1	Course Overview Introduction and History Data in Wireless Cellular Systems Data in Wireless Local Area Networks Internet Protocols Routing and Ad-Hoc Networks TCP over Wireless Link Services and Service Discovery System Support for Mobile Applications
2	Wireless Local Area Networks “Traditional” LANs: WaveLan, Proxim, IEEE 802.11 More specific “personal” LANs, also called “Personal Area Networks”: Bluetooth, IEEE 802.15 High-speed wireless LANs (approaching ATM data rates): HiperLAN
3	WaveLAN Commercial product, developed by Lucent Technologies (de-facto market leader), available since early 1990s Development closely aligned with early IEEE 802.11 standard effort, first product generation differs in key aspects from final IEEE 802.11 standard Will discuss WaveLAN version 1, newer version 2 follows finally approved 802.11 standard (plus enhancements to allow for data rates up to 10 Mbps) Physical layer: 915 MHz (902-928 MHz) or 2.4 GHz (2.412-2.475 GHz) ISM band Bands are divided into frequency channels of 26 MHz each Modulation scheme: DSSS, raw data rate of 2 Mbps
4	WaveLAN: Configurations
5	WaveLAN: Configurations
6	WaveLAN: Protocol Stack
7	WaveLAN: Frame Formats
8	WaveLAN MAC Protocol Basically CSMA/CA Sense media before transmission, if free, transmit Defer: wait until end of current transmission, plus fixed delay (WaveLAN InterFrame Space, WIFS) of 60 msec apply random backoff procedure: pick number between 0 and 31 (antenna slot number S) each slot corresponds to 23 ms wait S*23 ms, sense media again, if busy, double backoff range until we reach range 0-255 drop packet after 15 attempts If station has more than one packet to send: wait WIFS plus backoff-period in range 0-15 (avoid monopolization)
9	WaveLAN: MAC Protocol (Example)
10	WaveLAN: Higher Protocols
11	WaveLAN: Beacon (Higher Protocol Example)
12	IEEE 802.11 Standard for wireless local area networks, approved by IEEE in 1997 Scope: physical layer (PHY) and media access control sublayer (MAC) for wireless connectivity for fixed, portable, and moving stations with a local area Supports data rates of 1 or 2 Mbps, using infrared or radio Supports two basic architectures: independent basic support set (IBSS) and infrastructure networks Most recent commercial products (including the new WaveLAN generation) are compatible with 802.11
13	802.11 Infrastructure Network Station (STA) terminal with access mechanisms to the wireless medium 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 distribution system Portal bridge to other (wired) networks Distribution System interconnection network to form one logical network (EES: Extended Service Set) based on several BSS
14	802.11 Ad-hoc Network Direct communication within a limited range Station (STA): terminal with access mechanisms to the wireless medium Basic Service Set (BSS): group of stations using the same radio frequency
15	IEEE Family of Standards
16	802.11 Layers and Functions PLCP Physical Layer Convergence Protocol clear channel assessment signal (carrier sense) PMD Physical Medium Dependent modulation, coding PHY Management channel selection, MIB Station Management coordination of all management functions MAC access mechanisms, fragmentation, encryption MAC Management synchronization, roaming, MIB, power management
17	802.11 Physical Layer 3 versions: 2 radio (typ. 2.4 GHz), 1 IR data rates 1 or 2 Mbit/s FHSS (Frequency Hopping Spread Spectrum) spreading, despreading, signal strength, typ. 1 Mbit/s min. 2.5 frequency hops/s (USA), two-level GFSK modulation DSSS (Direct Sequence Spread Spectrum) DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying), DQPSK for 2 Mbit/s (Differential Quadrature PSK) preamble and header of a frame is always transmitted with 1 Mbit/s, rest of transmission 1 or 2 Mbit/s chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code) max. radiated power 1 W (USA), 100 mW (EU), min. 1mW Infrared 850-950 nm, diffuse light, typ. 10 m range carrier detection, energy detection, synchonization
