Data transmission

What are the three directions of transmission?

Simplex, half duplex, full duplex

What is simplex data transmission?

Data only goes one direction - sending to or receiving from a device

What is half duplex data transmission?

Sending data both to and from devices (only one at a time)

Simplex data transmission example

Microphone, webcam to computer, computer to speaker

Half duplex data transmission example

Computer to printer, walkie talkie (both parties can talk but not at the same time)

What is full duplex data transmission?

Both directions at the same time

Examples of full duplex data transmission

Broadband connections (upload/download at same time), telephone (both parties can talk at once)

What is an interface?

A point at which 2 computer systems communicate

What is a serial interface?

An interface to allow serial communication between one microcontroller/microprocessor and another using a serial cable

How are wires arranged in a serial cable?

One wire to transmit, one wire to receive

What is serial communication?

the process of sending data 1 bit at a time, sequentially, over a single communication channel

what is synchronised serial communication

continuous stream of data and timing signals generated by internal clock to synchronise sending and receiving signals

what happens in synchronised serial communication

timing for when each bit is sent is synchronised to the oscillations of the clock

what does the receiver do in synchronised serial communication?

counts how many bits were sent and reassembles bits into bytes

are timing signals sent before, with or after the data in synchronised serial communication?

timing signals are sent with the data

why must the timing be accurate in synchronised serial communication?

no control bits are used; timing signals are sent with the data

which one is faster: synchronised or asynchronous serial communication

synchronised, as only data bits are sent

why must the receiver and transmitter both be present in synchronised serial communication?

to coordinate timing of the messages in real time

what is asynchronous serial communication

data is packaged and sent to another device as a packet

what happens to files in asynchronous serial communication?

broken up into many packets and reassembled at the receiving end

what is the name given to the format of a packet?

frame

what is a frame?

the format of a packet

what defines the frame format?

the protocol being used

what is agreed before transmission in asynchronous serial communication?

communicating devices agree a protocol before transmission

example of protocol agreed by communicating devices before transmission (asynchronous)

bit pattern and bit rate (bits per second)

typical bit rates (asynchronous)

9600bps

why is asynchronous slightly slower than synchronous

more bits are sent

Why is synchronising to a system clock not needed for asynchronous communication?

Frame format has all information required to interpret data at the receiving end

Example of a frame format

Start - data - parity - stop

What is parity?

a simple form of error checking, used in frame formats (asynchronous)

Example uses of serial transmission

from computer to a printer in a different room; USB

Why are fast connections not needed for printers?

Printers are limited by their printing speed

What are USBs used for?

External data transfer between devices

What happens when a USB device is plugged into a computer’s USB port? (part 1)

device is automatically detected

What happens after a USB device is detected by the computer?

device driver has to be loaded

What happens with known USB devices after being detected by the computer?

automatically recognised; their device driver is loaded by the OS

What happens if the computer doesn’t know the USB device?

OS searches its device driver; if not found, the user is prompted to download it

What happens if the computer doesn’t find an unknown USB’s device driver?

User is prompted to download it

Give 2 disadvantages of USB

Max cable length only 5 metres; Older standard (1.1) becoming obsolete)

Advantage of USB (Ind…)

Industry standard: lots of compatibility and support available

Advantage of USB (Inc..)

Incorrect connections are prevented. Old USB connectors only fit one way and newer USB C connectors fit and work both ways

Advantage of USB (Dif…)

Different data transmission rates are supported - some are very fast

Advantage of USB (Aut…)

Automatically detects if the correct driver is installed

Advantages of USB (Some…)

Some devices (e.g. mobile phones) can be charged and powered at the same time

Advantage of USB (Doesn…)

Doesn’t require wireless, so can be used if a network is down

Advantages of USB (Som…)

Some USB standards are backwards compatible

Serial vs parallel transmission speed/price

Serial is slower but cheaper

Why is serial slower but cheaper than parallel?

Only 1 wire or data channel is used

Is serial transmission reliable over long distance?

Yes

Why is serial transmission reliable over long distance?

less errors from interference or cross-talk between other wires/data channels so bits stay in correct order

why are you less likely to get skewed/unsynchronised data at the receiving end with serial transmission?

only 1 wire is used

is it easier to collate data after transmission with parallel or serial transmission?

serial

USB-C pins

symmetrically double pins

Does USB have more or less power than older USBs

more; often 5A

Advantage of USB-C

almost any modern protocol can run over it

how come almost any modern protocol can run over usb-c?

any device can request use of spare signals

What is parallel communication?

several bits being sent simultaneously over several channels in parallel with eachother

why is parallel faster than serial?

many bits are sent over many channels at the same time

disadvantage of using parallel communication

unreliable over long distances

where is parallel communication mainly found

printed circuit boards; internal data transfer on buses

why is it safe to have parallel communication on printed circuit boards?

channels fixed in position and undisturbed; distances are small

what provides the timing for synchronisation for bits being sent or received in parallel communication?

system clock oscillations

examples of the devices where you could find parallel communication

buses - inside microchips in embedded systems; in CPUs

are most data channels inside a CPU/IC (integrated circuit) parallel or serial?

parallel

how wide can buses be

8, 16, 32, 64 or 128 bits

why is parallel transmission good for processors

keeps them working very fast

give 4 reasons why parallel transmission is not used more widely

signal degradation, timing issues, more crosstalk, complex design

disadvantage of parallel communication (sig…)

if data travels along more wires, there is more chance of signal degradation over long distances

disadvantage of parallel communication (timing)

without perfect synchronisation between multiple wires, data may be wrongly aligned and unrecognisable by a receiver

disadvantage of parallel communication (complex)

more wires complicates the motherboard design and takes up more space

what is a port?

connection point/interface between computer and int/external hardware device

what do internal ports do?

provide connections to hard drives or dvd drives

what do external ports connect?

printers, mice etc.

what is a software port?

virtual point where network connections start and end

what manages a software port

the computer’s OS

what do all ports have in common?

each port is numbered (0-65535) and associated with a specific protocol or service

what do ports help computers to do?

differentiate between different kinds of traffic; understand what to do with information from other hardware

what is the primary use of a port number

transfer data between a computer network and an application

what are protocols?

sets of rules and standards for how data is transmitted and received over a network

give 3 examples of things protocols determine

anything from: addressing, encoding methods, error correction/detection, how packets are structured, session persistence, security

what protocols determine (data packets)

format and structure of data packets (frame)

what protocols determine (encoding methods)

how data is encoded (ACII, Unicode) or representing data (binary, hex)

What protocols determine (errors)

the error correction or detection method used, e.g. parity

what protocols determine (address)

how IP addresses are identified on a network

what protocols determine (session persistence)

how long before a message timeouts (if it takes too long to find the address)

what protocols determine (security)

what encryption or authentication methods are used