9. wireless atm anywhere, anytime access to atm networks. voice, data, video, and images in any...
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9. WIRELESS ATM
• Anywhere, Anytime Access to ATM Networks.• Voice, Data, Video, and Images in Any Combination, Anywhere,
Anytime with Convenience and Economy.• Fixed Wireless & Mobile Users Wireless Equipment.• Problems
– Noisy Wireless Channels High BER.– Wireless Channel
Very bandwidth limited.ATM designed for bandwidth-rich environment.
– OverheadEvery ATM cell has overhead of 10%.For wireless channel, we need more control information which can far exceed the overhead limit.
Wireless ATM Network Architecture
Base Station
VLR
MSC
HLR
ATM Network
VLR: Visitor Location RegisterHLR: Home Location RegisterMSC: Mobile Switching Center (also ATM switch)
Wireless ATM in Digital Battlefield
Fixed ATM Network
FSC: Fixed Switch Center (ATM Switch)MBS: Mobile Base Station
Wireless LAN
Satellite
Military and CommercialWireless ATM Networks
Commercial MilitaryStatic network topology Highly dynamic topologyTypically single hop Multi hopStatic allocation n-band userand data channels
Dynamic bandwidthallocations; Priorities
Maximum number ofusers/hertz/area
Maximum transfer rate inhostile environment
Privacy High securityFixed infrastructure for openaccess
Constrained access
Quality of Service (QoS) Parameters
1. Throughput2. Delay3. Jitter4. Loss Probabilities5. Probability of Dropping the Call6. Expected BER; Packet Error Rate7. Expected Disruption Time During Handoffs8. Minimum or Maximum Level of Mobility9. QoS Renegotiation
Also in wired ATM network
Personal Mobility vs. Terminal Mobility
Network
Network
Wired
Wireless
User Terminal
Terminal Mobility
Personal Mobility
Protocol Stack For Wireless ATMQuality Critical
ApplicationsTime Critical Applications
TCP UDP
IP
AAL Layer
ATM Layer
Error Control
Medium Access Control
Physical Layer (Wireless Channel)
Link
Layer
ATM Layer
IP Layer
Specific Requirements for PHY Layer
Low Speed Wireless PHY HIGH Speed Wireless PHY
Frequency Band
Cell Radius
Frequency Reuse Factor
Transmit Power
Channel Bandwidth
Data Rate
Modulation
MAC Interface
Fixed Packet Length
5.15-5.35 GHz, 5.725-5.875 GHz 59 GHz - 64 GHz
80 m 10 - 15 m
100 mW 10 – 20 mW
up to 12 7
30 MHz 150 / 700 MHz
25 Mbit/s 155 / 622 Mbit/s
16 tone DQPSK 32 tone DQPSK
par., transf. speed 3.127 Mbyte/s par., transf. speed 87.5 Mbyte/s
PHY header + MAC header + 4*ATM cells
System Architecture and Protocol Model
ATMBackbone Network
Host
Host
Wireless Workstation
Wireless Workstation
User Applications(Quality-Critical Traffic)
TCP/IP
AAL Subsystem
ATM
Sonet DL Subsystem
Wired Line Wireless Link
Error Control
FEC
Hybrid ARQ
Time CriticalApplications
Quality Critical
Applications
Why FEC?
• ATM HEC performance is too low for
wireless ATM.
• High CLR and payload errors
• Cell delineation problem
FEC (for Time-Critical Applications)
• To correct channel errors at the expense of bandwidth by adding redundancy
Concatenated FEC Scheme
RS OuterEncoder
Symbol Interleaver
Conv. InnerEncoder
Bit LevelInterleaver
WirelessChannel
Bit LevelDeinterleaver
ViterbiDecoder
SymbolDeinterleaver
RS OuterDecoder
Cells
Cells
Transmitter FEC
Receiver FEC
• Why Hybrid ARQ? (for Quality Critical Traffic)– ARQ provides high reliability at good and moderate
channel qualities.– The throughput drops rapidly, if the channel error
rate is high as in wireless channels.
• Hybrid ARQ– FEC first tries to correct the frequent error patterns.
If it fails, then ARQ takes over.
• Hybrid ARQ Types– Type I Hybrid ARQ scheme– Type II Hybrid ARQ scheme: only additional parity
bits are retransmitted to combine with the previous packet (incremental redundancy).
