Overview of Bluetooth Overview of Bluetooth � Bluetooth data rate • Voice channel supports 64 kb/s 64 kb/s synchronous (voice) link • asynchronous channel can support an asymmetric link of maximally 721 kb/s 721 kb/s • maximally 432.6 kb/s 432.6 kb/s for symmetric link � Bluetooth network • A piconet contains a master and up to 7 slaves • Several piconets can be linked together, forming a scatternet • Each piconet is identified by a deferent frequency hopping sequence Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Inquiry & Inquiry Scan Inquiry & Inquiry Scan Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Step2 Page Step2 Page Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
The Bluetooth asymmetric point to point The Bluetooth asymmetric point to point connection establishment protocol connection establishment protocol Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Piconet & & Scatternet Scatternet Piconet Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
State diagram of Bluetooth State diagram of Bluetooth Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Protocol Stack of Bluetooth Protocol Stack of Bluetooth Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Scatternet establishment establishment Scatternet � Start up procedure • Enter Inquiry and Inquiry scan state in term for a period of time • Discovering neighbors • Arrange neighbors table(self id included) with device id by increasing order, therefore, each unit get a sequence number, we call this number as pseudo candidate sequence number, because the lack of communication channel between units; self device id should be at 8 th notch or before 8 th notch • Enter paging frame Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Paging frame Paging frame P1 P2 P3 P4 P5 P6 P7 P8 � A paging frame contains 8 paging slots � An unit enter the paging frame will waiting for a number of slots and stay in page scan state, say if one’s pseudo candidate sequence number is 5, then it should stay in page scan state for 4 paging slots long � During the waiting time, the unit should be ready to participate in any piconet, once it becomes a member of a piconet, the start up procedure ended, and any unit continuously enter page scan state periodically � If the unit does not participate in any piconet after the waiting time, it start to page and become a master itself, it will page all the items in the neighbors table Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Benefit of the procedure Benefit of the procedure � Each unit will participate in at least one piconet � By waiting for a period of time, less piconets are established, this will reduce the hopping overload � Because any unit will at latest establish a new piconet at the end of paging frame, the time complex of the scatternet establishment will be constant � Because after the start up procedure, each unit will enter page scan state periodically, so, overlapping between piconets are built during the procedure � A new start up unit will easily participate in the scatternet with the same start up procedure Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Routing over Baseband Baseband Routing over Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Packet field Packet field � Add a field in the packet, the field indicate the final destination � Routing table is kept in HCI firmware, so the packet could be rescheduled right away according the “Destination Device Id” field, no higher layer protocol is needed � HCI firmware adjust the “AM_ADDR” in the HEADER and replace “ACCESS CODE” if needed, then switch to the specified piconet or just transport the packet to the specified slave Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Benefit and disadvantage Benefit and disadvantage � SAR procedure are avoided during intermediate hopping, this is beneficial to the device with low computing capability � Rescheduling of the packet is direct and fast � Any Bluetooth device could be the intermediate ones no matter with what high layer protocols it supports � Each MAC layer packet has 48 bits overhead Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Routing over L2CAP layer Routing over L2CAP layer Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Packet field Packet field � L2CAP follows a communication based on channels � The channel ID identifies the destination channel endpoint o the packet � To achieve routing, a field “Destination Device ID” is added into the L2CAP layer payload � After the whole PDU is received, the L2CAP layer could decide the next hop according the routing table and the “Destination Device”, and then make a new channel to the next hop, if the channel is exist, it just replace the “Channel ID”, and then retransmit the PDU through the channel Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Benefit and disadvantage Benefit and disadvantage � Routing over L2CAP layer is based on channel transmission, if the channel to the desired existed, than a connect establishment is not needed, this reduce the overhead � A PDU could contain up to 64K bytes data, and only 48 bit overhead needed, its consuming is far less than the routing over baseband method � Disadvantage of this method is the additional work of SAR, but it is not serious if the device computing capability is good � The significant disadvantage is that the synchronous data not transmitted through L2CAP, so these data could not be routing by this method Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Unit discovering Unit discovering � The discussed routing method above is based on table driven, that is every unit will learn the routing information of the units in the scatternet, therefore, the unit discovering could be expanded to the scope of a scatternt Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Work in the future Work in the future � Multicast performance � Support of QoS through scheduling and priority � IP addressing � Mobile IP and scatternet interworking Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Multihop for for bluetooth bluetooth Multihop � Broadcast enabled over Bluetooth scatternet • Mac address identification • Broadcast address identification � IP transparent • Data forwarding protocol below IP layer � Multi-hop multimedia transmission support • Pre-probe polling method • Virtual Link Path(VLP) reservation protocol Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
System Description System Description � Wireless Personal Area Network (WPAN) � LAN-link environment • Several WPANs may form an Ad hoc network via Bluetooth radio � Multimedia transmission between WPANs Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Network scenario Network scenario Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Research Topic for Bluetooth Research Topic for Bluetooth � Multicasting � Scheduling � Scatter-net Formation\ � Integration with Cellular Systems Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Ultra WideBand Technology Ultra WideBand Technology (UWB) (UWB) Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Connecting Our World Connecting Our World Mobile Home Memory Stick i.LINK Internet Network Services Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
What is Ultra Wideband? What is Ultra Wideband? � Originally referred to • “baseband”, “carrier-free”, or impulse � Any wireless transmission scheme • occupies a bandwidth of more than 25% of a center frequency, or more than 1.5GHz Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Compare with narrowband and wideband Compare with narrowband and wideband UWB systems have two characteristics � Bandwidth is much greater, • Defined by the Federal Communications Commission (FCC), is more than 25% of a center frequency or more than 1.5GHz � Carrierless fashion • “narrowband” and “wideband” use RF • UWB directly modulate an "impulse" that has a very sharp rise and fall time Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Compare with IEEE 802.11 and Bluetooth Compare with IEEE 802.11 and Bluetooth Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Compare with IEEE 802.11 and Bluetooth (cont.) Compare with IEEE 802.11 and Bluetooth (cont.) � UWB have greater spatial capacity • From the Hartley-Shannon law � Potential • for support of future high-capacity wireless systems Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Notice of Proposed Rule Making Notice of Proposed Rule Making � In May of 2000, the FCC issued a Notice of Proposed Rule Making (NPRM) � limit UWB • transmitted power spectral density for frequencies greater than 2GHz. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.15.3 V.S HyperLAN HyperLAN II II IEEE 802.15.3 V.S � IEEE P802.15.3 : The IEEE High Rate WPAN standard. � HiperLAN2 Direct Mode (DM) : The Home Profile of the HiperLAN2 WLAN standard, which is being specified by the Broadband Radio Access Networks (BRAN) project within the European Telecommunications Standards Institute (ETSI). Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Comparison of Network Topology Comparison of Network Topology Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Comparison of The Superframe Comparison of The Superframe Structure Structure Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
802.15.3 – – has a variable duration has a variable duration 802.15.3 � Beacon used to transmit control information to the entire piconet (synchronization, Max Tx power level) and the allocation of resource (dedicated time slots) per Stream_ID for the incoming superframe. � Contention Access Period (CAP) which is mainly used for Authentication/Association Request and response, stream parameters negotiation and also possible exchange of asynchronous data. � Contention Free Period (CFP) composed of data streams, either asynchronous or isochronous, with quality of service provisions. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Basic Scenario Basic Scenario Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Hidden and Exposed Stations Hidden and Exposed Stations Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Capture Effect/Near Far Problem Capture Effect/Near Far Problem Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
802.11 E 802.11 E Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
802.11 802.11 DIFS RTS Data Src SIFS SIFS SIFS Dest CTS Ack CW Other Next MPDU NAV (RTS) NAV (CTS) Defer Access Backoff after Defer Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Interference Issue for CSMA/CA Interference Issue for CSMA/CA Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