18	IEEE 802.11 MAC Architecture
19	802.11 MAC Layer 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) Access methods DCF CSMA/CA (mandatory) collision avoidance via randomized „back-off“ mechanism minimum distance between consecutive packets ACK packet for acknowledgements (not for broadcasts) DCF w/ RTS/CTS (optional) Distributed Foundation Wireless MAC (DFWMAC) avoids hidden terminal problem PCF (optional) access point polls terminals according to a list
20	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 PIFS (PCF IFS) medium priority, for time-bounded service using PCF DIFS (DCF, Distributed Coordination Function IFS) lowest priority, for asynchronous data service
21	802.11 MAC: CSMA/CA station ready to send starts sensing the medium (Carrier Sense based on CCA, Clear Channel Assessment) if the medium is free for the duration of an Inter-Frame Space (IFS), the station can start sending (IFS depends on service type) if the medium is busy, the station has to wait for a free IFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot-time) if another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness)
22	802.11 MAC: Competing Stations
23	IEEE 802.11 DCF Protocol Sense media before transmission If media is free, transmit if media stays idle for a fixed amount of time (DCF Interframe Space, DIFS) Defer: wait until end of current transmission, plus DIFS apply random backoff procedure: pick number between 0 and 7, check whether medium is idle during each backoff slot if media is busy, suspend backoff process at beginning of current slot after media was idle for selected number of slots, transmit immediately if this transmission results in collision, backoff again, doubling the backoff Upon receipt of packet: receiver waits short interval (Short Interframe Space, SIFS) transmits acknowledgement frame (ACK) back to sender If sender receives no ACK within ACKTimeout interval, assume collision
24	802.11 MAC: CSMA/CA Sending unicast packets station has to wait for DIFS before sending data receivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC) automatic retransmission of data packets in case of transmission errors
25	802.11 MAC: RTS/CTS Sending unicast packets station can send RTS with reservation parameter after waiting for DIFS (reservation determines amount of time the data packet needs the medium) acknowledgement via CTS after SIFS by receiver (if ready to receive) sender can now send data at once, acknowledgement via ACK other stations store medium reservations distributed via RTS and CTS
26	IEEE 802.11: DCF and PCF Coexistence
27	802.11 MAC: Point Coordination Function
28	802.11 MAC: Point Coordination Function
29	802.11 MAC Frame Format Types control frames, management frames, data frames Sequence numbers important against duplicated frames due to lost ACKs Addresses receiver, transmitter (physical), BSS identifier, sender (logical) Miscellaneous sending time, checksum, frame control, data
30	MAC Address Format
31	802.11 MAC Management Synchronization try to find a LAN, try to stay within a LAN timer etc. Power management sleep-mode without missing a message periodic sleep, frame buffering, traffic measurements Association/Reassociation integration into a LAN roaming, i.e. change networks by changing access points scanning, i.e. active search for a network MIB - Management Information Base managing, read, write
32	Synchronization using a Beacon (Infrastructure Network)
33	Synchronization using a Beacon (Ad-hoc Network)
34	Power Management Idea: switch the transceiver off if not needed States of a station: sleep and awake Timing Synchronization Function (TSF) stations wake up at the same time Infrastructure Traffic Indication Map (TIM) list of unicast receivers transmitted by AP Delivery Traffic Indication Map (DTIM) list of broadcast/multicast receivers transmitted by AP Ad-hoc Ad-hoc Traffic Indication Map (ATIM) announcement of receivers by stations buffering frames more complicated - no central AP collision of ATIMs possible (scalability?)
