1. Fundamentals of Communication and Networking
Networks and Transmission

2. Communication Methods
Data not only needs to be transmitted around a device
It also needs to go from one device to another
Any series of connected devices is called a network
Text
Images
Sound Recordings
Salaries
Names … …
Storage / Transmission
Electrical
Magnetic
Electromagnetic …
Fundamentals of Communication and Networking: Networks and Transmission

3. Communication Methods
Data needs to be sent over a medium
A medium can include lots of things
Wired cables
Wireless systems
Transmitter
Communication Channel
Receiver
Electromagnetic Waves
Transmission Media
Guided
Unguided
Fundamentals of Communication and Networking: Networks and Transmission

4. Communication Methods
We break these in to two different types
Guided
Unguided
Guided involves physical cabling
Unguided involves wireless technology
Physical paths
Twisted pair Coaxial cable Fibre optic
Low
High
Microwaves
Transmitted electromagnetic waves
Radio Waves
Air
Vacuum
Sea Water
Fundamentals of Communication and Networking: Networks and Transmission

5. Communication Methods
Distance
Transmitter
Transmitted signals decrease in strength with distance
Failure to correct
Data encoded in signal won’t be accurately recoverable
Fundamentals of Communication and Networking: Networks and Transmission

6. Transmission Methods
Although data needs a medium to be transmitted down, we still need a way to transmit the data
Some kind of scheme is needed
Like encoding schemes are needed for encoding
This is also broken up into two types
Serial
Parallel
Fundamentals of Communication and Networking: Networks and Transmission

7. Transmission Methods: Serial
Serial transmission involves sending data in bits, one bit after the other
Usually done down a single medium
Signal Lamp
On 1
Off 0 X A B
5 V
Switch
Signal Wire
Return Wire
Lamp Bulb
Position A
Lamp bulb connected to 5 volts
Signal Lamp
On ?
Off ?
Signal Lamp
Binary Digit
Voltage
Represent On 1
5 volts
Data
Off
0 volts
Position B
Lamp bulb connected to 0 volts
Fundamentals of Communication and Networking: Networks and Transmission

8. Transmission Methods: Serial
Circuits will use different voltages to transmit data
Similar to how data is transmitted inside a device
Return Wire
5 V
0 V X
5 V
Fundamentals of Communication and Networking: Networks and Transmission

9. Transmission Methods: Serial
Two different devices on the same network need to be connected in some way
Computer A X
Computer B
Fundamentals of Communication and Networking: Networks and Transmission

10. Transmission Methods: Serial
One example of a serial transmission medium is the Cat cable
Typically used for connecting computers to the internet
Via a router
Two pairs crossed  Two pairs uncrossed 10BASE-T or 100BASE-TX crossover
Pin
Connection 1: T568A
Connection 2: T568B
Signal
Pair
Colour 1
BI_DA+ 3
BI_DB+ 2
BI_DA-
BI_DB- 4 5 6 7 8
Non-data
Un-crossed
Both ends wired according to Connection 1
Fundamentals of Communication and Networking: Networks and Transmission

11. Transmission Methods: Serial
USB cables are also used for serial transmission
Stands for Universal Serial Bus
Connects lots of different types of peripherals to a device
Personal computer
USB memory stick
USB port
Fundamentals of Communication and Networking: Networks and Transmission

12. Transmission Methods: Serial
Serial transmission is best used for long distance transmission
As serial guided medium only requires a single wire, it is cheaper per metre to make serial cables than parallel cables
Data is also prone to loss/corruption over long distances
Sending bits individually over time means we have a better chance at catching an error before the whole data is sent
Fundamentals of Communication and Networking: Networks and Transmission

13. Transmission Methods: Parallel
Parallel transmission involves simultaneous bit transmission
Multiple bits down several wires
Usually at the same time
COMPUTER
PRINTER
Ready/busy
Strobe
Data
Return
8 data wires 5 or 0 volts (individually shielded – if necessary)
1 return wire
1 strobe wire 5 or 0 volts
1 ready/busy wire 5 or 0 volts
Fundamentals of Communication and Networking: Networks and Transmission

14. Transmission Methods: Parallel
One use of parallel transmission is in older printer cables
Use different wires for
Sending data to print
Checking ready states
Sending busy state
Printer Ready to receive data
Sets ready/busy wire at 5 volts
Printer Detects strobe signal voltage
Reads data on data wires
Sets ready/busy wire at 0 volts
Printer Finished reading data
Computer Reads Printer as ready
Places data onto data wires
Computer After short time
Sets strobe wire to 5 volts
Computer Reads Printer as busy
Fundamentals of Communication and Networking: Networks and Transmission

