Chap 2 - Data transmission

Data packet structure

Packet header, payload, trailer

Inside the packet header

-Ip address of receiver and sender
-sequence of the packet
-packet size

Inside the payload

the actual data in the packet

Inside the trailer

-identification method
-error checking method

Cycle Redundancy Check (CRC)

the sending computer will add up all the 1-bits and stores it into the trailer, the receiver adds them to see if it's the same

Packet switching

A method of transmission when a message is broken up into a number of packets and sent through many routers

Pros of packet switching

relatively easy to expand package usage

Cons of packet switching

• packets can be lost and need to be re sent

• data may be skewed (when received)

Simplex transmission

one-way transmission

Half-duplex transmission

both directions but not at the same time

Full Duplex

Both directions at the same time

Serial data transmission

one bit at a time over a single wire
- longer distance
-slower

Parallel data transmission

Several bits of data over several wires/channels

USB general facts

Universal Serial Bus
-serial data transmission
-allows half and full duplex

Red and black wires in a usb

Used for power

Parity checks

Counting up the 1's for an even or odd parity

Check sum

when dats is sent, an additional value is sent as the checksum

Echo check

Data is sent and then sent back for the original sender to check, if it's correct it will be sent back

Check digit

A final digit included in a code that is calculated from the other digits in the code

ISBN 13

add even and odd, times odd by 3, add both together divide by 10 then 10- remainder is your check digit

Modulo-11

Multiply the number with the weighted number and add them all up, divide total by 11 and do 11-remainder

Automatic Repeat Request (ARQ)

Uses positive and negative acknowledgements and timeouts for error checking

Plaintext

data before encryption

Cipher text

Data that has been encrypted.

Symmetric encryption

uses the same key to encrypt and decrypt data

Asymmetric encryption

uses public and private keys to encrypt and decrypt data.

White and green wires in a usb

For data transmission