1 chapter 5 asynchronous transfer mode (atm). chapter 5 atm 2 introduction atm protocol architecture...
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Chapter 5Chapter 5
Asynchronous Asynchronous Transfer ModeTransfer Mode(ATM)(ATM)
Chapter 5 ATM2
Introduction Introduction
ATM Protocol ArchitectureATM Protocol ArchitectureLogical connectionsLogical connectionsATM cell structureATM cell structureService levels/categoriesService levels/categoriesATM Adaptation Layer (AAL)ATM Adaptation Layer (AAL)
Chapter 5 ATM3
Introduction Introduction ATM evolved from B-ISDN development ATM evolved from B-ISDN development
effortsefforts– Frame Relay: high-speed WAN (1.5+ Mbps)Frame Relay: high-speed WAN (1.5+ Mbps)– ATM: very high speed WAN (155 Mbps and ATM: very high speed WAN (155 Mbps and
622Mbps)622Mbps) ATM, like Frame Relay, was built on the ATM, like Frame Relay, was built on the
assumption that the underlying physical assumption that the underlying physical media was reliable and flexiblemedia was reliable and flexible– minimal error and flow control capabilitiesminimal error and flow control capabilities– even more streamlined, therefore faster, even more streamlined, therefore faster,
than Frame Relaythan Frame Relay Specifications developed by ITU-T and Specifications developed by ITU-T and
ATM ForumATM Forum
Chapter 5 ATM4
ATM Protocol ArchitectureATM Protocol Architecture
Fixed-size packets called cellsFixed-size packets called cells– ““cell switchingcell switching” like packet switching” like packet switching
2 primary protocol layers relate to 2 primary protocol layers relate to ATM functions:ATM functions:– Common layer providing packet Common layer providing packet
transfers, logical connections (transfers, logical connections (ATMATM))– Service dependent ATM adaptation Service dependent ATM adaptation
layer (layer (AALAAL))AAL maps other protocols to ATMAAL maps other protocols to ATM
– like IP (AAL5)like IP (AAL5)
Chapter 5 ATM5
Protocol Model has 3 planesProtocol Model has 3 planes
UserUser – provides for user information – provides for user information transfer and associated controls transfer and associated controls (flow control, congestion control)(flow control, congestion control)
ControlControl – performs call control and – performs call control and connection control functions connection control functions (signaling)(signaling)
ManagementManagement – provides plane – provides plane management and layer management and layer management and coordination management and coordination functionsfunctions
Chapter 5 ATM6
ATM Protocol Reference ATM Protocol Reference ModelModel
Various data rates (155.52 Mbps, 622.08 Mbps) over various physical media types (Fiber Optic, SONET, UTP, etc.)
Framing, cell structure& Logical Connections
Map data to the ATM cellstructure
Chapter 5 ATM7
User Plane LayersUser Plane Layers
AALAAL
ATMATM
User information
User information
AALAAL
ATMATM
PHYPHYPHYPHY
ATMATM
PHYPHY
ATMATM
PHYPHY
……
End systemEnd system End systemEnd systemNetworkNetwork
Chapter 5 ATM8
User Plane LayersUser Plane LayersUser
informationUser
information
Chapter 5 ATM9
Logical ConnectionsLogical ConnectionsVCC (VCC (Virtual ChannelVirtual Channel Connection): Connection):
a logical connection analogous to a logical connection analogous to a virtual circuit in X.25, or Frame a virtual circuit in X.25, or Frame Relay data link connectionRelay data link connection– full-duplex flow between end usersfull-duplex flow between end users– user-network control signalinguser-network control signaling– network-network network-network
management/routingmanagement/routing
VPC (VPC (Virtual PathVirtual Path Connection): a Connection): a bundle of VCCs with the bundle of VCCs with the same end same end pointspoints (not necessarily same end- (not necessarily same end-users)users)– and switched along the same pathand switched along the same path
Chapter 5 ATM10
ATM Connection ATM Connection RelationshipsRelationships
