Asynchronous Transfer Mode

1
Asynchronous Transfer Mode

• Pradeep Kumar
• CS 616
• Prof. C. Tappert

2
ATM

• Introduction
• ATM Overview
• Replacement of Traditional LAN technologies
• Introduction of ATM specific API
• Enhancement of Distributed Computing Environment
  Structure
• Future of ATM
• Conclusion
• Bibliography

3
Introduction

• ATM was formulated in the early 80s, as a result
  of ATT and French Telecompanys research in Fast
  Packets
• ITU-T chose ATM for B-ISDN, in the mid 80s
• In 1989, ATM packet size of 485 was adopted as a
  compromise between 645 (USA) and 324(Europe)
• ATM Forum was founded in 1991
• Originally intended for WANs, ATM is gaining
  acceptance as a LAN technology, to reduce
  bottlenecks in Distributed Computing
• We will study the ATM technology and its role in
  Distributed Computing

4
ATM Overview

• BASIC CONCEPTS
• Both a technology and a service (called Cell
  Relay)
• Offers low cost transmission of various types of
  data Voice, Video and Data
• Uses fixed, 53 bytes size packets with 5 bytes
  for header
• Handles both Constant Bit Rate(Voice and Video)
  and Variable Bit Rate(Data)
• Key to ATM success is cell switching, which is
  faster than traditional multiplexing techniques
• Connection oriented
• No guarantee of delivery, but does guarantee
  order of delivery
• Delivers speeds of 155 Mbps to 622 Mbps
  (compatible with SONET and can transmit HD TV)

5
ATM Overview

• B-ISDN ATM Model

5
48
ATM Cell 53 bytes
User Data
Header
Header 40 bits
GFC/4
VPI/8
VCI/16
PTI/3
HEC/8
CLP/1
VPI/12 for NNI
OSI
ATM
Functionality
ATM Sublayer
CS
Convergence - Provides standard interface
3/4
AAL
SAR
Segmentation and Reassembly
Flow Control Cell Header generator /
Extractor Virtual Circuit / Path Management Cell
Multiplexing / De-multiplexing
2/3
ATM
Cell Rate decoupling Header Checksum generation
and verification Cell and Frame
generation Packing / Unpacking Cells from
enclosing envelope
2
TC
Physical
1
PMD
Bit timing Physical Network access
6
ATM overview

• The Physical Layer
• Deals with medium, voltages, bit timing
• Medium is usually fiber optics but for runs less
  than 100m, coaxial or CAT5 twisted pair is OK
• Each link is unidirectional and two parallel
  lines are needed for duplex operation
• Connects a computer to an ATM switch or
  interconnects two ATM switches
• Multicasting is achieved by having the cell leave
  an ATM switch on multiple lines
• Cells are switched using either input or output
  queuing
• 5 bytes header 4 bytes for Virtual Circuit and
  control info 1 for HEC (Header Error Control)
• HEC is limited to the first 4 bytes of the
  header, due to the high reliability of fiber
  optics

7
ATM Overview

• ATM Layer
• Deals with cells and cell transport, congestion
  control and global addressing
• Has two interfaces UNI (User to Network
  Interface) and NNI (Network to Network Interface)
• Uses Setup, Call proceeding, connect, connect
  ACK, Release and Release complete for setup and
  release of connections Virtual Circuits
• Offers service categories QoS
• Congestion control through
• 1. Admission control fair denial of service to
  all classes
• 2. Resource reservation bandwidth to ensure
  peak cell rate
• 3. Rate-based sender is asked to slow down the
  traffic
• ATM LAN uses LEServer to lookup network addresses
• In IP over ATM LES is called ATMARP server

8
ATM Overview

• ATM Adaptation Layer
• Provides service to the application layer
• Convergence sublayer deals with messages and
  interface to the application
• Segments varying length messages into 48 or 44
  bytes(4 bytes for AAL info. Optional) each and
  assembles them at the other end
• Offers three types of services
• 1. Real-Time Vs Non Real-Time
• 2. Constant Bit Rate VS Variable Bit Rate
• 3. Connection-oriented VS Connectionless
• AAL is further divided into four protocols
• AAL1 Real-Time, CBR and Connection oriented and
  no error correction, for uncompressed data
• AAL2 same as AAL1 except for VBR, for
  compressed data
• AAL3/4 for transport of data sensitive to loss
  than time
• AAL5 for high speed transfer of data

