Title: Network Characteristics
Course: Informàtica 4t ESO v2 ang > Section: Topic 6. Networks and Device Connections

Network Characteristics

Types of Networks

Computer networks can be classified according to different criteria. Below are some of them. Information has been simplified to make it clearer.

By scale, networks can be:

- LAN (Local Area Network). The connected devices are in a very delimited physical area: an office, a high school, a building, etc.
- WAN (Wide Area Network). The connected devices are in an extensive geographical area: a region, a continent...

By functional relationship or architecture, networks can be:

- Client-Server. The function of the server computer is to offer a service to any client computer that seeks it: email, web page, remote file storage, printer, etc.

Client-server relationship. Source: Wikipedia

- Peer to Peer (P2P): the connected computers behave as clients and servers simultaneously and in a two-way fashion and there is no server computer involved. This is the communication mode that file sharing networks like Ares and eMule establish, or communications with VoIP phone apps like Skype and instant messaging.

Network Topology

Network topology is the form of physical and logical connection between different computers. The physical topology determines the spatial distribution and connections with communication cables of the different computers. There are diverse configurations but we will basically focus on two:
- Bus Topology. Bus topology is the simplest kind because all the devices are connected in parallel to the same line with a single cable.
Bus Topology. Source: Kioskea .
- Star topology. The computers are connected to a central node called a hub, taking the form of a star.
A hub is an electronic device that connects computers via cables and specific connectors . This topology allows for the creation of different networks which in turn are interconnected with hubs.
Star topology. Source: Kioskea.

Logical topology determines the form in which data is transmitted between devices. There are different types, but the most common in local networks is Ethernet .

Means of transmission

Transmission lines are the key element for transporting information between different nodes. In a data transmission process, data can travel via different technologies, adapting to the maximum allowed speed in each section. It is also necessary to consider wireless transmission, but we will look at that later on.

- Coaxial cable consists of two concentric conductor cables. The central cable is surrounded by an insulating layer, covered by a second conductor in the form of mesh. The central cable transports the data and the mesh reduces the effect of external interference. It allows for data transmission speeds of up to 10 Mb/s.

Coaxial cable. Source: Wikipedia Viquipèdia

- Twisted pair cabling consists of two insulated copper cables twisted together to reduce the effect of interference. It allows for data transmission speeds of up to 1 Gb/s.

Twisted pair. Source: Wikipedia.

Fibre optics consists of layers of plastic and glass material. It transports digital data via high-speed light pulses and is insensitive to electromagnetic interference. It can support higher transmission speeds than the copper cable system and has vastly more capacity.  It allows for data transmission speeds of up to 10 Gb/s.

Fibre optics. Source: Eroski-Consumer

Fibre optics usually forms part of the facilities of data service and phone companies, as well as large corporations and public administrations. Local networks in office buildings, universities, businesses and so on often use twisted pair cabling. Fibre optics is part of the external infrastructure and when it reaches the local network entry point it adapts to the copper cabling system.

Transfer speed

The transfer speed or bandwidth of a digital transmission system is measured by number of bits per second (bps or bit/s). There are different multiples for very high transfer speeds:

Kbps or kb/s - kilobits per second

Mbps or Mb/s - megabits per second

Gbps or Gb/s - gigabits per second

You can change the unit of measurement to bytes per unit of time by dividing by 8. However, it is most common to express speed in bits per unit of time.

The physical elements of a local network

Building a network system requires different physical elements which can vary in accordance with the network configuration. Below are the ones commonly used in domestic networks, small offices, schools, etc.

- Ethernet electrical interface is the network interface card that all computers and peripherals must have to connect to the internet. Laptop computers have it integrated in the motherboard. These boards are supplied by the manufacturer with an internal ID code that is essential to identifying each computer in the network in such a way that there cannot be two boards with the same code or address.  This is called MAC (Media Access Control).

- The hub is where the different computers or Ethernet devices of a single network segment or sector are connected. The electronic circuits included usually perform very simple actions.

Hub. Source: Wikipedia

- The switch is an electronic device where computers or different segments are connected to form a network that is much more extensive, with greater capacity and efficiency than a hub. It optimises data traffic in the network in an intelligent fashion, adapting to the maximum standard speeds of each connected device. It can have different layouts depending on the network infrastructure.

 | *

Switch. Source: Wikipedia

- The router is the device that connects a network and its devices with the internet. The router manages internet service requests from different computers in the network and returns the sought information. The router must be adapted to the external connection technology, whether fibre optics or phone cable with ADSL technology. Domestic routers have a connection to the ADSL line, a switch and a wifi access point.

* Domestic router. Source: Wikipedia. | * Router rack. Source: Wikipedia

- The RJ45 connector enables the physical connection between a device and the cable.

RJ45 interface card | RJ45 interface cable

Source Wikipedia