Telephone System Overview

 This slide presentation is a HTML version of a lesson plan originally built in Macromedia for CDA-2502 by L. Scott Freudenthal. It is intended to be presented in a classroom environment with the accompaniment of a lecturer (i.e. Scott) and a ~52 inch monitor (thus the large font selections).  

Why are we studying the phone system?

 Why are we studying the phone system?

The Phone system is the largest network in the World with over 170 million terminals (phones).

 Three major components:

  Central Switches



  Implementation media:

  Twisted Pair               Fiber optics

  Microwave                 Satellite links

Access and Control

  Access on demand

  Centralized control

Implementation Topologies:










What is a PBX? 

Switching Device, may be analog or digital.

Reduces cables to Central office switch.
Internal calls handled internally.

Reduces dependence on phone company.


Digital PBXs

  Faster than Analog.

  Higher data rates.
   More Features.
    - Call Back
    - Call Fwd
    - Least cost routing.

Digital PBXs

"Codec" - Coder-Decoder.
Digitized voice on digital phones.
May use analog devices witha digital switch.

Digital PBXs

Bandwidth for Voice call

Analog call requires 4kHz bandwidth, spaced by 4kHz.

Digital call requires 64kbps.


Bandwidth for Voice call

Codec digitizes at 8kHZ.

8 bits used to represent each sample.

8,000 samples x 8 bits/sample = 64,000 bps

Phone Systems

Integrated Services
Digital Network


Integrated Services

Digital Network

-End to end digital network




        Two types:

        1) PRI - Primary Rate Interface.

        2) BRI - Basic Rate Interface.


Primary Rate Interface.

  Interconnects switches with ISDN link.

   Typically a T1 line.

   23B + D


Basic Rate Interface.

  Connects ISDN terminals (phones) to the switch.

  Typically a twisted pair.

  2B + D


        What is 2B + D?


        What is 2B + D?

         2 - 64,000 bps clear channel

         1 - 16,000 bps control channel 



  Possible Applications
  Simultaneous Voice and Data Calls
  Automatic Call Distribution
  Automatic Call Return
  Call Screening
  Selective Messages
  Selective Forwarding
  Caller Authorization
  Automatic Database access / Voice Response

Phone Systems 


Data over phone systems 

Analog phone lines: must convert digital data (computer) into analog data.

Data over phone systems 

Data over phone systems 

Data over phone systems 
Speeds from 300 up to 56,000 bps with compression over analog phone line.

Data over digital phone lines 

Data over digital phone lines 

Using switched digital end to end phone line, up to 64,000 bps.

Modem not required, data access (DSU) can be built into the phone.

Carrier data services 

Dedicated analog circuits.

Up to 19,200 bps

Higher throughput with compression

Carrier data services 

Dedicated digital circuits.

DS-0 : 64 kbps, usable 56
DS-1 : (T1) 1.544 Mbps (24 x DS-0)
DS-2 : 6.312 Mbps (3 x DS-1)
DS-3 : 44.736 Mbps (7 x DS-2)
DS-4 : 274.176 Mbps (6 x DS-3)

Carrier data services 

Variations, other data offerings:

Fractional T1
Frame Relay
Native LAN Link

Phone Systems 

 FCCJ's Phone System

Northern Telecom Meridian

One switch per Campus
"Snowflake" topology
ISDN to every desk

Phone Systems 


Phone Systems 


Phone Systems