Introduction to Asynchronous Transfer Mode (ATM) N. Ganesan, Ph.D.(Copyrights of sections as acknowledged.)

AcknowledgmentThis presentation is based on ATM related information provided on the CISCO website, the IEC website and the ATM Forum. Asynchronous Transfer Mode (ATM) Switching ATM Fundamentals ATM Presentations (Good set of PowerPoint presentations).

Chapter Objectives

Chapter Modules

ATM DefinedATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic) CISCO. It utilizes fixed length cells to carry the information

Areas of ApplicationInfrastucture BackbonesLAN

LANsAsynchronous transfer mode (ATM) is a high-performance, cell-oriented switching and multiplexing technology that utilizes fixed-length packets to carry different types of traffic. ATM is a technology that will enable carriers to capitalize on a number of revenue opportunities through multiple ATM classes of services; high-speed local-area network (LAN) interconnection; voice, video, and future multimedia applications in business markets in the short term; and in community and residential markets in the longer term.

Infrastructure BackbonesLANApplication

ATM Connections

Circuit Switching and Packet SwitchingATM is circuit switched because it establishes virtual circuits for communicationAt the same time, the virtual circuits are established over packet switched networksAs such, it combines the benefits of circuit switched and packet switched technologies

ATM Usage and BandwidthIn theory, ATM can be deployed from small LANs to very large WANsAt present, it is used mostly on backbones, but this may change in the future with declining prices for ATM equipmentATM deployments can operate at speeds starting in the Mbps range scaling up to Gpbs rangeSpeed wise, it is very scalable

ATMs EfficiencyIt is an asynchronous technology and it uses the links based on the need for information to be transmittedATM is based on fixed length cells and the cells are small compared to many other forms of transmission such as frame relay etc.

ATM Cell BasicsATM carries information based on fixed length cellsCompare this to the other packet switching technologies such as Frame Relay etc. where each packet may be of a different lengthThe length of each cell is 53 BytesFirst 5 bytes are used as the cell headerNext 48 bytes are used as the payload carrying the data

ATM Cell FormatHeaderPayload (Data)5 Bytes48 Bytes

Fixed Length Cell AdvantageDelay or latency is significantly reducedATM is therefore suited for voice and video transmissionFixed length cells make it easier to switch data across multiple networksATM networks are built based on switches and not routersFixed length cell is similar to container based road transportationSome parallels can be drawn with respect to the advantage of fixed length transportation based on the benefits of container transportation

ATM Cell Header FormatATM Cell HeaderUNI Format

ATM Cell HeaderNNI Format

ATM DevicesATM networks are built around two categories of devicesATM SwitchATM end-pointAn ATM switch can be connected to either another ATM switch or and ATM end-point

ATM End-PointsWill contain and ATM end-point adapterExamples of ATM end-pointsWorkstationsLAN switchesRoutersDSU/CSU UnitsVideo Coder-Decoders (CODECs)

Devices on Which ATM Has Been Implemented PC, workstation, and server network interface cards switched-Ethernet and token-ring workgroup hubs workgroup and campus ATM switches ATM enterprise network switches ATM multiplexers ATMedge switches ATMbackbone switches Source: http://www.iec.org/online/tutorials/atm_fund/topic01.html?Next.x=33&Next.y=17

ATM Network ComponentsSource: CISCO

ATM Switches and InterfacesATM switch supports two types of interfacesUser-Network Interface (UNI)Connects an ATM end-point to a switchNetwork-Network Interface (NNI)Connects two ATM switches

Public and Private InterfacesUNI and NNI can further be divided to two typesOne is known as the private type and the other is known as the public type

Private and Public UNIPrivate UNIConnects an ATM end-point to a private ATM switchPublic UNIConnects an ATM end-point or a private ATM switch to a public ATM switch

Private and Public NNIPrivate NNIConnects two ATM switches within the same private organizationPublic NNIConnects two ATM switches within the same public organization

A third Type of InterfaceKnown as Broadband Inter-Carrier Interface (BICI)Connects two public switches from different service providers

Public and Private Interfaces Source: CISCO

ATM StandardsUNI 2.0, 3.0, 4.0P-NNILAN Emulation (LANE)For the use of ATM over Ethernet, Token ring etc. Multi-protocol Over ATM

ATM Standards for Digital LinesCheck the ATM Forum for approved standards for further information.

