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Cyber Book Wireless LAN What’s Wireless LAN? Communication system established through the use of RF technology Can function either as an extension to an existing LAN or an alternative for a wired LAN 2 Cyber Book of Internet Communication 2017-05-25 General Characteristics The need for WLAN resolving the problems of Hard-wired LAN providing user mobility and flexibility enabling to extend the range of an existing wired LAN being cheaper to install than traditional wired LAN 3 Cyber Book of Internet Communication 2017-05-25 Types of WLANs Radio WLAN DSSS uses signalling schemes which are based on some form of coding and which use a much wider bandwidth over the information bandwidth FHSS uses multiple frequency channel randomly (in a predefined pattern) 4 Cyber Book of Internet Communication 2017-05-25 Types of WLANs Infrared WLAN use part of the electromagnetic spectrum just below visible light as a media based on on-off pulse modulation and detection of the optical signal techniques Directed (line of sight) Diffuse (reflective) 5 Cyber Book of Internet Communication 2017-05-25 Infrastructure vs. ad-hoc networks Infrastructure networks Communications take place between the wireless nodes and AP, not directly between nodes. can use different access schemes collision wireless nodes and AP are not coordinated collision free AP controls medium access (QoS support) Ad-hoc networks medium access: collision wireless node may transfer data (router) 6 Cyber Book of Internet Communication 2017-05-25 WLAN Protocol Topologies Independent Topology supports peer-to-peer connectivity implemented quickly and easily no need for special tools or skills, no network administration in business meeting or in the setting up of temporary workgroups limited coverage area => all stations must be within the airwave distance of other stations with which they need to communicate 7 Cyber Book of Internet Communication 2017-05-25 Ad-hoc networks Independent Topology Ad hoc network BSS BSS 8 Cyber Book of Internet Communication 2017-05-25 WLAN Protocol Topologies Infrastructure topology using a AP transition from the wireless media to the wired media via an AP Access Point have network interface card connected to the wired LAN functions as a radio relay to the mobile stations involves the extension of an existing LAN through the use of a wireless AP all mobile stations must communicate with the AP within a predetermined distance, approximately 50~300m 9 Cyber Book of Internet Communication 2017-05-25 Infrastructure Configuration Infrastructure topology using a AP wired network AP AP: Access Point BSS 10 Cyber Book of Internet Communication 2017-05-25 WLAN Protocol Topologies Infrastructure topology using multiple AP can extend wireless LAN access capabilities over a relatively large area, such as college campus, industrial complex enables mobile stations to move within a larger coverage area provide effectively notebooks and PDAs with a roaming capability 11 Cyber Book of Internet Communication 2017-05-25 Infrastructure Configuration Infrastructure topology using multiple AP Infrastructure network BSS AP AP AP: Access Point wired network AP BSS BSS 12 Cyber Book of Internet Communication 2017-05-25 802.11 Protocol Entities LLC MAC MAC Sublayer MAC Layer Management Station Management PLCP Sublayer PHY PHY Layer Management PMD Sublayer 13 Cyber Book of Internet Communication 2017-05-25 IEEE 802 Network 802.2 LLC 802 802.1 802.3 MAC 802.5 MAC 802.3 PHY 802.5 PHY 802.11 MAC OUTLINE & MANAGEMENT ARCHITECTURE 14 Cyber Book of Internet Communication 802.11 FHSS PHY 802.11 DSSS PHY 802.11a 802.11b OFDM HR/DSSS PHY PHY 2017-05-25 IEEE 802.11 Standard Standard process 802.11 MAC(1997) 802.11a – PHY, 54Mbps, 5Ghz 802.11b – PHY, 11Mbps, 2.4Ghz 802.11g – PHY, 54Mbps, 2.4Ghz(Super set of 802.11b PHY) 802.11e for QoS support 802.11f for IAPP(Inter-Access Point Protocol) 802.11h for spectrum and transmit power management 802.11i for security enhancement 802.11k for radio resource management enhancement 802.11n for higher throughput 15 Cyber Book of Internet Communication 2017-05-25 802.11 - Architecture of an infrastruct ure 802.11 LAN BSS1 802.x LAN STA1 Portal AP Distribution System AP ESS Extended Service Set STA2 BSS2 STA3 802.11 LAN 16 Cyber Book of Internet Communication 2017-05-25 802.11 - Architecture of an infrastruct ure Station (STA) terminal with access mechanisms to the wireless mediu m