ATMATM

ATMATMAsynchronous Transfer ModeAsynchronous Transfer Mode

An Introduction to

John A. Clark

ATMATM

VOICEVOICE VIDEOVIDEO DATADATA

Unlike other standards, ATM has been designed Unlike other standards, ATM has been designed from the outset to support VOICE, VIDEO and from the outset to support VOICE, VIDEO and DATA.DATA.

ATM SWITCHATM SWITCH

ATMATM

Unlike contemporary shared bandwidth LANs, Unlike contemporary shared bandwidth LANs, ATM uses parallel bandwidth allocation for each ATM uses parallel bandwidth allocation for each user user

10 Mb/s10 Mb/s

User bandwidth User bandwidth = 10 Mb/s= 10 Mb/s

1 Ethernet/Token Ring User1 Ethernet/Token Ring User

5 Mb/s5 Mb/s5 Mb/s5 Mb/s

User bandwidth User bandwidth = 5 Mb/s= 5 Mb/s

2 Ethernet/Token Ring Users2 Ethernet/Token Ring Users

ATMATM

Unlike contemporary shared bandwidth LANs, Unlike contemporary shared bandwidth LANs, ATM uses parallel bandwidth allocation for each ATM uses parallel bandwidth allocation for each user user

155 Mb/s155 Mb/s

User bandwidth User bandwidth = 155 Mb/s= 155 Mb/s

1 ATM User1 ATM User

User bandwidth User bandwidth = 155 Mb/s= 155 Mb/s

2 ATM Users2 ATM Users

155 Mb/s155 Mb/s

155 Mb/s155 Mb/s

Provided the switches have sufficient aggregate bandwidth, NO degradation Provided the switches have sufficient aggregate bandwidth, NO degradation will occur under any load - NON BLOCKING SWITCHwill occur under any load - NON BLOCKING SWITCH

Bandwidth is allocated initially and is then reserved: thus it can never be Bandwidth is allocated initially and is then reserved: thus it can never be exhausted exhausted

ATMATM

Unlike traditional variable packet size LAN standards, Unlike traditional variable packet size LAN standards, ATM uses fixed length CELLSATM uses fixed length CELLS

Ethernet orEthernet orToken RingToken Ring

ATMATM

I.D.I.D. PAYLOADPAYLOAD5 bytes5 bytes 48 bytes48 bytes

53 BYTES TOTAL53 BYTES TOTAL

The payload contains protocol independent data of ANY bit pattern - these 48 The payload contains protocol independent data of ANY bit pattern - these 48 bytes are completely un-interrogated by the network switchesbytes are completely un-interrogated by the network switches

The lack of a trailing payload CRC field allows very rapid “CUT-THROUGH” The lack of a trailing payload CRC field allows very rapid “CUT-THROUGH” switching, based on the VCI (Virtual Channel Identifier) in the IDswitching, based on the VCI (Virtual Channel Identifier) in the ID

ATMATM

Although the fixed cell size makes ATM similar to Although the fixed cell size makes ATM similar to Time Division Multiplexing (TDM), empty time slots Time Division Multiplexing (TDM), empty time slots waste bandwidth on TDM where no data is ready waste bandwidth on TDM where no data is ready

ATMATM

TDMTDM

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 1 2 3

= Data frame= Data frame = Empty slot= Empty slot

= Data cell= Data cell = Video cell= Video cell = Voice cell= Voice cell

ATM channels are comprised of a continuous stream of voice, video and ATM channels are comprised of a continuous stream of voice, video and data cells - The small cell size is a result of the delays concerned with data cells - The small cell size is a result of the delays concerned with packetising digitised voice at 64 Kb/s that give unacceptable between packetising digitised voice at 64 Kb/s that give unacceptable between the North American proposal of 69 bytes and the European proposal of the North American proposal of 69 bytes and the European proposal of 36 bytes!36 bytes!

