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A synchronous T ransfer M ode

A synchronous T ransfer M ode. Pradeep Kumar CS 616 Prof. C. Tappert. 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.

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A synchronous T ransfer M ode

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  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 80’s, as a result of AT&T and French Telecompany’s research in Fast Packets • ITU-T chose ATM for B-ISDN, in the mid 80’s • In 1989, ATM packet size of 48+5 was adopted as a compromise between 64+5 (USA) and 32+4(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 it’s 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 5 48 B-ISDN ATM Model ATM Cell 53 bytes Header User Data 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 • ATM’s 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 vendor’s 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

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