Title: Network characteristics
Course: Appdate yourself 4t ESO (in English) - Curs 2016/17 > Section: Topic 8 Networks

Network characteristics

Types of networks

Computer networks can be classified according to different criteria.  Below you will see a few examples which have been simplified in order to ensure maximum comprehension.

Depending on the scale, networks can be:

- LAN (Local Area Network) Connected devices are in a limited space:  an office, a school, a building...
- WAN (Wide Area Network) Connected devices are in a large geographical area: a region, a country, a continent, ...

Depending on either the functional or architectural relationship, networks can be:

- Client - server.  The computer server's function is to give a service to any other client computer that requests it: an e-mail account, a web page, a remote filing system, a printer, etc...

Client server relationship. Source: Wikipedia

- Peer to Peer (P2P) Each host can simultaneously act as both a client and a server (unlike centralized servers of the client-server model) because each has equivalent responsibilities and status. This is the mode in which sharing networks exchange files, like 'eMule', 'Utorrent' or in the case of IP telephone lines, Skype of instant messaging.

Network topologies

The network topology is the physical and logical way in which different computers are connected. The physical topology determines the spatial distribution and connection of cables communicating from different computers. There are various configurations available however, we will concentrate on two of them:

- Bus topology: This is the most simple, being that all the devices are connected parallelly in the same row by means of one cable.

Bus topology. Source: http//www.computerhope.com

- Star topology: Computers are connected to a central node called concentrator or hub, creating the shape of a star.

Star topology. Source: http//www.computerhope.com.

A concentrator is an electronic device which is connected to other computers by means of cable and other specific connectors.  This topology allows the creation of different networks which in turn are interconnected with hubs.

The logical topology determines the way in which data is transmitted amongst and between devices. There are many different types but the most common one used in local networks is Ethernet.

Means of transmission

The transmission lines are key elements in transporting information amongst and between different nodes.  During the process of data transmission, information travels through the different tecnologies adapting its path along the way depending on the maximum speed permitted.  Wireless communication is also a possibility and will be mentioned in further units.

Coaxial Cable is made up of two concentric conductor cables.The cable core or inner cable is surrounded by a tubular insulating layer, which is surrounded by a tubular conducting shield. Many coaxial cables also have an insulating outer sheath or jacket.The cable carries the data and the sheath acts as shielding to reduce the effect of external interference. It allows the transfer of data at a speed of up to 10 Mb/s

Coaxial cable. Source: Wikipedia

- Twisted pair cables are made up of two isolated copper wires twisted together in order to avoid any interference.  They allow the transfer of data up to a speed of 1 Gb/s

Twisted pair. Source: Wikipedia

- Optical fiber is made up of layers of both plastic and glass. It carries digital data via a series of high velocity light pulses which are insensitive to any electromagnetic interference. It can support transfer speeds higher than the copper cable system and has a lot more capacity.  Data transfer can take place at speeds of up to 10 Gb/s

Optical fiber. Source: http://www.hill2dot0.com/wiki/images/f/fb/Optical_Fiber.jpg

Optical fibers are normally used in installations in data or telephone companies and they tend to be large public and administrative corporations. Local networks in office buildings, universities or companies tend to use the twisted pair cables. Optical fiber is generally part of a large external infrastructure and to reach the entry point of the LAN cable system, it adapts to the copper cable system.

Transmission speed

The transfer rate or bandwidth in a digital transmission system is measured by the number of bits per second (bps or bit / s). To transfer very high rates, there are different modules:

kbps o kb/s - kilobytes per second

Mbps o Mb/s - megabytes per second

Gbps o Gb/s - gigabytes per second

You can change the unit of measure in bytes per unit time dividing by 8. Even so, it is more common to express the speed in bits per unit time.

Physical elements of a local network

Building a network system requires several physical elements that may vary depending on network settings. Here are the common forms used in home networks, small offices, schools, etc...

- The electronic interface Ethernet is the electronic card that must be included in any computer or peripheral in order to be able to connect to a network. Laptops have this card integrated into the motherboard. Each motherboard has a factory code identifying each computer in the network.  In this way, no two computers can have the same code or address.  This control is referred to as MAC (Media Access Control
- The concentrator or hub is where multiple computers or devices are connected to the same Ethernet network segment or sector. ncorporating electronic circuits are usually very simple actions.

Concentrator. Source: Wikipedia

- The switch is an electronic device which connects computers or network segments to form a concentrator with much more capacity and efficiency.
- It optimizes data traffic network intelligently, adapting the standard speeds for each connected device.
- Depending on the network infrastructure, different models can be found.

 | *

Switch. Source: Wikipedia

- The router is the device that connects the network and its devices to the Internet. The router handles Internet service requests from different computers on the network and returns the requested information. The router must be adapted to the external connection technology, either fiber optic cable or telephone line with ADSL technology.
- Domestic routers bring connection for ADSL which is comprised of a switch and a WiFi access point.

* Domestic router. Source: Wikipedia. | * Rack router. Source: Wikipedia

- The RJ-45 connector allows the physical connection between a device and cable.

RJ-45 Network Card | Network cable with RJ-45 connectors

Source: Viquipèdia