Medium Access Control for Wireless ATM Networks
MT
MT
MT
Categorization of MAC Protocols
• Based on Channel Organization– TDMA-Based MAC Protocols– CDMA-Based MAC Protocols– Random MAC Protocols– Hybrid MAC Protocols
• Based on Duplex Mode of Uplink and Downlink– Time Division Duplex (TDD) (One Carrier
Frequency)– Frequency Division Duplex (FDD) (Two Carrier
Frequencies)
* Frequency Division Duplex (FDD) (Two Carrier Frequencies)
– Uplink frequency carries traffic from terminal to BS while downlink frequency carries traffic from BS to terminal.
– FDD allows almost immediate feedback from the BS enabling terminal to find out quickly if its contending reservation request was unsuccessful and a retransmission is necessary.
– Thus, FDD impacts the delay encountered by user traffic as well as the resource availability of the wireless channel.
TDMA Based MAC Methods– Dynamic Packet Reservation Multiple Access (DPRMA), by
Dyson and Haas in 1999. FDD– Mobile Access Scheme Based on Contention and
Reservation for ATM (MASCARA), by Bauchot et al. in 1996, and Passas et al. in 1997. TDD
– PRMA with Dynamic Allocation (PRMA/DA), by Kim and Widjaja in 1996. FDD
– PRMA with Adaptive TDD (PRMA/ATDD), by Priscoli in 1996. TDD
– Dynamic TDMA with Piggyback Reservation (DTDMA/PR), by Qiu et al. in 1996. FDD
– Distributed Queuing Request Update Multiple Access (DQRUMA), by Karol et al. in 1995. FDD
– Dynamic TDMA with TDD (DTDMA/TDD), by Xie et al. in 1995. TDD
Packet Reservation Multiple Access (PRMA) Protocol
(Goodman’91)
• Time is divided into slots of equal duration, and slots are grouped into frames.
• Each slot in a frame is either “reserved” or “available”. • BS controls the upstream traffic and broadcasts a
continuous stream of packetized information through the downstream channel
• The status of a slot is provided in feedback information supplied by BS.
• Terminals can send two types of information: “Periodic” information such as speech or “Random” information such as data.
• Frame rate is identical to the arrival rate of the speech packets.
• Uses S-ALOHA for time slot reservation and TDMA for data transmission.
Packet Reservation Multiple Access (PRMA) Protocol
(Goodman’91)
• A station contends for an available slot using S-ALOHA.
• If transmission is successful, BS responds with an ACK message and the slot is reserved in subsequent frames until the terminal relinquishes it by leaving the slot empty.
• A terminal with “random packets” contends for slots in the same way, but cannot reserve the same slot in a subsequent frame even after a successful transmission.
• Thus, terminal must contend again for another available time slot.• For unsuccessful transmission, a terminal with “periodic” packets
retransmits the packet with certain probability in subsequent unreserved slots until it receives an ACK signal from BS.
• Similarly, a terminal with “random” packets retransmits a packet in unreserved slots with certain probability.
Packet Reservation Multiple Access (PRMA) Protocol
(Goodman’91)
Advantages:• Simple
Disadvantages: * Upon congestion, the speech packet dropping rate
and data packet delay both increase. * Feedback information may cause waste of
bandwidth.
PRMA/DA — Services and the Frame Structure• Supports Multimedia Traffic
– Constant Bit Rate (CBR), Variable Bit Rate (VBR), Available Bit Rate (ABR).
• Frame Structure– It is organized according to traffic types.– Downlink transmission is not considered. FDD
… … … …1 2 Na 1 2 Nc 1 2 Nv Nd1 2
Available slots CBR reservation slots VBR reservation slots ABR reservation slots
ATM cellPRMA/DA
headerPRMA/DA
trailer
Wireless Packet
ATM cellPRMA/DA
headerPRMA/DA
trailer
Request packet
Variable Variable Variable
Operation Procedures of PRMA/DA
• Send Requests in Available Slots– Contention-based transmission.– Slotted ALOHA is used.
• Reserve Time Slots for each Successful Request– Dynamic allocation algorithm is used to allocate time
slots for CBR, VBR, and ABR connections.– The allocated time slots are reserved for the lifetime
of a connection.– Dynamic allocation algorithm is also used for
updating available time slots for the transmission of requests.
• Transmit Packets in Reserved Time Slots– Since time slots are reserved, contention is free in
this phase.
Contributions and Shortcomings of PRMA/DA
• Contributions– Dynamic allocation of slots for each sub-frame.
• Variable boundary can be easily implemented.• Bandwidth can be utilized efficiently.• Collisions can be resolved quickly
– No mini-slots; Easy for synchronization.– Multiple traffic classes supported.
• Shortcomings– A request packet has the same length as a data packet.
• If traffic rate high, this would cause inefficiency.– No mechanism is used to dynamically update VBR
resources.• VBR bandwidth is allocated according to the average
rate. The bursty requirement has to rely on the leftover bandwidth. QoS of VBR cannot be guaranteed.