and radio contact to the access point Basic Service Set (BSS) group of stations using the same radio frequency Access Point station integrated into the wireless LAN and the distrib ution system Portal bridge to other (wired) networks Distribution System interconnection network to form one logical network (E ES: Extended Service Set) based on several BSS 17 Cyber Book of Internet Communication 2017-05-25 802.11 - Architecture of an ad-hoc ne twork Direct communication within a limited range 802.11 LAN STA1 STA3 IBSS STA2 18 Cyber Book of Internet Communication Station (STA): terminal with access mec hanisms to the wireless medium Independent Basic Servic e Set (IBSS): group of stations using t he same radio frequency 2017-05-25 IEEE standard 802.11 mobile terminal infrastructure network access point Application Application TCP TCP IP IP LLC 19 Fixed terminal LLC LLC 802.3 MAC 802.11 MAC 802.3 MAC 802.3 MAC 802.3 PHY 802.11 PHY 802.3 PHY 802.3 PHY Cyber Book of Internet Communication 2017-05-25 802.11 - MAC layer - DFWMAC Traffic services Asynchronous Data Service (mandatory) exchange of data packets based on “best-effort” support of broadcast and multicast Time-Bounded Service (optional) implemented using PCF (Point Coordination Function) Contention-Free General PCF DCF 20 Cyber Book of Internet Communication < MAC Extent > 2017-05-25 802.11 - MAC layer - DFWMAC Distributed Foundation Wireless MAC DFWMAC-DCF CSMA/CA (mandatory) collision avoidance via randomized “back-off“ mechanism minimum distance between consecutive packets ACK packet for acknowledgements (not for broadcasts) DFWMAC-DCF w/ RTS/CTS (optional) Distributed Foundation Wireless MAC avoids hidden terminal problem DFWMAC- PCF (optional) access point polls terminals according to a list 21 Cyber Book of Internet Communication 2017-05-25 DCF (Distributed Coordination Function) 22 Distributed Contention-based channel access Based CSMA/CA Asynchronous data transport IBSS, Infrastructure BSS FIFO transmission queue Backoff Cyber Book of Internet Communication 2017-05-25 802.11 - MAC layer Priorities Defined through different inter frame spaces No guaranteed, hard priorities SIFS (Short Inter Frame Spacing) highest priority, for ACK, CTS, polling response 10usec (DSSS) PIFS (PCF IFS) medium priority, for time-bounded service using PCF SIFS + 1time slot (20 usec) DIFS (DCF, Distributed Coordination Function IFS) lowest priority, for asynchronous data service SIFS + 2 time slots 23 Cyber Book of Internet Communication 2017-05-25 802.11 - CSMA/CA access method DIFS DIFS Medium busy direct access if medium is free DIFS 24 Cyber Book of Internet Communication contention window (randomized back-off mechanism) Next frame t slot time 2017-05-25 CSMA/CA Explained Free access when medium is free longer than DIFS DIFS PIFS DIFS Contention Window SIFS Busy Medium Backoff-Window Next Window Slot time Defer Access 25 Cyber Book of Internet Communication Select Slot and Decrement Backoff as long as medium is idle 2017-05-25 CSMA/CA Explained Reduce collision probability where mostly needed Stations are waiting for medium to become free Select Random Backoff after a Defer, resolving contention to avoid collisions Efficient Backoff algorithm stable at high loads Exponential Backoff window increases for retransmissions Backoff timer elapses only when medium is idle Implement different fixed priority levels To allow immediate responses and PCF coexistence 26 Cyber Book of Internet Communication 2017-05-25 CSMA/CA + ACK protocol DIFS Sender DATA SIFS Receiver ACK DIFS Next MPDU Other stations t contention Defer Access 27 Cyber Book of Internet Communication Backoff after Defer 2017-05-25 CSMA/CA + ACK protocol Defer access based on Carrier Sense CCA from PHY and Virtual Carrier Sense state Direct access when medium is sensed free longer then DIFS, otherwise defer and backoff Receiver of directed frames to return an ACK immediately when CRC correct When no ACK received then retransmit frame after a random backoff (up to maximum limit) 28 Cyber Book of Internet Communication 2017-05-25 Contention Window CW(Contention Window) Contention window or backoff window Station selects random slot (probability same) [0,CW], (Cwmin = 7, Cwmax=255) DIFS PIFS DIFS Busy medium Contention window SIFS Backoff window Next frame Slot time Defer access Select slot and decrement backoff as long as medium is idle 29 Cyber Book of Internet Communication 2017-05-25 802.11 - CSMA/CA access method (ACK) Sending unicast packets Station has to wait for DIFS before sending data Receivers acknowledge at once (after waiti ng for SIFS) if the packet was received corr ectly (CRC) Automatic retransmission of data packets in case of transmission errors But the sender has to wait again and compete for the access right. 