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第五章 小覆盖无线网络 Chapter 5 Wireless Networks with Narrow Coverage

第五章 小覆盖无线网络 Chapter 5 Wireless Networks with Narrow Coverage. 电控学院 电子工程学科部 司鹏搏 综合楼 825 室 sipengbo@bjut.edu.cn. Main Contents. 5.1 Wireless Local Area Networks (WLANs) 5.1.1 Wireless Networks 5.1.2 IEEE 802.11 Overview 5.1.3 Components 5.1.4 Services 5.1.5 MAC Layer

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第五章 小覆盖无线网络 Chapter 5 Wireless Networks with Narrow Coverage

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  1. 第五章 小覆盖无线网络Chapter 5 Wireless Networks with Narrow Coverage 电控学院 电子工程学科部 司鹏搏 综合楼825室 sipengbo@bjut.edu.cn

  2. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.1.1 Wireless Networks • 5.1.2 IEEE 802.11 Overview • 5.1.3 Components • 5.1.4 Services • 5.1.5 MAC Layer • 5.1.6 Physical Layer • 5.1.7 IEEE 802.11 Protocols • 5.2 Wireless Personal Area Networks (WPANs) • 5.3 Wireless Body Area Networks (WBANs)

  3. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.2 Wireless Personal Area Networks (WPANs) • 5.2.1 Introduction to Bluetooth • 5.2.2 Protocol Stack • 5.2.3 Network Topology • 5.2.4 Packet Structure • 5.2.5 Connection States • 5.2.6 Security • 5.2.7 Technology Comparison and Target Markets • 5.3 Wireless Body Area Networks (WBANs)

  4. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.2 Wireless Personal Area Networks (WPANs) • 5.3 Wireless Body Area Networks (WBANs) • 5.3.1 Introduction to WBAN • 5.3.2 Three-Tier Architecture • 5.3.3 Comparison with Other Networks • 5.3.4 Designing WBANs • 5.3.5 Physical Layer Considerations • 5.3.6 MAC Layer Considerations • 5.3.7 Network Layer Considerations

  5. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.1.1 Wireless Networks • 5.1.2 IEEE 802.11 Overview • 5.1.3 Components • 5.1.4 Services • 5.1.5 MAC Layer • 5.1.6 Physical Layer • 5.1.7 IEEE 802.11 Protocols • 5.2 Wireless Personal Area Networks (WPANs) • 5.3 Wireless Body Area Networks (WBANs)

  6. 5.1.1 Wireless Internetworking Overview Residential/ Premise/ Campus Fixed Mobile Broadband Multiservice 2G+ Cellular 3G Cellular IEEE 802.11 BLUE TOOTH Data Services GPRS Mobile IP Packet Data/Voice UMTS MMDS LMDS

  7. Application Presentation ISO OSI 7-layer model Session IEEE 802 standards Transport Network Logical Link Control Data Link Medium Access (MAC) Physical Physical (PHY) 5.1.1 Standardization of Wireless Networks Wireless networks are standardized by IEEE. Under 802 LAN MAN standards committee.

  8. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.1.1 Wireless Networks • 5.1.2 IEEE 802.11 Overview • 5.1.3 Components • 5.1.4 Services • 5.1.5 MAC Layer • 5.1.6 Physical Layer • 5.1.7 IEEE 802.11 Protocols • 5.2 Wireless Personal Area Networks (WPANs) • 5.3 Wireless Body Area Networks (WBANs)

  9. 5.1.2 IEEE 802.11 Overview • Goals • To deliver services in wired networks • To achieve high throughput • To achieve highly reliable data delivery • To achieve continuous network connection • Adopted in 1997. • Defines • MAC sublayer • MAC management protocols and services • Physical (PHY) layers • IR • FHSS • DSSS

  10. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.1.1 Wireless Networks • 5.1.2 IEEE 802.11 Overview • 5.1.3 Components • 5.1.4 Services • 5.1.5 MAC Layer • 5.1.6 Physical Layer • 5.1.7 IEEE 802.11 Protocols • 5.2 Wireless Personal Area Networks (WPANs) • 5.3 Wireless Body Area Networks (WBANs)

  11. 5.1.3 Components • Station • BSS - Basic Service Set • IBSS : Independent BSS • ESS - Extended Service Set • A set of infrastructure BSSs • Connection of APs • Tracking of mobility • DS – Distribution System • AP communicates with another

