lect1. - 01/06/05
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CDA 6505 Network Architecture and Client/Server Computing. Lecture 5 Asynchronous Transfer Mode (ATM) by Zornitza Genova Prodanoff. Lect1..ppt - 01/06/05. Outline. ATM Protocol Architecture Logical connections ATM Cells Service categories ATM Adaptation Layer (AAL). ZGP00 2. - PowerPoint PPT PresentationTRANSCRIPT
Lect1..ppt - 01/06/05
CDA 6505 Network Architecture
and Client/Server Computing
Lecture 5
Asynchronous Transfer Mode(ATM)
byZornitza Genova Prodanoff
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Outline
•ATM Protocol Architecture•Logical connections•ATM Cells•Service categories•ATM Adaptation Layer (AAL)
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ATM Protocol Architecture
• Fixed-size packets called cells• Streamlined: minimal error and flow control• 2 protocol layers relate to ATM functions:
– Common layer providing packet transfers– Service dependent ATM adaptation layer (AAL)
• AAL maps other protocols to ATM
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Protocol Model has 3 planes
• User• Control• management
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Logical 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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Advantages of Virtual Paths
• Simplified network architecture• Increased network performance and reliability• Reduced processing and short connection setup
time• Enhanced network services
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VCC Uses
• Between end users• Between an end user and a network entity• Between 2 network entities
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VPC/VCC Characteristics
• Quality of Service (QoS)• Switched and semi-permanent virtual channel
connections• Cell sequence integrity• Traffic parameter negotiation and usage
monitoring• (VPC only) virtual channel identifier restriction
within a VPC
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Control 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 Signaling
• 3 methods for VPCs– Semi-permanent– Customer controlled– Network controlled
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ATM Cells
• Fixed size• 5-octet header• 48-octet information field• Small cells reduce delay for high-priority cells• Fixed size facilitate switching in hardware
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Header Format
• Generic flow control• Virtual path identifier (VPI)• Virtual channel identifier (VCI)• Payload type• Cell loss priority• Header error control
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Generic 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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Header 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 header• 2 modes:
– error detection– Error correction
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Service 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)
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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
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Applications of AAL and ATM
• Circuit emulation (e.g., T-1 synchronous TDM circuits)
• VBR voice and video• General data services• IP over ATM• Multiprotocol encapsulation over ATM (MPOA)• LAN emulation (LANE)
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Applications of AAL and ATM
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AAL 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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AAL Type 1
• Constant-bit-rate source• SAR simply packs bits into cells and unpacks
them at destination• One-octet header contains 3-bit SC field to
provide an 8-cell frame structure• No CS PDU since CS sublayer primarily for
clocking and synchronization
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AAL Type 3/4
• May be connectionless or connection oriented• May be message mode or streaming mode
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AAL 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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