module 3
Content
MOBILE COMPUTING
Module III
• Wireless LAN and ATM: - Infra red and Radio Transmission, Infrastructure and ad hoc networks, 802.11- Bluetooth- Architecture, Applications and Protocol, Layers, Frame structure, comparison between 802.11 and 802.16. • Wireless ATM- Services, Reference Model, Functions, Radio Access Layer. HandoverReference Model, Requirements, Types, handover scenarios. Location Management, Addressing, Access Point Control Protocol (APCP).
assignment 2
• WWW- HTTP, Usage of HTML, WWW system architecture.
Wireless LANs
• Restricted in their diameter • goal: replace office cabling –Introduce higher flexibility for adhoc communication
Characteristics of wireless LANs
• Types
– Infrastructure based – Ad-hoc
Advantages
• Flexibility: within radio coverage nodes can communicate without restriction • Planning: without previous planning possible • Design: allow for the design of small independent devices • Robustnes: more robust against disasters like, earthquakes, fire -or users pulling a plug...
WLAN…
Disadvantages
• Quality of service: lower quality than wired
– very low bandwidth due to limitations in radio xion
• • • • •
-1-10 Mbit/s) - higher error rates due to interference Cost: wireless LAN adapters cost high Proprietary solutions: due to slow standardization procedures , many companies have come up with proprietary solutions Restrictions: products have to follow many national regulations -restrict freqs to minimize interference safety and security: data xion may interfere with other equipments - open radio interface makes evesdropping.
WLAN…
• Design goals for wireless LANs • global operation: WLAN products sell in all countries – many national and international freq regulation have to be considered • low power for battery use : power saving modes and power management functions needes • Licence-free opn: no special permissions or licenses needed to use the LAN • robust transmission technology- facing all problems • simplified spontaneous cooperation : should not require complicated set up routine
Designgoals…
• easy to use : for everyone, simple management • protection of investment : should be interoperable with existing wired LAN. • Safety and security: safe to operate-low radiation – (no one should be able to read my data), privacy (no one should be able to collect user profiles)- encryption • Transparency for applications: the fact of wireless access and mobility should be hidden
Wireless transmission technologies
• Infrared light (900nm wavelength) -uses diffused light or directed light(LOS) -- senders can be LEDs or laser diodes --receivers are photodiodes • Ver 1.0 implements- 115kbps • Ver 1.1 upto 4Mbps • Radio xion in GHzs( 2.4 GHz- license-free ISM band)
IR Technology
• Advantages • simple, cheap, available in many mobile devices
– interface available everywhere-PDAs, laptops,mobile phone etc. have an infra red data association (IrDA)
• • • • •
no licenses needed Electrical devices do not interfere Disadvantages interference by sunlight, heat sources etc. Cannot penetrate thru obstacles many things shield or absorb IR light • low bandwidth
Radio transmission
Advantages • coverage of larger areas possible (radio can penetrate walls, furniture etc.) • No need for LOS • High xion rates Disadvantages • very limited license free frequency bands • shielding more difficult, -xion can interfere with other senders • interference with other electrical devices
infrastructure & ad-hoc networks
• Many WLAN of today need infrastructure networks • Provide access to other n/ws • Include forwarding functions, Medium access control etc. • Communication takes place only b.w wireless nodes and access point • not directly b.w the wireless nodes. • The access Pont act as a bridge to other wireless or wired n/ws.
infrastructure networks
Infrastructure networks…
• Several wireless n/ws form one logical wireless n/w • Access points together with fixed n/ws wireless n/ws can form a larger n/w beyond the radio coverage. • Design is simple as most of the n/w functionality lies within the access point • As the access point controls the medium access , no collision are possible
Infrastructure networks
• Do not have the flexibility that the wireless n/w can offer
– Cannot be used for disaster relief.
• Cellular phone n/ws are infrastructure based n/ws for wide area. • Infrastructure does not imply a wired fixed n/w
– Satellite is the infrastructure for satellite bases cellular phones
Ad-hoc networks
• Design complexity is higher
– Each node has to implement medium access mechanisms – Mechanisms to handle hidden and exposed terminals. – Priority mechanism to provide a certain QOS
• Provides greatest flexibility
– Unexpected meetings, quick replacement of infrastructure
• Nodes within an ad-hoc n/w can communicate if they can reach each other •Within the radio range
IEEE 802.11
• Specifies the most famous family of WLANs. • Goal:
– specification of a simple and robust WLAN which offers time bounded and asynch. services – Support for power management. – Handling the hidden nodes – Ability to operate worldwide uses 2.4 GHz ISM band ,which is available in most countries – Data rates 1Mbps mandatory and 2 Mbps optional
System Architecture
• 2 basic architectures- infrastructure based and ad hoc • Several nodes, called Station (STA) • STAs are connected to APs. • STA terminals 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
802.11 – System Architecture
SystemArchitecture… • Access Point: station integrated into the wireless LAN and the distribution system Portal : bridge to other (wired) networks Distribution System or interconnection network to form one logical network • ESS (Extended Service Set):several BSS Distribution
IEEE standard 802.11
802.11 -Layers and functions
• Physical layer is subdivided into PLCP( physical layer convergence protocol) and PMD (physical medium dependant sublayer) • PLCP : provides a carrier sense signal called clear channel assessment (CCA) • PMD : modulation, coding/decoding of signals
• Basic tasks of MAC layer: access mechanisms, fragmentation, encryption
802.11 –Layers…
• 802.11 specifies management layers and the station management. • PHY Management:
– channel selection,PHY MIB(management information base) maintenance
• MAC Management :
– association of a station to AP and roaming b.w access points – Controls authentication mechanisms, encryption, synchronization of station with regards to an AP, MIB, power management, – MAC MIB maintenance
• Station Management:
– Interacts with both the management layers – coordination of all management functions
802.11 –Layers…
802.11 -Physical layer
• Supports 3 xion techniques.
– One based on infra red and 2 based on radio xion using FHSS and DSSS.
• Supports clear channel assessment (CCA) signal
– Needed for the MAC mechanisms controlling medium access and indicates if the medium is currently idle.
• Infrared – The physical layer based on IR xion uses 850-950 nm,
– – – – – diffuse light, 10 m range Sunlight or heat sources interfere with xion. Will only work in buildings. Shielding is easy –a wall is enough to shield one IR based n/w carrier detection, energy detection, synchronization
Spread Spectrum
•
SpreadSpectrum…
Signal is spread over a larger freq range by the Sender before the transmission
• Energy is constant
•
•
During xion narrow band and broadband interference add to the signal
Receiver despreads the signal and spreads the narrow band interference
•
• • • •
Receiver applies a bandpass filter to cut off freqs left and right of the narrowband signal.
Receiver can reconstruct the original data as the power level is high enough. advantage - resistance to narrow band interference - Several users can independently use the same higher bandwidth with very little interference
Two major types: –Frequency Hopping Spread Spectrum –Direct Sequence Spread Spectrum
Physicallayer…
• FHSS (Frequency Hopping Spread Spectrum)
• Uses 79 channels with 1MHz width. spreading, despreading, signal strength, typ. 1 Mbit/s
FHSS…
• Signal is broadcast over random series of frequencies
• – A number of channels allocated for the signal
• – Width of each channel corresponds to bandwidth of input signal • Signal hops from frequency to frequency at fixed intervals • – Transmitter operates in one channel at a time • – Bits are transmitted using some encoding scheme
• – At each successive interval, a new carrier frequency is selected
• •Receiverhopsbetweenfrequenciesinsynchronizationwith transmitter • •Advantages:
• Eavesdroppers hear only unintelligible signals
FHSS frame
• Synchronization:synch with 010101... pattern
• SFD (Start Frame Delimiter):0000110010111101 start pattern • PLW (PLCP_PDU Length Word):length of payload incl. 32 bit CRC of payload, PLW < 4096 • PSF (PLCP Signaling Field):data rate of the payload (1 or 2 Mbit/s)- 1 bit used • HEC (Header Error Check):CRC
DSSS (Direct Sequence Spread Spectrum)
•Separating by code not by freq. •User bit stream is X-ORed with a bit seq called chipping seq
•Wireless LANs (IEEE 802.11) use 10110111000, called Barker code.