ATM ServicesThere are basically three types of ATM services Permanent Virtual Circuits (PVC)Switched Virtual Circuits (SVC)Connectionless ServiceNote: SVC is the most widely used service

ATM Virtual ConnectionsTwo types of connections existOne is known as the Virtual Path (VP)The other is known as the Virtual Circuit (VC)

Virtual Connection CompositionThere can be a number of virtual paths along a physical connection and there can be a number of virtual circuits within a virtual path

Virtual Circuits and PathsSource: CISCO

Transmission Path (Physical Media)Physical medium standards to carry ATM include the following:Synchronous Digital Hierarchy/Synchronous Optical Network (SDH/SONET)DS3/E3Over Multi-Mode Fiber (MMF) at 155 MbpsOver Shielded Twisted Pair (STP) at 155 Mbps

ISO-OSI and ATM Models

LAN Emulation (LANE)Defined by the ATM forum to emulate popular LAN protocols such as Ethernet and Token Ring In other words, the LANE protocol makes an ATM network look and behave like either the Ethernet or the Token Ring network CISCOAn emulated LAN is known as ELAN

Multi-Protocol Over ATM (MPOA)Enables the transmission of data between ELANs without having to continuously go through certain routersAfter the initial flow of data through routers known as Multi-Protocol Servers (MPS), it would be directed along the path of ATM switches (See next slide and CISCO documentation)

Data Flow Between ELANs with and without MPOAWithout MPOAWith MPOA

ATM Quality of Service (QoS)ATMs advantage over competing technologies is that it is able to offer a specified QOS For example, ATM providers can guarantee to their customers that the end-to-end latency will not exceed a specified level

QoS Offered by ATMConstant Bit Rate (CBR)Variable Bit Rate (VBR)Unspecified Bit Rate (UBR)Available Bit Rate (ABR)

Constant Bit Rate (CBR)Highest grade service (Grade A)A constant bandwidth is available for the virtual channelSuitable for voice-over-IP (Transfer fixed rate uncompressed video), and other traffic that requires steady, guaranteed throughput

Variable Bit Rate (VBR)Second in the level of service (Grade B)It is divide into to categoriesVariable Bit Rate Non-Real Time (VBR-NRT)Variable Bit Rate Real Time (VBR-RT)

Variable Bit Rate Non-Real Time VBR-NRTProvides bandwidth only as neededTraffic that is not very sensitive to cell-delay or latency is handled by this serviceAn example use would be to send multimedia e-mail

Variable Bit Rate Real Time VBR-RTAgain, this is similar to VBR-RT in providing bandwidth as neededBut VBR-RT is designed for applications where cell-delay or latency cannot be accommodated

Sample Applications for VBR-RTVoice with speech activity detectionTelephony Compressed interactive videoVideo conferencing

Available Bit Rate (ABR)Third in the level of service (Grade C)Bandwidth is adjusted based on the amount of traffic in the network Suitable for data traffic such as file transfer and Email that are basically not time sensitive

Unspecified Bit Rate (UBR)Fourth in the level of service (Grade D)Dose not offer any fixed values for the traffic parameters

QoS EnforcementTraffic contractTraffic shapingTraffic policing(See CISCO document for more details)

Competing Technologies Frame Relay competes at the backboneEventually, ATM will be the choice for backbone technologyGigabit EthernetATMs competition on the desktop area and LANs will be challenged effectively by high speed and proven Ethernet technologies

End of Module

Practical ATM Networks N. Ganesan, Ph.D.

Chapter Objectives

ATM InterfacesATM and other technologies. ATMSource: CISCO

ATM Network Building Block The main building block of ATM networks is the ATM switchWorkgroup switchCampus switchEnterprise switchMulti-service access switch

ATM Network HierarchySource: CISCO

Work Group SwitchThese switches will have Ethernet and ATM portsUsed for connecting Ethernet networks to ATM switches Note: At the desktop level Ethernet still remains as the leading network technology

Campus SwitchUsed for designing small-scale ATM backbones Can be used for connecting various campus backbone technologies FDDIGigabit Ethernet etc.

Move from Traditional to New Backbones

Enterprise ATM SwitchUsed in building large enterprise backbonesCan be used for integrating different services and technologies on the backbone

Multi-Service Access SwitchA common ATM infrastructure can be used in a public network to support disparate servicesFrame relayLAN interconnectionPublic ATM services Their use usually extends beyond a private network to a public network Used by service providers to connect MANs and WANs for example

ATM Interface TypesUser-to-Network Interface (UNI)Network-to-Network Interface (NNI)

Interface Types in a Network Source: CISCO

ATM InterfacesLAN interfacesBackbone interfaces

ATM to LAN InterfaceSource: http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2008.htm#28807

LAN Emulation IssuesEmulate an Ethernet LANsMap traditional LAN addresses to ATM addresses

ATM to WAN InterfaceSource: CISCODXI Data Exchange InterfaceHSSI High Speed Serial InterfaceDSU Data Service Unit

Load Balancing with ATM SwitchesSource: CISCO

SummaryATM networks are basically built around ATM switchesATM interfaces can be used for integrating disparate WAN technologiesAt the desktop LAN, ATM can be used for emulating the traditional Ethernet environment for exampleBut, in general, the Ethernet technology is very popular in terms of ease of use and speedTherefore, ATM at the LAN front is likely to be used for connecting Ethernet LANs to the backbone if the backbone is based on ATM For the backbone and large public backbones, ATM is bound to become the technology of choice

ReferencesAt CISCOhttp://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2008.htm http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2012.htm ATM Forum http://www.atmforum.org/