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Flashcards in Networks Deck (74):
1

Computer Network

When two or more computers are connected together through a communication medium, either physically using a cable or wirelessly.

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What is the purpose of a Computer Network?

To exchange information and data and to share network resources like printers.

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Server

A powerful computer that provides services to the other computers on the net work

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Client

Computers that use the service of a server. Less powerful than the server.

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Communication Medium

This describer how the computers are connected and provides a communication channel along which data can be sent.
Guided Medium: Cables- fibre optic, coaxial, CAT6
Unguided Medium: Wireless.

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Network Adaptor

Can provide a wired and wireless connectivity.
Commonly referred to as a NIC- Network Interface Card

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Protocols

A formal set or written rules that control the communication process. There are different protocols for different purposes: mail, file transfer.

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TCP

Transmission Control Protocol
Breaks data into small units called packets to be sent across the internet, puts packets in correct order at receiving end.

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IP

Internet Protocol
Provides an addressing scheme that is used to identify individual computers/networks on the internet.

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Mail protocols

SMTP
Simple Mail Transfer Protocol
Sends mail
POP3
Post office protocol
Receiving mail

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HTTP

Hypertext Transfer Protocol
Allows you to send website pages

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HTTPS

Secure protocol
Used for secure connections such as online banking

13

FTP

File Transfer Protocol
Used to copy files from one computer to another over a network.

14

Advantages of a Computer Network

• Sharing devices such as printers saves money.
• Files can easily be shared between users.
• Site (software) licences are likely to be cheaper than buying several standalone licences.
• Data is easy to backup as all the data is stored on the File server.
• Security is good - users cannot see other users' files unlike on stand-alone machines.

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Disadvantages of a Computer Network

• Purchasing the network cabling and file servers can be expensive.
• Managing a large network is complicated, requires training and a network manager usually needs to be employed.
• Virus can spread to other computers throughout a computer network.
• There is a danger of hacking, particularly with wide area networks. Security procedures are needed to prevent such abuse, e.g. a firewall
• The network has to be administrated.

16

WAN

Wide Area Network
It is created when LANs are connected.
Wide area network. The internet is a WAN.
Uses services of telecommunications companies i.e. BT, Virgin media

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LAN

Local Area Network
A LAN (local area network) is a network of computers within the same building, such as a school, home or business. Uses physical cable or wireless.

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PAN - WiFi - MiFi

Personal area network
Interconnects devices centred around an individual persons workspace- within 10m
Uses wireless technology such as Bluetooth
MIFI - wireless devices that enable multiple users to share a single mobile broadband connection while they are on the go.
i.e. personal hotspot

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Network Topology

Defines the way in which all network devices are interconnected to create a LAN.
There are three main types: Bus, Star

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Most used topology?

Star topology is most commonly used.

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What is a bus topology?

In a bus network all the workstations, servers and printers are joined to one cable (the bus). At each end of the cable a terminator is fitted to stop signals reflecting back down the bus.

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What is a star topology?


In a star network each device on the network has its own cable that connects to a switch or hub. A hub sends every packet of data to every device, whereas a switch only sends a packet of data to the destination device.

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Advantages of Bus topology

-Easy to install
-Cheap to install, as it doesn't require much cable

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Disadvantages of Bus topology

-If the main cable fails or gets damaged the whole network will fail.
-As more workstations are connected the performance of the network will become slower because of data collisions.
-Every workstation on the network "sees" all of the data on the network - this is a security risk

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Advantages of star topology


- Very reliable - if one cable or device fails then all the others will continue to work.
-High performing as no data collisions can occur

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Disadvantage of star topology

-Expensive to install as this type of network uses the most cable (network cable is expensive)
-Extra hardware required (hubs or switches) which adds to cost.
-If a hub or switch fails all the devices connected to it will have no network connection

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Benefits of a wireless network

Portable, no wires

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Drawbacks of a wireless network

Less secure
Slower connection speed poor reception.

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Benefits of a wired network

Faster, stronger

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Drawbacks of a wired network

Not portable

31

Client Server Network

A computer network in which one centralised, powerful computer (called the server) is a hub to which many less powerful personal computers or workstations (called clients) are connected. Reliance on server.

32

What is handshaking?

The process by which two devices initiate communications. Handshaking begins when one device sends a message to another device indicating that it wants to establish a communications channel. The two devices then send several messages back and forth that enable them to agree on a communications protocol.

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Handshaking Process

Request to connect send,
Connection granted,
Protocol parameters agreed,
Data sent.

