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Chapter 4

Chapter 4. Wireless LAN Technologies and Products. General Description. Overview of Technologies. Technology Trends. Physical layers of WLAN are based on SS (FHSS and DSSS) and IR technologies Frequency bands: ISM band Date rate: Current products/standards: 1~54 Mbps

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Chapter 4

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  1. Chapter 4 Wireless LAN Technologies and Products Prof. Huei-Wen Ferng

  2. General Description Overview of Technologies Prof. Huei-Wen Ferng

  3. Technology Trends • Physical layers of WLAN are based on SS (FHSS and DSSS) and IR technologies • Frequency bands: ISM band • Date rate: • Current products/standards: 1~54 Mbps • Future: 100 Mbps and above Prof. Huei-Wen Ferng

  4. Wireless LAN Wish List • High speed • At least as fast as today’s Ethernet • Low cost • Not much more than today’s Ethernet • Coverage • Throughout the building or campus • No use of the battery of the mobile computer, or at least minimal impact • No interference with other equipments • Easy installation, use, and management • Easy repair and upgrading • PCMCIA form factor • No external antenna • Co-operability of different wireless LAN systems Prof. Huei-Wen Ferng

  5. Effect of Multi-path Fading • Multi-path: a number of different paths of signals arrives at the receiver • Signals of different propagation delays can degrade performance Prof. Huei-Wen Ferng

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  8. Network Architecture Prof. Huei-Wen Ferng

  9. Network Architecture (Cont’d) • Infrastructure • Connectivity is accomplished by access point (AP) between a station and other station or network • Ad-hoc network • This network is set up temporarily to meet some immediate need • It has no centralized server, like AP Prof. Huei-Wen Ferng

  10. MAC Protocols • Three MAC protocols for wireless LANs • Listen Before You Talk MAC protocol • Integrated wireless LAN MAC protocol • Polling MAC protocol Prof. Huei-Wen Ferng

  11. Listen Before You Talk MAC protocol • LBT is basically a non-persistent CSMA protocol • It differs from CSMA in two ways • An RTS packet is transmitted before data is transmitted to the receiver, then the receiver transmits a CTS packet to be heard by all nodes to grant data transfer from the sending node • After RTS/CTS packets, the sending node transmit the data • LBT or RTS/CTS scheme avoids the hidden node problem Prof. Huei-Wen Ferng

  12. Integrated CSMA/TDMA MAC Protocol • A hybrid of reservation and random access • The frame is segmented into • Two reservation intervals for isochronous Traffic • One interval for random access traffic • Movable boundary by a control function • Infrastructure: by AP • Ah-hoc: the function is distributed among the nodes Prof. Huei-Wen Ferng

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  14. Contents of Headers • Header AH: • Length of TA, TB, TC • BSID: Unique ID of the AP • NET_ID: Network ID • NEXT_FREQ/NEXT_CODE/NEXT_CHNL • <Si, Wi>: AP transmit Si packets to user Wi Prof. Huei-Wen Ferng

  15. Contents of Headers (Cont’d) • Header BH: • The length of TB, TC • <Si, Vi, Wi>: User Vi transmits Si packets to user Wi • Header CH: • The length of TC • K: current estimate of users attempting transmission in random access section Prof. Huei-Wen Ferng

  16. Polling MAC Protocol • Incorporate the fairness issue • E.g., stock trading application • Mechanism • A node has a packet to send, it first sends a request to the control point • The control point polls the users in turn by referencing the request queue • Data needs ACK and goes through an AP, therefore, no ad-hoc networking Prof. Huei-Wen Ferng

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  18. Power Management • In order to achieve low power budgets, the WLAN adaptor must sleep as much as possible • Three States are defined for WLAN adapter: • Transmit state • Transmitter is turned on • Awake state • Receiver is powered on and ready to receive • Doze state • Transceiver dozing Prof. Huei-Wen Ferng

  19. Power Management (Cont’d) • The power savings scheme is with the help of AP • The AP buffers traffic for dozing nodes • The AP informs nodes of traffic in broadcast packets called Traffic Delivery Information Messages (TDIM) • The frame header include: which stations have data to receive, how much data to receive, and when it will be delivered Prof. Huei-Wen Ferng

  20. Power Management (Cont’d) • The node will wake up when • they are transmitting • they have data to receive in the specify time • during the frame header to check the TDIM • The node periodically check the frame header • Palm-top computer do not wake up every frame. They remain sleep as long as they wish Prof. Huei-Wen Ferng

  21. Interconnection with Backbone Networks • Connecting with the same network • Done below the network layer using MAC layer bridges • Mobility between different networks • Done at the network layer via new protocols such as Mobile IP Prof. Huei-Wen Ferng

  22. Mobility within the Same Network • Mobile nodes are roaming in the same area that are covered by different APs in the same network • Each AP contains three components • A WLAN interface card (AP<->Node) • A wired LAN interface card (AP<->Network) • A MAC layer bridge to filter the traffic between the wireless subnet and the backbone Prof. Huei-Wen Ferng

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  24. Bridges • Bridging is used to filter traffic from different wired segments of a large LAN • Differences among repeater, bridge, and router? Prof. Huei-Wen Ferng

