ATM NETWORKS

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

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Wireless ATM Network Architecture
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Wireless ATM in Digital Battlefield
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Military and CommercialWireless ATM Networks
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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
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Personal Mobility vs. Terminal Mobility
User
Terminal
Network
Wired
Wireless
Terminal Mobility
Personal Mobility
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Protocol Stack For Wireless ATM
IP Layer
ATM Layer
Link Layer
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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
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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
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Error Control
Time Critical Applications
FEC
Hybrid ARQ
Quality Critical Applications
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• 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

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Concatenated FEC Scheme
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• 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).

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Medium Access Control for Wireless ATM Networks
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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)

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• 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.

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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

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• 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.

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• 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.

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• 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.

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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
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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.

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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.

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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.

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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.

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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
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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.

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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
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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 ?
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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).

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Location Management
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Cost Tradeoff
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Solution

• Location Areas (GSM) Registration Areas (IS-41)

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

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Location Service Method 1 Two Tier Database
(Akyol/Cox96)
PREVIOUS ZONE
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• 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.

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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
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• 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.

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Comparison of LocationManagement Techniques
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• 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.

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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
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• References
• J. McNair, Mobility Management Protocols for
  Wireless ATM
• Networks, BWN Lab Technical Report, 1997.
  (Available on the
• WEB).
• 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.