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Data Source

Where the data originates

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Transmitter

device used to transmit

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Transmission medium

cables or other method

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Destination

Where data will be placed or displayed.

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What are the five basic needs of a communication system?

Data Source
Transmitter
Transmission medium
Receiver
Destination

39

Bandwidth

The amount of data that can be sent from one point to another in a certain period of time. It is measured as a bit rate expressed in bits per second (bits/s). Is a measure of transmission speed.

40

Baud rate

The measure of how fast a change of state occurs i.e. zero to one

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Data Packet

A data packet is a unit of data made into a single package that travels along a given network path. Data packets are used in Internet Protocol (IP) transmissions for data that navigates the Web, and in other kinds of networks.

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Client-side

Web browser that runs on users device and connects to a server as necessary. not secure.

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Server-side

a computer application such as a web server that runs on a remote server. secure.

44

4 security measures

Authentication
encryption
firewall
MAC address

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Why is network security necessary?

protects your information.

46

What is encryption?

The process of converting information or data into code, especially to prevent unauthorised access.

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Key

a field that you use to sort data.

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Algorithm

a set of instructions to solve a problem.

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What is Authentication?

The process of identifying an individual, usually based on a username and password.

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What is a MAC address?

a unique identifier assigned to network interfaces for communication at the data link layer of a network.

51

What is a white list?

a list of items that are granted access to a certain system or protocol. when someone isn't on the list they cannot log on.

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What is a firewall?

a system designed designed to prevent unauthorised access to or from a private network.

53

What is a port?

an endpoint of a communication in an operating system.

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What are the four layers in the TCP/IP protocol stack, in order?

Application layer
transport layer
network layer
link layer

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Advantages to a layered approch

-each layer decomposes th problem
-changes in one layer does not impact the other layers
-provides a universal standard for hardware and software manufactures to follow
-Each layer carries out a specific function and therefore avoids repetition of tasks.

56

what does a 'suite' of protocols mean?

it consists of a number of protocols.They collectively allow data packets to be sent and retrieved.

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application layer

closest layer to user
Is where applications such as web browsers and email clients operate.
data being sent is encoded so that it will be understood by the recipient.
an appropriate header is added, according to the protocol being used, before passing the data to the transport layer.

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FTP

File transport protocol- determins rules for files being transmitted between computers.

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HTTP

Hypertext transfer protocol-used for accessing and receiving webpages in the form of HTML files.

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HTTPS

Hypertext transfer protocol secure- combination of HTTP with secure socket layer (SSL).
This provides a layer of encryption to keep personal information secure, such as payment details.

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SMTP

simple mail transfer protocol - used for sending email messages from client to server and server to server until it reaches its destination.

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POP

Post office protocol- used by a client to retrieve emails from a mail server. All emails are downloaded when there is a connection between client and server.

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IMAP

Internet Message Access Protocol- similar to POP but messages do not have to be downloaded as they can be read and stored on the server. this is better for users with multiple devices as they can be accessed from all devices.

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Transport layer

Sets up the communication between the hosts and agrees settings such as language and packet size.
divides data received from application layer into packets the correct size and adds packet information such as packet number and total number of packets.
Checks that packets arrive safely (TCP) and sends acknowledgements when receiving data.

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TCP

Transmission Control Protocol- defines how messages are split into packets and reassembled at the destination.
detects errors and resends lost packets.

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UDP

User Datagram Protocol- has no error checking or correction.
maintains an open connection between sender and receiver for the duration of the communication.
Often used for online gaming and live broadcasting where speed id desirable and error correction in not necessary.

67

IP

Internet Protocol- identifies the location of a device on the internet.
Routes individual packets from source to destination via routers.

68

Link layer

Concerned with transmitting the data through the local network using the protocols of the specific network.
The MAC address of the sender and recipient are attached to the data allowing the packet to be directed to a specific device on a local network.
This is where network hardware is located, such as the NIC, and the operating system device drivers.

69

Ethernet

refers to a suite of networking protocols used in LANs.
describes hoe devices should format data ready for transmission between computers on the same network
nodes wait until the connection is quiet before attempting to transmit
two nodes attempting to transmit simultaneously will stop and wait a random period of time before re attempting.

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What protocols are in the application layer?

FTP, HTTP, HTTPS, SMTP, POP, IMAP

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What protocols are in the transport layer?

TCP, UDP

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What protocols are in the Network layer?

IP

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What protocols are in the link layer?

Ethernet

74

Network layer

Addresses and packages data for transmission
attaches source and destination IP address which are used to route the packet across the internet.