Post on 26-Mar-2015
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