QoS issue for 802.11 issue for 802.11 QoS Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.11 IEEE 802.11 Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.11 Protocol Entities IEEE 802.11 Protocol Entities LLC LLC MAC Layer MAC Layer MAC MAC Management Management Sublayer Sublayer MAC MAC Station Station Management Management PHY Layer PHY Layer PLCP Sublayer Sublayer PLCP Management Management PHY PHY PMD Sublayer Sublayer PMD Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.11 Protocol Architecture IEEE 802.11 Protocol Architecture � � MAC Entity MAC Entity • • basic access mechanism basic access mechanism • • fragmentation fragmentation • • encryption ( RC4 PRNG Algo Algo. 40 bit secret key ) . 40 bit secret key ) encryption ( RC4 PRNG � � MAC Layer Management Entity MAC Layer Management Entity • • synchronization synchronization • • power management power management • • roaming roaming • • MAC MIB MAC MIB � � Physical Layer Convergence Protocol (PLCP) Physical Layer Convergence Protocol (PLCP) • • PHY- PHY -specific, supports common PHY SAP specific, supports common PHY SAP • • provides Clear Channel Assessment signal (carrier sense) provides Clear Channel Assessment signal (carrier sense) Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.11 Protocol Architecture IEEE 802.11 Protocol Architecture � Physical Medium Dependent Sublayer (PMD) • modulation and encoding � PHY Layer Management • channel tuning • PHY MIB � Station Management • interacts with both MAC Management and PHY Management Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
名詞解釋 名詞解釋 � Basic Service Set ( BSS ) � Basic Service Set ( BSS ) - - is the fundamental building block of the is the fundamental building block of the IEEE 802.11 architecture. A BSS is defined as a group of stations s IEEE 802.11 architecture. A BSS is defined as a group of station that are under the direct control of a single coordination function , ion , that are under the direct control of a single coordination funct i.e. , a DCF or PCF . i.e. , a DCF or PCF . Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
名詞解釋 名詞解釋 � Coordination � Coordination Fuction Fuction ( CF ) ( CF ) - - That logical function which That logical function which determines when a station operating within a Basic Service Set determines when a station operating within a Basic Service Set transmits and receives via the wireless medium. transmits and receives via the wireless medium. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.11 Wireless LAN Architecture IEEE 802.11 Wireless LAN Architecture � Ad Hoc Network ( Independent Basic Service Set Network : IBSS � Ad Hoc Network ( Independent Basic Service Set Network : IBSS Network ) Network ) � Infrastructure Network � Infrastructure Network Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.11 Configurations - IEEE 802.11 Configurations - Independent Independent Station AH2 Ad Hoc Network AH3 � Independent � Independent Station • one Basic Service Set • one Basic Service Set - - BSS BSS AH1 • Ad Hoc network • Ad Hoc network • direct communication • direct communication • limited coverage area • limited coverage area Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
IEEE 802.11 Configurations - IEEE 802.11 Configurations - Infrastructure Infrastructure Server DISTRIBUTION SYSTEM AP AP A B BSS-B Station A1 Station Station B2 A2 Station BSS-A B1 � � Infrastructure Infrastructure • • Access Points and stations Access Points and stations � � Distribution System Distribution System interconnects Multiple Cells via Access Points interconnects Multiple Cells via Access Points to form a single Network. to form a single Network. • • extends wireless coverage area extends wireless coverage area Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Distribution System Distribution System Used to interconnect wireless cells Used to interconnect wireless cells multiple BSSs BSSs connected together form an ESS, Extended connected together form an ESS, Extended multiple Service Set Service Set Not part of 802.11 standard Not part of 802.11 standard could be bridged IEEE LANs, wireless, other networks could be bridged IEEE LANs, wireless, other networks Distribution System Services are defined Distribution System Services are defined Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Access Point Access Point Stations select an AP and Associate with it Stations select an AP and Associate with it Support roaming Support roaming Provide other functions Provide other functions time synchronization ( beaconing ) time synchronization ( beaconing ) power management support power management support point coordination function point coordination function Traffic typically (but not always) flows through AP Traffic typically (but not always) flows through AP direct communication possible direct communication possible Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Services Provided by MAC Services Provided by MAC � Distribution System Service � Distribution System Service - - Divided into six kinds of service. Let data be Divided into six kinds of service. Let data be received or sent between station and station. received or sent between station and station. � Station Service � Station Service - - Divided into three kinds of service. Controlling access and Divided into three kinds of service. Controlling access and privacy of IEEE 802.11 Wireless Network. privacy of IEEE 802.11 Wireless Network. