Fundamentals of Communication and Networking Networks and Transmission

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 … 0110011011101010 0101011111001010 0000110101011000 01011110100101… Storage / Transmission Electrical Magnetic Electromagnetic 0110000010101010 0010011011010010 0101110101011000 01011010100101… Fundamentals of Communication and Networking: Networks and Transmission

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

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

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

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

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

Transmission Methods: Serial Circuits will use different voltages to transmit data Similar to how data is transmitted inside a device Return Wire 5 V 0001 1011 0101 0 0 V X 5 V Fundamentals of Communication and Networking: Networks and Transmission

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

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

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

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

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

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

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

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

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

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

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

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 0 1 0 0 0 0 1 0 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

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

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

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

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

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

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 1 0 0 1 0 0 1 0 1 Fundamentals of Communication and Networking: Networks and Transmission

! 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 1 0 0 1 0 0 1 0 1 Fundamentals of Communication and Networking: Networks and Transmission

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 1 0 0 1 0 0 1 0 1 Fundamentals of Communication and Networking: Networks and Transmission

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 1 0 0 1 0 0 1 0 1 Fundamentals of Communication and Networking: Networks and Transmission

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 0 0 1 1 0 0 1 1 0 Parity bit Data bits Even parity for 8 bits 1 0 1 1 0 0 1 1 0 Parity bit Data bits Odd parity for 8 bits Fundamentals of Communication and Networking: Networks and Transmission

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 ! 1 1 0 1 1 0 0 1 1 0 0 Parity bit Data bits Stop bit Start bit Parity-protected character coded in 8 bits Fundamentals of Communication and Networking: Networks and Transmission

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

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

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

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

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

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