3 Communications

What is a network?

A collection of computing devices connected together

What are the advantages of networks?

* Hardware can be shared
* Software can be shared
* Data can be shared
* Computers may communicate between each other with messages or email
* Administration is centralised

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What are the disadvantages of networks?

- Viruses can be spread to all devices on a network

- Hackers may access computers on a network

- Can be expensive to install

- Networks may be slower than using standalone computers

What are the 2 main types of network?

Local Area Network (LAN)

Wide Area Network (WAN)

What is a LAN network?

A network in which all the computer systems are located in a fairly small geographical area

What is a WAN network?

-A network in which all the computer systems are located over a large geographical area

-Many LANs can be linked using a WAN

What is a widely known example of a WAN?

the internet

What does a star network topology look like?

Each node is connected to a central node which may be another computer or a hub

What are the advantages of a star network topology?

- Faster connection speed - each node has a dedicated cable

- Won't slow down as much when many people online

- Fault finding is simples - individual faults easier to trace

- Relatively secure - client-server connection is unique

- New nodes can be added without affecting others

What are the disadvantages of a star network topology?

- Expensive setup - increased cabling costs

- If a cable fails

node unable to recieve data

- Difficult to install - multiple cables - increased if LAN is over a number of buildings

- Server can get congested - all communications must pass through

What does a ring network topology look like?

The nodes are connected in a ring

What are the advantages of a ring network topology?

- Data transfer is quick without bottleneck - consistent data transfer speeds

- Simple transmission of data - only one direction

- Adding additional nodes has little impact on bandwidth

- Prevents network collisions

What are the disadvantages of a ring network topology?

- If one CS fails

- If theres a problem with main cable or connection

whole network goes down

- Difficult to troubleshoot

- To add another node

network must temporarily be shut down as all nodes are wired together

What does a bus network topology look like?

What are the advantages of a bus network topology?

- Cheaper to install

- Easy to install

- Easy to add new nodes by branching them off the main cable

What are the disadvantages of a bus network topology?

- Not that secure as all data transmitted down one cable

- Transmission times slower with more users online

- If main cable fails

all clients affected

- More difficult to find faults

What does a mesh network topology look like?

Every node is directly connected to every other node

What are the advantages of a mesh network topology?

- Very reliable for data transmission

- Very robust as no single point will bring down the network if it fails

What are the disadvantages of a mesh network topology?

- Expensive setup

- Complex to install

What is a file server?

The computer on a network that stores the files used by other workstation

How does a wireless router connect devices?

Via radio signals

How does a wireless device connect to a router?

using access points

How does a wired network connect devices?

using physical connections

What are the disadvantages of a wired network?

- Difficult to install as wires must be routed to every station

- Expensive to install

What are the advantages of a wired network?

- Faster transmission speeds

- More secure

What are the advantages of a wireless network?

- Mobile equipment can easily log in

- Easy to install

- Cheap to install

What are the disadvantages of a wireless network?

- Can be hacked more easily

- Transmission speeds slow as more users connect

What is the purpose of a router?

- Forwards packets of data along a network

- Determines the best path for the packets

What is the purpose of a hub?

Connection point between cables in a network

What is the purpose of a switch?

Filters and forwards packets to intended destination

What is the purpose of a bridge?

Connects one LAN to another

What is the purpose of a gateway?

Connects a LAN to a WAN such as the internet

What are the two ways data can travel around networks?

- circuit switching

- packet switching

What is circuit switching?

- a dedicated link between 2 nodes

- no other data can be transmitted along the same route when the connection is open

Advantages of circuit switching?

- Very reliable

- Once the connection is established

it is fast

- Tends to be error free

Disadvantages of circuit switching?

- Takes time to establish a connection

- The connection will be broken if anywhere on the route fails

What is packet switching?

- Data is split up into packets

- When the packet arrives at a switch/router the address is read and it is sent along the next free path

- Packets may arrive at the destination in a different order to which they were sent

but can reassemble using info in the packet when all the packets have arrived

What is contained in a data packet?

- Source address

- Destination address

- How many packets are in the message

- Info on how this packet fits into the message

- Other tracking info

- The data itself

- A checksum showing the data hasn't been corrupted

Advantages of packet switching?

- Packets do not need a dedicated line

- If a route is blocked or busy

the packet can take an alternate route

- Efficient - if one packet doesn't arrive

only that one needs to be resent

- Tends to be error free

Disadvantages of packet switching?

- Packets may arrive in the wrong order

- Can cause a delay until all packets arrive

- Large memory needed to hold packets until all the message is assembled

What are protocols?

a set of rules that defines a method for transmitting data between different devices over a network.

In general

what should a protocol contain?

- a type of error checking

- a data compression method

- how the sending device will indicate that it has finished sending

- how the receiving device will indicate that it has recieved the message

What is the Ethernet protocol?

Describes how network devices can format data for transmission using frames and packets along a wired network and the standards for types of network cabling used

What is the Wifi protocol?

Describes how wireless protocols can be sent and received. A common protocol is 801.11

What is the TCP/IP protocol used for?

Transmission control protocol (TCP) and internet protocol (IP). These two distinct network protocols are used to send data around the internet.

What is the HTTP protocol?

Hyper Text Transfer Protocol describes the rules used to identify and transfer multi-media webpages over the internet