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Distribution System Services Distribution System Services � Distribution � Distribution - - Send data , which is in distribution system , to correct addres Send data , which is in distribution system , to correct address s � Integration � Integration - - Exchange data between Distribution System and existent wired Exchange data between Distribution System and existent wired network network Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Distribution System Services Distribution System Services � Association � Association Mobility of Station Mobility of Station • No • No- -Transition Transition � � Static Static � � Local Movement Local Movement • BSS • BSS- -Transition Transition • ESS • ESS- -Transition Transition Stations must establish connection with AP before sending data t Stations must establish connection with AP before sending data to it. This o it. This action is provided by Association service. action is provided by Association service. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Distribution System Services Distribution System Services � Reassociation � Reassociation Requested by station Requested by station • Move a current association from one AP to another • Move a current association from one AP to another • Change connection type • Change connection type Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Distribution System Services Distribution System Services � Deassociation � Deassociation Requested by station or AP Requested by station or AP • Stations leave the wireless network • Stations leave the wireless network • AP close or can • AP close or can’ ’t provide some services t provide some services Station or AP can Station or AP can’ ’t refuse t refuse Deassociation Deassociation sent by the other sent by the other Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Distribution System Services Distribution System Services � MSDU delivery � MSDU delivery Frames received or sent between stations and stations is provided by this d by this Frames received or sent between stations and stations is provide service service � MSDU � MSDU - - MAC Service Data Unit MAC Service Data Unit Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Station Service Station Service � Authentication � Authentication • Open System • Open System • Shared Key • Shared Key � Deauthentication � Deauthentication - - When Authentication is cancelled , Association will be When Authentication is cancelled , Association will be cancelled at the same time cancelled at the same time � Privacy � Privacy - - The 802.11 embeds the WEP ( Wired Equivalent Privacy ) The 802.11 embeds the WEP ( Wired Equivalent Privacy ) mechanism within the MAC that covers station- mechanism within the MAC that covers station -to to- -station transmission station transmission Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Relationships between Services Relationships between Services There two state variable ( Authentication , Association ) create There two state variable ( Authentication , Association ) create three station states : three station states : � Initial State , Unauthenticated , Unassociated � Initial State , Unauthenticated , Unassociated � Authenticated , not Associated � Authenticated , not Associated � Authenticated and Associated � Authenticated and Associated Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
State 1 Authenticate Successful Deauthenticate Deauthenticate Associate or reassociate successful State 2 State 3 Disassociate Relations Between State Variables and Services Relations Between State Variables and Services Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
MAC Frame Formats MAC Frame Formats 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 � � MAC Header format differs per Type: MAC Header format differs per Type: • Control Frames (several fields are omitted) • Control Frames (several fields are omitted) • Management Frames • Management Frames • Data Frames • Data Frames � � Includes Sequence Control Field for filtering of duplicate caused by ACK mechanism. d by ACK mechanism. Includes Sequence Control Field for filtering of duplicate cause Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Address Field Description Address Field Description 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 � Addr � Addr 1 = All stations filter on this address. 1 = All stations filter on this address. � Addr � Addr 2 = Transmitter Address (TA) 2 = Transmitter Address (TA) • Identifies transmitter to address the ACK frame to. • Identifies transmitter to address the ACK frame to. � Addr � Addr 3 = Dependent on 3 = Dependent on To To and and From DS From DS bits. bits. � Addr � Addr 4 = Only needed to identify the original source of WDS ( 4 = Only needed to identify the original source of WDS ( Wireless Wireless Distribution System) frames. frames. Distribution System) Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