Virtual ChannelVirtual Channel: basic logical communications channel: basic logical communications channelVirtual PathVirtual Path: groups of “common” virtual channels: groups of “common” virtual channelsPhysical Transmission PathPhysical Transmission Path: physical communications link: physical communications link
Chapter 5 ATM12
Advantages of Virtual PathsAdvantages of Virtual PathsSimplified network architecture – Simplified network architecture – allows allows
separation of functionality into into individual logical separation of functionality into into individual logical connections and related groups of logical connections and related groups of logical connectionsconnections
Increased network performance and Increased network performance and reliability – reliability – network consists of fewer aggregated network consists of fewer aggregated entitiesentities
Reduced processing and short Reduced processing and short connection setup time – connection setup time – complex setup complex setup tasks are in virtual paths, simplifies setup of new tasks are in virtual paths, simplifies setup of new virtual channels over existing virtual pathvirtual channels over existing virtual path
Enhanced network services – Enhanced network services – supports supports user-specified closed groups/networks of VC bundlesuser-specified closed groups/networks of VC bundles
Chapter 5 ATM13
Virtual Path/Virtual Channel Virtual Path/Virtual Channel TerminologyTerminologyVirtual ChannelVirtual Channel (VC) A generic term used to (VC) A generic term used to
describe unidirectional transport describe unidirectional transport of cells associated by a common of cells associated by a common unique identifierunique identifier
Virtual Channel Identifier Virtual Channel Identifier (VCI) A unique numerical tag for (VCI) A unique numerical tag for a particular VC linka particular VC link
Virtual Channel LinkVirtual Channel Link A means of unidirectional A means of unidirectional transport of cells between the transport of cells between the point where a VCI is assigned point where a VCI is assigned and where it is translated or and where it is translated or terminatedterminated
Virtual Channel Connection Virtual Channel Connection (VCC) (VCC) A concatenation of VC links that A concatenation of VC links that extends between two connected extends between two connected ATM end-pointsATM end-points
Chapter 5 ATM14
Virtual Path/Virtual Channel Virtual Path/Virtual Channel TerminologyTerminologyVirtual Path Virtual Path (VP) A generic term which (VP) A generic term which
describes unidirectional transfer of describes unidirectional transfer of cells that are associated with a cells that are associated with a common unique identifiercommon unique identifier
Virtual Path IdentifierVirtual Path Identifier (VPI) Identifies a particular VP(VPI) Identifies a particular VPVirtual Path LinkVirtual Path Link A group of VC links identified by a A group of VC links identified by a
common identifier between the common identifier between the point where the identifier (VPI) is point where the identifier (VPI) is assigned and where it is translated assigned and where it is translated or terminatedor terminated
Virtual Path Connection Virtual Path Connection (VPC) A concatenation of VP links (VPC) A concatenation of VP links that extends between ATM end-that extends between ATM end-points where the VCIs are assigned points where the VCIs are assigned and where they are translated or and where they are translated or terminatedterminated
Chapter 5 ATM15
ATM VPC/VCCATM VPC/VCC
c ATMSw1
ATMSw4
ATMSw2
ATMSw3
ab
de
VP3 VP5
VP2
VP1
a
bc
de
Sw = switch
DCC = Cross-connect switch
ATMDCC
VP6
Chapter 5 ATM16
ATM Connection ATM Connection RelationshipsRelationships
Chapter 5 ATM17
VPC/VCC CharacteristicsVPC/VCC CharacteristicsQuality of Service (Quality of Service (QoSQoS))Switched and semi-permanentSwitched and semi-permanent
