AS Computing F451 F451 Data Transmission
What data is transmitted? Phone SMS Radio TV Internet
Networks Allow communication between users Sharing of software & hardware LAN WAN
LAN & WAN Local Area Network Covers a small area eg. Building or single site More secure than a WAN Wide Area Network Covers wide geographical area – countries and even continents
Network Interface Card NIC Connects PC or peripheral to network Network Operating System
Other Network Hardware Routers Servers Printer Servers File Servers Servers Bridges Gateways
What do you need for a LAN? NIC Cabling Server
How is Data Transmitted? Binary numbers are sent as either electronic pulses or fibre optic light beams
Methods of Transmitting Serial Parallel
Serial & Parallel Transmission Serial 1 bit is transmitted at a time Single wire Parallel Many bits transmitted at a time Many wires
Methods of Transmission Simplex One direction Duplex Both directions simultaneously Half Duplex Both directions – one at a time
Handshaking Signal sent between 2 devices to ensure they are both ready to communicate 1 st Device sends a handshake signal which is acknowledged by the other device This states that each is now ready for communication
Bit Rates Number of bits that can be sent in 1 second. Units of Baud I bit per second = 1 Baud
Transmission Errors Binary numbers can be corrupted during transmission Echoing back Parity Odd & Even Check sum Part of the Transmission Protocol
Parity Bits Parity Bit Even Parity Parity Bit 1 0
Parity Bits Parity Bit Odd Parity Parity Bit 0 1
Checksum – Detecting Transmission Errors Bytes send in blocks Value of bytes within the block are added together That value is also sent in a byte Checksum byte is checked at receiving end If checksum is incorrect then a transmission error has occured
Protocols Set of rules that govern the transmission of data e.g. http or TCP/IP Logical Parts of Protocol Type of error checking used Packet size used Baud Rate Physically Parts of Protocol Cabling used Wireless or Hard wire Frequency data is sent
Circuit Switching Message is sent in its entirety through one predetermined route Ties up large areas of network Message packets remain in correct order Message can be more easily intercepted as it stays on the same route
Packet Switching A message is split into packets Each packet is sent to the destination via different routes Packets arrive at destination in different times and different order Put back into order when all packets arrive Maximises use of network Message cannot be (easily) intercepted