AS AS ComputingComputing

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AS AS ComputingComputing

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Data TransmissionData Transmission

What data is transmitted?

PhoneSMSEmailRadioTVInternet

NetworksNetworksAllow communication between usersSharing of software & hardware

LANWAN

LAN & WANLAN & WAN

Local Area NetworkCovers a small area eg. Building or single siteMore secure than a WAN

Wide Area NetworkCovers wide geographical area – countries and even continents

Network Interface CardNetwork Interface CardNICConnects PC or peripheral to networkNetwork Operating System

Other Network HardwareOther Network Hardware

RoutersServers

Printer ServersFile ServersEmail Servers

BridgesGateways

What do you need for a What do you need for a LAN?LAN?

NICCablingServer

How is Data Transmitted?How is Data Transmitted?

Binary numbers are sent as either electronic pulses or fibre optic light beams

Methods of TransmittingMethods of Transmitting

Serial

Parallel

Serial & Parallel Serial & Parallel TransmissionTransmission

Serial1 bit is transmitted at a timeSingle wire

ParallelMany bits transmitted at a timeMany wires

Methods of TransmissionMethods of Transmission

SimplexOne direction

DuplexBoth directions simultaneously

Half DuplexBoth directions – one at a time

HandshakingHandshakingSignal sent between 2 devices to ensure they are both ready to communicate1st Device sends a handshake signal which is acknowledged by the other deviceThis states that each is now ready for communication

Bit RatesBit Rates

Number of bits that can be sent in 1 second.Units of BaudI bit per second = 1 Baud

Transmission ErrorsTransmission Errors

Binary numbers can be corrupted during transmission

Echoing backParity

Odd & EvenCheck sumPart of the Transmission Protocol

Parity BitsParity Bits

1 1 0 0 1 1 0Parity BitParity BitParity BitParity Bit

EvenEven ParityParity

1 1 0 1 0 0 0Parity BitParity BitParity BitParity Bit

1

0

Parity BitsParity Bits

1 1 0 0 1 1 0Parity BitParity BitParity BitParity Bit

OddOdd ParityParity

1 1 0 1 0 0 0Parity BitParity BitParity BitParity Bit

0

1

Checksum – Detecting Checksum – Detecting Transmission ErrorsTransmission Errors

Bytes send in blocksValue of bytes within the block are added togetherThat value is also sent in a byteChecksum byte is checked at receiving endIf checksum is incorrect then a transmission error has occured

ProtocolsProtocolsSet of rules that govern the transmission of data e.g. http or TCP/IPLogical Parts of Protocol

Type of error checking usedPacket size usedBaud Rate

Physically Parts of ProtocolCabling usedWireless or Hard wireFrequency data is sent

Circuit SwitchingCircuit Switching

Message is sent in its entirety through one predetermined routeTies up large areas of networkMessage packets remain in correct orderMessage can be more easily intercepted as it stays on the same route

Packet SwitchingPacket Switching

A message is split into packetsEach packet is sent to the destination via different routesPackets arrive at destination in different times and different orderPut back into order when all packets arriveMaximises use of networkMessage cannot be (easily) intercepted