35	Power saving with wake-up patterns (Infrastructure Network)
36	Power saving with wake-up patterns (Ad-hoc Network)
37	802.11 Roaming No or bad connection? Then perform: Scanning scan the environment, i.e., listen into the medium for beacon signals or send probes into the medium and wait for an answer Reassociation Request station sends a request to one or several AP(s) Reassociation Response success: AP has answered, station can now participate failure: continue scanning AP accepts Reassociation Request signal the new station to the distribution system the distribution system updates its data base (i.e., location information) typically, the distribution system now informs the old AP so it can release resources
38	Future Developments IEEE 802.11a compatible MAC, but now 5 GHz band transmission rates up to 20 Mbit/s close cooperation with BRAN (ETSI Broadband Radio Access Network) IEEE 802.11b higher data rates at 2.4 GHz proprietary solutions already offer 10 Mbit/s IEEE WPAN (Wireless Personal Area Networks) market potential compatibility low cost/power, small form factor technical/economic feasibility è Bluetooth
39	Bluetooth: “Personal Area Networks” open specification for wireless communication of data and voice based on a low-cost short-range radio link, built into a 9 x 9 mm microchip (design goal: cost of US$ 5/device) facilitates protected ad hoc connections for stationary and mobile communication environments Bluetooth is a cooperation between computer and telecommunication industries (Ericsson, IBM, Toshiba, Intel, Nokia, …) SIG started in February 1998 with above five members, has grown since (64 companies joined in January 1999 alone)
40	Bluetooth Vision
41	Bluetooth General Characteristics operates in the 2.4 GHz Industrial-Scientific-Medical (ISM) band nominal link range: 10 cm to 10 m, can be increased to 100 m (transmitting with more power) uses Frequence Hop (FH) spread spectrum supports up to 8 devices in a piconet (two or more Bluetooth units sharing a channel) built-in security non line-of-sight transmission through walls and briefcases (distinguishes it from IrDA) omni-directional supports both isochronous and asynchronous services; easy integration of TCP/IP for networking
42	Bluetooth Intended Uses connect a wide range of computing and telecommunications devices without the need to buy, carry, or connect cables delivers opportunities for rapid, ad hoc connections, and in the future, possibly for automatic, unconscious, connections between devices power-efficient radio technology can be used in many of the same devices that use IR: Phones and pagers Modems LAN access devices Headsets Notebook, desktop, and handheld computers
43	Bluetooth Radio frequency hopping in 79 hops displaced by 1 MHz, starting at 2.402 GHz and stopping at 2.480 GHz to function on a worldwide basis, Bluetooth requires a radio frequency that is license-free and open to any radio 2.45 GHz ISM band satisfies these requirements, although it must cope with interference from baby monitors, garage door openers, cordless phones and microwave ovens, which also use this frequency. due to local regulations the bandwidth is reduced in Japan, France and Spain. This is handled by an internal software switch the maximum frequency hopping rate is 1600 hops/s.
44	Bluetooth Frequency Hopping/Time Division Duplex Scheme
45	Bluetooth MAC protocol Time Division Duplex (TDD) scheme for full-duplex transmissions master device establishes connection, slave devices synchronize their clock with master clock for duration of connection Synchronous Connection Oriented (SCO) type (used primarily for voice) channel symmetric, only data packets retransmitted Asynchronous Connectionless (ACL) type (used primarily for packet data) master unit controls the link bandwidth and decides how much piconet bandwidth is given to each slave, and the symmetry of the traffic slaves must be polled before they can transmit data. The ACL link also supports broadcast messages from the master to all slaves in the piconet
46	Bluetooth MAC Protocol Error correction: 1/3 rate forward error correction code (FEC) for SCO only 2/3 rate forward error correction code FEC Automatic repeat request (ARQ) scheme for data data transmitted in one slot is directly acknowledged by the recipient in the next slot. Authentication and Privacy one-way, two-way, or no authentication possible use stream cipher based on secret keys (0, 40, 64 bits) key management left to higher layer software if stronger protection (longer key is needed), use better encryption at network and/or application level
47	Bluetooth Data Rates
48	Bluetooth PicoNet Example
49	Bluetooth Power States
50	Bluetooth Scatternets
51	Bluetooth Scatternets Multiple overlapping piconets (sets of communicating devices) with own hopping sequence, max of one master and 8 slaves Collisions do occur when two piconets use same frequency at the same time as more piconets overlap, performance degrades degradation gradual: 10 overlapping piconets reduce aggregate bandwidth by 10% Single device can participate in multiple piconets, though only one at a time need to re-adjust clock to re-sync with master when entering a piconet inform master when device leaves piconet, will suppress data being sent/device being polled
52	Bluetooth Scatternet
53	HIPERLAN ETSI standard European standard, cf. GSM, DECT, ... Enhancement of local Networks and interworking with fixed networks integration of time-sensitive services from the early beginning HIPERLAN family one standard cannot satisfy all requirements range, bandwidth, QoS support commercial constraints HIPERLAN 1 standardized since 1996