DSSS …
Synchronization: SFD (Start Frame Delimiter):1111001110100000 Signal: data rate of the payload ( 0x0A: 1 Mbit/s DBPSK;0x 14: 2 Mbit/s DQPSK) Service : future use Length:length of the payload
HEC (Header Error Check):protection of signal, service and length fields are protected
MAC layer
• • • • Control medium access Support roaming Authentication, power conservation Mandatory asynchronous data service and optional time bounded service • 802.11 only offers asynchronous data service in adhoc mode • Both the service types can be offered using infrastructure based n/w • Async. Service supports broadcast and multicast packets
– exchangeofdatapacketsbasedon―best-effort‖
Access mechanisms
• 3 Access methods 1. Mandatory basic method based on CSMA/CA 2. Optional method avoiding the hidden terminal problems 3. Contention free polling method for time bounded service. • MAC mechanisms also called Distributed Foundation Wireless Medium Access Control(DFWMAC)
• 1 and 2 are termed as distributed coordination function-DFWMAC-DCF
– Offers asynch. service
• 3 is called point coordination function -- DFWMACPCF
– Offers async. and time based services – Needs an AP to control medium access and to avoid contention
Accessmechanisms…
• 3 diff parameters defining the priorities of medium access
•Medium can be busy or idle—detected by CCA b •Busy-due to data frames or control frames •Contention- several nodes try to access the medium
Accessmechanisms…
1. DCF inter-frame spacing(DIFS): longest waiting time and lowest priority for medium access—lowest priority – This waiting time is used for asynchronous data service within a contention period. 2. PCF inter-frame spacing(PIFS ) : waiting time b.w DIFS and SIFS , used for a time-bounded service
3. Short inter-frame spacing(SIFS ) : shortest waiting time for medium access –highest priority -defined for short control messages—ack ,polling responses
Basic DFWMAC-DCF using CSMA/CA • Mandatory access mechanism • Random access scheme with carrier sense and collisionavoidancethrurandomized‘‗back-off― mechanism
CSMA/CA… • If the medium is sensed idle for duration of at least DIFS a node can access the medium.
• If the medium is busy ,nodes have to wait for the duration of DIFS • Enter a contention mode • Each node chooses a random back off time within a contention window – Delays medium access for this random amount of time.
CSMA/CA… randomized additional waiting time is over and the medium idle, - the node can access the medium at once.
- the additional waiting time is measured in multiples of slots.
- Slot time is derived from the medium propogation delay ,transmitter delay and other PHY dependant parameters.
CSMA/CA…
Independent of the overall waiting time each node has the same chance for xmitting data in the next cycle - to provide fairness, adds a backoff timer • Each node selects a random waiting time within the range of the contention window. • certain station does not get access to medium in the first cycle
– stops its back off timer,waits for the channel to be idle for DIFS and starts counter again.
• As the Counter expires the node access the medium. • The deferred stations do not choose a randomized backoff time again ,
– continue to count down.
• --longer waiting stns have the advantage over newly entering stns.
CSMA/CA…
Collision triggers a rexion with a new selection of backoff time
CSMA/CA…
• Have problems under heavy or light load
– Depending on the size of window (cw), the random values can be too close causing collisions,value are too high causing unnecessary delay – System tries to adapt to the current number of stns trying to send – CW starts with size of Cwmineg: 7 – Collision indicates higher load, CW doubles up to max of eg:255 – 7,15,31,63,127,255 – Called exponential backoff
CSMA/CA…
Additional feature is provided by the std for unicast data xfer
Receiver access the medium after waiting SIFS
No collision for ACKenvironment
Important in error-prone
DFWMAC-DCF with RTS/CTS
• Optional method avoiding the hidden terminal problems
• Hidden terminal problem occurs when one stn can receive 2 others, but those stns cannot receive each other
• To deal with this problem, the std defines an additional mechanism using 2 control packets, RTS,CTS
--station can send RTS with reservation parameter after waiting for DIFS • (reservation parameter determines amount of time the data packet needs the medium)
• acknowledgement via CTS after SIFS by receiver (if ready to receive)
RTS/CTS…
and C want to send to B- – A sends RTS first--– C waits after receiving CTS from B
–A
RTS/CTS…
• sender can now send data at once
•
acknowledgement via ACK
--other stations store medium reservations distributed via RTS and CTS
NAV—net allocation vector
--collision for RTSs possible --overhead- wastage of b.w
--higher delay
DFWMAC-DCF with RTS/CTS…
DFWMAC-PCF
• For time bounded service.
– Point co-ordination function -requires an access point , controls the medium access and polls -in ad-hoc not possible -noQOS,but‗besteffort‘service -point co-ordinator in the AP splits the access time into super frame periods. --consists of contention free period and contention period. -in contention period other methods
DFWMAC-PCF …
DFWMAC-PCF …
DFWMAC-PCF …
• • • • • • • • • • • • At t0 contention free period theoretically starts PCF changes to DCF Start of super frame is postponed After idle the point co-ordinator(PC) has to wait for PIFS No other stns can start sending PC sends data D1 to the first wireless stn Stn answer after SIFS time After SIFS PC polls second stn. D2 Stn answer U2 Continues to third node ,no answer after SIFS After waiting PIFS PC resumes polling PC can issue an end marker CFend , contention period starts again
DFWMAC-PCF …
• PCF automatically sets the NAV preventing other stns from sending • At t4 next super frame starts. • If only PCF is used ,bandwidth is divided evenly among nodes • Will be a static, centrally controlled TDMA
– Overhead if nodes have nothing to send. – AP polls them permanently.
MAC Frame format
MACFrameformat…
Frame Types control frames – used for handshaking and ACKs management frames – used for timing & synchronization,node association & deassociation with AP, andauthentication & deauthentication data frames - Frame control: - Type - Subtype:fragmented - DS bits:distribution system bits- indicating the meaning of 4 address fields - WEP-privacy infmn-Wired Equipment Privacy
MACFrameformat…
• Duration ID: reservation mechanism using RTS/CTS and during fragmentation.
– Period of time in which the medium is occupied
• Addresses:4 address fields • Sequence control: important against duplicated frames due to lost ACKs • Data: • CRC:
MAC address format
Wi Max/IEEE 802.16
• Network covering a country, continent or entire globe • interconnecting several WMANs and providing anywhere,anytime access • Broadband Wireless • radio waves in frequency range 2 GHz to 60 GHz. – Know as "last mile" fixed broadband access – Wi-Fi: 802.11 may be not the best way for last mile connection • WiMAX standard provides the missing link for the "last mile" connection in metropolitan area networks where DSL, Cable and other broadband access methods are not available or too expensive.
802.16…
802.11 has performance limitations when supporting larger numbers of users needing guaranteed bandwidth RF interference is often a significant problem with 802.11 • The 802.16 medium access control (MAC) layer (define) supports many different physical layer specifications, both licensed and unlicensed. • Examples: • Cellular networks • Satellite systems
802.16…
• WiMAX also offers an alternative to satellite Internet services for rural areas and allows mobility of the customer equipment.
IEEE 802.16 Standards
•
• • • • •
Range: 30 mile (50 Km) radius from base station Speed: 70 Mbit/s Line-of-sight not needed Bandwidth: between 10 and 66 GHz Define both the MAC and PHY layers and allows multiple PHY layer specifications Services: Digital audio/video multicast, digital telephony,Internet protocol, etc.
IEEE 802.16 Standards….
• 2 versions for IEEE 802.16 standards
– fixed WiMax standard IEEE 802.16-2004 (802.16d) approved by the IEEE in June 2004, – provides fixed, point-to-multi point broadband wireless access service – In Dec. 2005, IEEE approved the mobile WiMax standard, the 802.16-2005 (802.16e) – based on the early WiMax standard 802.16a, – adds mobility features to WiMAX in the 2 to 11 GHz licensed bands. – 802.16e allows for fixed wireless and mobile Non Line of Sight (NLOS)
comparison
• IEEE Standards: – Wi-Fi is based on IEEE 802.11 standard where as WiMAX is based on IEEE 802.16.
• Range: – Wi-Fi typically provides local network access for around a few hundred feet with speeds of up to 54 Mbps, – WiMAX antenna is expected to have a range of up to 30 miles with speeds of 70 Mbps or more. – WiMAX can bring the Internet connection needed to service local Wi-Fi networks.
