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Networks - Typologies and Protocols continued (Packet Switching: (Packet…
Networks - Typologies and Protocols continued
Packet Switching:
Packet switching is used by routers to direct data packets on the Internet and other IP networks.
(1) The sending device splits the data into packets to be sent across the network. Each packet is given a packet number to show the order of the data.
(2) Each router reads the packet header and decides which way to send the packet next, according to the IP rules.
(3) The way the data is sent changes depending on network traffic, so the packets can take different routes. If a router receives too many packets at once it may prioritise some over others.
(4) As the packets can take different routes, they can arrive in the wrong order. The receiving device uses the packet numbers to reassemble them in the right order.
(5) Packets sometimes go missing in transit, so the receiving device checks periodically that all packets have been received. If not, all packets have been received then a timeout message will be sent back to the sending device.
(6) If all data is received and the checksum match, a receipt conformation is sent to the sending device.
It is efficient because there are so many possible routes that data can take – packets can reach their receiving device even if there's heavy "traffic".
Connections:
• Cable copper wire is common within buildings.
• Fibre optic is used outside buildings for long distances. It is very fast and very secure.
• Ethernet connects computers within the LAN.
IP address:
a unique string of numbers separated by full stops that identifies each computer using the internet Protocol to communicate over a network
Similar to a postcode
Changes over time – just assigning IP addresses to working computers
IP address example: 186.135.25.67
IP classes
:
• They identify the class of network that the user is on.
• This indicates the number of possible users and the purpose of the network.
Class A: 0-127 bytes
Class B: 128 – 191 bytes
Class C: 192-223 bytes
Class D: 224-239 bytes
Class E: 240-255 bytes
• Classes C and D are used for research purposes.
Packets:
Data sent between networks is split into equal sized packets.
Every data packet has a header – this contains the control information.
The data packet's payload may be part of an email, document, web page or streamed video.
Packets will also include a checksum number – a form of validation used to check the payload hasn't been corrupted during transit.
The sending and receiving devices both calculate a checksum value by performing a function on the payload data. If both checksum values match, then the data has been received correctly.
The packet's header includes the packet's destination address, the source address and the packet number.
Wireless:
• Increasingly common.
• Convenient for connecting new devices in public areas.
• Brings security issues.
MAC address
It is the physical address of the network card.
Uses hexadecimal as a number base
Use hex over binary for it is easier for humans to understand and there are more combinations to work with.
Doesn’t change.
MAC address example: AA-34-G4-44-23-F1