  12. 5.1.3 BSS • A set of stations controlled by a single “Coordination Function” • = the logical function that determines when a station can transmit or receive • Similar to a “cell” in pre IEEE terminology • A BSS can • Have an Access-Point (both in standalone networks and in building-wide configurations), • Or can run without and Access-Point (in standalone networks only) • Diameter of the cell is approximately twice the coverage-distance between two wireless stations

  13. 5.1.3 BSS BSS

  14. 5.1.3 IBSS A Basic Service Set (BSS) which forms a self-contained network in which no access to a Distribution System is available A BSS without an Access-Point One of the stations in the IBSS can be configured to “initiate” the network and assume the Coordination Function Diameter of the cell determined by coverage distance between two wireless stations

  15. 5.1.3 IBSS IBSS

  16. 5.1.3 ESS and DS • Extended Service Set (ESS): • A set of one or more Basic Service Sets interconnected by a Distribution System (DS) • Traffic always flows via Access-Point • Diameter of the cell is double the coverage distance between two wireless stations • Distribution System (DS): • A system to interconnect a set of Basic Service Sets • Integrated; A single Access-Point in a standalone network • Wired; Using cable to interconnect the Access-Points • Wireless; Using wireless to interconnect the Access-Points

  17. 5.1.3 ESS, Single BSS with Integrated DS BSS

  18. 5.1.3 ESS, BSSs with Wired DS Distribution System BSS BSS

  19. 5.1.3 ESS, BSSs with Wireless DS BSS Distribution System BSS

  20. 5.1.3 SSID and BSSID • Service Set Identifier (SSID): • “Network name” • 32 octets long • Similar to “Domain-ID” in the pre-IEEE WaveLAN systems • One network (ESS or IBSS) has one SSID • Basic Service Set Identifier (BSSID) • “cell identifier” • 6 octets long (MAC address format) • Similar to NWID in pre-IEEE WaveLAN systems • One BSS has one SSID • Value of BSSID is the same as the MAC address of the radio in the Access-Point

  21. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.1.1 Wireless Networks • 5.1.2 IEEE 802.11 Overview • 5.1.3 Components • 5.1.4 Services • 5.1.5 MAC Layer • 5.1.6 Physical Layer • 5.1.7 IEEE 802.11 Protocols • 5.2 Wireless Personal Area Networks (WPANs) • 5.3 Wireless Body Area Networks (WBANs)

  22. 5.1.4 Services • Station services: • Authentication • De-authentication • Privacy • Delivery of data • Distribution Services (A thin layer between MAC and LLC) • Association • Disassociation • Reassociation • Distribution • Integration

  23. Main Contents • 5.1 Wireless Local Area Networks (WLANs) • 5.1.1 Wireless Networks • 5.1.2 IEEE 802.11 Overview • 5.1.3 Components • 5.1.4 Services • 5.1.5 MAC Layer • 5.1.6 Physical Layer • 5.1.7 IEEE 802.11 Protocols • 5.2 Wireless Personal Area Networks (WPANs) • 5.3 Wireless Body Area Networks (WBANs)

  24. 5.1.5 Medium Access Control • Functionality • Reliable data delivery • Fairly control access • Protection of data • Deals • Noisy and unreliable medium • Frame exchange protocol - ACK • Overhead to IEEE 802.3 • Hidden Node Problem – RTS/CTS • Participation of all stations • Reaction to every frame

  25. 5.1.5 Medium Access Control • Retry Counters • Short retry counter • Long retry counter • Lifetime timer • Basic Access Mechanism • CSMA/CA • Binary exponential back-off • NAV – Network Allocation Vector • Timing Intervals: SIFS, Slot Time, PIFS, DIFS, EIFS • DCF Operation • PCF Operation

  26. 5.1.5 Hidden Node Problem A B C • A and C cannot see each other, B can see both

  27. 5.1.5 CSMA/CA Sender sends Request to Send (RTS) Receiver sends Clear to Send (CTS) Sender transmits for required time

  28. 5.1.5 DCF Operation

  29. 5.1.5 PCF Operation • Poll – eliminates contention • PC – Point Coordinator • Polling List • Over DCF • PIFS • CFP – Contention Free Period • Alternate with DCF • Periodic Beacon – contains length of CFP • CF-Poll – Contention Free Poll • NAV prevents during CFP • CF-End – resets NAV

