Communication Methods

Overview

CraigNDave

https://www.youtube.com/watch?v=6KsEiwCZi4g&list=PLCiOXwirraUAVO2FCJUdKRM6hYj9teHVe

TRC PowerPoint

Comms Methods

Parallel Vs Serial

Computer Science Tutor

https://www.youtube.com/watch?v=CGulJriYNSI&list=PL04uZ7242_M6O_6ITD6ncf7EonVHyBeCm&index=25

Serial Data Transmission

In serial data transmission each bit is sent one after another by varying the line voltage between 0 & 5 volts for each bit, for two way communication a return wire is required. Serial Data Transmission is commonly used in USB and crossover cables.

Uses

Long distance communication

Advantages

Only need one signal path per way, can be used to route over telecommunications, saves cost of cabling

Disadvantages

Signal strength degrades over distance, so repeaters and so on required

Parallel Data Transmission

Each binary word is transmitted as one, with a signal path for each bit, additional signal paths for Return, Ready/Busy, & one strobe wire are required Ready/Busy is the status of the receiver, strobe wire used after signal placed onto wires on Strobe receiver will set Busy & read after read the receiver sets Ready.

Uses

Short distance data communication

Advantages

Offers faster transmission when compared to Serial

Disadvantages

Skew can easily affect data transmission, leading to errors. This is a result of distance, some bits may arrive at slightly different times. Reading the value could be inaccurate if you read before all bits have arrived.

Synchronous vs Asynchronous

Computer Science Tutor

https://www.youtube.com/watch?v=SLjjgjp2bAA&list=PL04uZ7242_M6O_6ITD6ncf7EonVHyBeCm&index=26

Synchronous means at the same time

• 2 devices will synchronise their transmission signals (based on system clock)
• Sending device will control transmission rate to match receiving device
• Once synchronised data can be sent with no other information
• If devices aren’t synchronised data will be lost

Asynchronous is simply transmission between 2 devices that don’t share a common clock signal.

Asynchronous Transmission

one character is transmitted at a time using start and stop bits to identify the beginning and the end of the character. A parity bit is usually sent to allow for checking for errors during the transmission. It is suitable for relatively small amounts of data.

Start & Stop Bits

• Arrival of data signaled by start bit
• Arrival can’t be predicted so it wakes receiver
• Clock & timing must match on both machines
• End of transmission is signaled by a stop bit
• Each unit of data is transmitted separately with start & stop bits

Baud Rate - Bit Rate - Bandwidth - Latency

CraigNDave

https://www.youtube.com/watch?v=I4dSIZM7Qdk&list=PLCiOXwirraUAVO2FCJUdKRM6hYj9teHVe&index=2

Computer Science Tutor

https://www.youtube.com/watch?v=8wm0QlbW9cQ&list=PL04uZ7242_M6O_6ITD6ncf7EonVHyBeCm&index=27

Baud Rate

Frequency at which a signal can change (ie from 0 to 5 volt), a baud signal of one changes once per second

Bit Rate

Number of bits transmitted per second, bit rate does not equal Baud rate if more than one bit is sent per time, 2 bits can be sent each time with more voltage levels.

Bandwidth

How fast data can be transmitted over a transmission media without significant reduction in strength greater bandwidth means greater the data rate can be sent there is a direct relationship between bit rate and bandwidth. The greater the bandwidth of the transmission system, the higher is the bit rate that can be transmitted over that system. On a cable, bandwidth is measured in Mhz, network Cable has 500 Mhz bandwidth which means 500 million cycles per second more cycles = more data.

