Chapter 21: Networks Flashcards
Network
An arrangement of computers or other electronic devices connected together to enable communication and share resources, data & information.
LAN
Network that covers a small geographical area-often a single site
WLAN
A LAN in which connected devices use high-frequency radio waves to communicate
WAN
Network that covers a large geographical area-connects together two or more LANs; usually under shared ownerships
PAN
Network used for data transmission over short distances by computer devices
Client-server network
Network that has at least one server to provide services to the client computers
Peer- To- Peer network
Network which doesn’t have dedicated servers-each computer can act as client & server-each computer can provide service and request service
Network topologies
Describes how devices on a network are connected together
Bus
Type of network topology in which each network device is connected to a single cable (bus), terminated at each end
Terminators
Absorb signals that reached the end of the cable; prevent messages bouncing back & causing interference
CSMA/CD
System dealing with multiple messages being sent simultaneously. Two messages sent at same time causes collision & makes messages unreadable.
CSMA/CD algorithm
Checks if bus is busy, if not then sends message & listens whether received correctly. If not, it retries sending message, else it goes back to listening
Ad. bus (2)
- Easy to add new devices
- Cheap & easy to install since 1 cable needed only
Dis. bus (4)
- If cable cut/damaged, whole network fails
- Difficulty identifying fault
- The more devices, the slower they run; only one message can be sent at a time, more frequent collisions
- All devices receive all data; security risk
Ring
Network in which the cable connects one network device to another in a closed loop/ring
Ring features (2)
- Messages travel in same direction, therefore no collisions
- Data passed around ring until it reaches its destination
Ad. ring (3)
- Easy to add new devices
- Extra devices do not affect network performance
- No collisions
Dis. ring (3)
- If cable/network device fails, whole network fails
- Difficulty identifying fault
- Adding/removing devices shuts down network temporarily
Star
Network in which each network device is connected to a central hub/switch, which receives & redirects messages to correct recipients
Ad. star (4)
- Damaged cable only stops device connected to it from working, not whole network
- More secure; messages only sent to devices needing them if switch used
- Easy locating faults (1 device involved)
- Adding/removing devices does not shut down network
Dis. star (2)
- If hub/switch fails, whole network fails
- Expensive to install due to Hub/switch & amount of cable
Mesh
A network where each network device is interconnected with one another. Can be wired or wireless
Ad. mesh (3)
- Fault tolerant; if device fails, message is simply re-routed
- High performance; each network device is likely to be connected to multiple other devices
- In wireless; each node extends range of network
Dis. mesh (2)
- Difficult & expensive to install
- Difficult to manage due to high number of connections
Wired connection
Involve a physical connection between the computer & the network
Wireless connectivity
Does not require a physical connection between devices. Most transmit & receive radio signals
Ad. wired (3)
- Faster than wireless
- Not easy to intercept/eavesdrop data
- Less susceptible to interference
Dis. wired (2)
- Expensive to install & reconfigure
- Requires many cables at a premises
Ad. wireless (3)
- No need for cable to connect devices/connect to internet
- Allows users to use their own devices
- Not dependent on having correct cable, therefore wider range of devices can comminucate with each other/a network
Dis. wireless (3)
- Slower data transmission than wired
- Data must be encrypted to prevent interception/eavesdropping
- Walls, physical objects & interference from other wireless devices can adversely affect perfomance
How are network data speeds measured?
Bits per second (Mbps, Gbps)
Need for network protocols
Protocols allow connected devices to communicate with each other, regardless of their differences in their internal processes, structure & design.
Protocol
A set of rules that control how communications between devices are formatted & how these communications will be sent & received
SMTP (Simple Mail Transfer Protocol)
Used when emails are sent through the internet. Details format messages are sent in, the commands the email servers should understand & how they should respond to them
POP 3 (Post Office Protocol V. 3)
Used for retrieving email from an email server. When client connects to mail server, they download any messages & then delete them from server
IMAP (Internet Message Access Protocol)
Allows emails to be accessed using multiple email clients. Leaves messages on server until deleted by the client.
Ethernet
Family of protocols used in wired LANs. Cover the physical & logical parts of a network
WI-FI
Digital communication protocol that sets out how data is transmitted on wireless LANs
TCP (Transmission Control Protocol)
Provides reliable connection between computers. Receiving computer is certain that it has received all data & data is identical to data sent. Used when accessing web pages, send/receive email or upload/download files.
TCP/IP (Transmission Control Protocol/Internet Protocol.)
Collection of protocols that work together
4 Layers of TCP/IP protocol stack
Application, Transport, Internet, Link
Application
(Top layer which interacts with user to provide access to services & data that is sent/received over a network
Transport
Manages end-to-end communication over a network. 2 Main protocols operating here are TCP & UDP
Internet
Deals with sending data across multiple networks, from source network to destination network (routing)
Link
Controls transmission & reception of data to/from a local network
Packet
A small quantity of data being sent through a network
How is data sent using TCP/IP?
Data broken up into packets
What does packet header contain details of?
- Sending computer
- Receiving computer
- The number of packets the data has been split into
- Number of this packet
Web server
Powerful computer system that stores web pages & any mulimedia that the pages might contain