  30. 5.1.5 Frame Types Upper layer data • 2048 byte max • 256 upper layer header • NAV information Or • Short Id for PS-Poll FC Duration /ID Address 1 Address 2 Address 3 Sequence Control Address 4 DATA FCS 2 2 6 6 6 2 6 0-2312 4bytes • IEEE 48 bit address • Individual/Group • Universal/Local • 46 bit address • MSDU • Sequence Number • Fragment Number • CCIT CRC-32 Polynomial • Protocol Version • Frame Type and Sub Type • To DS and From DS • More Fragments • Retry • Power Management • More Data • WEP • Order • BSSID –BSS Identifier • TA - Transmitter • RA - Receiver • SA - Source • DA - Destination

  31. Bytes: 2 2 6 6 6 2 6 0-2312 4 Frame Frame Duration Sequence Addr 1 Addr 2 Addr 3 Addr 4 CRC Body Control ID Control 802.11 MAC Header Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field 5.1.5 Frame Control Field MAC Header format differs per Type: • Control Frames (several fields are omitted) • Management Frames • Data Frames

  32. Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field To DS From DS Address 1 Address 2 Address 3 Address 4 0 0 DA SA BSSID N/A 0 1 DA BSSID SA N/A 1 0 BSSID SA DA N/A 1 1 RA TA DA SA 5.1.5 Address Field Addr. 1 = All stations filter on this address. Addr. 2 = Transmitter Address (TA), Identifies transmitter to address the ACK frame to. Addr. 3 = Dependent on To and From DS bits. Addr. 4 = Only needed to identify the original source of WDS (Wireless Distribution System)frames

  33. Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field 5.1.5 Type Field Type and subtype identify the function of the frame: • Type=00 Management Frame Beacon (Re)Association Probe (De)Authentication Power Management • Type=01 Control Frame RTS/CTS ACK • Type=10 Data Frame

  34. 5.1.5 MAC Management Frames • Beacon • Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters • Traffic Indication Map • Probe • SSID, Capabilities, Supported Rates • Probe Response • Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters • Same as Beacon except for TIM • Association Request • Capability, Listen Interval, SSID, Supported Rates

  35. 5.1.5 MAC Management Frames • Association Response • Capability, Status Code, Station ID, Supported Rates • Re-association Request • Capability, Listen Interval, SSID, Supported Rates, Current AP Address • Re-association Response • Capability, Status Code, Station ID, Supported Rates • Dis-association • Reason code • Authentication • Algorithm, Sequence, Status, Challenge Text • De-authentication • Reason

  36. 5.1.5 Frame Subtypes CONTROL DATA MANAGEMENT • RTS • CTS • ACK • PS-Poll • CF-End & CF-End ACK • Data • Data+CF-ACK • Data+CF-Poll • Data+CF-ACK+CF-Poll • Null Function • CF-ACK (nodata) • CF-Poll (nodata) • CF-ACK+CF+Poll • Beacon • Probe Request & Response • Authentication • Deauthentication • Association Request & Response • Reassociation Request & Response • Disassociation • Announcement Traffic Indication Message (ATIM)

  37. 5.1.5 Other MAC Operations • Fragmentation • Sequence control field • In burst • Medium is reserved • NAV is updated by ACK • WEP Details • Two mechanism • Default keys • Key mapping • WEP header and trailer • KEYID in header • ICV in trailer • dot11UndecryptableCount • Indicates an attack. • dot11ICVErrorCount • Attack to determine a key is in progress. • Privacy • WEP bit set when encrypted. • Only the frame body. • Medium is reserved • NAV is updated by ACK • Symmetric variable key

  38. 5.1.5 MAC Management and Authentication • Security Problem • A rogue AP • SSID of ESS • Announce its presence with beaconing • An active rogue AP reaches higher layer data if unencrypted • MAC Management • Interference by users that have no concept of data communication. Ex: Microwave • Interference by other WLANs • Security of data • Mobility • Power Management • Authentication • Prove identity to another station. • Open system authentication • Shared key authentication • A sends • B responds with a text • A encrypt and send back • B decrypts and returns an authentication management frame. • May authenticate any number of station

  39. 5.1.5 Association • Transparent mobility • After authentication • Association request to an AP • After established, forward data • To BSS, if DA is in the BSS. • To DS, if DA is outside the BSS. • To AP, if DA is in another BSS. • To “portal”, if DC is out of the ESS. • New AP after reassociation, communicates with the old AP.

