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Chapter 20
Asynchronous Transfer Mode
(ATM) |
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Fixed size cell (53 Bytes) |
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Telephony Standard – Intended as a universal,
shared bandwidth service |
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Typically 155 Mbit/sec (OC-3, STS-3) user
interface with low latency |
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Virtual Path Identifier (VPI) |
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High-level route identifier |
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Virtual Channel Identifier (VCI) |
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Sub-route identifier |
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Connections |
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PVC
Permanent Virtual Connection |
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SVC (normal)
Switched Virtual
Connection |
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Fast |
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Simple HW |
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Fixed cell size |
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Flexible BW sharing |
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Small cells |
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Low latency |
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User Network Interface (UNI) |
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Generic Flow Control: Not currently in use |
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VPI/VCI: Identify the next destination of the
cell (which switch) |
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Payload Type: Data/control, congestion,
terminating |
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Congestion Loss Priority: High/low, determines
QoS |
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Header Error Control: Weak CRC on header only |
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Network-to-Network Interface (NNI) |
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Constant bit rate traffic |
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i.e. |
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64 Kb Telephony |
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Variable bit rate traffic |
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i.e. |
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Compressed audio |
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Variable Frame length |
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Error control |
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Variable delay |
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Efficient LAN emulation |
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Control info in
the last cell |
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ATM |
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Supports real-time |
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Offers QoS support |
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Good as a WAN |
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Gigabit Ethernet |
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QoS add-on (802.1Q) supports priority delivery |
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Low cost |
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Replaced ATM in LAN backbones, also used for
short haul WAN connectivity |
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Notes