Data Transmission Flashcards
(30 cards)
Types of transmissions
Serial transmission
Parallel transmission
Serial transmission, advantages and disadvantages
-Single wire
-Bits transmitted one at a time
-More reliable over long distances (bits less likely to be lost on the way)
-Order of arrival not mixed up
-Relatively slower than parallel
-Not suitable for large amounts of data over short distances
Parallel transmission, advantages and disadvantages
-8 wires
-8 bits transmitted at a time
-Faster than serial
-May arrive out of order
-Expensive
Types of data transmissions
-Simple
-Half-duplex
-Full-duplex
Simplex transmission and example
-Only one sender device (one-way)
-e.g printer and computer using USB cable
Half-duplex transmission and example
-Both devices can transmit and receive data (not at the same time)
-e.g walkie-talkies
Full-duplex transmission and example
-Both devices transmit and receive data at the same time
-e.g using broadband connection to play a video game
Data packets
Small units of data that are transmitted from a sending device to a receiving device
-Transmitted through a network communication protocol
Structure of a data packet
-Header
-Payload
-Trailer
Data packet Header
-IP address of sender
-IP address of receiver
-Packet number
Data packet Payload
-Actual data being sent
Data packet Trailer
Bits to show end of packet
What determines which route is taken by data packets?
Router
Factors that affect what route is taken by the packet
-Route availability
-Detected errors (corrupted/missing packets)
Packet switching
Data packets are each sent through different routes to get to destination
Advantages of Packet Switching
-Can take different routes
Disadvantages of Packet Switching
-May be dropped if moves around network for certain period without being delivered
Time to live (TTL)
Maximum amount of time a packet can stay on a network without being delivered
Measured in hops
USB
-Universal Serial Bus - communication interface used to connect devices to host computers
-Serial transmission
-USB device is plugged into USB port. USB cable connects the two.
Check Digit
-Extra digit added to a number calculated from the number’s existing digits.
-Used to check for errors during data entry
Parity checks
-Used to check data transmission errors
-Data in bytes
-Two types: even, odd
-Using a parity bit at the end or start of the binary number and sent another the data
-Cannot tell which bit was corrupted or changed during transmission
Checksum (4 steps)
Error detection method
1) If sum of bytes in block is less than or equal to 255, value is checksum
2) If sum of bytes in block is more than 255
a) Divide bytes by sum of 260 to get quotient
b) Round to nearest integer
c) Multiply int by 256
d) Subtrackt product from bytes sum to get chucksum
Echo check
-Receiving computer send exact copy of data to sending computer
-S. computer compares the original and new data
-If error detected, data is resent and echo check process restarts
ARQ
Automatic Repeat Query
-Set of rules established between Sending and Receiving computers to control errors.
-If error detected, S computer requested to resend packet
