Network Structure

In this course, our target is understand the meaning of network infrastructure, differentiate between core and access networks, understanding the meaning of ‘bearer’, and which bearers are used in different parts of the network and ‘node’, and the network configurations to interconnect nodes

Network Infrastructure
• Lines
• Equipment to interconnect the lines

Network Transmission Media
• Copper wire
• Radio transmission lines
• Silicon fibre strands

Types of Copper Wire Lines
• Overhead copper wire
• Twisted pair cable
• Polyquad cable
• Coaxial Cable

Overhead Copper Wire Lines
• Wires suspended from poles and masts
• Wires have to be insulated from one another
• Wires have to be insulated from earth
• Wires have to form a complete end-to-end circuit

Twisted Pair Cable
• Same characteristics as overhead wires
• Less unsightly
• More circuits per route

Polyquad Cable
• Can be used for low frequency radio signals
• Can be used for low rate digital transmission

Coaxial Cable
• Better direct current characteristics than overhead wires or twisted pair cable
• Can be used to transmit high frequency radio signals

Types of Radio Lines
• Microwave - line of sight terrestrial
• Microwave - earth satellite

Microwave Radio - Line of Sight
• Can be affected by adverse weather
• May be subjected to physical obstruction
• Could be harmful to people and/or animals

Fibre Optic Technology
• Uses Light Amplification by Stimulated Emission of Radiation (LASER)
• Precursor was clear atmosphere line of sight
• Then wave guidance
• Technology is still being refined after more than 30 years

Nodes
• Used to:
** Interconnect links or bearers
** Derive communications channels
** Enhance network signals
** Produce, accept, or pass signals

Network Topology
• Fully Interconnected
• Bus
• Ring
• Star
• Interconnected Star
• Interconnected Star Plus Ring
• Through Connected Link
• The Tandem Principle
• Hierarchical Structure

Bearers
• Consist of:
** Copper wire cables
** Fibre-optic cables
** Radio transmission links
• Serve:
** User access networks
** Wide area networks

User Access Networks
• Traditionally a copper wire pair connecting users’ premises to the public network
Often referred to as:
** the local loop
** the last kilometre or mile
** the local distribution network

Transmission Bearer Networks
• Used to link:
** telephone exchanges
** packet switching exchanges
** frame relay exchanges etc
• Analogue networks used coaxial cable and microwave links
• Digital networks use fibre-optic cable
• Used to provide transmission infrastructure