Introduction to Communications and Networks ECI-2-830

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Introduction to Communications and
NetworksECI-2-830

• Dr. Vincent Siyau

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Communication System Model
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A Simple Telephone
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A More Realistic Telephone
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Signalling in Telephone Network
LE Local Exchange (i.e., Central Office)
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Dialling in Telephone Network
Dual-tone Multi-frequency (DTMF) (Touch-tone
dialing )
Rotary dialling (Pulse dialling)
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Why DTMF ?

• allows dialling numbers via microphone
• allows in-band signalling
• allows end-to-end signalling between two
  telephones

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Telephone Network
Point-to-point telephone connection
connection
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Telephone Network
Star network

• More efficient resource utilisation
• Scalable
• Allows hierarchical routing

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Telephone Network Routing Circuit Switching
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Routing in Telephone Network
LATA Local access transport areas

• Hierarchical routing paradigm

• Intra-LATA services are offered by common
  carriers (Telephone Companies) within a LATA.
  Handled by local exchange carrier (LEC).
• Inter-LATA services between LATAs are handled by
  interexchange carriers (IXCs) or (long distance
  companies).

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National/International Routing
POP Points of Presence A switching office that
handles carriers exchange LEC IXC
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Voice Communication Service Offerings

• Wide Area Telecommunication Services (WATS)
• non-standard billing for businesses with high
  call volume
• Inward WATS
• business agrees to pay for all INCOMING
  long-distance calls from certain areas (e.g.,
  0800, 0870)
• Foreign exchange
• phone numbers in distant cities where your
  customers can call your company at local charges
• Leased lines
• permanent point-to-point connection
• annual rent

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Customer Premises Equipment

• Centrex
• Central Office is acting as the customers
  exchange or switch
• Private Branch Exchange (PBX)
• Acts as a mini-central office for a company,
  dedicated to customer who owns it (not owned by
  Central-Office).

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Customer Premises Equipment
Centrex service

• Very Dependable Reliable -
• because services are maintained by Central-office
  (full-time maintenance troubleshooting staff).

• Hence expensive regular fees for each month

• Inflexible additional lines can only be fitted
  by central-office.
• Inefficient Calls within company are routed
  all the way through Central Office and back.

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Customer Premises Equipment
Private Branch Exchange (PBX)

• Suitable for large business provide thousands
  of lines.

• Internal calls are free using ext. assigned to
  each one.

• Does not need local loop for each employee. Only
  a few local loops are needed for external call.

• VERY flexible can add/remove a line anytime
• Efficient internal calls are routed within PBX
  without going through Central-office, hence
  provide quick access.
• Maintenance is CRUCIAL need a team to always
  maintain it.

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Regulatory Bodies
OFCOM(Office of Communications)
Radio Authority
ITC(Independent Television Commission)
Radio Communications Agency
OFTEL (Office of Telecommunications)
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Regulatory Bodies

• OFTEL's functions
• Promoting the interests of consumers.
• Maintaining and promoting effective competition.
• Making sure that telecommunications services are
  provided in the UK to meet all reasonable
  demands, including

• emergency services
• public call boxes
• directory information and
• services in rural areas

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Recommended reading

• Beyda, W.J. Basic Data Communications
• Chapter-2, Prentice-Hall, 1989.
• Forouzan, B. Data Communications and
  Networking 3rd Ed., Chp8.
• http//www.ofcom.org.uk/

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Tutorial 1   Describe the signaling procedure for
making a call through telephone network. List
three signals that your phone sends to local
exchange   List three signals that local exchange
sends to your phone   Describe how rotary dialing
and touch-tone dialing is made. What is a mesh
network?   What is a star network?   What is
local loop and Central Office?  
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Why Telephone network uses star
network? Describe how your local call is routed.
  Describe how your international call is
routed. Briefly describe two types of Customer
Premises Equipment Describe the advantages and
disadvantages of using a Centrex
Service?   Describe the advantages and
disadvantages of using a private branch exchange
(PBX)?