Chapter Objectives After completing this chapter you will be able to: –Understand the basic concepts of ATM –List some reasons for implementing an ATM service –Describe the general format of the ATM structure –Understand the basic concept of virtual circuits –Describe ATM’s handling of traffic types

Never Underestimate Famous quotes “I think there’s a world market for maybe 5 computers” - Thomas Watson, IBM chairman, 1943 “Computers in the future will weigh no more than 1.5 tons” - Prediction in Popular Mechanics, 1949 “Clever, but, what is a microchip good for?” - Engineer at IBM, 1952 “There is no reason why anyone would want to have a computer in their home” - Ken Olson, DEC chairman, 1977 “640K (RAM) ought to be enough for anybody” - Bill Gates Microsoft chairman, 1981 "There is one big problem -- telecommunications bandwidth” - Andy Grove, Intel, 1997

Modern Requirements Traditional voice, data, fax etc. Plus –High-quality audio –High-quality video –Voice over the Internet –HTML –Multimedia etc. Only networking standards supported –Scalability from office through corporate to operator –Same standards from operator down to the desktop –Guaranteed quality of service where appropriate

Multimedia What is multimedia? Single Point of Access

Multimedia Storage Impact on file size Text in kilobytes Graphics in Megabytes Video/sound in Gigabytes

Demand for Bandwidth Multiple users accessing multimedia - Creates a bandwidth bottleneck

Bandwidth Use Large files use a lot of bandwidth – Or response times become unacceptably long. 0.5 Gbyte Mbps 155 Mbps 33 MIN. 26 SEC. Frame Relay ATM

Integration Different media types have different requirements Video Conference    Sensitive High Telephone Connectionless Connection- oriented Delay variance Bandwidth requirement Constant bit rate Variable bit rate   Sensitive Low Internet   Insensitive Medium

ATM & ISDN Narrowband ISDN (N-ISDN) Broadband ISDN (B-ISDN) Primary rate ATM Basic rate 2 x B(earer)64 kbit/s 1 x D(ata)16 kbit/s 30 x B(earer)64 kbit/s 1 x D(ata)64 kbit/s 2 24 x B(earer)variable In-band signalling

ATM Technology Traditional Communications: –Circuit switching Inefficient for bursty data –Packet switching Unpredictable delays ATM blends the best features of each system –Establishes end-to-end connections –Traffic is sent in packets and multiplexed on connections –Standards-based handling allows predictable delays

The ATM Cell Fixed packet size 48-Byte Payload 5-Byte Header

Transport Bearer channel based on fixed-length cells 5-byte header byte payload – Offers low latency at switches – Delays are more predictable

ATM Connections Connections are virtual channels –Permanent (PVC) –Switched (SVC) signalling

Circuits Channels are connection-oriented – Cells arrive in sequence No re-ordering required Simplifies processing B5 A1 A2 A3 B6 A4 B7 B4 B3 B2 B1 A B A B

ATM Switching InputsOutputs Cell Queues The ATM switch simply performs a hardware lookup of the connection identifier, and switches the cell accordingly. A new connection identifier is allocated at the output. 56Payload

ATM Multiplexing Constant bit rate (low) Constant bit rate (high) Packetised (bursty data) Variable bit rate Supported services AAL SAR Cells at required rate Multiplexing ATM cell stream

ATM Protocol Suite Not all ATM standards are yet in place Promises to be the complete suite of protocols – From desktop to desktop – Over LAN and WAN Seamless operation without conversion or encapsulation WorkgroupCorporate network Public network Corporate network

ATM Basics The core network must be fast and reliable ATM networks do not perform error correction ATM does not work on Plain Old Telephone System (POTS) network Analogue

Summary of Features Connection-oriented No out-of-sequence data AAL to support connectionless data Attempts to provide advantages of: Circuit switching – low or no call set-up time – low predictable delays – bandwidth always available Packet switching – efficient use of bandwidth – route switching