MASCARA(Mobile Access Scheme based on Contention and Reservation
for ATM)• Supports CBR, real-time VBR (rt-VBR), non-real-time VBR (nrt-VBR), ABR, UBR traffic.
• Demand assignment scheme with contention based reservations.• Uplink subframe is divided into a contention period to transmit reservation
requests or some control information, and uplink period for uplink data traffic.• Each period within a frame has a variable length depending on the instantanous
traffic to be carried.
FH Period Uplink Period Downlink Period ContentionPeriod
MPDU 1 MPDU n… …
1 time slot n time slots
MPDU 2
PHYHdr
MPDUHdr MPDU payload: Cell train (many ATM cells)
Operation Procedures of MASCARA• If a terminal has cells to transmit, it sends a reservation request
either piggybacked in the MPDUs uplink period or in special control MPDUs sent in the contention period.
• Base station schedules transmissions of the next frame according to reservation requests, arriving cells for each downlink connection, traffic characteristics and QoS requirements of all connections.
• In the Frame Header of the downlink, BS broadcasts information which contains a descriptor of the current time frame (including the lengths of each period), the results of the contention procedures from the previous frame and the position of the slot allocated to each downlink and uplink connection.
• To minimize PHY layer overhead, MASCARA uses the concept of a CELL TRAIN (a sequence of (1-n) ATM cells belonging to a terminal and having a common header).
• Length of overhead plus that of the MPDU header is equal to one time slot, which is defined as the length of an ATM cell.
Priority Regulated Allocation Delay-Oriented Scheduling (PRADOS)
* Assigns priorities for each connection according to its service class.
* PRADOS combines priorities with a leaky bucket traffic regulator.• Regulator uses a token pool introduced for each connection.• Tokens are generated at a fixed rate equal to the mean ATM cell rate of
each VC.• Size of the pool is equal to the maximum number of ATM cells that can
be transmitted with a rate greater than the declared mean.• Starting at priority 5 and ending with priority 2, scheduler satisfies
requests for connections as long as tokens and slots are available. • For every slot allocated to a connection, a token is removed from the
corresponding pool.
Traffic Priority Token Pool
CBR 5 Yes
rt-VBR 4 Yes
nrt-VBR 3 Yes
ABR 2 Yes
UBR 1 No
Contributions and Shortcomings of MASCARA
• Contributions– Cell train concept is used.– A novel scheduling scheme - PRADOS.– Dynamic TDD is implicitly implemented.– Multiple traffic classes are supported.
• Shortcomings– With each request corresponding to a time slot, too
many requests are transmitted in the protocol. This results in wasting bandwidth.
– Large size of request packet results in reduction of good throughput.
– Connection admission control (CAC) is separate from the MAC protocol. The overall performance of the integrated system is unpredictable.
Comparisons of TDMA MAC Protocols
Protocols PRMA/DA MASCARA DPRMA
Duplex Mode FDD TDD FDD
Frame Type Fixed Variable Fixed
Random Access Slotted ALOHA
Slotted ALOHA
Reservation ALOHA
Mini-slot No No No
CAC In MAC Separate Separate
Traffic Classes CBR, VBR, ABR
CBR, nt-VBR, nrt-VBR, ABR, UBR
Voice, video, data
Network Layer ATM ATM ATM
Control Overhead Medium High Medium
Mobility Management in W-ATM Networks
• Location Management Handoff Handoff ManagementManagement
Base StationBase Station
MT A is receiving a call !MT A is receiving a call !How will the networkHow will the networkdeliver the call to A ?deliver the call to A ?
A
Types of Mobility
• TERMINAL MOBILITY
(network should route calls to the MT
regardless of its point of attachment)• PERSONAL MOBILITY
(users should access the network wherever they are; UPT (Universal Pers. Tel #))
• SERVICE PROVIDER MOBILITY
(allow user to roam beyond regional networks).