ATMATM

Unlike the connectionless approach used in Bus or Unlike the connectionless approach used in Bus or Ring Layer 2 standards, ATM is connection orientatedRing Layer 2 standards, ATM is connection orientated

PhysicalPhysical

Data Link Data Link

NetworkNetwork

TransportTransport

ApplicationApplication

SessionSession

PresentationPresentation

ATM ADAPTATIONATM ADAPTATION

ATMATM

The ATM layer is concerned with the cell structures and handling of The ATM layer is concerned with the cell structures and handling of virtual connections - The ATM Adaptation Layer (AAL) is where a virtual connections - The ATM Adaptation Layer (AAL) is where a higher layer service (voice, video or data) is adapted for transport over higher layer service (voice, video or data) is adapted for transport over the ATM networkthe ATM network

ATMATM

Unlike the connectionless approach used in Bus or Unlike the connectionless approach used in Bus or Ring Layer 2 standards, ATM is connection orientatedRing Layer 2 standards, ATM is connection orientated

The ATM switch simply maps input and output port numbers to Virtual The ATM switch simply maps input and output port numbers to Virtual Channel Identifiers to produce a true end to end switching capabilityChannel Identifiers to produce a true end to end switching capability

ATM SWITCHATM SWITCH

1111

2222

4141

424233 55

VCIVCI PORTPORT PORTPORT VCIVCI

In PortIn Port VCIVCI Out PortOut Port VCIVCI

3355

11114242

55 414133 2222

Thus, ATM is essentially fixed size fast packet switching, superimposed Thus, ATM is essentially fixed size fast packet switching, superimposed on the circuit switching schemeon the circuit switching scheme

ATMATM

Standards now approximately 2/3 completeStandards now approximately 2/3 complete

ATM FORUMATM FORUM

Ad-hoc committeeAd-hoc committee

CCITTCCITTConsultative committee for Consultative committee for International Telegraph & International Telegraph & Telephony - now the ITU - Telephony - now the ITU - International International Telecommunications UnionTelecommunications Union

Collective agreementsCollective agreements

DE FACTO STANDARDSDE FACTO STANDARDS FORMAL STANDARDSFORMAL STANDARDS

In practice, the ATM Forum produces all standards concerned with LAN In practice, the ATM Forum produces all standards concerned with LAN services (e.g. Ethernet, Token Ring etc.). The CCITT is not involved with services (e.g. Ethernet, Token Ring etc.). The CCITT is not involved with this at all and concentrates heavily on telephony and PTT usage of ATM - this at all and concentrates heavily on telephony and PTT usage of ATM - The IETF (Internet Engineering Task Force) also defines the The IETF (Internet Engineering Task Force) also defines the encapsulation of various protocols over ATM in RFCs (Request For encapsulation of various protocols over ATM in RFCs (Request For Comment), such as RFC1483 (multiprotocol), RFC894 (Ethernet), Comment), such as RFC1483 (multiprotocol), RFC894 (Ethernet), RFC1042 (Token Ring) etc.RFC1042 (Token Ring) etc.

ATMATM

ATM LANs ran first in 1992ATM LANs ran first in 1992

ATM HISTORYATM HISTORY

* 1983* 1983 First ATM papers publishedFirst ATM papers published* 1987* 1987 CCITT selected ATM for B-ISDNCCITT selected ATM for B-ISDN* 1990* 1990 CCITT issued 13 ATM recommendationsCCITT issued 13 ATM recommendations* 1992* 1992 First ATM LANs installedFirst ATM LANs installed* 1993* 1993 First ATM WANs installedFirst ATM WANs installed

Several manufacturers have ATM switch products shipping already (e.g. Several manufacturers have ATM switch products shipping already (e.g. Bay Networks !) and many will role out switches during 1995 (e.g. 3Com, Bay Networks !) and many will role out switches during 1995 (e.g. 3Com, Chipcom, Dec etc.).Chipcom, Dec etc.).