virtual channel connectionsvirtual channel connectionsCell sequenceCell sequence integrity integrityTraffic parameterTraffic parameter negotiation and negotiation and
usage monitoringusage monitoring– average rate, peak rate, burstiness, average rate, peak rate, burstiness,
peak duration, etc.peak duration, etc. ((VPC onlyVPC only) virtual channel ) virtual channel
identifier restriction within a VPCidentifier restriction within a VPC
Chapter 5 ATM20
Control SignalingControl SignalingA mechanism to A mechanism to establish and release establish and release
VPCs and VCCsVPCs and VCCs (per ITU-T Rec. I.150) (per ITU-T Rec. I.150)4 methods for VCCs:4 methods for VCCs:
– Semi-permanent VCC:Semi-permanent VCC: no control no control signaling requiredsignaling required
– Meta-signaling channel:Meta-signaling channel: permanent, low permanent, low data rate channel for setting up data rate channel for setting up signaling channelssignaling channels
– User-to-network signaling virtual User-to-network signaling virtual channel:channel: set up between user and set up between user and network network
– User-to-user signaling virtual channel:User-to-user signaling virtual channel: set up between users within a VPC, set up between users within a VPC, allowing users to set up and tear down allowing users to set up and tear down VCCs, without network interventionVCCs, without network intervention
Chapter 5 ATM22
ATM CellsATM Cells
Fixed sizeFixed size– 5-octet header5-octet header– 48-octet information field48-octet information field
Small cells may reduce queuing Small cells may reduce queuing delay for high-priority cells delay for high-priority cells ((essential for low delayessential for low delay))
Fixed size facilitates more efficient Fixed size facilitates more efficient switching in hardware (switching in hardware (essential essential for very high data ratesfor very high data rates))
Chapter 5 ATM23
ATM Cell Format ATM Cell Format (p. 98)(p. 98)
Chapter 5 ATM24
Header FormatHeader Format
Generic flow control (Generic flow control (more ->more ->))Virtual path identifier (VPI)Virtual path identifier (VPI)Virtual channel identifier (VCI)Virtual channel identifier (VCI)Payload type (3 bits: identifies cell Payload type (3 bits: identifies cell
as user data or network as user data or network management cell, presence of management cell, presence of congestion, SDU type)congestion, SDU type)
Cell loss priority (0: high; 1: low)Cell loss priority (0: high; 1: low)Header error control (Header error control (more ->more ->))
Chapter 5 ATM25
Generic Flow ControlGeneric Flow ControlUsed to Used to control traffic flowcontrol traffic flow at user- at user-
network interface (UNI) to alleviate network interface (UNI) to alleviate short-term overload conditionsshort-term overload conditions– Note: Note: not employed in network corenot employed in network core
When GFC is enabled at the UNI, When GFC is enabled at the UNI, two procedures are used:two procedures are used:– Uncontrolled transmission: not subject Uncontrolled transmission: not subject
to flow controlto flow control– Controlled transmission: flow control Controlled transmission: flow control
constraints (using GFC mechanism) constraints (using GFC mechanism) are in forceare in force
Chapter 5 ATM27
Header Error ControlHeader Error Control8-bit field - calculated based on 8-bit field - calculated based on
the other 32 bits in the headerthe other 32 bits in the header– CRC based on xCRC based on x88 + x + x22 + x + 1 + x + 1
-> generator is 100000111 -> generator is 100000111error detectionerror detection in some cases, error correction of in some cases, error correction of
single-bit errors in headersingle-bit errors in header2 modes: 2 modes:
– Error detectionError detection– Error correctionError correction
Chapter 5 ATM28
HEC Operation at ReceiverHEC Operation at Receiver
Based on recognition of fact Based on recognition of fact that bit errors occur in bursts. that bit errors occur in bursts.