30 Cyber Book of Internet Communication 2017-05-25 RTS / CTS Concept C A B D A RTS DATA (1) RTS (2) CTS B (3) DATA C (4) ACK 31 Cyber Book of Internet Communication D CTS ACK NAV (RTS overhearing) NAV (CTS overhearing) 2017-05-25 802.11 - DFWMAC Sending unicast packets Station can send RTS with reservation param eter (duration) after waiting for DIFS (reserva tion determines amount of time the data pack et needs the medium) Acknowledgement via CTS after SIFS by recei ver (if ready to receive) Sender can now send data at once, acknowle dgement via ACK Other stations store medium reservations dist ributed via RTS and CTS NAV (Net Allocation Vector) 32 Cyber Book of Internet Communication 2017-05-25 Hidden Node Problem Using an RTS-CTS handshake to resolve hidden node problems A B C 1. A transmits request (RTS) to B 2. B replies that the channel is Clear (CTS). Both A & C overhear the broadcast (1) RTS (2) CTS (3) DATA 3. A sends its data to B. C is blocked from transmitting. 4. B acknowledges the data transfer (4) ACK 33 Cyber Book of Internet Communication 2017-05-25 Exposed Node Problem 1. B is transmitting to A 2. C overhears this, and is blocked A B C D 3. P wants to transmit to Q, but is being blocked by B (1) RTS B (2) CTS A (3) DATA C (4) ACK CTS_overhear 34 others DATA RTS CTS ACK NAV (RTS overhearing) NAV (CTS overhearing) RTS_overhear Cyber Book of Internet Communication 2017-05-25 802.11 - DFWMAC DIFS sender RTS DATA SIFS receiver other stations 35 Cyber Book of Internet Communication CTS SIFS SIFS ACK NAV(RTS) NAV(CTS) t 2017-05-25 Fragmentation RTS Sender frag1 frag2 DIFS CTS Receiver SIFS ACK1 SIFS SIFS ACK2 SIFS SIFS NAV (RTS) NAV (CTS) Other stations NAV (frag1) NAV (ACK1) DIFS data t contention 36 Cyber Book of Internet Communication 2017-05-25 Optional PCF Contention Free Service Contention Service PCF Optional MAC DCF (CSMA/CA) PHY 37 Cyber Book of Internet Communication 2017-05-25 Optional PCF Contention Free Service uses Point Coordination Function (PCF) on a DCF Foundation PCF can provide lower transfer delay variations to support Time Bounded Services Async Data, Voice or mixed implementations possible Point Coordinator resides in AP Coexistence between Contention and optional Contention Free does not burden the implementation 38 Cyber Book of Internet Communication 2017-05-25 PCF(Point Coordination Function) Point Coordination Function centrally controlled multiple access mechanism uses a poll and response protocol to eliminate the possibility of contention for the medium point coordinator (PC) is always located in an AP supports time bounded services 39 Cyber Book of Internet Communication 2017-05-25 Contention Free operation PCF Defers for Busy Medium CFP repetition interval Contention Free Period PCF (Optional) CFP repetition interval Contention Period DCF Busy medium CF-Burst Variable Length ”Reset NAV” PCF Defers NAV 40 Cyber Book of Internet Communication 2017-05-25 Contention Free operation Alternating Contention Free and Contention operation under PCF control NAV prevents Contention traffic until reset by the last PCF transfer So variable length Contention Free period per interval Both PCF and DCF defer to each other causing PCF Burst start variations 41 Cyber Book of Internet Communication 2017-05-25 PCF Burst CFP repetition interval Contention Free Burst PIFS Busy medium Contention Period D2 D1 U1 SIFS D3 U2 D4 No Up U4 CF_End Dx = AP-Frame Ux = Station-Frame Reset NAV NAV Min Contention Period 42 Cyber Book of Internet Communication 2017-05-25 PCF Burst CF-Burst by Polling bit in CF-Down frame. Immediate response by Station on a CF_Poll. Stations to maintain NAV to protect CF-traffic. Responses can be variable length. “Reset NAV” by last (CF_End) frame from AP. "ACK Previous Frame" bit in Header. 