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These usually contain:
-Some form of header to identify them
-Sender's and receiver's IP adress
-How many data packets make up the whole message
-The identity number of each packet
The information allows:
-Router to route a packet across a network to its correct destination
-Data packets to be reassembled in their correct order according to the identity number at the receiving station

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* The screen is smaller than the one of a desktop computer.
* Require expensive dongles to access phone networks.
* Processors are not as powerful as those in desktops.
* Are more mobile than desktops .
* Touchpads and keyboards are not as easy to use as those in a desktop.

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Expensive to use without Wi-Fi
Displays are smaller (difficult to read websites)
Keyboard are smaller
Signal less likely to be stable
Very portable
Easier to use

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Significa red de amplea area
Are used where computers or networks are situated a long distance from each other geographically.
Because of the long distances between devices , WANs usually make use of public comunication networks.

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They usually have more powerful and and faster processors than other devices. They tend to have a more reliable internet connection and all web pages are accsesible because of the large screen size. Because of the separate parts, they are not portable and the dongles to access the phone network are very expensive.

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A typical lan consists of a group of computers and devices which are connnected to hubs or switches
·Advantages:
-Sharing resources
-Ease of communication between users
-A network administrator

·Disadvantages:
-Easier spread of viruses
-Printer queues developing
-Slower access to external networks
-Increased security risk

-If the main server breaks down, in

most cases network wil no longer work

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Internet is a worldwide collection of networks which allows users to:
1.send and recieve emails
2.chat online
3.transfer files from computer to computer
4.browse the worldwide web

Intranet is also used by many companies nowadays. Intranet is a network which belongs to an organization, created to meet the internal needs of the same.
Advantages:
1. safer as there are not viruses or external hacks
2. possible to prevent external links
3. offer better bandwith than internet
4. easier to send sensitive messages which will remain within the company

Extranets allow intranets to be extended outside the organisation but with the same advantages.

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º Hubs are hardware devices.
º  have number of devices or computers connected to them.
º Used to connect together a number of devices to form a LAN (a group of computers and devices which are connnected to hubs or switches) ;for example, a star network
º Main task:
Take any data packet (this is a group of data being transmitted) received at one of its ports and broadcast it to every computer in the network. Using a hub is not a very secure or efficient method of data distribution.

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A wireless transmitter(WAP) recieves information from a network via its connection(e.g. broadband connection).  This transmitter converts the recieved information into radio waves and then transmits them. A device recieves the radio waves via an installed wireless adapter which allows it to download the information from the data source.
Wi-fi offers much faster data transfers, better range and better security than Bluetooth. A Wi-Fi-enabled device can access the internet wirelessly at any ACCESS POINT(AP) up to 100m away.

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-node that acts as an entrance to another network
Networks have boundaries. If a network node needs to communicate with another network, it will do so via gateway
Alasia y Guttelsohn

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Switches distribute data packets.It checks the data packet received and works out its destination adress and sends the data to the appropiate computer only.This makes using a switch a more secure way of distributing data.

Each device has a MAC (media access control) which identifies the source of the data.

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Are devices that connect one LAN to another LAN that uses the same protocol.
figure 4.3.
Are used to communicate with other networks, such as internet.

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This consist in sending and recieving radio waves in a band of 79 different frequencies (channels).
Devices using Bluetooth automatically dectect and conect each other but it dont interfere with other divices.
When divices want to communicate, it picks one of the 79 channels at random.If the channel is already use it picks another.This process its call spread-spectrum frequency hopping.
To minimise interference,the communication pairs constantly change the channels they are using.
Bluetooth is useful:

when transferring data between two devices.

when the speed of data trasmission is not critical.

for low bandwidth application

Bluetooth also creates a secure wireless personal area network (wpan) based on key encription

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Cada dispositivo en internet tiene un INTERNET PROTOCOL ADDRESS (32-bit number) asignado por the ISP. Los unicos IP addresses que no cambian son los de los servidores web. Pueden ser utilizados en vez de copiar todo el URL. La diferencia entre IP and MAC addresses es que el primero da la localidad del dispositivo mientras que el segundo lo identifica. El IP puede cambiar pero el MAC address no.

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- Enable data packet to be routed between the different networks
- Would typically have an internet cable plugged into it and several cables connecting to computers and other devices on the LAN.
Its main function is to transmit internet and transmission protocols between two networks and also allow private networks to be connected together.
Routers inspect the data packet sent to it from any computer on any of the networks connected to it.

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Is a circuit board or card that is installed in a computer so that it can be connected to a network. It provides the computer with a dedicated, full-time connection to a network.

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They provide faster transfer of data than with wifi and can be more secure than wireless networks.

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means "modulator demodulator",(ie ,modulates) is a device that converts a computer's digital signalinto a analogue signal. (ie, demodulates) the reverse process, converts analogue signals from a telephone line into digital lines. to enable the computer to process the data. Modems are essentially used to allow computers to connect to de network.
Dial-up modem: operate at transmission speeds of about 60 kilobits per second
ºADSL: modems operate at up 100 megabits  per second. the "asyimmetric" actually means  that the modem is faster at downloading data that it is at uploading data.