1、Asynchronous Transfer Mode,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,Introduction,ATM was formulated
2、 in the early 80s, as a result of AT&T and French Telecompanys research in Fast Packets ITU-T chose ATM for B-ISDN, in the mid 80s 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 gaini
3、ng acceptance as a LAN technology, to reduce bottlenecks in Distributed Computing We will study the ATM technology and its role in Distributed Computing,ATM Overview,BASIC CONCEPTS Both a technology and a service (called Cell Relay) Offers low cost transmission of various types of data Voice, Video
4、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 guarant
5、ee order of delivery Delivers speeds of 155 Mbps to 622 Mbps (compatible with SONET and can transmit HD TV),ATM Overview,B-ISDN ATM Model,User Data,Header,5,48,ATM Cell 53 bytes,OSI,ATM,ATM Sublayer,Functionality,GFC/4,VPI/8,CLP/1,VCI/16,PTI/3,HEC/8,Header 40 bits,VPI/12 for NNI,3/4,2/3,1,2,Physical
6、,ATM,AAL,CS,SAR,TC,PMD,Convergence - Provides standard interface,Flow Control Cell Header generator / Extractor Virtual Circuit / Path Management Cell Multiplexing / De-multiplexing,Cell Rate decoupling Header Checksum generation and verification Cell and Frame generation Packing / Unpacking Cells f
7、rom enclosing envelope,Bit timing Physical Network access,Segmentation and Reassembly,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 li
8、nes 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
9、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,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 (Netw
10、ork 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
11、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,ATM Overview,ATM Adaptation Layer Provides service to the application layer Convergence sublayer deals with messages
12、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 Connectionle
13、ss 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 timeAAL5 for high speed transfer of data,Replacement of T
14、raditional 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
15、 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)
16、and software (Protocol stack exploiting the network),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
17、 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,Enhancement of
18、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 enha
19、ncements 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
20、latency concurrent thread execution and use of all available resources allocated on a per task basis,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 ban
21、dwidth 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 t
22、hat ATM is here to stay and that, in the network industry, there is room for both the ATM and Gigabit Ethernet,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 pot
23、ential 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.,Bibliography,R
24、egis 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 T
25、echnology 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:/ http:/www.npac.syr.edu/users/mahesh/homepage/atm tutorial/p slide.htm http:/www.sic.ohio-state.edu/jain/netsem/netsem2.htm http:/ http:/