54	Original HIPERLAN Protocol Family
55	HIPERLAN 1 Characteristics Data transmission point-to-point, point-to-multipoint, connectionless 23.5 Mbit/s, 1 W power, 2383 byte max. packet size Services asynchronous and time-bounded services with hierarchical priorities compatible with ISO MAC Topology infrastructure or ad-hoc networks transmission range can be larger then coverage of a single node („forwarding“ integrated in mobile terminals) Further mechanisms power saving, encryption, checksums
56	HIPERLAN 1 Services and Protocols CAC service definition of communication services over a shared medium specification of access priorities abstraction of media characteristics MAC protocol MAC service, compatible with ISO MAC and ISO MAC bridges uses HIPERLAN CAC CAC protocol provides a CAC service, uses the PHY layer, specifies hierarchical access mechanisms for one or several channels Physical protocol send and receive mechanisms, synchronization, FEC, modulation, signal strength
57	HIPERLAN 1 Physical Layer Scope modulation, demodulation, bit and frame synchronization forward error correction mechanisms measurements of signal strength channel sensing Channels 3 mandatory and 2 optional channels (with their carrier frequencies) mandatory channel 0: 5.1764680 GHz channel 1: 5.1999974 GHz channel 2: 5.2235268 GHz optional (not allowed in all countries) channel 3: 5.2470562 GHz channel 4: 5.2705856 GHz
58	HIPERLAN 1 Physical Layer Frames Maintaining a high data-rate (23.5 Mbit/s) is power consuming - problematic for mobile terminals packet header with low bit-rate comprising receiver information only receiver(s) address by a packet continue receiving Frame structure LBR (Low Bit-Rate) header with 1.4 Mbit/s 450 bit synchronization minimum 1, maximum 47 frames with 496 bit each for higher velocities of the mobile terminal (> 1.4 m/s) the maximum number of frames has to be reduced Modulation GMSK for high bit-rate, FSK for LBR header
59	HIPERLAN 1 CAC Sublayer Channel Access Control (CAC) assure that terminal does not access forbidden channels priority scheme, access with EY-NPMA Priorities 5 priority levels for QoS support QoS is mapped onto a priority level with the help of the packet lifetime (set by an application) if packet lifetime = 0 it makes no sense to forward the packet to the receiver any longer standard start value 500ms, maximum 16000ms if a terminal cannot send the packet due to its current priority, waiting time is permanently subtracted from lifetime based on packet lifetime, waiting time in a sender and number of hops to the receiver, the packet is assigned to one out of five priorities the priority of waiting packets, therefore, rises automatically
60	HIPERLAN 1 EY-NPMA EY-NPMA (Elimination Yield Non-preemptive Priority Multiple Access) 3 phases: priority resolution, contention resolution, transmission finding the highest priority every priority corresponds to a time-slot to send in the first phase, the higher the priority the earlier the time-slot to send higher priorities can not be preempted if an earlier time-slot for a higher priority remains empty, stations with the next lower priority might send after this first phase the highest current priority has been determined
61	HIPERLAN 1 EY-NPMA Several terminals can now have the same priority and wish to send contention phase Elimination Burst: all remaining terminals send a burst to eliminate contenders (11111010100010011100000110010110, high bit- rate) Elimination Survival Verification: contenders now sense the channel, if the channel is free they can continue, otherwise they have been eliminated Yield Listening: contenders again listen in slots with a nonzero probability, if the terminal senses its slot idle it is free to transmit at the end of the contention phase the important part is now to set the parameters for burst duration and channel sensing (slot-based, exponentially distributed) data transmission the winner can now send its data (however, a small chance of collision remains) if the channel was idle for a longer time (min. for a duration of 1700 bit) a terminal can send at once without using EY-NPMA synchronization using the last data transmission
62	HIPERLAN 1 MAC Layer Compatible to ISO MAC Supports time-bounded services via a priority scheme Packet forwarding support of directed (point-to-point) forwarding and broadcast forwarding (if no path information is available) support of QoS while forwarding Encryption mechanisms mechanisms integrated, but without key management Power conservation mechanisms mobile terminals can agree upon awake patterns (e.g., periodic wake-ups to receive data) additionally, some nodes in the networks must be able to buffer data for sleeping terminals and to forward them at the right time (so called stores)
63	Information Bases Route Information Base (RIB) - how to reach a destination [destination, next hop, distance] Neighbor Information Base (NIB) - status of direct neighbors [neighbor, status] Hello Information Base (HIB) - status of destination (via next hop) [destination, status, next hop] Alias Information Base (AIB) - address of nodes outside the net [original MSAP address, alias MSAP address] Source Multipoint Relay Information Base (SMRIB) - current MP status [local multipoint forwarder, multipoint relay set] Topology Information Base (TIB) - current HIPERLAN topology [destination, forwarder, sequence] Duplicate Detection Information Base (DDIB) - remove duplicates [source, sequence]
64	Ad-hoc Networks using HIPERLAN 1