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9. WIRELESS ATM

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Title: 9. WIRELESS ATM


1
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.
  • Overhead
  • Every ATM cell has overhead of 10.
  • For wireless channel, we need more control
    information which can far exceed the overhead
    limit.

2
Wireless ATM Network Architecture
3
Wireless ATM in Digital Battlefield
4
Military and CommercialWireless ATM Networks
5
Quality of Service (QoS) Parameters
  1. Throughput
  2. Delay
  3. Jitter
  4. Loss Probabilities
  5. Probability of Dropping the Call
  6. Expected BER Packet Error Rate
  7. Expected Disruption Time During Handoffs
  8. Minimum or Maximum Level of Mobility
  9. QoS Renegotiation

Also in wired ATM network
6
Personal Mobility vs. Terminal Mobility
User
Terminal
Network
Wired
Wireless
Terminal Mobility
Personal Mobility
7
Protocol Stack For Wireless ATM
IP Layer
ATM Layer
Link Layer
8
Specific Requirements for PHY Layer
Low Speed Wireless PHY
HIGH Speed Wireless PHY
Frequency Band
5.15-5.35 GHz, 5.725-5.875 GHz
59 GHz - 64 GHz
Cell Radius
80 m
10 - 15 m
Transmit Power
10 20 mW
100 mW
Frequency Reuse Factor
7
up to 12
Channel Bandwidth
30 MHz
150 / 700 MHz
Data Rate
25 Mbit/s
155 / 622 Mbit/s
Modulation
16 tone DQPSK
32 tone DQPSK
MAC Interface
par., transf. speed 87.5 Mbyte/s
par., transf. speed 3.127 Mbyte/s
Fixed Packet Length
PHY header MAC header 4ATM cells
9
System Architecture and Protocol Model
Wireless Workstation
User Applications (Quality-Critical Traffic)
Host
TCP/IP
AAL Subsystem
ATM Backbone Network
ATM
Sonet
DL Subsystem
Wireless Workstation
Wired Line
Wireless Link
Host
10
Error Control
Time Critical Applications
FEC
Hybrid ARQ
Quality Critical Applications
11
  • 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

12
Concatenated FEC Scheme
13
  • 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).

14
Medium Access Control for Wireless ATM Networks
15
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)

16
  • 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.

17
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

18
  • Packet Reservation Multiple Access (PRMA)
    Protocol (Goodman91)
  • 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.


19
  • Packet Reservation Multiple Access (PRMA)
    Protocol (Goodman91)
  • 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.


20
  • Packet Reservation Multiple Access (PRMA)
    Protocol (Goodman91)
  • Advantages
  • Simple
  • Disadvantages
  • Upon congestion, the speech packet dropping
    rate and data packet delay both increase.
  • Feedback information may cause waste of
    bandwidth.


21
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

Variable
Variable
Variable
22
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.

23
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.

24
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.

25
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.

26
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
27
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.

28
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
29
Mobility Management in W-ATM Networks
  • Location Management
  • Handoff Management

Base Station
A
MT A is receiving a call ! How will the
network deliver the call to A ?
30
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).

31
Location Management
32
Cost Tradeoff
33
Solution
  • Location Areas (GSM) Registration Areas (IS-41)

Registration Area Boundary
Center Cell
34
Handoff Types
35
W-ATM Architecture
36
LOCATION MANAGEMENT TECHNIQUES FOR W-ATM
37
  • 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.

38
Location Service Method 1 Two Tier Database
(Akyol/Cox96)
PREVIOUS ZONE
39
  • Explanation
  • Bi-level databases are distributed to ZONES
    throughout the network.
  • Each zone is maintained by a ZONE MANAGER
    controlling the zones location update
    procedures.
  • Each MT has a home zone where it is
    permanently registered.
  • MT transmits a location registration request
    message to the new zone. Message contains User ID
    Number, authentication data and ID of the
    previous zone.
  • Current zone manager determines the home zone of
    the MT from the previous zone ID.
  • Current and home zone managers authenticate the
    user and update home user profile with the new
    location information.
  • Home zone sends a copy of the profile to the
    current zone manager which stores the profile in
    the visitor tier of its database.
  • Current zone manager sends a purge message to the
    previous zone manager so that users profile is
    deleted from the visitor tier before.

40
Location Advertisement Method 1 Virtual
Connection Tree (Veeraraghavan et.al.97)
Portable Base Station (PBS)
Cell Boundary
De-registration message
MTs Former position
Registration message
41
  • 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 MTs ID
    into its current list.

42
Comparison of LocationManagement Techniques
43
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44
  • 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.

45
Comparison of Handoff Management Approaches
Full
Extension
Partial
Multicast
Advantages
Optimal route existing methodology
Fast maintains cell sequence
Maintains cell sequence reduced resource
utilization
Fast maintains cell sequence
Disadvantages
Slow inefficient resource re-assignment
Wastes bandwidth inefficient connection route
Complex added switch processing reqs
Added buffering requirements bandwidth pre-alloca
tion
46
  • 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.
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