Location Management
Call Delivery(Paging)
Location Update(Registration)
Cost Tradeoff
Too Many Location Updates
Too Few Location Updates
Low Paging CostsHigh Update Costs
High Paging CostsLow Update Costs
Solution
• Location Areas (GSM) = Registration Areas (IS-41)
Registration Area BoundaryRegistration Area Boundary
Center CellCenter Cell
Handoff Types
Intra-CellIntra-Cell Inter-CellInter-Cell
Soft HandoffSoft Handoff Hard HandoffHard Handoff
W-ATM Architecture
ATMSwitch
ATMSwitch
ATM Backbone Network
ATMSwitch
ATMSwitch
CellBS
MT
Wireline connections to ATM switch
Wireless connections to BS
LOCATION MANAGEMENT
LOCATIONSERVICE
TERMINALPAGING
TWO-TIERDATABASES
LOCATIONREGISTERS
LOCATIONADVERTISEMENT
VIRTUALCONNECTION
TREE
INTEGRATEDLOCATION
RESOLUTION
MOBILE PNNI
LOCATION MANAGEMENT TECHNIQUES FOR W-ATM
• LOCATION SERVICE * Use of DATABASES to maintain records of MTs. * When location information is obtained from
DATABASE, TERMINAL PAGING is used to deliver calls to MTs.
* Requires signaling, querying and paging.
• LOCATION ADVERTISEMENT * No databases but location information is
broadcast throughout the network.
Location Service: Method 1: Two Tier Database (Akyol/Cox’96)
PREVIOUSZONE
HomeTier
VisitorTier
HomeTier
VisitorTier
CURRENTZONE
ZoneManager
HomeTier
VisitorTier
HOMEZONE
(1)(2)
(5)
(3)
(4)
Explanation: * Bi-level databases are distributed to ZONES throughout the network.
* Each zone is maintained by a ZONE MANAGER controlling the zone’s location update procedures.
* Each MT has a home zone where it is permanently registered. 1. MT transmits a location registration request message to the new zone. Message
contains User ID Number, authentication data and ID of the previous zone.2. Current zone manager determines the home zone of the MT from the previous
zone ID.3. Current and home zone managers authenticate the user and update home user
profile with the new location information.4. Home zone sends a copy of the profile to the current zone manager which stores
the profile in the visitor tier of its database.5. Current zone manager sends a purge message to the previous zone manager so
that user’s profile is deleted from the visitor tier before.
Location Advertisement: Method 1:
Virtual Connection Tree (Veeraraghavan et.al.’97)
Portable Base Station (PBS) Cell
Boundary
De-registrationmessage
MT’s Formerposition
Registrationmessage
• VCT advertises location information via provisioned virtual paths.• A collection of PBSs connected via provisioned VPs forms a connection tree.• PBSs are equipped with switching capabilities and limited buffering capabilities.• Trees are based on the mobility indications of the MT.• Each PBS maintains a running list of resident MTs in its coverage area.• Location registration occurs when MT is on/off or it moves to a new service
area.• On/Off case, MT sends a message to its local (current) PBS which then
adds/deletes the MT to/from the service list.• When MT moves to a new service area of a PBS, the PBS sends a de-registration
message to the old PBS on behalf of the MT and enters the MT’s ID into its current list.
Comparison of LocationManagement Techniques
Advantages Disadvantages
No Paging No Scalability
No Database Wasted
Admin Bandwidth
Advantages Disadvantages
Flexibility Database Admin
Scalability Signaling Load
Location AdvertisementLocation Service
Handoff Management
Full Connection Re-Routing
RouteAugmentation
Partial ConnectionRe-Routing
Multicast Connection Re-Routing
Virtual Connection
Tree Re-Routing
Nearest Connection
Node Re-Routing
InterWorking Devices
Connection Extension
InterWorking Devices
Connection Re-Routing
HybridConnection Re-Routing
Homing BaseStation
Re-Routing
Full Connection Re-Routing: Maintains the connection by establishing a completely new route for each
handoff as if it were brand new call.
Route Augmentation:Extends the original connection with a hop to the MTs next location.
Partial Connection Re-Routing: Re-establishes certain segments of the original connection, while preserving the
remainder.
Multicast Connection Re-Routing:Combines the 3 techniques but includes the maintenance of potential handoff
connection routes to support the original connection, reducing the time spent in finding a new route for handoff.
Comparison of Handoff ManagementApproaches
Full Extension Partial MulticastAdvantages
Optimalroute;
existingmethodology
Fast;maintains
cellsequence
Maintains cell sequence;reduced
resource utilization
Fast;maintains
cellsequence
Slow;inefficient resource
re-assignment
Disadvantages
Wastes bandwidth;inefficient
connection route
Complex;added switch
processing reqs
Added bufferingrequirements;
bandwidthpre-allocation
References:
1. J. McNair, “Mobility Management Protocols for Wireless
ATM Networks”, BWN Lab Technical Report, 1997. (Available on the WEB).
2. I.F. Akyildiz, J. McNair, J. Ho, H. Uzunalioglu, W. Wang,
“Mobility Management in Next Generation Wireless Systems”,
Proceedings of the IEEE Journal,
Vol, 87, No.8, pp.1347-1384, August 1999.