chapter 2 protocols and the tcp/ip suite 1 chapter 5 asynchronous transfer mode (atm)
TRANSCRIPT
Chapter 2 Protocols and the TCP/IP Suite1
Chapter 5Chapter 5
Asynchronous Transfer Mode(ATM)
Chapter 2 Protocols and the TCP/IP Suite2
Introduction Introduction
ATM Protocol ArchitectureLogical connectionsATM CellsService categoriesATM Adaptation Layer (AAL)
Chapter 2 Protocols and the TCP/IP Suite3
ATM Protocol ArchitectureATM Protocol Architecture
Fixed-size packets called cellsStreamlined: minimal error and flow
control2 protocol layers relate to ATM functions:
– Common layer providing packet transfers– Service dependent ATM adaptation layer
(AAL)AAL maps other protocols to ATM
Chapter 2 Protocols and the TCP/IP Suite4
Protocol Model has 3 planesProtocol Model has 3 planes
UserControlmanagement
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Figure 5.1Figure 5.1
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Logical ConnectionsLogical Connections
VCC (Virtual Channel Connection): a logical connection analogous to virtual circuit in X.25
VPC (Virtual Path Connection): a bundle of VCCs with same endpoints
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Figure 5.2Figure 5.2
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Advantages of Virtual PathsAdvantages of Virtual Paths
Simplified network architectureIncreased network performance and
reliabilityReduced processing and short connection
setup timeEnhanced network services
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Table 5.1Table 5.1
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VCC UsesVCC Uses
Between end usersBetween an end user and a network entityBetween 2 network entities
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Figure 5.3Figure 5.3
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VPC/VCC CharacteristicsVPC/VCC Characteristics
Quality of Service (QoS)Switched and semi-permanent virtual
channel connectionsCell sequence integrityTraffic parameter negotiation and usage
monitoring(VPC only) virtual channel identifier
restriction within a VPC
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Control SignalingControl Signaling
A mechanism to establish and release VPCs and VCCs
4 methods for VCCs:– Semi-permanent VCCs– Meta-signaling channel– User-to-network signaling virtual channel– User-to-user signaling virtual channel
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Control SignalingControl Signaling
3 methods for VPCs– Semi-permanent– Customer controlled– Network controlled
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ATM CellsATM Cells
Fixed size5-octet header48-octet information fieldSmall cells reduce delay for high-priority
cellsFixed size facilitate switching in hardware
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Header FormatHeader Format
Generic flow controlVirtual path identifier (VPI)Virtual channel identifier (VCI)Payload typeCell loss priorityHeader error control
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Figure 5.4Figure 5.4
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Generic Flow ControlGeneric Flow Control
Control traffic flow at user-network interface (UNI) to alleviate short-term overload conditions
When GFC enabled at UNI, 2 procedures used:– Uncontrolled transmission– Controlled transmission
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Table 5.3Table 5.3
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Header Error ControlHeader Error Control
8-bit field calculated based on remaining 32 bits of header
error detection in some cases, error correction of single-
bit errors in header2 modes:
– error detection– Error correction
Chapter 2 Protocols and the TCP/IP Suite21
Figure 5.5Figure 5.5
Chapter 2 Protocols and the TCP/IP Suite22
Figure 5.6Figure 5.6
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Figure 5.7Figure 5.7
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Service CategoriesService Categories
Real-time service– Constant bit rate (CBR)– Real-time variable bit rate (rt-VBR)
Non-real-time service– Non-real-time variable bit rate (nrt-VBR)– Available bit rate (ABR)– Unspecified bit rate (UBR)– Guaranteed frame rate (GFR)
Chapter 2 Protocols and the TCP/IP Suite25
Figure 5.8Figure 5.8
Chapter 2 Protocols and the TCP/IP Suite26
ATM Adaptation Layer (ATM)ATM Adaptation Layer (ATM)
Support non-ATM protocols– e.g., PCM voice, LAPF
AAL Services– Handle transmission errors– Segmentation/reassembly (SAR)– Handle lost and misinserted cell conditions– Flow control and timing control
Chapter 2 Protocols and the TCP/IP Suite27
Applications of AAL and ATMApplications of AAL and ATM
Circuit emulation (e.g., T-1 synchronous TDM circuits)
VBR voice and videoGeneral data servicesIP over ATMMultiprotocol encapsulation over ATM
(MPOA)LAN emulation (LANE)
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AAL ProtocolsAAL Protocols
AAL layer has 2 sublayers:– Convergence Sublayer (CS)
Supports specific applications using AAL
– Segmentation and Reassembly Layer (SAR)Packages data from CS into cells and unpacks at
other end
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Figure 5.9Figure 5.9
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Figure 5.10Figure 5.10
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AAL Type 1AAL Type 1
Constant-bit-rate sourceSAR simply packs bits into cells and
unpacks them at destinationOne-octet header contains 3-bit SC field to
provide an 8-cell frame structureNo CS PDU since CS sublayer primarily
for clocking and synchronization
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AAL Type 3/4AAL Type 3/4
May be connectionless or connection oriented
May be message mode or streaming mode
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Figure 5.11Figure 5.11
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Figure 5.12Figure 5.12
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AAL Type 5AAL Type 5
Streamlined transport for connection oriented protocols– Reduce protocol processing overhead– Reduce transmission overhead– Ensure adaptability to existing transport
protocols
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Figure 5.13Figure 5.13