Comparison…
• Scalability:
•
Wi-Fi is intended for LAN applications
– users scale from one to tens with one subscriber for each CPE(Customer premises equipment) device.
–
•
Fixed channel sizes (20MHz).
WiMAX is designed to efficiently support from one to hundreds of CPEs, with unlimited subscribers behind each CPE. – Flexible channel sizes from 1.5MHz to 20MHz.
Comparison…
• Bit rate:
• Wi-Fi works at 2.7 bps and can peak up to 54 Mbps in 20 MHz channel. • WiMAX works at 5 bps and can peak up to 100 Mbps in a 20 MHz channel.
• Quality of Service:
• Wi-Fi does not guarantee any QoS • WiMax will provide several levels of QoS.
• WiMAX can bring the Internet connection needed to service local Wi-Fi networks.
Comparsion Table
Freature Primary Application WiMax (802.16a) Broadband Wireless Access Wi-Fi (802.11) Wireless LAN
Frequency Band Channel Bandwidth
Half/Full Duplex
Licensed/Unlicensed 2 G to 11 GHz Adjustable 1.25 M to 20 MHz
Full
2.4 GHz ISM 25 MHz
Half
Radio Technology
OFDM (256-channels)
BPSK, QPSK
Direct Sequence Spread Spectrum
QPSK
Modulation
Comparsion Table…
Encryption Mandatory- 3DES Optional- AES Optional- RC4 (AES in 802.11i)
Mobility
Mobile WiMax (802.16e) Request/Grant
In development
Access Protocol
CSMA/CA
FEC
Convolutional Code Reed-Solomon
None
Wireless ATM
ATM?
Asynchronous Transfer Mode (ATM) • A networking technology developed by the telephone companies • handle all types of data using fixed 53-byte cells, or packets. • Creates virtual point-to-point circuit connections between the source and the destination. • Data rates from 25 to 622 Mbps.
ATM?
• The small cell size allows ATM to transmit video, audio, and computer data over the same network, while guaranteeing a preset QoS level for each.
Why wireless ATM?
• Need for the integration of wireless terminals to wired ATM • ATM networks scale l from LANs to WANs
– Mobility needed -- extend ATM for wireless access in local and global environments.
• • •
•
•
– mobile phones and mobile communications have an ever increasing importance in everyday life current wireless LANs do not offer adequate support for multimedia data streams Do not offer adequate QoS. merging of mobile communication and ATM leads to wireless ATM goal: integration of mobility into B-ISDN -- B-ISDN uses ATM as backbone infrastructure . Problem: high complexity of the system
Wireless ATM Working Group
• ATM Forum founded the Wireless ATM Working Group in June 1996 • Task: development of specifications to enable the use of ATM technology also for wireless networks • compatibility to existing ATM Forum standards is important • it should be possible to easily upgrade existing ATM networks with mobility functions and radio access
WATM services
Example scenarios in which WATM can be used • Office environment
– multimedia conferencing, online multimedia database access
• Universities, schools, training centers
– distance learning, teaching
• Industry
– database connection,infmn retreival, surveillance, realtime data xion , factory management
• Hospitals
– Transfer of medical images, remote access to patient records, remote monitoring, remote diagnosis of patient at home or in an ambulance
WATMservices…
• Home
– high-bandwidth interconnect of devices (TV, CD player, PC, ...)
• Networked vehicles
– trucks, aircraft etc. –high quality access to internet,company databases, multimedia conferencing etc.
Reference model
• WMT (Wireless Mobile ATM Terminal)—have radio links to RT • RT (Radio Transceiver)—connected to AP via wires • AP (Access Point)—controls several RTs
– Implements all radio access functions to handle radio resource management, radio medium access control and other radio-specific functions
• EMAS-E (End-user Mobility-supporting ATM Switch - Edge)- several APs are connected to
– Exchange signaling messages with WMT and offer mobility functions
Referencemodel…
• EMAS-N (End-user Mobility-supporting ATM Switch - Network)—communicates with EMAS-E via NNI+M protocol • APCP (Access Point Control Protocol) – Coordinate the radio related signalling b.w AP and WMT and ATM related signalling b.w EMASE and WMT.
• UNI+M (User-to-Network Interface with Mobility support) • NNI+M (Network-to-Network Interface with Mobility support)
Referencemodel…
EMAS-N WMT RT AP
RT WMT
RT APCP UNI+M
EMAS-E NNI+M
EMAS-N AP
protocol layers
radio segment MATM terminal WATM terminal adapter WATM access point fixed network segment ATM switch fixed end system
EMAS-E
EMAS-N
user process AAL ATM PHY ATM PHY RAL ATM RAL PHY ATM PHY PHY ATM PHY PHY ATM PHY PHY
user process AAL ATM PHY
MATM terminal
WATM adapter
WATM access point
EMAS-E
EMAS-N
ATM switch
ATM terminal
Functions
Many additional functions are needed to support mobility ,wireless access and security at the user side and n.w side - user identification module (UIM) is part of WMT - WMT is connected to AP via radio link
WMT side functions
• Identity Management Function (IMFT)
– functions to store identification and security related information – user dependent
• Mobile Terminal Security Agent (MTSA)
– additional security information stored in UIM – user independent – authenticate the terminal as hardware
• Call control and Connection control Function (CCFT)
– call set-up and release, access control, connection control • Mobility Management Function (MMFT) – analysis and monitoring of the network, location update.
MTSA
CCF
NSA
IMFT
UIM
CCFT
MMFT
MMF
APCF
SCF
APCF
ACFT ATMCT RRCT ACF RRC ATMC ATMC
RTRT WMT
RTR AP EMAS-E
Functions and logical interconnection
WMT side functions...
• ATM Connection function (ATMCT) – responsible for ATM connections—conn. setup, release, and modification – provides bearer service – controls ATM connection elements providing standard services (CBR, rt-VBR, ABR, UBR) • Radio Transmission and Reception (RTRT) – basic functions enabling sending and receiving of data – consists of LLC, MAC, PHY layers for radio transmission • Radio Resource Control function (RRCT) – select,release and reserve of radio resources – trigger handovers, monitor radio access
WMT side functions...
• Association Control Function (ACFT) – handles the association of a wireless terminal to its AP – set-up and release access to access point – support for intra-AP handover – power saving – radio handover.
Mobility supporting at network side
• Access Point Control Function (APCF)
– implemented in AP and EMAS-E – paging, handover, AP management
• Call control and Connection control Function (CCF)
– call set-up and release, connection control, requests network and radio resources
• Network Security Agent (NSA)
– to control the wireless terminals – identity management, authentication, encryption, confidentiality control
• Service Control Function (SCF)
– supports storage and access to service profiles – provides consistency check on these profiles
Mobility supporting at network side...
• Mobility Management Function (MMF)
– mobility support – location management, handover, – storage of location data and subscriber identity
• Association Control Function (ACF)
– set-up and release access to mobile terminal
• Radio Resource Control function (RRC)
– management of radio channels, initiate handover
• Radio Transmission and Reception function (RTR)
– LLC, MAC, PHY layers, support of ATM traffic parameters
• ATM Connection function (ATMC)
– responsible for ATM connections, standard services (CBR, VBR, ABR, UBR)
Radio Access Layer (RAL)
• wireless access is provided by adding RAL under ATM specific layers • RAL should operate in 5GHz Requirements for an RAL?
• requirement 1.physical layer:
• must specify • frequencies, efficient re-use of frequencies • antennas, xmit power, maximum range • cell characteristics • Carrier frequency, symbol rate, modulation scheme, coding, training sequences etc. • interfaces for data and control flow
RAL...
• Requirements specified for the physical layer: – Bit Error Rate (BER) <= 10-4, availability 99.5 % – packet size:several cells per PDU – data rate: 25 Mbit/s – range: indoor 30-50 m, outdoor 200-300 m – error correction – xmit power: 100 mW
RAL...
requirements 2: MAC layer • controls simultaneous access of several mobile terminals to the medium • includes defn of a MAC protocol,PDU format and MAC control algorithm • support user mobility • provide interfaces to physical and LLC layers
RAL...
• Requirements specified by MAC
• 1. logical channels: MAC layer within RAL connects ATM layers of the AP and WMT
– must support logical channels for ATM virtual connection 2. QoS parameters: should support QoS and traffic parameters in accordance with the ATM specification 3. Architecture: should support infrastructure network
RAL...