  40. 5.1.5 Power Management • Overhead • Sender • Announcement frame • Buffer • Power consumption in ATIM • Receiver • Awake for every Beacon and ATIM • Independent BSS • Distributed • Data frame handshake • Wake up every beacon. • Awake a period of ATIM after each beacon. • Send ACK if receive ATIM frame & awake until the end of next ATIM. • Estimate the power saving station, and delay until the next ATIM. • Multicast frame : No ACK : optional

  41. 5.1.5 Power Management • Infrastructure BSS • Centralized in the AP • Greater power saving • Mobile Station sleeps for a number of beacon periods. • Awake for multicast indicated in DTIM in Beacon. • AP buffer, indicate in TIM • Mobile requests by PS-Poll

  42. 5.1.5 Synchronization • Timer Synchronization in an Infrastructure BSS • Beacon contains TSF • Station updates its with the TSF in beacon. • Timer Synchronization in an IBSS • Distributed. Starter of the BSS send TSF zero and increments. • Each Station sends a Beacon • Station updates if the TSF is smaller • Take into account the contention time

  43. 5.1.5 Scanning & Joining • Scanning • Passive Scanning : only listens for Beacon and get info of the BSS. Power is saved • Active Scanning: transmit and elicit response from APs. If IBSS, last station that transmitted beacon responds. Time is saved • Joining a BSS • Synchronization in TSF and frequency : Adopt PHY parameters : The BSSID : WEP : Beacon Period : DTIM

  44. 5.1.5 Operational Process • Association • To establish relationship with Access-Point • Stations scan frequency band to and select Access-Point with best communications quality • Active Scan (sending a “Probe request” on specific channels and assess response) • Passive Scan (assessing communications quality from beacon message) • Access-Point maintains list of associate stations • Record station capability (data-rate) • To allow inter-BSS relay • Station’s MAC address is also maintained in bridge learn table associated with the port it is located on

  45. 5.1.5 Operational Process • Authentication • To control access to the infrastructure via an authentication • Stations identify themselves to other stations (or Access-Points) prior to data traffic or association • Open System Authentication • Uses null authentication algorithm • Default • Shared Key Authentication • Uses WEP privacy algorithm • Optional

  46. 5.1.5 Operational Process • Starting an ESS • The infrastructure network is identified by its ESSID • All Access-Points will have been set according to this ESSID • Wireless stations will be configured to set their desired SSID to the value of ESSID • On power up stations will issue Probe Requests and will locate the Access-Point that they will associate with: • “Best” Access-Point with matching ESSID • “Best” Access-Point if the “desired SSID” has been set to “ANY”

  47. 5.1.5 Operational Process • Starting an IBSS • Station configured for IBSS operation will: • “look” for Beacons that contain a network name (SSID) that matches the one that is configured • When Beacons with matching Network Name are received and are issued by an AP, Station will associate to the AP • When Beacons with matching Network Name are received and are issued by another Station in IBSS mode, the station will join this IBSS • When no beacons are received with matching Network Name, Station will issue beacons itself. • All Stations in an IBSS network will participate in sending beacons. • All stations start a random timer prior to the point in time when next Beacon is to be sent. • First station whose random timer expires will send the next beacon

  48. Free access when medium DIFS is free longer than DIFS Contention Window PIFS DIFS SIFS Backoff-Window Next Frame Busy Medium Slot time Select Slot and Decrement Backoff as long as medium is idle. Defer Access 5.1.5 Operational Process • Inter-Frame Spacing • Inter frame spacing required for MAC protocol traffic • SIFS = Short interframe space • PIFS = PCF interframe space • DIFS = DCF interframe space • Back-off timer expressed in terms of number of time slots

  49. DIFS Src Data SIFS Dest ACK DIFS Contention Window Other Next MPDU Backoff after Defer Defer Access 5.1.5 Operational Process • Data Frames and their ACK • Acknowledgment are to arrive at within the SIFS • The DCF interframe space is observed before medium is considered free for use

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