Comms 2 (Mod 3 & 5) Flashcards
Number of binary bits 1’s or 0’s to be transmitted per second
Bit rate
The number of line “symbols” transmitted per second
Baud rate
Number of transmission channels
Channels
Machine code is also called
Machine language
In machine code when we say possible combination it refers to
Code points
Types of characters in machine codes
- Alphanumeric
- Format Effector
- Control (device and transmission)
4 types of specific code
- Baudot code
- American Standard Code for Information Exchange (ASCII)
- Extended Binary Coded Decimal Interchange Code (EBCDIC)
- UNICODE
How many bits and code points does baudot code have
- 5 bits
- 32 code points
What institution created ASCII
American National Standard Institution
How many bits does ASCII have
- 7 bits
- 8 bits for parity bit
How many most significant bits and least significant bits does ASCII have
- 6 to 4 MSB
- 3 to 0 LSB
What type of specific code is used by microcomputers
ASCII
Baudot code is also called as
International teleprinter code
How many characters in ASCII
128
How many bits in EBCDIC
8 bits
What type of specific code is used on IBM mainframe computers
EBCDIC
How many most significant bits and least significant bits does EBCDIC have
- 0 to 3 MSB
- 4 to 7 LSB
Types of signal
- Digital
- Analog
No. of signal changes (amplitude, frequency, or phase) on a circuit per second
Signal rate (baud)
No. of bits that a circuit can carry in 1 second
Speed (bps)
- Height of the signals
- Susceptible to noise and interference
Amplitude modulation (AM)
- Frequency shift keying (FSK)
- Width of the signals
- Less interference than AM
Frequency modulation (FM)
Phase shift keying (PSK): a change from 1 to 0, or 0 to 1
Phase modulation (PM)
In phase modulations how many bits are the following
- 180 deg
- 90 deg
- 45 deg
- 1 bit
- 2 bits
- 3 bits
In this modulation it combines phase and amplitude
Quadrature Amplitude modulation (QAM)
what does 16QAM mean
16 different events with 4 bits/baud
Types of modulation
- Amplitude modulation
- Frequency modulation
- Phase modulation
- Quadrature amplitude modulation
Amplitude refers to
Loudness
Frequency refers to
Vibration speed
Phase refers to
position of wave measured in degree
2 station data communication circuit diagram/flow
Digital information source -> Transmitter -> Transmission medium -> Receiver -> Digital information destination
may come from a mainframe computer, personal computer, workstation, or any other digital equipment.
source/destination
encodes the source information and converts it to a different form and the transmitter acts as an interface between the source equipment and the transmission medium.
transmitter
carries the encoded signals from the transmitter to the receiver.
transmission medium
types of transmission medium
- free space radio transmission
- Metallic cables
- Optical fiber cables
converts the encoded signals received from the transmission medium back to their original form. The receiver acts as an interface between the transmission medium and the destination equipment.
receiver
used to represent characters and symbols such as letters, digits and punctuation marks
data communication codes
data communication codes are called
- character code
- character sets
- character languages
- symbol codes
it interface computers, computer networks and other digital terminal equipment to analog communication lines and radio channels
data modem
a modem is sometimes called
- Data communication equipment
- Data Set
- Data phone
Modem use one of the following modulation technique
- Amplitude shift keying
- Frequency shift keying
- Phase shift keying
- Quadrature amplitude modulation
2 types of modems
- Synchronous
- Asynchronous
In these type of Modems, clocking information is recovered in the receiver.
Synchronous
In these type of Modems it uses the modulation technique PSK and QAM
Synchronous
In these type of Modems it can be used for medium and high speed applications up to 57.6 Kbps
Synchronous
In these type of Modems, clocking information is not recovered at receiver and may not require.
Asynchronous
In these type of Modems it uses the modulation technique ASK and FSK
Asynchronous
In these type of Modems it can be used for low speed applications below 2.4 Kbps
Asynchronous
Modem Control
AT - Attention
A - Answer an incoming call
DT - Dial using DTMF tones
DP - Dial using Pulse dialing
E0 - Do not echo transmitted data to terminal screen
E1 - Echo transmitted data to terminal screen
F0 - Half duplex communication
F1 - Full duplex communication
H - Go on hook (hang up)
O - Switch from command to on-line mode
Z - Reset mode
+++ - Switch from on-line mode to command mode (escape code)
Types of AT mode
- AT command mode
- AT on-line mode
All modem commands in the AT command set begin with the ASCII characters
AT (Attention)
Once communications have been established with a remote modem, the local modem switches to the
on-line mode
2 categories of error control
- Error detection
- Error correction
What error control category is being referred when transmitted data is corrupted
Error detection
What error control category is being referred when original data is corrupted
Error correction
Baud rate of sync modem
2400
Baud rate of async modem
1200 - 1800
In a frame, there is only one bit, anywhere though, which is corrupt
single bit error
Frame is received with more than one bits in corrupted state
multiple bit error
Frame contains more than 1 consecutive bits corrupted
burst error