• 4 . service provision:
– services offered should include the ATM service classes CBR,rt-VBR,ABR,UBR
– MAC efficiency: higher than 60-75 % (over 90% is possible)
– data rates • peak 25 Mbit/s • sustained 6 Mbit/s
RAL...
requirements 3: LLC layer
• Layer between ATM and MAC layers to solve specific problems of the wireless transmission • Definition of LLC protocol and LLC PDU – wireless headers for data packets, control messages • main functions of LLC: – error control • error detection and correction using selective retransmission and forward error correction
RAL...
• Requirements for LLC:
– mandatory: ARQ (Automatic Repeat Request): – optional: FEC for real-time services – should provide means to support handover and to restore cell sequence during handover – authentication,encryption,other security mechanisms.
Handover
• Procedure to hand over connection(s) from a mobile ATM terminal from one access point to another access point • main problem for WATM handover is rerouting of all connections and maintaining connection quality • A handover domain – several access points cover a certain area – common handover protocol and strategy – all access points and switches belong to one administrative domain
Simple handover reference model
handover segment anchor point RT
WMT
AP RT
fixed segment RT AP
handover domain
Handover reference model
• an ATM end-to-end conn is seperated into diff segments.
• a fixed segment is a part of the conn that is not affected by the handover
• a handover segment is affected by the handover and is located completely within a handover domain • anchor point is the boundary b.w a handover segment and a fixed segment
• if both the end systems are wireless mobile ATM terminals there might be no fixed segments .
• the anchor point then connects the 2 handover segments which might be in diff handover domains
Handover Requirements
• multiple connection handover: end-to-end systems can support many conns at the same time.
Handover of point-to-multipoint connections: QoS support: preserve Qos of all conns during handover. data integrity and security: should minimize cell loss and avoid cell duplication signaling and routing support:WATM should provide means
to identify mobility enabled switches To reroute partial conns in handover domain
high performance and low complexity
Types of handover
• Hard handover – WMT can have only one connection to one access point possible • Terminal initiated – WTM initiates HO based on, e.g., signal quality • Network initiated – Network initiates HO based on, e.g., network load • Network initiated, terminal assisted – WTM provides information about radio conditions and other parameters. • Network controlled – HO decision always at network
• Infmn about the current load situation, free resources,etc. resides in n.w
Typesofhandover…
• Backward handover
– standard type – WMT notices a signal fading and initiates HO to a new AP. – terminal continues to maintain radio conn while HO is in process and switches over to a new AP after resources have been reserved and all entities involved are prepared for HO.
• Forward handover
– WMT suddenly arrives at a new AP, connection loss possible – Has to initiate the HO.
Handover scenarios
Intra-EMAS-E/ Intra-AP RT1 EMAS-E1
EMAS-N COS
RT2
WMT RT3 Intra-EMAS-E/ Inter-AP Inter-EMAS-E/ Inter-AP
AP1
EMAS-E2 AP2
RT4
RT5
RT6
AP3
Handover scenarios
• Intra EMAS-E/Intra-AP: WMT moves from RT1 to RT2
– The main task of AP IS to switch b/w the RTs.
• Intra EMAS-E/Inter-AP :WMT moves from RT3 to RT4
– HO remains in the domain of EMAS-E1
• Inter EMAS-E/Inter-AP:WMT moves from RT5 to RT6
– Another intermediate switch known as Cross Over Switch has to manage HO.
Location management
• Special fns are reqd for looking up the current position of the mob terminal. • Requirements – Transparency of mobility – Security:privacy of location and user information – Identification: must provide means to identify radio cells,terminals ,switches etc. – Efficiency and scalability: every fn involved in LM must be scalable and efficient.
Locationmanagement…
• standardized method for registration • ATM end system address (AESA) : mobile terminals need a temporary, routable address as soon as it is outside its home n.w – AESAmustbeforwardedtotheterminal‘shome location. • Interworking and standards: LM fns must co-operate with existing ATM functions—routing – Must be harmonized with other LM schemes such as used in GSM,UMTS,mobile IP
Procedures and entities
• Several entities which support LM have been identified. • Mobile terminal: execute functions to initiate location updates and participates in authentication and privacy protocols • EMAS: are necessary to identify conn setup msgs for WMTs and to invoke location resolution fns. -- some of EMAS maintain location and authentication servers LS : maintains a db containing the current AESA and the permanent AESA of a WMT AUS: maintains a secure db of authentication and privacy related infmn of each WMT - also includes access rights and equipment identification.
Registration and location update
visited EMAS-E home EMAS home home AUS LS
WMT
AP
Broadcast_ID Association Register
Loc_Update_Home
Loc_Update_Reply
Loc_Update_Home_Reply
Auth_Req Auth_Req_Reply Loc_Update_LS Loc_Update_LS_Reply
8.39.1
Registrationandlocationupdate…
Registration and locn update msgs flow after a WMT has moved to a new AP. • AP broadcast a Broadcast-ID to identify the n.w,current locn and RT. • WMT can now decide to associate with this AP if access rights permit.
• Send a registration msg to the EMAS-E visited
– Includes the address of the home EMAS and requests a temporary AESA.
• The visited EMAS-E performs the req Loc_Update_Home to the home EMAS of the WMT
Registrationandlocationupdate…
• Home EMAS checks the access right and identity of the WMT by means of the msg Auth_Req • If Auth_Req_reply signals that everything is okay the home EMAS updates the home LS with new location.
• LS acknowledges • Visited EMAS-E returns a temporary AESA to the WMT in a Loc_Update_Reply.
2 EMAS-E2 WMT LS 3 AP1 EMAS 1
8
EMAS-E1
RT1
AP2
4 5 T
7 RT2 network without mobility support
6
LS home network
visited network
Incoming connection setup, WMT in foreign network
Incoming connection setup
•
•
Arbitrary n.w, home n.w and n.w currently visited.
Home n.w contains the EMAS-E to which all conns are routed for the WMT.
•
Other n.ws are foreign n.ws for WMT.
Steps reqd for localization of WMT and conn. setup:
1. T only knows the permanent address WMT - sets up a conn with WMT. - EMAS-E2 detects the incoming conn setup.
Incoming connection setup
2. EMAS-E2 lookup the current loc of WMT by sending a location request to the LS.
- LS has mapping of permanent address to current foreign address of all WMTs it is responsible for
- if several hierarchical look-up steps are needed ,LS maps the permanent address to the EMAS in the visited n.w
Incoming connection setup
3. LS returns the current address of either the WMT or EMAS responsible for further lookup
- hierarchical approach make sense to avoid too frequent LS updates 4. EMAS-E2 redirect incoming conn to the EMAS in the visited n.w.
5.
-
EMAS responsible for n.w currently visited can determine the loc of WMT in greater detail.
It issues a req to its LS.
-
This EMAS may be an EMAS-E or EMAS-N
Incomingconnectionsetup…
6. The LS answers with the exact current loc as represented in its database . 7. conn setup can be forwarded to the EMAS-E1,which is directly connected to the AP to which the WMT is also connected. final step is the conn setup to the WMT itself via the AP and RT.
8.
Addressing
Basic requirements for WATM address:
• should support all formats of ATM end-system addresses (AESA)
• Must have a permanent, location independent address which can be used by other commn partners for contacting the WMT • WMT must support the assignment of temporary, routable addresses during registration of the mobile terminal in a foreign domain
Access Point Control Protocol
• Every AP exchanges multitude of msgs with EMAS-E • The protocol used to communicate
• Main purpose:
– Reserving and releasing resources in the AP for conn(memory,radio freqs ..) – A switch can prepare AP for new conns and assist in handover via APCP – AP uses APCP to inform EMAS-E about the newly associated WMT.
AcessPointControlProtocol…
• Reasons for the separation of AP and EMAS-E and a standardized interface are:
– All radio issues are kept separate from the switch.
– The switch only needs support for mobility – Separation and standardized interfaces allow multivendor solutions
APCP -Functional architecture
• AP contain process directly related to radio issues such as WCAC and RRM
• APCM handles the current conns.
