Switching

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Jaringan Komputer
Jaringan Komputer

Public Switched Telephone Network (PSTN)

Traffic over a major “highway” system. PSTN constructed by AT&T’s research division, Bell Labs, by standardized transfer methods and central office switches.

Public Switched Telephone Network (PSTN)
Public Switched Telephone Network (PSTN)

Switching

(definition) “The establishment on demand, of an individual connection from a desired inlet to a desired outlet within a set of inlets and outlets for as long as is required for the transfer of information.”

“The establishment on demand, of an individual connection from a desired inlet to a desired outlet within a set of inlets and outlets for as long as is required for the transfer of information.”

(definition) What goes in, comes out, for as long as desired from within the network until one party hangs up.

Intro to Switching

A switch routes a call based on a number system

e.g13023696923
 access code   
  area code  
   exchange code 
    subscriber code
Intro to Switching
Intro to Switching

Switching System

Switching System
Switching System

Essential Switch Functions

  • Interconnection
  • Control
  • Alerting
  • Attending
  • Information receiving
  • Information sending
  • Busy Testing
  • Supervising

Functions of Switching Systems

  1. Signaling
    • monitor line activity
    • send incoming information to control function
    • send control signals to outgoing lines
  2. Control
    • process signaling and set-up/knock down connections
  3. Switching
    • make connections between input and output lines
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Basic Switch Requirements

A switch must be able to connect any incoming call to one of a multitude of outgoing calls. Switch must have the ability to hold and terminate calls. A switch has to prevent new calls from intruding into circuits already in use.

General Switch Requirements

  1. Speed of call setup should be kept short relative to the call holding time
  2. Grade of service should be high
    • .99 overall
    • .95 busy-hour
  3. HIGH availability!

Switching Methods

  1. Connectivity
    • Full: any input to any output
  2. Blocking
    • Blocking: Possibility exists that call setup may fail due to insufficient switching resources
    • Non-blocking: If any input Ij and output Oj are free, they can be connected

Time Division Switching

The Time mapping of inputs and outputs:

Time Division Switching
Time Division Switching

Space Division Switching

Spatial mapping of inputs and outputs. Used primarily in analog switching systems.

Space Division Switching
Space Division Switching

Space-Time-Space Switching

Space-Time-Space Switching
Space-Time-Space Switching

Single Stage Switches

  • Crosspoint switches
    • Complex – many crosspoints ( i × j )
    • Poor utilization of crosspoints
    • Not fault tolerant
Single Stage Switches
Single Stage Switches

Multiple Stage Switches

Input connected to output via two or more smaller switches. Crosspoints shared by several possible connections (potential for blocking). Possible to provide multiple paths between any 2 ports.

Three Stage Switch Matrix (Multiple Stage Switch example)

Three Stage Switch Matrix (Multiple Stage Switch example)
Three Stage Switch Matrix (Multiple Stage Switch example)

Reducing Cross-point Complexity

  • Increase number of stages
  • Allow some blocking
  • Switch in more than one dimension
Reducing Cross-point Complexity
Reducing Cross-point Complexity

Number of Cross-points Non-blocking Switch

Nbr of Lines3-Stage1-Stage
1287,68016,256
51263,488261,635
2K516,0964.2M
8K4.2M67M
32K33M1B
128K268M17B
Number of Cross-points Non-blocking Switch
Number of Cross-points Non-blocking Switch

Digital Switching

  • Most of the switching in US is digital, why?
    • Transmission is digital
    • Maintenance of signal quality
    • Leverage improvements in density of Integrated Circuits
    • Advanced features and services through software
    • Integration of voice/data services
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The End of The Word

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