Latency

It is the time delay between initiation and the first effect, WAN latency due to distance eg: between ground stations and satellites

Propagation Latency

Time taken to pass through a logic gate

Transmission Latency

Time taken to pass through a medium

Processing Latency

Time taken to pass around a network

Protocols

Is a set of agreed:

• Rules
• Codes
• Signals

That allow the transfer of data from one system to another And consists of:

• Handshake
• Message
• Goodbye

There are multiple commonly used protocols:

TCP/IP and UDP

Sending and receiving data over a network

HTTP and HTTPS

Retrieve pages from the world wide web

FTP

Transfer and upload files, often anonymously

TELNET, SSH

To connect to and manage a server

POP3 and SMTP

Send and receive email

Handshaking

Handshaking sets several variables required for the data transmission:

• Communication protocol
• Pre-agreed signal, codes, rules to ensure successful transmission

Sender checks receiver is connected & ready Sender waits for response Sender signals it will start sending data Receiver signals ready, and sender sends data Receiver indicates data received & ready

Communication protocol Pre-agreed signal, codes, rules to ensure successful transmission Handshaking protocol - Exchange of signals to establish a connection Sender checks receiver is connected & ready Sender waits for response Sender signals it will start sending data Receiver signals ready, and sender sends data Receiver indicates data received & ready

Revision Questions

1. Define the term "bit rate".

	The number of bits transmitted per second.
→	Epic.
	The number of bits transmitted in a year.
→	Remember it is per second.
	The amount of bits a computer can store.
→	Bit rate is the number of bits transmitted per second.
	The frequency that signals may change.
→	Bit rate is the number of bits transmitted per second.

2. Define the term "baud rate".

	The frequency at which signals may change.
→	Epic.
	The number of bits transmitted in a second.
→	Remember that it is the frequency at which signals may change.
	How fast the computer can process.
→	Remember that it is the frequency at which signals may change.
	The bandwidth.
→	Remember that it is the frequency at which signals may change.

3. What is the difference between bit rate and baud rate?

	Bit rate is the amount of bits of data transferred ,whereas baud rate is just the amount of time between signal changes.
→	Good job,epic dude!
	The Baud Rate pegged is a bank's own internal interest rate mechanism.
→	no that is a silly, silly boy :(
	Bit rate is the rate at which a computer's CPU can process data and baud rate is the time taken to transfer a signal.
→	that is not that
	Bit rate is the measurement of the bits speed in m/s, baud rate is the significance of each bit.
→	try harder

4. Which communication method is best to use for long distance communication and why?

	Parallel data transmission because it only uses one wire
→	This is incorrect because parallel data uses multiple wire in which data is transmitted at the same time.
	Parallel data transmission because its really fast
→	This is incorrect because although its fast it cannot be transferred more then a couple of meters
	Serial data transmission because it sends 1 bit after another
→	This is correct.
	Serial data transmission because its really fast
→	This is incorrect because serial data transmission is not fast, that is parallel data serial data.

5. Select the following answers which need to be agreed upon in a protocol

	Rules
	Time
	Power
	Codes
	Signals
	Frequency

6. What is Latency?

	The time taken for data to pass through a medium.
→	The correct answer is the time delay between initiation and the initial effect.
	The time delay from each effect to the next.
→	The correct answer is the time delay between initiation and the initial effect.
	The time delay between initiation and the initial effect.
→	That is correct. Latency can also happen at any stage of the transmission.
	The frequency at which signals may change.
→	The correct answer is the time delay between initiation and the initial effect.

7. Bandwidth is the amount of data that can be transmitted in a fixed amount of time over a medium.

	TRUE.
	FALSE.

8. Select all that are advantages of parallel transmission.

	Capable of sending data over long distances
→	This is incorrect, parallel transmission suffers from skew over longer distances
	Data is sent as multiple bits per pulse.
→	This is correct, as it makes it more efficient than one bit at a time.
	High speed data transfer over a short distance
→	This is correct, as it is used mainly in the internal circuitry of a computer
	It uses a single wire to send and a single wire to receive
→	This is incorrect, serial transmission uses a send and a receive wire to achieve full duplex communication

9. Parallel transmission is when (select one or more):

	Two or more wires are used for transmission
→	Correct answer
	One wire is used for transmission
→	Incorrect answer
	One or more byte sent at the same time
→	Correct answer
	One bit is sent per second

10. What is Bandwidth measured in:

	Mbps
→	Incorrect answer
	Mhz
→	Correct answer
	Db
→	Incorrect answer

11. Define the term propagation latency:

	Time taken to pass through a medium
→	Transmission Latency
	Time taken to pass around a network
→	Processing Latency
	Time taken to pass through a logic gate
→	propagation Latency