  25. Mechanism of Bridges • When a bridge is first installed, it acts as a repeater • Then as a traffic goes through it, it learns which nodes are on which LAN segment and forms a table • Next time it receives a packet, it forwards it only on the LAN segment destined; otherwise, it broadcasts on all LAN segments Prof. Huei-Wen Ferng

  26. Timers • The entries in the table are not kept forever • Bridges have a timer for each node • The age-out timers in wired LANs are on the order of hours • The age-out timers in wireless LANs are on the order of minutes • What happen if the age-out timer is too short? • What happen if the age-out timer is too long? Prof. Huei-Wen Ferng

  27. Additional Functions of Bridges • Buffering between different speed LANs • Changing frame formats between incompatible LANs • Adding and deleting fields within the frame, e.g., 802.3 has a data length field but 820.4 doesn’t Prof. Huei-Wen Ferng

  28. MAC Layer Bridging Protocols • Spanning tree bridges • Need a distributed database of where all the nodes are and the best way to reach any node • The network topology takes shape using multiple bridges • The way to form the topology • Using a distributed algorithm for selecting a root bridge and a tree that reaches every other bridge • Source routing bridges • Rely on the source node, which keeps a table of where other nodes are • It includes the route the packet is to take in the header • Places greater burden on the nodes Prof. Huei-Wen Ferng

  29. Mobility among Different Networks (Mobile IP) • The goals of mobile IP are: • Mobility is handled at the network layer • Transport and higher layers are unaffected • Applications do not need to change • The infrastructure of non-mobile routers are unaffected • Non-mobile hosts are unaffected • Continuous operation occurs across multiple networks • Security is as good as with existing networks Prof. Huei-Wen Ferng

  30. Mobile IP • Briefly Speaking, to take a mobile IP address for mobility with minor changes • At present, IP address is associated with a fixed network location like a phone number Prof. Huei-Wen Ferng

  31. Mobile IP (Cont’d) • Terms Definition used in Mobile IP operations: • Mobile host (MH): a movable host • Home address (HA): a permanent IP address used to identify an MH anytime • Home network (HN): the logical network where an MH’s HA resides • Care of address (COA): a temporary address used to locate an MH at some particular instant Prof. Huei-Wen Ferng

  32. Mobile IP (Cont’d) • Agents: in the routers to implement the new software offering mobile capabilities • Home Agent (->HLR): An agent that redirects packet from a home network to the COA of an MH • Foreign Agent (->VLR): a specialized forwarding agent that • Offers a COA • Maintains and performs mapping between the COA and HA of an MH Prof. Huei-Wen Ferng

  33. Mobile IP (Cont’d) Boston San Francisco Washington Triangle routing Prof. Huei-Wen Ferng

  34. Mobile IP (Cont’d) • Triangle routing • Not too bad if only one or two packets • For many packets, FA in Boston sends a message to the fixed node in Washington and asks it to use the mobile node’s COA instead its HA, the packets then go directly from Washington to Boston Prof. Huei-Wen Ferng

  35. The operation of Mobile IP Prof. Huei-Wen Ferng

  36. The Operation of Mobile IP (Cont’d) • How does a MH find an FA? • Through the advertisements • FAs send out service advertisements that announce their willingness to provide COA to visiting MHs • MH can send out a solicitation packet asking if a FA is in the vicinity Prof. Huei-Wen Ferng

  37. Packet Types of Mobile IP • Advertisement packet • Solicitation packet • Registration • MH to FA registration packet • FA to HA registration packet • HA to FA registration ACK packet • FA to MH registration ACK packet Prof. Huei-Wen Ferng

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  39. The PCS Model for Mobility • In cellular and PCS networks, each person has a unique number similar to Mobile IP address • This number is stored in Home Location Register (HLR) • When user is visiting foreign location, he/she is automatically registered with a Visitor Location Register (VLR) Prof. Huei-Wen Ferng

  40. PCS Call Flow Destination HLR (4) (3) Originating network Terminating network Calling UPT user Called UPT user (1) Authentication: (1),(2) Service profile, routing: (3),(4) (2) Source HLR Prof. Huei-Wen Ferng

  41. Wireless LAN Standards • IEEE 802.11 • IEEE 802.11 • IEEE 802.11a • IEEE 802.11b • High-performance radio LAN (HiperLAN) • HiperLAN type 1 • HiperLAN type 2 Prof. Huei-Wen Ferng

  42. IEEE 820.11 Prof. Huei-Wen Ferng

  43. HiperLAN • HiperLAN Type 1 (H/1) • A connectionless packet-based broad-band WLAN standard at 5 GHz in 1996 • HiperLAN Type 2 (H/2) • A connection-oriented high-performance technology at 5 GHz in 2000 Prof. Huei-Wen Ferng

  44. Resources • ETSI/BRAN website • http://www.etsi.org/bran Prof. Huei-Wen Ferng

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  46. References • R. A. Dayem, Mobile Data and Wireless LAN Technologies • William Stallings, “IEEE 802.11: Moving Closer to Practical Wireless LANs”, IEEE IT Pro, 2001 • B. H. Walke et al., “IP over Wireless Mobile ATM-Guaranteed Wireless QoS by HiperLAN/2”, Proc. Of IEEE, 2001 • Perkins, “Mobile Networking Through Mobile IP”, IEEE Internet Computing, 1998 Prof. Huei-Wen Ferng

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