3.3 - Digital Transmission of Digital Data Flashcards
All computer systems produce _____________
binary data
The _____________ is the language that computers use to represent data
coding scheme
A ___________ is a symbol that has a common, constant meaning
character
Characters in _______ ____________, as in computer systems, are represented by groups of bits that are binary zeros (0) and ones (1)
data communications
The groups of bits representing the set of characters that are the “alphabet” of any given system are called a ______ _______, or simply a code
coding scheme
A ______ is a group of consecutive bits that is treated as a unit or character
byte
One (1) byte is normally composed of ___ bits and usually represents one character
8
Three predominant coding schemes in use today:
- American Standard Code for Information Interchange (ASCII)
- ISO 8859
- Unicode
The most popular code for data communications and is the standard code on most microcomputers
ASCII
There are two types of ASCII:
- 7-Bit Code ASCII
- 8-Bit Code ASCII
Has 128 valid characters (2^7 = 128)
7-Bit Code ASCII
Has 256 characters (2^8 = 256)
8-Bit Code ASCII
Standardized by the International Standards Organization
ISO 8859
An 8-bit code that includes the ASCII codes plus non-English letters used by many European languages (e.g., letters with accents)
ISO 8859
_____________ often uses ISO 8859
HTML or Hypertext Markup Language
An information technology (IT) standard for the consistent encoding, representation, and handling of text expressed in most of the world’s writing systems
Unicode
Unicode versions:
- UTF-8 (8-Bit Version)
- UTF-16 (16-Bit Version)
Similar to ASCII
UTF-8
Uses 2 bytes (called a “word”); used by Windows; beyond English or Latin characters, has Cyrillic or Chinese
UTF-16
The way the internal transfer of binary data takes place inside a computer; data element is transferred simultaneously
Parallel transmission
If the internal structure of the computer is 8 bit, then all 8 bits of the data element are transferred between main memory and the central processing unit simultaneously on 8 separate connections
Parallel transmission
A stream of data is sent over a communication circuit sequentially in a bit-by-bit fashion
Serial transmission
There is only one physical wire inside the bundle, and all data must be transmitted over that one physical wire
Serial transmission
It takes n iterations or cycles to transmit n bits — thus, it is considerably slower than parallel transmission
Serial transmission
The transmission of binary electrical or light pulses in that it only has two possible states, a 1 or a 0
Digital transmission
The most commonly encountered voltage levels range from a low of +3/-3 to a high of +24/-24 volts
Digital transmission
All digital transmission techniques require:
- A set of symbols
- The symbol rate
- Unipolar Signaling
- Bipolar Signaling
Digital Transmission Techniques
Voltage is always positive or negative (single polarity, like in DC current)
Unipolar Signaling
A 0 volts (no current) is used to transmit a 0 and a signal of +5v is used to transmit a 1
Unipolar Signaling
The ones and zeros vary from a pulse voltage to a minus voltage (like an AC current)
Bipolar Signaling
A bipolar technique where the voltage alternates from +5 volts (a symbol indicating a 1) to -5 volts (a symbol indicating a 0) without ever returning to 0 volts
Nonreturn to zero (NRZ)
Another bipolar technique where it always returns to 0 volts after each bit before going to +5 volts (the symbol for a 1) or -5 volts (the symbol for a 0) — half of every bit pulse starts with zero
Return to zero (RZ)
A third bipolar technique where a 0 is always sent using 0 volts, but 1s alternate between +5 volts and -5 volts
Alternate mark inversion (AMI)
AMI is used on ____ and ____ circuits
T1…T3
The signaling used in Ethernet
Manchester
A special type of bipolar signaling in which the signal is changed from high to low or from low to high in the middle of the signal
Manchester
In Europe, bipolar signaling is sometimes called _____________ signaling because you are moving between a positive and negative voltage potential
double current
In general, ___________ signaling experiences fewer errors than __________ signaling because the symbols are more distinct
bipolar…unipolar
Changing the ___________ of a current (from positive to negative, or vice versa) is more difficult than changing its magnitude
polarity