12. Define the term processing latency:

	Time taken to pass through a medium
→	Transmission Latency
	Time taken to pass around a network
→	Processing Latency
	Time taken to pass through a logic gate
→	propagation Latency

13. Define the term transmission latency:

	Time taken to pass through a medium
→	Transmission Latency
	Time taken to pass around a network
→	Processing Latency
	Time taken to pass through a logic gate
→	propagation Latency

14. What type of latency is the time taken to pass through a logic gate?

	Propagation Latency
→	Correct answer
	Transmission Latency
→	Wrong answer, it was Propagation Latency
	Processing Latency
→	Wrong answer, it was Propagation Latency

15. What type of latency is the time taken to pass through a medium?

	Transmission Latency
→	Correct answer
	Propagation Latency
→	Wrong answer, it was Transmission Latency
	Processing Latency
→	Wrong answer, it was Transmission Latency

16. What type of latency is the time taken to pass around a network?

	Transmission Latency
→	Correct answer
	Propagation Latency
→	Wrong answer, it was Transmission Latency
	Processing Latency
→	Wrong answer, it was Transmission Latency

17. What potential issue may arise using parallel transmission?

	Data may arrive in the wrong order over distance.
→	Correct, this is called skew and may occur because data is sent on different cables; it is possible that one cable is shorter than the rest resulting in data arriving sooner than it should.
	Data is more prone to degradation.
→	All methods of transmitting data are prone to degradation, this is not exclusive to parallel
	It is more expensive and time consuming to lay down the cables over a long distance.
→	Correct, because parallel transmission uses several cables to send data, it becomes incredibly costly over a longer distance as opposed to series, also if the wires are not the same length then skewing can occur so it must be ensured that the wires would also be the same length.

18. Define the term "protocol".

	A set of instructions on how to use a computer.
→	It is a set of rules on how computers communicate.
	A set of rules on how computers communicate.
→	Epic.
	A set of emergency instructions.
→	It is a set of rules on how computers communicate.
	The delay of transmission.
→	It is a set of rules on how computers communicate.

19. What is half-duplex?

	Data being sent in either direction across multiple wires.
→	This is incorrect, half-duplex data can flow in either direction on a single wire but not at the same time.
	Data being sent in one direction so requires multiple wires.
→	This is full-duplex. Half-Duplex is when data can flow in either direction on a single wire but not at the same time.
	Data can flow in either direction on a single wire but not at the same time.
→	This is half-duplex
	Data can flow in either direction on a single wire at the same time.
→	Half-duplex data cannot flow on a single wire at the same time.

20. What is full-duplex?

	Data being sent in either direction across multiple wires.
→	This is incorrect, Full-duplex data can only flow in one direction.
	Data can flow in one direction on a single wire.
→	This is incorrect. Full-duplex data is being sent in one direction but requires multiple wires.
	Data can flow in either direction on a single wire but not at the same time.
→	This is half-duplex. Full-duplex data is being sent in one direction so requires multiple wires.
	Data being sent in one direction so requires multiple wires.
→	This is full-duplex.

21. what is baud rate

	The amount of bits sent per second
→	bit rate
	the frequency at which a signal can change
→	this is correct, it changes from 0-5v, it occurs every second
	the time it takes from initiation and the first effect.
→	this is latency
	the amount of bits created per second

22. select all that applies to parallel transmission

	It is over a single wire
→	this is serial
	Multiple bits are sent at the same time
→	this is true
	It is sent over multiple wires
	It can be affected by skew
	It is good for long distance
→	this is only applicable to serial

23. What is the difference between synchronous and asynchronous data?

	Synchronous is two sets of data that is sent at different times when Asynchronous is two sets of data that is sent at the same time
→	nah its not opposite day
	Two devices synchronise data signals
→	no
	The number of bits sent per second
→	Drop your computer science A level right now
	synchronous is data sent between devices that are synchronised whereas asynchronous is where they aren't
→	correct

24. Explain in the context of networking, why parallel transmission might be preferred to serial transmission (Multiple Answers)

	Data is sent over much faster
	Can transfer data over large distances much better than serial
	Easier to send large amounts of data
	It's less costly overall

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