Public WAN services could be several years away - The European ATM Public WAN services could be several years away - The European ATM WAN pilot scheme was launched in Brussels and Dublin during November WAN pilot scheme was launched in Brussels and Dublin during November 94 and involved 15 cross connects running over 34 Mb/s E3 bearers. 94 and involved 15 cross connects running over 34 Mb/s E3 bearers.

ATMATM

Private UNI, the NNI & public UNIPrivate UNI, the NNI & public UNI

PUBLIC ATMPUBLIC ATMPRIVATE ATMPRIVATE ATM

UNI UNI NNINNI UNIUNI

The private UNI (User/Network Interface) and NNI (Network/Network The private UNI (User/Network Interface) and NNI (Network/Network Interface) define the physical, electrical, optical, management and data Interface) define the physical, electrical, optical, management and data structures between the edge station and switch and between two switches structures between the edge station and switch and between two switches respectively - as the whole private network is considered a user edge to the respectively - as the whole private network is considered a user edge to the PTOs, the interface to the public ATM switch is also denoted as a UNIPTOs, the interface to the public ATM switch is also denoted as a UNI

The PNNI (Private NNI) is yet to be ratified by the ATM Forum (Q3 95?), when The PNNI (Private NNI) is yet to be ratified by the ATM Forum (Q3 95?), when the functionality will be extended to re-route failing switch links the functionality will be extended to re-route failing switch links

ATMATM

PVCs & SVCsPVCs & SVCs

PVCPVC

PVCs (Permanent Virtual Circuits) must be statically configured using PVCs (Permanent Virtual Circuits) must be statically configured using network management before the circuit is usednetwork management before the circuit is used

SVCSVC

SignallingSignalling

SVCs (Switched Virtual Circuits) are dynamically configured using SVCs (Switched Virtual Circuits) are dynamically configured using signalling - Two ATM Forum signalling standards exist (V3.0 & V3.1) as signalling - Two ATM Forum signalling standards exist (V3.0 & V3.1) as well as the ITU Q2931 standard - It will be the extension of Q2931 that will well as the ITU Q2931 standard - It will be the extension of Q2931 that will re-route down NNI linksre-route down NNI links

Signalling between UNI NNI etc. requires global addressing agreement!Signalling between UNI NNI etc. requires global addressing agreement!

ATMATM

ATM uses network address & telephone numbersATM uses network address & telephone numbers

VOICEVOICE E.164 ISDN AddressesE.164 ISDN Addresses

DATADATA 48 bit MAC addresses48 bit MAC addresses

VIDEOVIDEO No AddressesNo Addresses

The addressing scheme must account for any virtual circuit, regardless The addressing scheme must account for any virtual circuit, regardless of the type of traffic - Three forms currently exist : DCC (Data Country of the type of traffic - Three forms currently exist : DCC (Data Country Code), ICD (International Code Designator) and E.164 Private Address:Code), ICD (International Code Designator) and E.164 Private Address:

4545 E.164 ISDN BCD NumberE.164 ISDN BCD Number MAC AddressMAC Address

E.164 addressing is generally used with Q.2931 signalling today over the E.164 addressing is generally used with Q.2931 signalling today over the a version of the ATM Adaptation Layer called AAL5a version of the ATM Adaptation Layer called AAL5

ATMATM

ITU have defined 5 Classes of ServiceITU have defined 5 Classes of Service

The ITU B-ISDN 5 classes of service have been designed to account for The ITU B-ISDN 5 classes of service have been designed to account for the fact that voice, video and data have differing requirements on the the fact that voice, video and data have differing requirements on the bit ratebit rate

