1. Chapter 18. Virtual-Circuit Networks: Frame Relay and ATM
18.3 ATM LANs
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2. Wide area network and switching methods
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3. Circuit switching
Create a real circuit (dedicated line) between source and destination
Physical layer technology
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4. Packet Switching: Datagram Approach
Mostly used in the network layer
Routing (selecting the best route for a packet) is performed at each router
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5. Packet Switching: Virtual Circuit Approach
Packets (frames) are switched along a pre-determined path from source to destination
Virtual circuit network has two addresses
Global address which is unique in the WAN
Virtual circuit identifier which is actually used for data transfer
VCI has switch scope; it is used between two switches
Each switch can use its own unique set of VCIs
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6. VCI Phases Two approaches for the VC setup
Permanent virtual circuit (PVC):
Switched virtual circuit (SVC): setup, data transfer, teardown
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7. Data Transfer Phase
All switches need to have a table entry for the virtual circuit
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8. Data Transfer using VCI
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9. SVC Setup: Request and Acknowledgment
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10. Frame Relay Frame Relay is a virtual circuit wide area network
VCIs in Frame Relay are called DLCIs(Data Link Connection Identifier)
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11. Frame Relay Features
Frame relay operates at a higher speed. It can easily be used instead of a mesh of T-1 or T-3 lines (1.544 Mbps or Mbps)
Frame relay operates just the physical and data link layers. It is good as a backbone to provide services to protocols that already have a network layer protocol, such as Internet
It allows bursty data
It allows a frame size of 9000 bytes accommodating all LAN frame sizes
It is less expensive than other traditional WANs
It has error detection at the data link layer only. There is no flow control pr error control
X.25  Leased Lines  Frame Relay
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12. Frame Relay vs. T-line Network
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13. Frame Relay vs. X.25 Network
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14. Frame Relay Layers
Frame relay operates only at the physical and data link layers
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15. Comparing Layers: X.25 & Frame Relay
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16. Frame Relay Frame
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17. Congestion Control Frame relay requires congestion control, because
Frame Relay does not have a network layer
No flow control at the data link layer
Frame Relay allows the user to transmit bursty data
Congestion avoidance
Two bits in the frame are used
BECN(Backward Explicit Congestion Notification)
FECN(Forward Explicit Congestion Notification)
Discard eligibility(DE):
Priority level of the frame for traffic control
Discarding frame to avoid the congestion or collapsing
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18. BECN
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19. FECN
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20. Four Cases of Congestion
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21. Extended Address: Three Address Formats
FRAD
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22. ATM Asynchronous Transfer Mode
ATM is the cell relay protocol designed by ATM forum and adopted by ITU-T
ATM uses asynchronous TDM
Cells are transmitted along virtual circuits
Design Goals
Large bandwidth and less susceptible to noise degradation
Interface with existing systems without lowering their effectiveness
Inexpensive implementation
Support the existing telecommunications hierarchies
Connection-oriented to ensure accurate and predictable delivery
Many functions are hardware implementable
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23. Multiplexing using Cells
The variety of packet sizes makes traffic unpredictable
A cell network uses the cell as the basic unit of data exchange
A cell is defined as a small, fixed sized block of information
Cells are interleaved so that non suffers a long delay
A cell network can handle real-time transmissions
Network operation is more efficient and cheaper
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24. Synchronous vs. Asynchronous TDM
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25. ATM Architecture UNI: user-to-network interface
NNI: network-to-network interface
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26. Virtual Connection
Connection between two endpoints is accomplished through
Transmission path (TP)
Virtual path (VP)
Virtual circuit (VC)
A virtual connection is defined by a pair of numbers: VPI and VCI
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27. VPI and VCI: Hierarchical Switching
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28. Identifiers and Cells
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29. VP Switch and VPC Switch
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30. ATM Layers
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31. ATM Layer and Headers
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32. Application Adaptation Layer (AAL)
Convert data from upper-layer into 48-byte data units for the ATM cells
AAL1 – constant bit rate (CBR) video and voice
AAL2 – variable bit rate (VBR) stream  low-bit-rate traffic an short-frame
traffic such as audio (ex: mobile phone)
AAL3/4 – connection-oriented/connectionless data
AAL5 – SEAL (Simple and Efficient Adaptation Layer)
No sequencing and error control mechanisms
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33. AAL1
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34. AAL2
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35. AAL3/4
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36. AAL5
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37. ATM LAN
ATM is mainly a wide-area network (WAN ATM); however, the technology can be adapted to local-area networks (ATM LANs). The high data rate of the technology has attracted the attention of designers who are looking for greater and greater speeds in LANs.
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38. Pure and Legacy ATM LAN
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39. Mixed Architecture ATM LAN
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40. LAN Emulation (LANE) Connectionless versus connection-oriented
Physical addresses versus virtual-circuit identifiers
Multicasting and broadcasting delivery
Interoperability
Client/Server model in a LANE
LANE Configuration Server (LECS), LANE Server (LES), LANE Client (LEC)
Broadcast/Unknown Server (BUS)
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41. Mixed Architecture Using LANE
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