AP
WCAC
RM
EMAS-E
RM:
CC: CAC:
switch resource management
call control connection admission control mobility management radio resource management
RRM
APCM
CC
CAC
MM
MM: RRM:
WCAC: wireless CAC
radio sub-system
APCM: AP connection management
APCP
APCP: AP control protocol
Module III
• Wireless LAN and ATM: - Infra red and Radio Transmission, Infrastructure and ad hoc networks, 802.11- Bluetooth- Architecture, Applications and Protocol, Layers, Frame structure, comparison between 802.11 and 802.16. • Wireless ATM- Services, Reference Model, Functions, Radio Access Layer. HandoverReference Model, Requirements, Types, handover scenarios. Location Management, Addressing, Access Point Control Protocol (APCP).
assignment 2
• WWW- HTTP, Usage of HTML, WWW system architecture.
Wireless LANs
• Restricted in their diameter • goal: replace office cabling –Introduce higher flexibility for adhoc communication
Characteristics of wireless LANs
• Types
– Infrastructure based – Ad-hoc
Advantages
• Flexibility: within radio coverage nodes can communicate without restriction • Planning: without previous planning possible • Design: allow for the design of small independent devices • Robustnes: more robust against disasters like, earthquakes, fire -or users pulling a plug...
WLAN…
Disadvantages
• Quality of service: lower quality than wired
– very low bandwidth due to limitations in radio xion
• • • • •
-1-10 Mbit/s) - higher error rates due to interference Cost: wireless LAN adapters cost high Proprietary solutions: due to slow standardization procedures , many companies have come up with proprietary solutions Restrictions: products have to follow many national regulations -restrict freqs to minimize interference safety and security: data xion may interfere with other equipments - open radio interface makes evesdropping.
WLAN…
• Design goals for wireless LANs • global operation: WLAN products sell in all countries – many national and international freq regulation have to be considered • low power for battery use : power saving modes and power management functions needes • Licence-free opn: no special permissions or licenses needed to use the LAN • robust transmission technology- facing all problems • simplified spontaneous cooperation : should not require complicated set up routine
Designgoals…
• easy to use : for everyone, simple management • protection of investment : should be interoperable with existing wired LAN. • Safety and security: safe to operate-low radiation – (no one should be able to read my data), privacy (no one should be able to collect user profiles)- encryption • Transparency for applications: the fact of wireless access and mobility should be hidden
Wireless transmission technologies
• Infrared light (900nm wavelength) -uses diffused light or directed light(LOS) -- senders can be LEDs or laser diodes --receivers are photodiodes • Ver 1.0 implements- 115kbps • Ver 1.1 upto 4Mbps • Radio xion in GHzs( 2.4 GHz- license-free ISM band)
IR Technology
• Advantages • simple, cheap, available in many mobile devices
– interface available everywhere-PDAs, laptops,mobile phone etc. have an infra red data association (IrDA)
• • • • •
no licenses needed Electrical devices do not interfere Disadvantages interference by sunlight, heat sources etc. Cannot penetrate thru obstacles many things shield or absorb IR light • low bandwidth
Radio transmission
Advantages • coverage of larger areas possible (radio can penetrate walls, furniture etc.) • No need for LOS • High xion rates Disadvantages • very limited license free frequency bands • shielding more difficult, -xion can interfere with other senders • interference with other electrical devices
infrastructure & ad-hoc networks
• Many WLAN of today need infrastructure networks • Provide access to other n/ws • Include forwarding functions, Medium access control etc. • Communication takes place only b.w wireless nodes and access point • not directly b.w the wireless nodes. • The access Pont act as a bridge to other wireless or wired n/ws.
infrastructure networks
Infrastructure networks…
• Several wireless n/ws form one logical wireless n/w • Access points together with fixed n/ws wireless n/ws can form a larger n/w beyond the radio coverage. • Design is simple as most of the n/w functionality lies within the access point • As the access point controls the medium access , no collision are possible
Infrastructure networks
• Do not have the flexibility that the wireless n/w can offer
– Cannot be used for disaster relief.
• Cellular phone n/ws are infrastructure based n/ws for wide area. • Infrastructure does not imply a wired fixed n/w
– Satellite is the infrastructure for satellite bases cellular phones
Ad-hoc networks
• Design complexity is higher
– Each node has to implement medium access mechanisms – Mechanisms to handle hidden and exposed terminals. – Priority mechanism to provide a certain QOS
• Provides greatest flexibility
– Unexpected meetings, quick replacement of infrastructure
• Nodes within an ad-hoc n/w can communicate if they can reach each other •Within the radio range
IEEE 802.11
• Specifies the most famous family of WLANs. • Goal:
– specification of a simple and robust WLAN which offers time bounded and asynch. services – Support for power management. – Handling the hidden nodes – Ability to operate worldwide uses 2.4 GHz ISM band ,which is available in most countries – Data rates 1Mbps mandatory and 2 Mbps optional
System Architecture
• 2 basic architectures- infrastructure based and ad hoc • Several nodes, called Station (STA) • STAs are connected to APs. • STA terminals 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
802.11 – System Architecture
SystemArchitecture… • Access Point: station integrated into the wireless LAN and the distribution system Portal : bridge to other (wired) networks Distribution System or interconnection network to form one logical network • ESS (Extended Service Set):several BSS Distribution
IEEE standard 802.11
802.11 -Layers and functions
• Physical layer is subdivided into PLCP( physical layer convergence protocol) and PMD (physical medium dependant sublayer) • PLCP : provides a carrier sense signal called clear channel assessment (CCA) • PMD : modulation, coding/decoding of signals
• Basic tasks of MAC layer: access mechanisms, fragmentation, encryption
802.11 –Layers…
• 802.11 specifies management layers and the station management. • PHY Management:
– channel selection,PHY MIB(management information base) maintenance
• MAC Management :
– association of a station to AP and roaming b.w access points – Controls authentication mechanisms, encryption, synchronization of station with regards to an AP, MIB, power management, – MAC MIB maintenance
• Station Management:
– Interacts with both the management layers – coordination of all management functions
802.11 –Layers…
802.11 -Physical layer
• Supports 3 xion techniques.
– One based on infra red and 2 based on radio xion using FHSS and DSSS.
• Supports clear channel assessment (CCA) signal
– Needed for the MAC mechanisms controlling medium access and indicates if the medium is currently idle.
• Infrared – The physical layer based on IR xion uses 850-950 nm,
– – – – – diffuse light, 10 m range Sunlight or heat sources interfere with xion. Will only work in buildings. Shielding is easy –a wall is enough to shield one IR based n/w carrier detection, energy detection, synchronization
Spread Spectrum
•
SpreadSpectrum…
Signal is spread over a larger freq range by the Sender before the transmission
• Energy is constant
•
•
During xion narrow band and broadband interference add to the signal
Receiver despreads the signal and spreads the narrow band interference
•
• • • •
Receiver applies a bandpass filter to cut off freqs left and right of the narrowband signal.
Receiver can reconstruct the original data as the power level is high enough. advantage - resistance to narrow band interference - Several users can independently use the same higher bandwidth with very little interference
Two major types: –Frequency Hopping Spread Spectrum –Direct Sequence Spread Spectrum
Physicallayer…
• FHSS (Frequency Hopping Spread Spectrum)
• Uses 79 channels with 1MHz width. spreading, despreading, signal strength, typ. 1 Mbit/s
FHSS…
• Signal is broadcast over random series of frequencies
• – A number of channels allocated for the signal
• – Width of each channel corresponds to bandwidth of input signal • Signal hops from frequency to frequency at fixed intervals • – Transmitter operates in one channel at a time • – Bits are transmitted using some encoding scheme
• – At each successive interval, a new carrier frequency is selected
• •Receiverhopsbetweenfrequenciesinsynchronizationwith transmitter • •Advantages:
• Eavesdroppers hear only unintelligible signals
FHSS frame
• Synchronization:synch with 010101... pattern
• SFD (Start Frame Delimiter):0000110010111101 start pattern • PLW (PLCP_PDU Length Word):length of payload incl. 32 bit CRC of payload, PLW < 4096 • PSF (PLCP Signaling Field):data rate of the payload (1 or 2 Mbit/s)- 1 bit used • HEC (Header Error Check):CRC
DSSS (Direct Sequence Spread Spectrum)
•Separating by code not by freq. •User bit stream is X-ORed with a bit seq called chipping seq
•Wireless LANs (IEEE 802.11) use 10110111000, called Barker code.
