Switches

1
Switches

• By Roger G. Clery
• CST331
• Roosevelt University
• 2002-2005

2
Effective Telecommunications Networks have these
attributes

• Connectivity
• Ease of addressing
• Interconnectivity
• Robustness
• Capacity

3
Network Terms

• A Node (a switching point)
• Trunks
• Stations
• Lines

4
Two Types of Switches

• Space Division (Circuit)
• Time Division (Bit or Packet)

5
All Switches have concentration

• Therefore all have potential for blockage

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A PBX should be NON-Blocking for Internal calls

• Every Station (phone) needs a line and an access
  port into the PBX
• The Required number of Trunks to the telephone
  companys office Central office (CO) is
  determined by a process called traffic
  engineering.
• Every PBX should have enough internal talk paths

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Calculating the talk paths required
8
Calculate the talk paths required

• TP Trunks (Lines-Trunks) / 2
• Why?

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Parts of a switch

• The switching network or fabric, that connects
  paths between input and output
• A Controller
• A Database
• Line Ports
• Trunk Ports
• Service Units Dial Tone, Ringing, Busy Tone
• Common Equipment Power Supply/Batteries, Clock,
  Administration/ Test Facilities.

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Some History

• No switching
• Manual -Operator
• Step by Step - Strowger
• Cross Bar
• Electronic
• Digital

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A fully connected circuit network with no switch
requires lots of connections

• Lines (Nodes x Nodes -1)/2

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Manual Switchboard

• The Bell System used Operators
• Independent Phone Companies developed the first
  automatic switched

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Step-By-Step
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Step-By-Step
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Cross Bar
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Electronic and Digital
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Switch Matrix Blocking
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Switch Matrix Non Blocking
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Digital Switch
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Digital Switch
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Tandem Switch (No Stations attached)
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New Packet Networks use Routing

• In a routing network the address is in every
  packet
• Internet IP routing
• Ethernet 802.11 ???
• ATM Not true routing
• Must create a virtual circuit
• Must have one path

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END
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