15. Transmission Methods: Parallel
Parallel transmission is best used for short distances
Like internal networks (i.e. a house)
More cables are required
Making it more expensive
But faster at sending data
As multiple bits are sent at once
Skew
Problem of keeping voltages on 8 wires in line
Leads to voltage on each being read incorrectly
Restricted to computer-to-printer and computer busses
Fundamentals of Communication and Networking: Networks and Transmission

16. Important Terms: Baud Rate
Let’s go over some important terms
One being the baud rate
It’s the number of signal changes over a medium per second 10 11 1 2 3 4 5 6 7 8 9
Voltage (V)
Time (S)
Can change here
1 Baud
Computer signal can only change when 1 second has elapsed
(1 signal change per second)
Baud rate
Time between signal changes (s)
Rate of signal change (changes per second) 2
0.5 4
0.25
1000
0.001
10,000
0.0001
Fundamentals of Communication and Networking: Networks and Transmission

17. Important Terms: Bit Rate
Then there’s bit rate
It’s the number of bits transmitted per second
Baud rate = Bit rate
When 1 bit is sent between consecutive signal changes
Signal level (volts)
Decimal number
Binary number 00
2.5 1 01 5 2 10
7.5 3 11
Use more than 2 voltage levels to encode bits to
Send more than 1 bit between signal changes 10 11 1 2 3 4 5 6 7 8 9
Voltage (V)
Time (S)
7.5
2.5 01 00
1 baud line
2 bit encoding
Bit rate = 2 bits per second
Fundamentals of Communication and Networking: Networks and Transmission

18. Important Terms: Bandwidth
Then we have bandwidth
It determines the amount of data that can be sent per second
It usually determines the maximum amount of data that can be sent at any given time
Greater bandwidth
Greater rate of transmission
Fundamentals of Communication and Networking: Networks and Transmission

19. Important Terms: Bandwidth
Bandwidth is measured in hertz (Hz)
Means cycles-per-second
Hz can be used for anything that repeats so many times per second
Effect of transmission on two different frequencies A B
Low-frequency signal
Injected onto wire at A and arrives at B (Undiminished signal strength) A B
Higher-frequency signal
Injected onto wire at A and arrives at B (Significantly diminished signal strength)
Fundamentals of Communication and Networking: Networks and Transmission

20. Important Terms: Bandwidth
Limited band
Given signal
Contains frequencies over broad range
Transmission medium
Accommodates only limited frequency band
Frequency Effect
Bandwidth: 500Hz
Bit rate: 2000 bits per second
Bits
Pulses before transmission.
Bit rate 2000 bps
Pulses after transmission become the solid line.
Bandwidth 500 Hz
Fundamentals of Communication and Networking: Networks and Transmission

21. Greater rate of transmission
Bit Rate and Bandwidth
Bandwidth directly affects bit rate
The greater the bandwidth, the greater the bit rate
Greater bandwidth
Greater rate of transmission
Bandwidth  Bit rate
(data rate of digital signal = W)
Single data rate = WHz
Double data rate = 2 WHz
Fundamentals of Communication and Networking: Networks and Transmission

22. Important Terms: Latency
We also have something called latency
It is the delay between starting an action/transmission, and the action/transmission being completed
Unguided medium are more prone to latency than guided medium
Due to physical obstacles
Geostationary satellites
Ground stations
Bit rate of uplink/downlink is high
(large bandwidth)
Considerable delays for 1 webpage
Microwave speed 3 x 108m/s
Round-trip distance over 143,200km
Propagation time delay approx. 0.4s
Fundamentals of Communication and Networking: Networks and Transmission

23. Asynchronous Data Transmission
We can also try and keep data in a group sent at the same time
Sending data in any order as fast as possible is known as asynchronous data transmission
No synchronisation between transmitter and receiver
Synchronisation
Only at time of transmission
Receiver synched with transmitter
a bc d efg hi j kl m
Asynchronous transmission
Each character contains its own start and stop pulses
No control over time between characters
a b c d e f g h i j k l m
Synchronous transmission
Fundamentals of Communication and Networking: Networks and Transmission

24. The Start Bit Receiver Arrival of data signalled by special bit
Wakes receiver
Sets receiver clock ticking
Transmitter
Operates clock
Determined by baud rate
00:00:25
Start Bit
Asynchronous
Arrival of data is unpredictable by receiver
00:00:25
Baud rate
Rate at which signals on a wire/line may change
Fundamentals of Communication and Networking: Networks and Transmission

25. Synchronise receiver clock
The Start Bit
Regular signal changes
Receiver and transmitter timing devices
Synchronised rate
Received bits read at same regular time intervals
Receiver
Must read bits in time interval between changes
Must match
Timing of transmitter’s transmission
Timing of receiver’s reading
Bits
09:42:36
11:42:36
Synchronise receiver clock
Match tick rate
Not match time
Synchronisation
Achieved by Start Bit
Fundamentals of Communication and Networking: Networks and Transmission