DSSS …
Synchronization: SFD (Start Frame Delimiter):1111001110100000 Signal: data rate of the payload ( 0x0A: 1 Mbit/s DBPSK;0x 14: 2 Mbit/s DQPSK) Service : future use Length:length of the payload
HEC (Header Error Check):protection of signal, service and length fields are protected
MAC layer
• • • • Control medium access Support roaming Authentication, power conservation Mandatory asynchronous data service and optional time bounded service • 802.11 only offers asynchronous data service in adhoc mode • Both the service types can be offered using infrastructure based n/w • Async. Service supports broadcast and multicast packets
– exchangeofdatapacketsbasedon―best-effort‖
Access mechanisms
• 3 Access methods 1. Mandatory basic method based on CSMA/CA 2. Optional method avoiding the hidden terminal problems 3. Contention free polling method for time bounded service. • MAC mechanisms also called Distributed Foundation Wireless Medium Access Control(DFWMAC)
• 1 and 2 are termed as distributed coordination function-DFWMAC-DCF
– Offers asynch. service
• 3 is called point coordination function -- DFWMACPCF
– Offers async. and time based services – Needs an AP to control medium access and to avoid contention
Accessmechanisms…
• 3 diff parameters defining the priorities of medium access
•Medium can be busy or idle—detected by CCA b •Busy-due to data frames or control frames •Contention- several nodes try to access the medium
Accessmechanisms…
1. DCF inter-frame spacing(DIFS): longest waiting time and lowest priority for medium access—lowest priority – This waiting time is used for asynchronous data service within a contention period. 2. PCF inter-frame spacing(PIFS ) : waiting time b.w DIFS and SIFS , used for a time-bounded service
3. Short inter-frame spacing(SIFS ) : shortest waiting time for medium access –highest priority -defined for short control messages—ack ,polling responses
Basic DFWMAC-DCF using CSMA/CA • Mandatory access mechanism • Random access scheme with carrier sense and collisionavoidancethrurandomized‘‗back-off― mechanism
CSMA/CA… • If the medium is sensed idle for duration of at least DIFS a node can access the medium.
• If the medium is busy ,nodes have to wait for the duration of DIFS • Enter a contention mode • Each node chooses a random back off time within a contention window – Delays medium access for this random amount of time.
CSMA/CA… randomized additional waiting time is over and the medium idle, - the node can access the medium at once.
- the additional waiting time is measured in multiples of slots.
- Slot time is derived from the medium propogation delay ,transmitter delay and other PHY dependant parameters.
CSMA/CA…
Independent of the overall waiting time each node has the same chance for xmitting data in the next cycle - to provide fairness, adds a backoff timer • Each node selects a random waiting time within the range of the contention window. • certain station does not get access to medium in the first cycle
– stops its back off timer,waits for the channel to be idle for DIFS and starts counter again.
• As the Counter expires the node access the medium. • The deferred stations do not choose a randomized backoff time again ,
– continue to count down.
• --longer waiting stns have the advantage over newly entering stns.
CSMA/CA…
Collision triggers a rexion with a new selection of backoff time
CSMA/CA…
• Have problems under heavy or light load
– Depending on the size of window (cw), the random values can be too close causing collisions,value are too high causing unnecessary delay – System tries to adapt to the current number of stns trying to send – CW starts with size of Cwmineg: 7 – Collision indicates higher load, CW doubles up to max of eg:255 – 7,15,31,63,127,255 – Called exponential backoff
CSMA/CA…
Additional feature is provided by the std for unicast data xfer
Receiver access the medium after waiting SIFS
No collision for ACKenvironment
Important in error-prone
DFWMAC-DCF with RTS/CTS
• Optional method avoiding the hidden terminal problems
• Hidden terminal problem occurs when one stn can receive 2 others, but those stns cannot receive each other
• To deal with this problem, the std defines an additional mechanism using 2 control packets, RTS,CTS
--station can send RTS with reservation parameter after waiting for DIFS • (reservation parameter determines amount of time the data packet needs the medium)
• acknowledgement via CTS after SIFS by receiver (if ready to receive)
RTS/CTS…
and C want to send to B- – A sends RTS first--– C waits after receiving CTS from B
–A
RTS/CTS…
• sender can now send data at once
•
acknowledgement via ACK
--other stations store medium reservations distributed via RTS and CTS
NAV—net allocation vector
--collision for RTSs possible --overhead- wastage of b.w
--higher delay
DFWMAC-DCF with RTS/CTS…
DFWMAC-PCF
• For time bounded service.
– Point co-ordination function -requires an access point , controls the medium access and polls -in ad-hoc not possible -noQOS,but‗besteffort‘service -point co-ordinator in the AP splits the access time into super frame periods. --consists of contention free period and contention period. -in contention period other methods
DFWMAC-PCF …
DFWMAC-PCF …
DFWMAC-PCF …
• • • • • • • • • • • • At t0 contention free period theoretically starts PCF changes to DCF Start of super frame is postponed After idle the point co-ordinator(PC) has to wait for PIFS No other stns can start sending PC sends data D1 to the first wireless stn Stn answer after SIFS time After SIFS PC polls second stn. D2 Stn answer U2 Continues to third node ,no answer after SIFS After waiting PIFS PC resumes polling PC can issue an end marker CFend , contention period starts again
DFWMAC-PCF …
• PCF automatically sets the NAV preventing other stns from sending • At t4 next super frame starts. • If only PCF is used ,bandwidth is divided evenly among nodes • Will be a static, centrally controlled TDMA
– Overhead if nodes have nothing to send. – AP polls them permanently.
MAC Frame format
MACFrameformat…
Frame Types control frames – used for handshaking and ACKs management frames – used for timing & synchronization,node association & deassociation with AP, andauthentication & deauthentication data frames - Frame control: - Type - Subtype:fragmented - DS bits:distribution system bits- indicating the meaning of 4 address fields - WEP-privacy infmn-Wired Equipment Privacy
MACFrameformat…
• Duration ID: reservation mechanism using RTS/CTS and during fragmentation.
– Period of time in which the medium is occupied
• Addresses:4 address fields • Sequence control: important against duplicated frames due to lost ACKs • Data: • CRC:
MAC address format
Wi Max/IEEE 802.16
• Network covering a country, continent or entire globe • interconnecting several WMANs and providing anywhere,anytime access • Broadband Wireless • radio waves in frequency range 2 GHz to 60 GHz. – Know as "last mile" fixed broadband access – Wi-Fi: 802.11 may be not the best way for last mile connection • WiMAX standard provides the missing link for the "last mile" connection in metropolitan area networks where DSL, Cable and other broadband access methods are not available or too expensive.
802.16…
802.11 has performance limitations when supporting larger numbers of users needing guaranteed bandwidth RF interference is often a significant problem with 802.11 • The 802.16 medium access control (MAC) layer (define) supports many different physical layer specifications, both licensed and unlicensed. • Examples: • Cellular networks • Satellite systems
802.16…
• WiMAX also offers an alternative to satellite Internet services for rural areas and allows mobility of the customer equipment.
IEEE 802.16 Standards
•
• • • • •
Range: 30 mile (50 Km) radius from base station Speed: 70 Mbit/s Line-of-sight not needed Bandwidth: between 10 and 66 GHz Define both the MAC and PHY layers and allows multiple PHY layer specifications Services: Digital audio/video multicast, digital telephony,Internet protocol, etc.
IEEE 802.16 Standards….
• 2 versions for IEEE 802.16 standards
– fixed WiMax standard IEEE 802.16-2004 (802.16d) approved by the IEEE in June 2004, – provides fixed, point-to-multi point broadband wireless access service – In Dec. 2005, IEEE approved the mobile WiMax standard, the 802.16-2005 (802.16e) – based on the early WiMax standard 802.16a, – adds mobility features to WiMAX in the 2 to 11 GHz licensed bands. – 802.16e allows for fixed wireless and mobile Non Line of Sight (NLOS)
comparison
• IEEE Standards: – Wi-Fi is based on IEEE 802.11 standard where as WiMAX is based on IEEE 802.16.
• Range: – Wi-Fi typically provides local network access for around a few hundred feet with speeds of up to 54 Mbps, – WiMAX antenna is expected to have a range of up to 30 miles with speeds of 70 Mbps or more. – WiMAX can bring the Internet connection needed to service local Wi-Fi networks.
Comparison…
• Scalability:
•
Wi-Fi is intended for LAN applications
– users scale from one to tens with one subscriber for each CPE(Customer premises equipment) device.
