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

Question 1

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Question 2

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Question 3

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Question 4

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Question 5

1. What is the baud rate?

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Question 6

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.

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Question 7

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Question 8

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Question 9

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Question 10

1. Explain in the context of networking, why parallel transmission might be preferred to serial transmission

	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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Question 11

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Question 12

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