26. Asymmetrical to serial cable
The Start Bit
Serial connection
Null modem cable
Connects 2 computers
Asymmetrical to serial cable
Internal wiring ensures each wire connects to correct pin on each computer’s serial port
Computer A
Computer B
Fundamentals of Communication and Networking: Networks and Transmission

27. ! The Start Bit Link cable Idle state Start transmission Transmitter
Kept at voltage level of binary digit 1
Start transmission
Change voltage level to level for binary digit 0
Transmitter
Follows start bit with 7 or 8 data bits
If parity is enabled, last bit is followed by parity bit !
LSB
Idle Stop Parity
Idle state
Computer A
Computer B
Start
Bit
MSB
Start
Fundamentals of Communication and Networking: Networks and Transmission

28. Often represent character data from ASCII
The Start Bit
End of transmission
Transmitter attaches Stop bit
Chosen voltage level is level for binary digit 1
Stop bit time interval
Allows receiver to deal with received bits
Transfer to RAM
7 or 8 bits transmission
Often represent character data from ASCII
LSB
Idle Stop Parity
Idle state
Computer A
Computer B
MSB
Start
Fundamentals of Communication and Networking: Networks and Transmission

29. Often represent character data from ASCII
Odd/Even Parity
Check digit (parity bit)
Checks for changes in transmitted data
Parity bit set to 1 or 0
Even: Number of 1s across data and parity bits is even
Odd: Number of 1s across data and parity bits is odd
7 or 8 bits transmission
Often represent character data from ASCII
LSB
Idle Stop Parity
Idle state
Computer A
Computer B
MSB
Start
Fundamentals of Communication and Networking: Networks and Transmission

30. Odd/Even Parity Check digit (parity bit)
Checks for changes in transmitted data
Parity bit set to 1 or 0
Even: Number of 1s across data and parity bits is even
Odd: Number of 1s across data and parity bits is odd
Parity bit
Data bits
Even parity for 8 bits
Parity bit
Data bits
Odd parity for 8 bits
Fundamentals of Communication and Networking: Networks and Transmission

31. Parity-protected character coded in 8 bits
Odd/Even Parity
Transmitter
Generates correct parity bit
Attaches to end of data bits
Receiver
Regenerates parity bit from received data
Matching
Received parity bit against regenerated parity bit
An error is flagged where there is a difference
Only detects odd number of errors !
Parity bit
Data bits
Stop bit
Start bit
Parity-protected character coded in 8 bits
Fundamentals of Communication and Networking: Networks and Transmission

32. Handshaking Protocols
Data transmission protocol
Ensure successful communakazion
Between computers
Between computer and peripheral
Communikazshion protocol
A set of pre-agreed signals, codes and rules
2 T x Data
3 R x Data
4 DTR Data terminal ready
Ground
7 RTS (request to send)
8 CTS (clear to send)
Socket 5
Socket 1
Socket 9
Socket 6
Serial Port (COM 1)
Pin 2 Transmission
Pin 3 Reception
Pins 4, 7, 8 Control
Looking out of the COM 1 port from PC to peripheral
Fundamentals of Communication and Networking: Networks and Transmission

33. Handshaking Protocols
Involving exchange of signals
Transmitter
Checks if receiver is present
Checks if receiver is ready
Waits for response
RTS CTS
RTS
Data
Data terminal ready
Common 7 8 2 3 4
Printer
Computer
Fundamentals of Communication and Networking: Networks and Transmission

34. Handshaking Protocols
Transmitter
Receives signal ready
Coordinates data transmission
Informs receiver of incoming data
Waits for ready-for-more-data signal
RTS CTS
RTS
Data
Data terminal ready
Common 7 8 2 3 4
Printer
Computer
Fundamentals of Communication and Networking: Networks and Transmission

35. Handshaking Protocols
Computer   Printer
Serial ports C
Are you ready? P
Clear to send
(P pin 8)
Yes I am
Request to send
(C pin 7)
Here it is
Start bit
Busy
That’s it
Stop bit
I’m ready again
Fundamentals of Communication and Networking: Networks and Transmission

36. LAN operates in baseband mode
Network cable shared
Only 1 station transmits at any 1 time
Transmission Medium
Network cable
Entire bandwidth dedicated to
1 transmitter and 1 receiver !
Transmission medium
Turn taking
LAN operates in baseband mode
Short distance use
High performance
Low cost
Fundamentals of Communication and Networking: Networks and Transmission

37. Parallel transmissions
Broadband
Multichannel system
Several data channels combined onto carrier signal
Bandwidth shared by all
Single data streams would be wasteful
Multichannel
WAN operates in broadband mode
Long distance use
Expensive install/maintain
Parallel transmissions
2 or more data streams
Fundamentals of Communication and Networking: Networks and Transmission