–
•
Fixed channel sizes (20MHz).
WiMAX is designed to efficiently support from one to hundreds of CPEs, with unlimited subscribers behind each CPE. – Flexible channel sizes from 1.5MHz to 20MHz.
Comparison…
• Bit rate:
• Wi-Fi works at 2.7 bps and can peak up to 54 Mbps in 20 MHz channel. • WiMAX works at 5 bps and can peak up to 100 Mbps in a 20 MHz channel.
• Quality of Service:
• Wi-Fi does not guarantee any QoS • WiMax will provide several levels of QoS.
• WiMAX can bring the Internet connection needed to service local Wi-Fi networks.
Comparsion Table
Freature Primary Application WiMax (802.16a) Broadband Wireless Access Wi-Fi (802.11) Wireless LAN
Frequency Band Channel Bandwidth
Half/Full Duplex
Licensed/Unlicensed 2 G to 11 GHz Adjustable 1.25 M to 20 MHz
Full
2.4 GHz ISM 25 MHz
Half
Radio Technology
OFDM (256-channels)
BPSK, QPSK
Direct Sequence Spread Spectrum
QPSK
Modulation
Comparsion Table…
Encryption Mandatory- 3DES Optional- AES Optional- RC4 (AES in 802.11i)
Mobility
Mobile WiMax (802.16e) Request/Grant
In development
Access Protocol
CSMA/CA
FEC
Convolutional Code Reed-Solomon
None
Wireless ATM
ATM?
Asynchronous Transfer Mode (ATM) • A networking technology developed by the telephone companies • handle all types of data using fixed 53-byte cells, or packets. • Creates virtual point-to-point circuit connections between the source and the destination. • Data rates from 25 to 622 Mbps.
ATM?
• The small cell size allows ATM to transmit video, audio, and computer data over the same network, while guaranteeing a preset QoS level for each.
Why wireless ATM?
• Need for the integration of wireless terminals to wired ATM • ATM networks scale l from LANs to WANs
– Mobility needed -- extend ATM for wireless access in local and global environments.
• • •
•
•
– mobile phones and mobile communications have an ever increasing importance in everyday life current wireless LANs do not offer adequate support for multimedia data streams Do not offer adequate QoS. merging of mobile communication and ATM leads to wireless ATM goal: integration of mobility into B-ISDN -- B-ISDN uses ATM as backbone infrastructure . Problem: high complexity of the system
Wireless ATM Working Group
• ATM Forum founded the Wireless ATM Working Group in June 1996 • Task: development of specifications to enable the use of ATM technology also for wireless networks • compatibility to existing ATM Forum standards is important • it should be possible to easily upgrade existing ATM networks with mobility functions and radio access
WATM services
Example scenarios in which WATM can be used • Office environment
– multimedia conferencing, online multimedia database access
• Universities, schools, training centers
– distance learning, teaching
• Industry
– database connection,infmn retreival, surveillance, realtime data xion , factory management
• Hospitals
– Transfer of medical images, remote access to patient records, remote monitoring, remote diagnosis of patient at home or in an ambulance
WATMservices…
• Home
– high-bandwidth interconnect of devices (TV, CD player, PC, ...)
• Networked vehicles
– trucks, aircraft etc. –high quality access to internet,company databases, multimedia conferencing etc.
Reference model
• WMT (Wireless Mobile ATM Terminal)—have radio links to RT • RT (Radio Transceiver)—connected to AP via wires • AP (Access Point)—controls several RTs
– Implements all radio access functions to handle radio resource management, radio medium access control and other radio-specific functions
• EMAS-E (End-user Mobility-supporting ATM Switch - Edge)- several APs are connected to
– Exchange signaling messages with WMT and offer mobility functions
Referencemodel…
• EMAS-N (End-user Mobility-supporting ATM Switch - Network)—communicates with EMAS-E via NNI+M protocol • APCP (Access Point Control Protocol) – Coordinate the radio related signalling b.w AP and WMT and ATM related signalling b.w EMASE and WMT.
• UNI+M (User-to-Network Interface with Mobility support) • NNI+M (Network-to-Network Interface with Mobility support)
Referencemodel…
EMAS-N WMT RT AP
RT WMT
RT APCP UNI+M
EMAS-E NNI+M
EMAS-N AP
protocol layers
radio segment MATM terminal WATM terminal adapter WATM access point fixed network segment ATM switch fixed end system
EMAS-E
EMAS-N
user process AAL ATM PHY ATM PHY RAL ATM RAL PHY ATM PHY PHY ATM PHY PHY ATM PHY PHY
user process AAL ATM PHY
MATM terminal
WATM adapter
WATM access point
EMAS-E
EMAS-N
ATM switch
ATM terminal
Functions
Many additional functions are needed to support mobility ,wireless access and security at the user side and n.w side - user identification module (UIM) is part of WMT - WMT is connected to AP via radio link
WMT side functions
• Identity Management Function (IMFT)
– functions to store identification and security related information – user dependent
• Mobile Terminal Security Agent (MTSA)
– additional security information stored in UIM – user independent – authenticate the terminal as hardware
• Call control and Connection control Function (CCFT)
– call set-up and release, access control, connection control • Mobility Management Function (MMFT) – analysis and monitoring of the network, location update.
MTSA
CCF
NSA
IMFT
UIM
CCFT
MMFT
MMF
APCF
SCF
APCF
ACFT ATMCT RRCT ACF RRC ATMC ATMC
RTRT WMT
RTR AP EMAS-E
Functions and logical interconnection
WMT side functions...
• ATM Connection function (ATMCT) – responsible for ATM connections—conn. setup, release, and modification – provides bearer service – controls ATM connection elements providing standard services (CBR, rt-VBR, ABR, UBR) • Radio Transmission and Reception (RTRT) – basic functions enabling sending and receiving of data – consists of LLC, MAC, PHY layers for radio transmission • Radio Resource Control function (RRCT) – select,release and reserve of radio resources – trigger handovers, monitor radio access
WMT side functions...
• Association Control Function (ACFT) – handles the association of a wireless terminal to its AP – set-up and release access to access point – support for intra-AP handover – power saving – radio handover.
Mobility supporting at network side
• Access Point Control Function (APCF)
– implemented in AP and EMAS-E – paging, handover, AP management
• Call control and Connection control Function (CCF)
– call set-up and release, connection control, requests network and radio resources
• Network Security Agent (NSA)
– to control the wireless terminals – identity management, authentication, encryption, confidentiality control
• Service Control Function (SCF)
– supports storage and access to service profiles – provides consistency check on these profiles
Mobility supporting at network side...
• Mobility Management Function (MMF)
– mobility support – location management, handover, – storage of location data and subscriber identity
• Association Control Function (ACF)
– set-up and release access to mobile terminal
• Radio Resource Control function (RRC)
– management of radio channels, initiate handover
• Radio Transmission and Reception function (RTR)
– LLC, MAC, PHY layers, support of ATM traffic parameters
• ATM Connection function (ATMC)
– responsible for ATM connections, standard services (CBR, VBR, ABR, UBR)
Radio Access Layer (RAL)
• wireless access is provided by adding RAL under ATM specific layers • RAL should operate in 5GHz Requirements for an RAL?
• requirement 1.physical layer:
• must specify • frequencies, efficient re-use of frequencies • antennas, xmit power, maximum range • cell characteristics • Carrier frequency, symbol rate, modulation scheme, coding, training sequences etc. • interfaces for data and control flow
RAL...
• Requirements specified for the physical layer: – Bit Error Rate (BER) <= 10-4, availability 99.5 % – packet size:several cells per PDU – data rate: 25 Mbit/s – range: indoor 30-50 m, outdoor 200-300 m – error correction – xmit power: 100 mW
RAL...
requirements 2: MAC layer • controls simultaneous access of several mobile terminals to the medium • includes defn of a MAC protocol,PDU format and MAC control algorithm • support user mobility • provide interfaces to physical and LLC layers
RAL...
• Requirements specified by MAC
• 1. logical channels: MAC layer within RAL connects ATM layers of the AP and WMT
– must support logical channels for ATM virtual connection 2. QoS parameters: should support QoS and traffic parameters in accordance with the ATM specification 3. Architecture: should support infrastructure network
RAL...