43 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 Standardization IEEE802.11 MAC & Other Activities Ad-Hoc Publicity Ad-Hoc Regulatory MAC Layer 802.11 MAC 802.11 MAC 802.11e / TGe MAC Enhancements -QoS 802.11f / TGf Inter-Access Point Protocol 802.11i / TGi Enhanced Security Mechanisms 44 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 Standardization IEEE802.11 current status TG 45 Substances Remarks 802.11 Develop three PHY's and MAC Standards capable of providing the transmission rate of 1,2Mbps, using IR, 2.4 GHz FHSS and DSSS Completed (1997.6) 802.11a Develop a PHY to operate in the newly allocated UNII band (5GHz) Completed (1999.9) 802.11b Develop a standard for a higher rate (11Mbps) PHY in the 2.4GHz band Completed (1999.9) 802.11b cor1 Corrigendum to the MIB (802.11b) Completed 802.11d Extensions to Operate in Additional Regulatory Domains 802.11e MAC Enhancements for Quality of Service Cyber Book of Internet Communication Ongoing Ongoing (D1.4) 2017-05-25 IEEE 802.11 Standardization IEEE802.11 current status TG 46 Substances Remarks Ongoing (D2.0) 802.11f Recommended Practice for Inter Access Point Protocol 802.11g Standard for Higher Rate (20+ Mbps) Extensions in the 2.4GHz Band 802.11h Spectrum Managed 802.11a Ongoing (D1.0) 802.11i MAC Enhancements for Enhanced Security Ongoing (D1.0) WNGSC Synthesize industry inputs for the Next Generation WLAN and recommends a global standard initiative Cyber Book of Internet Communication Ongoing (CCK-OFDM) Ongoing 1st draft 2017-05-25 IEEE 802.11 WG & Activities IEEE802.11e/TG e enhance the 802.11 MAC to improve and manage Quality of Service provide classes of service, and enhanced security and authentication mechanisms consider efficiency enhancements in the areas of the DCF and PCF applications transport of voice, audio, video video conferencing, media stream distribution, enhanced security applications mobile and nomadic access applications 47 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 WG & Activities IEEE802.11f/TG f develop recommended practices for an InterAccess Point Protocol (IAPP) which provides the necessary capabilities to achieve multivendor Access Point interoperability across a Distribution System supporting IEEE P802.11 Wireless LAN Links This IAPP will be developed for the following environment(s) A DS consisting of IEEE 802 LAN supporting an IETF IP environment Others as deemed appropriate 48 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 WG & Activities IEEE802.11g/TG g to develop a higher rate PHY extension to 802.11b date rates more than 20Mbps backwards compatible and interoperable with existing 2.4GHz IEEE 802.11b 11Mbps standard uses existing MAC layer Extended rate OFDM : mandatory mode using 802.11a and 802.11b the capability to detect either 802.11a or 802.11b preambles automatically Optional modes CCK-OFDM PBCC-22, PBCC-33 49 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 WG & Activities IEEE802.11h/TG h enhance the current 802.11 MAC and 802.11a PHY in 5GHz license exempt bands, enabling regulatory acceptance of 802.11 5GHz products. provide improvements in channel energy measurement and reporting, channel coverage to improve spectrum and transmit power management provide Dynamic Channel Selection and Transmit Power Control mechanisms Dynamic Channel Selection Transmit Power Control 50 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 WG & Activities IEEE802.11i/TG i enhance the 802.11 MAC to enhance security and authentication mechanisms Address security mechanisms beyond RC4 WEP 40-bit encryption, more robust against eavesdropping Focus on key distribution and authentication between Stations and Stations to APs Scaleable security framework to serve: home networks, enterprise, Ad-Hoc, Public Environments Data traffic: Voice, Data, Multi-media 51 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 WG & Activities WNG SC changed from 5GSG which has investigated the globalization and harmonization of the 5GHz band jointly with ETSI-BRAN, and MMAC PPDU frame format synthesize industry inputs for the Next Generation WLAN and recommend a global standard initiative will deliver recommended requirements and standards plan 52 Cyber Book of Internet Communication 2017-05-25 IEEE 802.11 WG & Activities Roadmap 1st Generation 2nd Generation 3rd Generation 4th Generation Analog Cellular IMT-2000 Cellular PCS - 2.5G WCDMA/CDMA2000 Mobile 384kbps Stationary : 2Mbps 2.4GHz 2Mbps, 11Mbps IEEE802.11x 1Mbps Wired LAN 53 • Outdoor 5.15-5.35GHz 25-50Mbps Digital Cellular 825-890MHz Voice only HiperLAN2 IEEE802.11a IEEE802.11 IEEE802.11b Wireless LAN Wireless LAN Wireless Wireless Multimedia Multimedia Internet Internet Appliance Appliance IEEE802.11a+ 5G NG WLAN • Indoor 60-65GHz 155-622Mbps • 5GHz/24Mbps • 5GHz/54Mbps • Cyber Book of Internet Communication 2017-05-25