9
Replacement of Traditional LAN technologies, with
ATM

• Comparison of ATM and the traditional LAN
  environments such as Ethernet and FDDI, show that
  Ethernet and FDDI suffer from high latency and
  low bandwidth and that only one host can
  communicate at a time.
• With multiprocessors FDDI speedup is capped at 8
  processors and no speedup for Ethernet
• ATM is fully bi-directional and offers
  simultaneous communication
• ATM offers high bandwidth 155Mbps to 622 Mbps and
  the delay in the speed of ATM is at the host
• Full potential of ATM is achievable, only by
  improvements in hardware(bus design controller
  implementation) and software (Protocol stack
  exploiting the network)

10
ATM specific API

• ATMs high bandwidth moves the bottleneck from
  the network to the Host and Protocols
• To overcome the the overhead of the protocols,
  applications should be able to access ATM
  directly.
• Two approaches to the ATM specific API
• 1. Leave transport functionalities to the
  application
• 2. Modify message passing libraries
• Compared to other APIs(PVM, RPC) ATM API offers
  best performance
• Modifying message passing libraries to support
  ATM API has a drawback requires a specific
  version of the library for each vendors ATM API

11
Enhancement of Distributed Computing Environment

• ATM API level enhancements include very fast RPC
  models
• Occurs in user space, thus avoiding memory
  copying buffering overhead
• Increases complexity for the programmer, to
  exploit the interface, which is being hidden,
  more and more by applications
• Transport level enhancements are made possible by
  the high reliability of current networks and
  include,
• Implementation of Protocol processing in a
  special communication processor
• Modified Protocol to implement basic
  functionality of message passing library
• Application level enhancements, use
  multithreading to decrease latency concurrent
  thread execution and use of all available
  resources allocated on a per task basis

12
Future of ATM

• ATM is finally catching up with the hype due to
  falling prices and wider acceptance
• Wider acceptance, as a result of telephone and
  cable companies response to the demands for
  higher bandwidth
• Sprint offers its ION network based on ATM
• Lucent Technologies bought out Yurie Systems for
  ATM equipment
• Cisco acquired Stratacom and Lighstream
• ATM is one of the fastest growing network
  industries - at more than 60, despite
  encroachments by the high powered Gigabit
  Ethernet
• Experts agree that ATM is here to stay and that,
  in the network industry, there is room for both
  the ATM and Gigabit Ethernet

13
Conclusion

• Advances in network performance have triggered
  research in parallel computing using workstation
  clusters
• High speed networks such as ATM move the
  bottleneck to the hosts
• Full potential of ATM can only be achieved by
  advances in both the hardware and software
• Demands of Distributed / Parallel computing are
  resulting in ATM technology, not only in WANs but
  also in LANs
• With increased acceptance by the telephone, cable
  and network industries ATM is here to stay.

14
Bibliography

• Regis j. Bate Donald Gregory
• Voice and Data Communications Handbook, Signature
  edition, McGraw Hill, 1998
• Andrew S. Tenenbaum
• Computer Networks, Third Edition, Prentice Hall
  PTR, 1996
• David E. McDysan / Darren L. Spohn
• ATM Theory and Application, McGraw Hill, 1995
• Abhjit S. Pandya / Ercan Sen
• ATM Technology for Broadband Telecommunications
  Networks, CRC Press, 1999
• J. Vila-Sallent and J. Sole-Pareta. High
  Performance Distributed Computing over ATM
  Networks A Survey of Strategies
• http//www.atmforum.com/
• http//www.npac.syr.edu/users/mahesh/homepage/atm
  tutorial/p slide.htm
• http//www.sic.ohio-state.edu/jain/netsem/netsem2
  .htm
• http//www.byte.com/art/9608/sec7/art4.htm
• http//new.cnet.com/news/0,10000,0-1003-200-329815
  ,00.htm