiple Continuous operation occurs across multiple

networksnetworks• Security is as good as with existing networksSecurity is as good as with existing networks


Mobile IPMobile IP Briefly Speaking, to take a mobile IP Briefly Speaking, to take a mobile IP

address for mobility with minor address for mobility with minor changes changes

At present, At present, IP address isIP address is associated associated with a with a fixedfixed network location like a network location like a phone numberphone number


Mobile IP (Cont’d)Mobile IP (Cont’d) Terms Definition used in Mobile IP operaTerms Definition used in Mobile IP operations:tions:

• Mobile host (MH): a movable hostMobile host (MH): a movable host• Home address (HA): a permanent IP address Home address (HA): a permanent IP address used to identify an MH anytimeused to identify an MH anytime• Home network (HN): the logical network whHome network (HN): the logical network where an MH’s HA residesere an MH’s HA resides• Care of address (COA): a temporary address Care of address (COA): a temporary address used to locate an MH at some particular instused to locate an MH at some particular instantant


Mobile IP (Cont’d)Mobile IP (Cont’d) Agents: in the routers to implement the Agents: in the routers to implement the

new software offering mobile capabilitiesnew software offering mobile capabilities Home Agent (->HLR): An agent that Home Agent (->HLR): An agent that

redirects packet from a home network to redirects packet from a home network to the COA of an MHthe COA of an MH

Foreign Agent (->VLR): a specialized Foreign Agent (->VLR): a specialized forwarding agent thatforwarding agent that• Offers a COAOffers a COA• Maintains and performs mapping between the Maintains and performs mapping between the

COA and HA of an MHCOA and HA of an MH


Mobile IP (Cont’d)Mobile IP (Cont’d)

San FranciscoSan Francisco WashingtonWashington

BostonBoston

Triangle routingTriangle routing


Mobile IP (Cont’d)Mobile IP (Cont’d) Triangle routingTriangle routing

• Not too bad if only one or two packetsNot too bad if only one or two packets For many packets, FA in Boston For many packets, FA in Boston

sends a message to the fixed node in sends a message to the fixed node in Washington and asks it to use the Washington and asks it to use the mobile node’s COA instead its HA, mobile node’s COA instead its HA, the packets then go directly from the packets then go directly from Washington to BostonWashington to Boston


The operation of Mobile IPThe operation of Mobile IP


The Operation of Mobile IP (Cont’d)The Operation of Mobile IP (Cont’d)

How does a MH find an FA?How does a MH find an FA?• Through the advertisementsThrough the advertisements

FAs send out service advertisements that annouFAs send out service advertisements that announce their willingness to provide COA to visiting Mnce their willingness to provide COA to visiting MHsHs• MH can send out a solicitation packet askinMH can send out a solicitation packet asking if a FA is in the vicinityg if a FA is in the vicinity


Packet Types of Mobile IPPacket Types of Mobile IP Advertisement packetAdvertisement packet Solicitation packetSolicitation packet RegistrationRegistration MH to FA registration packetMH to FA registration packet FA to HA registration packetFA to HA registration packet HA to FA registration ACK packetHA to FA registration ACK packet FA to MH registration ACK packetFA to MH registration ACK packet


The PCS Model for MobilityThe PCS Model for Mobility In cellular and PCS networks, each In cellular and PCS networks, each

person has a unique number similar person has a unique number similar to Mobile IP addressto Mobile IP address

This number is stored in Home This number is stored in Home Location Register (HLR)Location Register (HLR)

When user is visiting foreign location, When user is visiting foreign location, he/she is automatically registered he/she is automatically registered with a Visitor Location Register (VLR)with a Visitor Location Register (VLR)


Source HLRSource HLR

Calling Calling UPT userUPT user

Destination HLRDestination HLR

OriginatingOriginatingnetworknetwork

TerminatingTerminatingnetworknetwork

Called Called UPT userUPT user

(1)(1)(2)(2)

(3)(3)(4)(4)

Authentication: (1),(2)Authentication: (1),(2)Service profile, routing: (3),(4)Service profile, routing: (3),(4)

PCS Call FlowPCS Call Flow


Wireless LAN StandardsWireless LAN Standards IEEE 802.11IEEE 802.11

• IEEE 802.11IEEE 802.11• IEEE 802.11aIEEE 802.11a• IEEE 802.11bIEEE 802.11b

High-performance radio LAN (HiperLAN)High-performance radio LAN (HiperLAN)• HiperLAN type 1HiperLAN type 1• HiperLAN type 2HiperLAN type 2


IEEE 820.11IEEE 820.11


HiperLANHiperLAN HiperLAN Type 1 (H/1)HiperLAN Type 1 (H/1)

• A connectionless packet-based broad-band A connectionless packet-based broad-band WLAN standard at 5 GHz in 1996WLAN standard at 5 GHz in 1996 HiperLAN Type 2 (H/2)HiperLAN Type 2 (H/2)

• A connection-oriented high-performance teA connection-oriented high-performance technology at 5 GHz in 2000 chnology at 5 GHz in 2000


ResourcesResources

ETSI/BRAN websiteETSI/BRAN website• http://www.etsi.org/branhttp://www.etsi.org/bran


ReferencesReferences R. A. Dayem, Mobile Data and Wireless LAN TecR. A. Dayem, Mobile Data and Wireless LAN Technologieshnologies William Stallings, “IEEE 802.11: Moving Closer William Stallings, “IEEE 802.11: Moving Closer to Practical Wireless LANs”, IEEE IT Pro, 2001to Practical Wireless LANs”, IEEE IT Pro, 2001 B. H. Walke et al., “IP over Wireless Mobile ATB. H. Walke et al., “IP over Wireless Mobile ATM-Guaranteed Wireless QoS by HiperLAN/2”, M-Guaranteed Wireless QoS by HiperLAN/2”, Proc. Of IEEE, 2001Proc. Of IEEE, 2001 Perkins, “Perkins, “Mobile Networking Through Mobile Networking Through

Mobile IPMobile IP”, IEEE Internet Computing, 1998”, IEEE Internet Computing, 1998

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