• 4 . service provision:
– services offered should include the ATM service classes CBR,rt-VBR,ABR,UBR
– MAC efficiency: higher than 60-75 % (over 90% is possible)
– data rates • peak 25 Mbit/s • sustained 6 Mbit/s
RAL...
requirements 3: LLC layer
• Layer between ATM and MAC layers to solve specific problems of the wireless transmission • Definition of LLC protocol and LLC PDU – wireless headers for data packets, control messages • main functions of LLC: – error control • error detection and correction using selective retransmission and forward error correction
RAL...
• Requirements for LLC:
– mandatory: ARQ (Automatic Repeat Request): – optional: FEC for real-time services – should provide means to support handover and to restore cell sequence during handover – authentication,encryption,other security mechanisms.
Handover
• Procedure to hand over connection(s) from a mobile ATM terminal from one access point to another access point • main problem for WATM handover is rerouting of all connections and maintaining connection quality • A handover domain – several access points cover a certain area – common handover protocol and strategy – all access points and switches belong to one administrative domain
Simple handover reference model
handover segment anchor point RT
WMT
AP RT
fixed segment RT AP
handover domain
Handover reference model
• an ATM end-to-end conn is seperated into diff segments.
• a fixed segment is a part of the conn that is not affected by the handover
• a handover segment is affected by the handover and is located completely within a handover domain • anchor point is the boundary b.w a handover segment and a fixed segment
• if both the end systems are wireless mobile ATM terminals there might be no fixed segments .
• the anchor point then connects the 2 handover segments which might be in diff handover domains
Handover Requirements
• multiple connection handover: end-to-end systems can support many conns at the same time.
Handover of point-to-multipoint connections: QoS support: preserve Qos of all conns during handover. data integrity and security: should minimize cell loss and avoid cell duplication signaling and routing support:WATM should provide means
to identify mobility enabled switches To reroute partial conns in handover domain
high performance and low complexity
Types of handover
• Hard handover – WMT can have only one connection to one access point possible • Terminal initiated – WTM initiates HO based on, e.g., signal quality • Network initiated – Network initiates HO based on, e.g., network load • Network initiated, terminal assisted – WTM provides information about radio conditions and other parameters. • Network controlled – HO decision always at network
• Infmn about the current load situation, free resources,etc. resides in n.w
Typesofhandover…
• Backward handover
– standard type – WMT notices a signal fading and initiates HO to a new AP. – terminal continues to maintain radio conn while HO is in process and switches over to a new AP after resources have been reserved and all entities involved are prepared for HO.
• Forward handover
– WMT suddenly arrives at a new AP, connection loss possible – Has to initiate the HO.
Handover scenarios
Intra-EMAS-E/ Intra-AP RT1 EMAS-E1
EMAS-N COS
RT2
WMT RT3 Intra-EMAS-E/ Inter-AP Inter-EMAS-E/ Inter-AP
AP1
EMAS-E2 AP2
RT4
RT5
RT6
AP3
Handover scenarios
• Intra EMAS-E/Intra-AP: WMT moves from RT1 to RT2
– The main task of AP IS to switch b/w the RTs.
• Intra EMAS-E/Inter-AP :WMT moves from RT3 to RT4
– HO remains in the domain of EMAS-E1
• Inter EMAS-E/Inter-AP:WMT moves from RT5 to RT6
– Another intermediate switch known as Cross Over Switch has to manage HO.
Location management
• Special fns are reqd for looking up the current position of the mob terminal. • Requirements – Transparency of mobility – Security:privacy of location and user information – Identification: must provide means to identify radio cells,terminals ,switches etc. – Efficiency and scalability: every fn involved in LM must be scalable and efficient.
Locationmanagement…
• standardized method for registration • ATM end system address (AESA) : mobile terminals need a temporary, routable address as soon as it is outside its home n.w – AESAmustbeforwardedtotheterminal‘shome location. • Interworking and standards: LM fns must co-operate with existing ATM functions—routing – Must be harmonized with other LM schemes such as used in GSM,UMTS,mobile IP
Procedures and entities
• Several entities which support LM have been identified. • Mobile terminal: execute functions to initiate location updates and participates in authentication and privacy protocols • EMAS: are necessary to identify conn setup msgs for WMTs and to invoke location resolution fns. -- some of EMAS maintain location and authentication servers LS : maintains a db containing the current AESA and the permanent AESA of a WMT AUS: maintains a secure db of authentication and privacy related infmn of each WMT - also includes access rights and equipment identification.
Registration and location update
visited EMAS-E home EMAS home home AUS LS
WMT
AP
Broadcast_ID Association Register
Loc_Update_Home
Loc_Update_Reply
Loc_Update_Home_Reply
Auth_Req Auth_Req_Reply Loc_Update_LS Loc_Update_LS_Reply
8.39.1
Registrationandlocationupdate…
Registration and locn update msgs flow after a WMT has moved to a new AP. • AP broadcast a Broadcast-ID to identify the n.w,current locn and RT. • WMT can now decide to associate with this AP if access rights permit.
• Send a registration msg to the EMAS-E visited
– Includes the address of the home EMAS and requests a temporary AESA.
• The visited EMAS-E performs the req Loc_Update_Home to the home EMAS of the WMT
Registrationandlocationupdate…
• Home EMAS checks the access right and identity of the WMT by means of the msg Auth_Req • If Auth_Req_reply signals that everything is okay the home EMAS updates the home LS with new location.
• LS acknowledges • Visited EMAS-E returns a temporary AESA to the WMT in a Loc_Update_Reply.
2 EMAS-E2 WMT LS 3 AP1 EMAS 1
8
EMAS-E1
RT1
AP2
4 5 T
7 RT2 network without mobility support
6
LS home network
visited network
Incoming connection setup, WMT in foreign network
Incoming connection setup
•
•
Arbitrary n.w, home n.w and n.w currently visited.
Home n.w contains the EMAS-E to which all conns are routed for the WMT.
•
Other n.ws are foreign n.ws for WMT.
Steps reqd for localization of WMT and conn. setup:
1. T only knows the permanent address WMT - sets up a conn with WMT. - EMAS-E2 detects the incoming conn setup.
Incoming connection setup
2. EMAS-E2 lookup the current loc of WMT by sending a location request to the LS.
- LS has mapping of permanent address to current foreign address of all WMTs it is responsible for
- if several hierarchical look-up steps are needed ,LS maps the permanent address to the EMAS in the visited n.w
Incoming connection setup
3. LS returns the current address of either the WMT or EMAS responsible for further lookup
- hierarchical approach make sense to avoid too frequent LS updates 4. EMAS-E2 redirect incoming conn to the EMAS in the visited n.w.
5.
-
EMAS responsible for n.w currently visited can determine the loc of WMT in greater detail.
It issues a req to its LS.
-
This EMAS may be an EMAS-E or EMAS-N
Incomingconnectionsetup…
6. The LS answers with the exact current loc as represented in its database . 7. conn setup can be forwarded to the EMAS-E1,which is directly connected to the AP to which the WMT is also connected. final step is the conn setup to the WMT itself via the AP and RT.
8.
Addressing
Basic requirements for WATM address:
• should support all formats of ATM end-system addresses (AESA)
• Must have a permanent, location independent address which can be used by other commn partners for contacting the WMT • WMT must support the assignment of temporary, routable addresses during registration of the mobile terminal in a foreign domain
Access Point Control Protocol
• Every AP exchanges multitude of msgs with EMAS-E • The protocol used to communicate
• Main purpose:
– Reserving and releasing resources in the AP for conn(memory,radio freqs ..) – A switch can prepare AP for new conns and assist in handover via APCP – AP uses APCP to inform EMAS-E about the newly associated WMT.
AcessPointControlProtocol…
• Reasons for the separation of AP and EMAS-E and a standardized interface are:
– All radio issues are kept separate from the switch.
– The switch only needs support for mobility – Separation and standardized interfaces allow multivendor solutions
APCP -Functional architecture
• AP contain process directly related to radio issues such as WCAC and RRM
• APCM handles the current conns.
AP
WCAC
RM
EMAS-E
RM:
CC: CAC:
switch resource management
call control connection admission control mobility management radio resource management
RRM
APCM
CC
CAC
MM
MM: RRM:
WCAC: wireless CAC
radio sub-system
APCM: AP connection management
APCP
APCP: AP control protocol