VOICEVOICE CONSTANT BIT RATECONSTANT BIT RATE

DATADATA VARIABLE BIT RATEVARIABLE BIT RATE

VIDEOVIDEO CONSTANT BIT RATECONSTANT BIT RATE

A B C DA B C D

Yes Yes No NoYes Yes No No

Cnst Var Var VarCnst Var Var Var

Yes Yes Yes No Yes Yes Yes No

End to end timingEnd to end timing

Bit RateBit Rate

Connection orientatedConnection orientated

ITU SERVICE CLASSITU SERVICE CLASS

AAL5 - SEALAAL5 - SEALAAL5, sometimes known as SEAL (Simple & Efficient Adaptation Layer) AAL5, sometimes known as SEAL (Simple & Efficient Adaptation Layer) was the ATM Forum’s response to the ITU’s complex AAL3/4 - AAL5 is was the ATM Forum’s response to the ITU’s complex AAL3/4 - AAL5 is being increasingly used for data and variable data rate video and audiobeing increasingly used for data and variable data rate video and audio

ATMATMATMATM

LUNI the LAN Emulation UNILUNI the LAN Emulation UNI

LAN Emulation ServerLAN Emulation Server

Broadcast Unknown ServerBroadcast Unknown Server

LAN EmulationLAN EmulationClientClient

LAN EmulationLAN EmulationClientClient

The LAN Emulation part of the UNI is needed to translate Ethernet or The LAN Emulation part of the UNI is needed to translate Ethernet or Token Ring MAC addresses to ATM addresses and to mimic broadcasts Token Ring MAC addresses to ATM addresses and to mimic broadcasts in the ATM connection orientated environmentin the ATM connection orientated environment

The standard defines an LEC (Lan Emulation Client), an LES (Lan The standard defines an LEC (Lan Emulation Client), an LES (Lan Emulation Server) which does the address mapping and a BUS Emulation Server) which does the address mapping and a BUS (Broadcast Unknown Server) which provides broadcasts for ARP etc.(Broadcast Unknown Server) which provides broadcasts for ARP etc.

ATMATM

00

1010

100100

10001000

1985 1990 19951985 1990 1995

386386

486486

MIPSMIPS

Token Ring 16 Mb/sToken Ring 16 Mb/sEthernet 10 Mb/sEthernet 10 Mb/s

FDDI 100 Mb/sFDDI 100 Mb/sATM 155 Mb/sATM 155 Mb/s

ATM 622Mb/sATM 622Mb/s

ATM 2 Gb/sATM 2 Gb/s

ALPHA,R6000ALPHA,R6000SPARC,PentiumSPARC,Pentium

AMDAHL’s LAW : 1 MIP requires 1 Mb/s I/OAMDAHL’s LAW : 1 MIP requires 1 Mb/s I/O

Fibre optic interfaces running 155 Mb/s SONET (Synchronous Optical Fibre optic interfaces running 155 Mb/s SONET (Synchronous Optical NETwork) / SDH (Synchronous Digital Heirachy) standards are NETwork) / SDH (Synchronous Digital Heirachy) standards are available now - these will be scaled to 622 Mb/s.available now - these will be scaled to 622 Mb/s.

155 Mb/s Interfaces for Category 5 UTP are also available.155 Mb/s Interfaces for Category 5 UTP are also available.

ATM is fast enough for the foreseeable future !ATM is fast enough for the foreseeable future !

ATMATM

Data RateData Rate SDH DesignationSDH Designation SONET DesignationSONET Designation Framing TypeFraming Type

51.84 Mb/s51.84 Mb/s -------------------------- OC-1OC-1 STS-1STS-1155.52 Mb/s155.52 Mb/s STM-1STM-1 OC-3OC-3 STS-3STS-3622.08 Mb/s622.08 Mb/s STM-4STM-4 OC-12OC-12 STS-12STS-121.244 Gb/s1.244 Gb/s STM-8STM-8 OC-24OC-24 STS-24STS-242.488 Gb/s2.488 Gb/s STM-16STM-16 OC-48OC-48 STS-48STS-48

STM-n : Synchronous Transfer Mode - n x 155.52 Mb/sSTM-n : Synchronous Transfer Mode - n x 155.52 Mb/s

OC : Optical Carrier OC : Optical Carrier

STS : Synchronous Transport SignalSTS : Synchronous Transport Signal

ATM is fast enough for the foreseeable future !ATM is fast enough for the foreseeable future !