Chapter 5 ATM31
ATM Service CategoriesATM Service Categories
Real-time serviceReal-time service– Constant bit rate (Constant bit rate (CBRCBR))– Real-time variable bit rate (Real-time variable bit rate (rt-VBRrt-VBR))
Non-real-time serviceNon-real-time service– Non-real-time variable bit rate (Non-real-time variable bit rate (nrt-nrt-
VBRVBR))– Available bit rate (Available bit rate (ABRABR))– Unspecified bit rate (Unspecified bit rate (UBRUBR))– Guaranteed frame rate (Guaranteed frame rate (GFRGFR))
Chapter 5 ATM32
ATM Bit Rate Service LevelsATM Bit Rate Service Levels
Chapter 5 ATM33
ATM Adaptation Layer (AAL)ATM Adaptation Layer (AAL)
Support higher-level protocols Support higher-level protocols and/or native applicationsand/or native applications– e.g., PCM voice, LAPF, e.g., PCM voice, LAPF, IPIP
AAL ServicesAAL Services– Handle transmission errorsHandle transmission errors– Segmentation/reassembly (Segmentation/reassembly (SARSAR))– Handle lost and misinserted cell Handle lost and misinserted cell
conditionsconditions– Flow control and timing controlFlow control and timing control
Chapter 5 ATM34
ATM Adaptation Layer (AAL)ATM Adaptation Layer (AAL)
Chapter 5 ATM35
Applications of AAL and Applications of AAL and ATMATMCircuit emulation (e.g., T-1 Circuit emulation (e.g., T-1
synchronous TDM circuits)synchronous TDM circuits)VBR voice and videoVBR voice and videoGeneral data servicesGeneral data services IP over ATMIP over ATMMultiprotocol encapsulation over Multiprotocol encapsulation over
ATM (MPOA)ATM (MPOA)LAN emulation (LANE)LAN emulation (LANE)
Chapter 5 ATM36
AAL Protocol and ServicesAAL Protocol and Services
Basis for classification:Basis for classification:•requirement for a timing relationship requirement for a timing relationship between source and destinationbetween source and destination
•requirement for a constant bit rate data requirement for a constant bit rate data flowflow
•connection or connectionless transferconnection or connectionless transfer
Chapter 5 ATM37
AAL ProtocolsAAL ProtocolsAAL layer has 2 sublayers:AAL layer has 2 sublayers:
– Convergence SublayerConvergence Sublayer (CS) (CS) Supports specific applications/protocols Supports specific applications/protocols
using AALusing AAL Users attach via the Service Access Users attach via the Service Access
Point (like a port number)Point (like a port number) Common part (CPCS) and application Common part (CPCS) and application
service-specific part (SSCS)service-specific part (SSCS)
– Segmentation and Reassembly Segmentation and Reassembly SublayerSublayer (SAR) (SAR)
Packages data from CS into ATM cells Packages data from CS into ATM cells and unpacks at other endand unpacks at other end
Chapter 5 ATM38
AAL Protocols and PDUsAAL Protocols and PDUs
Chapter 5 ATM39
AAL Protocol DescriptionsAAL Protocol Descriptions
Chapter 5 ATM40
Segmentation and Segmentation and Reassembly PDUsReassembly PDUs
Chapter 5 ATM41
AAL Type 1AAL Type 1
Constant-bit-rate sourceConstant-bit-rate sourceSAR simply packs bits into cells SAR simply packs bits into cells
and unpacks them at destinationand unpacks them at destinationOne-octet header contains 3-bit One-octet header contains 3-bit
SC field to provide an 8-cell frame SC field to provide an 8-cell frame structurestructure
No CS PDU structure is defined No CS PDU structure is defined since CS sublayer primarily for since CS sublayer primarily for clocking and synchronizationclocking and synchronization
Chapter 5 ATM42
AAL Type 1AAL Type 1
Chapter 5 ATM43
AAL Type 2AAL Type 2
Intended for variable bit rate Intended for variable bit rate applications that generate bursty data applications that generate bursty data and demand low lossand demand low loss
Originally, connectionless (AAL4) or Originally, connectionless (AAL4) or connection (AAL3) oriented, now connection (AAL3) oriented, now combined into single format (AAL 3/4)combined into single format (AAL 3/4)
Provides comprehensive sequencing Provides comprehensive sequencing and error control mechanismsand error control mechanisms
AAL Type 3/4AAL Type 3/4
Intended for use with applications with Intended for use with applications with variable bit-rate service on multiple variable bit-rate service on multiple channels (multiplexing), or low bit rate, channels (multiplexing), or low bit rate, short-frame trafficshort-frame traffic
Chapter 5 ATM45
AAL 3/4AAL 3/4
Chapter 5 ATM46
AAL Type 5AAL Type 5
Streamlined transport for Streamlined transport for connection oriented protocolsconnection oriented protocols– Reduce protocol processing Reduce protocol processing
overheadoverhead– Reduce transmission overheadReduce transmission overhead– Ensure adaptability to existing Ensure adaptability to existing
transport protocolstransport protocols– primary function is segmentation primary function is segmentation
and reassembly of higher-level PDUsand reassembly of higher-level PDUs
Chapter 5 ATM48
AAL5AAL5
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