ATM and Switches

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Lecture 14

• ATM and Switches
• Homework 3.21-38
• Next Class Selected Homework Solutions

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Cell Switching (ATM)

• Fixed Size Cells-53 bytes
• 48 bytes of data
• 5 bytes of header
• Address formats-Network Service Access Point
  (NSAP) or E.164 formats-Not the same as ethernet
  MAC addresses.

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ATM and Telephone Traffic

• 8 bit sampling at 8KHz
• 125msec/ 1 Byte sample
• Time to accumulate a N byte cell is N125 msec
• 48 byte cell takes 6 msec

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ATM Header

• Generic Flow Control
• Virtual Circuit Identifier
• VPI Virtual Path Identifier
• VCI-Virtual Channel Identifier

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VPI-Hierarchy in ATM
24 bits virtual circuit identifier for UNI
Interface (28 for NNI) Virtual Path Identifier8
Most Significant Bits (MSBs) Virtual Circuit
Identifier16 bits Purpose To minimize switching
tables in the public network
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ATM LAN Emulation (LANE)

• Purpose to make the ATM network operate like
  ethernet
• Broadcast
• Multicast
• High bandwidthe.g. 622 Mbps
• QOS

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An ATM LAN backbone
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LANE Protocol Stack
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LANE Servers

• LECS-LANE Configuration Server
• LESLAN Emulation Server
• BUSBroadcast and Unknown Server

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LANE Servers

• LEConfigurationS-
• LANE clients set up VC to LECS
• Client provides ATM address to LES
• LECS
• identifies type of LAN being emulated
• Identifies maximum packet size
• ATM address of LES

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Lane Servers

• LES
• Client sets up VC to LES
• Registers MAC and ATM addresses
• LES provides ATM address of BUS

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LANE SERVERS

• BUS
• LANE Clients (LECs) set up a point-to-point VC to
  the Bus
• Bus maintains a single point-to-multipoint VC to
  all registered clients-

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LANE Schematic
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The LEC Viewpoint

• Initially,
• VCs to BUS and LES
• Does not know MAC or ATM address of other LECs
• Sends first packet to BUS for broadcast
• Sends address resolution request to LES which
  returns ATM address for specified MAC address

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The LEC Viewpoint

• Sets up VC to destination for all subsequent
  frames
• Closes unused VCs

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Switch Design Goals

• Throughput
• Scalability
• Cost
• Metrics e.g.
• per unit cost
• Cost/port with a given throughput

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Throughput

• Concerns
• Bits/second
• Packets/second
• Throughput depends on traffic pattern
• Contention

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Scalability

• Cost
• Physical Limits

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Switch Terminology
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Port Functions in a VC network

• Input port
• Determine output port for a given VCI
• Output port
• Remaps VCI for the outbound link
• Buffering

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Input Buffering Head-of-line blocking
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Cross-bar Switch
Every input connected to every output Complexity
grows as n2 We dont need this flexibility most
of the time
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8 X 4 Knockout Concentrator
Section
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Output buffering for a knock-out switch
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Shared Media Switches

• Better buffer utilization
• Buses must run n-times faster than line
  speed-wide buffers
• Control electronics must really be fast

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Self-routing fabricsEight input banyan network
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Packet Routing through a banyan network
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8 X 8 Batcher Network
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Routing Packets through a Batcher Network
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Sunshine Network