ATMATM

Floor HubsFloor HubsDesk StationsDesk Stations

BasementBasementSwitchSwitch

Bridge/Bridge/RouterRouter

100 Mb/s FDDI100 Mb/s FDDI

10 Mb/s10 Mb/s10BaseT10BaseT

64Kb/s - 34 Mb/s64Kb/s - 34 Mb/sE1/E3/ISDNE1/E3/ISDNFrame Relay/ SMDSFrame Relay/ SMDS

10 Mb/s10 Mb/s10BaseT10BaseT

Today’s typical collapsed backbone LANs, with switched or routed Today’s typical collapsed backbone LANs, with switched or routed basement hubs and varied WAN bearer services are anything but basement hubs and varied WAN bearer services are anything but homogeneoushomogeneous

Fibre Campus backboneFibre Campus backbone

Category 5 UTPCategory 5 UTP

ATMATM

Initially, the availability of ATM switch modules for basement and top Initially, the availability of ATM switch modules for basement and top range floor hubs will make 155 Mb/s fibre risers and campus backbones range floor hubs will make 155 Mb/s fibre risers and campus backbones a viable upgrade - Compute intensive workstations will also take a viable upgrade - Compute intensive workstations will also take advantage of 12/16 port fibre ATM switches to gain 155 Mb/s dedicated advantage of 12/16 port fibre ATM switches to gain 155 Mb/s dedicated pipes at competitive price per port - 100 Mb/s switching hubs are likely pipes at competitive price per port - 100 Mb/s switching hubs are likely to offer 155 Mb/s fibre interfaces, or Cat 5 copper interfacesto offer 155 Mb/s fibre interfaces, or Cat 5 copper interfaces

Floor HubsFloor HubsDesk StationsDesk Stations

BasementBasementSwitchSwitch

100 Mb/s100 Mb/s100BaseT100BaseT

Category 5 UTPCategory 5 UTP155 Mb/s ATM155 Mb/s ATM

Fibre Campus backboneFibre Campus backbone

155 Mb/s155 Mb/sATMATM

Risc/PentiumRisc/PentiumWorkstationWorkstation

155 Mb/s155 Mb/sATMATM

FibreFibre

64Kb/s - 34 Mb/s64Kb/s - 34 Mb/sE1/E3/ISDNE1/E3/ISDNFrame Relay/ SMDSFrame Relay/ SMDS

ATMATM

ATM switchingATM switchingFloor HubsFloor Hubs

Desk StationsDesk Stations

ATM SwitchATM Switch155 Mb/s155 Mb/sATMATM

Public ATMPublic ATMBearersBearers

Eventually, when the PTO’s make full wide area ATM bearer services Eventually, when the PTO’s make full wide area ATM bearer services available, it will be possible to implement a completely ATM homogeneous available, it will be possible to implement a completely ATM homogeneous LAN/WAN supporting voice, video and data for bandwidth hungry, LAN/WAN supporting voice, video and data for bandwidth hungry, multimedia applicationsmultimedia applications

PABXPABX

ATM EdgeATM EdgeSwitchSwitch2 Gb/s ATM Fibre2 Gb/s ATM Fibre

Campus backboneCampus backbone

VideoVideoConferenceConference

155 Mb/s155 Mb/sATMATM

622 Mb/s622 Mb/sATMATM

622 Mb/s622 Mb/sATMATM

Cat 5 UTPCat 5 UTP

ATMATM

ATMATMTHE GIGABIT PER SECOND THE GIGABIT PER SECOND FUTURE FOR MULTIMEDIA FUTURE FOR MULTIMEDIA ENTERPRISE NETWORKSENTERPRISE NETWORKS