CSMA/CA Protocol CSMA/CA Protocol � IEEE 802.11 use CSMA/CA protocol � IEEE 802.11 use CSMA/CA protocol � IEEE 802.11 provide two categories of basic access method � IEEE 802.11 provide two categories of basic access method • Distributed Coordination Function ( DCF ) • Distributed Coordination Function ( DCF ) • Pointed Coordination Function ( PCF ) • Pointed Coordination Function ( PCF ) � � Provide Time Bounded Service Provide Time Bounded Service Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Optional Point Coordination Function (PCF) Optional Point Coordination Function (PCF) Time Bounded / Async Async Contention Free Service Contention MAC Service PCF Optional DCF (CSMA/CA ) PHY • Contention Free Service uses Point Coordination • Contention Free Service uses Point Coordination Function (PCF) on a DCF Foundation. Function (PCF) on a DCF Foundation. – PCF can provide lower PCF can provide lower transfer delay transfer delay variations to variations to – support Time Bounded Services Time Bounded Services . . support – Async Async Data, Voice or mixed implementations possible. Data, Voice or mixed implementations possible. – – Point Coordinator resides in AP. Point Coordinator resides in AP. – • • Coexistence between Contention and optional Contention Coexistence between Contention and optional Contention Free does not burden the implementation. Free does not burden the implementation. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Distributed Coordination Function Distributed Coordination Function � Priority access to the wireless medium is controlled through the � Priority access to the wireless medium is controlled through the use of Inter use of Inter- - Frame Space ( IFS ) time intervals between the transmission of frames. rames. Frame Space ( IFS ) time intervals between the transmission of f Three IFS intervals are specified in the standard. Three IFS intervals are specified in the standard. • Short • Short- -IFS ( SIFS ) IFS ( SIFS ) • Point Coordination Function • Point Coordination Function- -IFS ( PIFS ) IFS ( PIFS ) • Distributed Coordination Function • Distributed Coordination Function- -IFS ( DIFS ) IFS ( DIFS ) Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
CSMA/CA Explained CSMA/CA Explained Free access when medium DIFS is free longer than DIFS Contention Window PIFS DIFS SIFS Backoff-Window Busy Medium Next Frame Slot time Select Slot and Decrement Backoff as long as medium is idle. Defer Access � Backoff � Backoff Time = INT( CW * Random() ) * Slot Time Time = INT( CW * Random() ) * Slot Time CW = An integer between CW = An integer between CWmin CWmin and and CWmax CWmax Random() = random number between 0 and 1 Random() = random number between 0 and 1 Slot Time = Transmitter turn Slot Time = Transmitter turn- -on delay + on delay + medium propagation delay + medium propagation delay + medium busy detect response time and is medium busy detect response time and is PHY dependent PHY dependent Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
DIFS DIFS DIFS A B C D Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
DIFS Data RTS Src SIFS SIFS SIFS Dest CTS Ack CW Other Next MPDU NAV (RTS) NAV (CTS) Defer Access Backoff after Defer • Duration field in RTS and CTS frames distribute field in RTS and CTS frames distribute Medium Medium • Duration Reservation information which is stored in a information which is stored in a Network Network Reservation Allocation Vector (NAV) . . Allocation Vector (NAV) • Defer on either NAV or "CCA" indicating Medium Busy Medium Busy . . • Defer on either NAV or "CCA" indicating • Use of RTS / CTS is optional but must must be implemented. be implemented. • Use of RTS / CTS is optional but Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
PCF Defers for Busy Medium CFP repetition interval CFP repetition interval Contention Free Period Contention Period DCF B CF-Burst PCF (original) Busy medium "Reset NAV" PCF Async traffic Defer Variable Length Defer NAV • Alternating Alternating Contention Free Contention Free and and Contention Contention • operation under PCF control. operation under PCF control. • NAV prevents NAV prevents Contention Contention traffic until reset by the traffic until reset by the • last PCF transfer. last PCF transfer. – So variable length So variable length Contention Free Contention Free period per period per – interval. interval. • Both PCF and DCF defer to each other causing Both PCF and DCF defer to each other causing • PCF Burst start variations. PCF Burst start variations. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
PCF Burst PCF Burst CFP repetition interval Contention Free Burst PIFS Contention Period D1 D3 D2 D4 Busy Medium CF_End U1 U4 U2 Dx = AP-Frame No Up Ux = Station-Frame SIFS Reset NAV NAV Min Contention Period • CF CF- -Burst by Polling bit in CF Burst by Polling bit in CF- -Down frame. Down frame. • • Immediate response by Station on a CF_Poll. Immediate response by Station on a CF_Poll. • • Stations to maintain NAV to protect CF Stations to maintain NAV to protect CF- -traffic. traffic. • • Responses can be variable length. Responses can be variable length. • • Reset NAV by last (CF_End) frame from AP. Reset NAV by last (CF_End) frame from AP. • • "ACK Previous Frame" bit in Header. "ACK Previous Frame" bit in Header. • Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
Fragmentation Fragmentation DIFS PIFS SIFS Other NAV (RTS) NAV (Fragment 0) Backoff-Window NAV (ACK 0) NAV (CTS) SIFS Src Fragment 1 RTS Fragment 0 Dest ACK 1 CTS ACK 0 � � Burst of Fragments which are individually acknowledged. Burst of Fragments which are individually acknowledged. • For • For Unicast Unicast frames only. frames only. � � Random backoff backoff and retransmission of failing fragment when no ACK is returned. and retransmission of failing fragment when no ACK is returned. Random � � Duration information in data fragments and Duration information in data fragments and Ack Ack frames causes NAV to be set, for medium frames causes NAV to be set, for medium reservation mechanism. reservation mechanism. Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory
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