Chapter 2-Data Transmission
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What are data packets+ 2 other names
Packets, datagrams A small part of a message/data that is sent over a network which after transmission reassemble to form the original message/data
Why are data packets used
They are usually 64KiB, †hey are much easier to control and splitting them up means that they can be sent along different routes
When would data packets be particularly beneficial
When a particular transmission route is out of action or blocked
What is a drawback of packets
The packets all need to be reassembled at the destination
Parts of data packets (3)
Packet header Payload Trailer
packet headers components (4)
IP address of the sender IP adress of the reciever Sequence number of packet Packet size
What does a payload consist of
The actual data in the packet Usually 64 KiB
What does a packet trailer contain
A method of identifying end of packet- allows them to separate from eachother A method of error checking
What are CRC’s
Cyclic redundancy checks Sending: adds all the one bits in payload and stores as hex value in the trailer Recieve: recalculates no of bits in payload Compares to trailer Asks to resend
What does a router do
Receives data packet and based on info in header decides where to send it next
Describe the stages of packet switching
The message is split up into smaller data packets. These packets are then independently sent over the network Along the transmission route are nodes containing router which use the header/ IP address to determine where to send the packet The shortest possible route is chosen Packets reach destination in the wrong order
What are the benefits of packet switching(4)
No need to tie up single communication line Possible to overcome faulty lines by rerouting Relatively easy to expand package usage High data transmission rate is possible
What are the drawbacks of packet switching (3)
Packets can be lost and need to be resent Delay while packets are being reordered More prone to errors with real-time streaming
What is hopping
Hopping is the use of a hop number that decreases by one each time a packet leaves a router
What 3 factors need to be considered when transmitting data By what are they considered
Direction of data(1 or 2 directions) Method of transmission(how many bits at a time) How will data be synchronised (to end up in the right order) Communication protocols
When does simplex data transmission occur
When data can only be sent in One direction Eg. Computer toPrinter
When does Half Duplex data transmission occur
When data is sent in Both directions but not at the same time Eg. Walkie talkie
When does Full-duplex data transmission occur
When data can be sent in both directions at the Same time Eg. Broadband network connection
What is serial data transmission Benefit Drawback Eg
When data is sent over a single wire one bit at a time in a single stream(can be simplex etc.) Data arrives in order Can be slower than parallel Computer->USB->printer
What is parallel data transmission Benefit Drawback Eg
When several bits of data are sent over multiple Chanel’s/wires at the same time Good over short, faster than serial Can become skewed 20m+ Internal circuits in computer
What is skewed data
Data that is out of order
What is a USB
a type of serial data transmission which has become the industry standard for connecting computers to devices via a USB port
What kind of data transmission is used by USB
Half and full duplex
What does a USB cable consist of
A 4-wire shielded cable with a red and black cable for power and green and white for data transmission Red-5V Black-ground White+ Green- -