Chapter 3

is the alternative used by IM and many other applications that provide voice services over lower speed digital circuits, works in same way as PCM in many ways. It samples incoming voice signal
8000 times per second and calculates the same 8 bit amplitude value as PCM. It transmits the difference between the 8 bit value instead

Pronounced "ask-e". An eight level code for data transfer adopted by the ANSI to achieve compatibility among
data devices

first height of the wave. Measured by decibals.
Our ears detect amplitude as loudness or volume of sound.

AKA amplitude shift keying (ASK), the amplitude or height of the wave is changed.

AKA Amplitude Modulation (AM), the amplitude or height of the wave is changed.

transmission of a continuously variably signal as opposed to a discrete on/off signal. The traditional way of
transmitting a telephone or voice signal is analgo

the difference between the highest and lowest frequencies in a band. For example, a voice grade circuit has a 4,000 Hz bandwidth. In common usage, bandwidth refers to circuit capacity. When people say they need more bandwidth, they need a higher transmission speed

a baud is a unit of signaling speed used to indicate the number of
time per second the signal on the communication circuit changes, AKA "symbol rate"

in bipolar signaling, the 1's and
0's vary from a plus voltage to a
minus voltage. NRZ, RZ.
signaling experiences fewer
errors than unipolar signaling
because symbols are more
distinct

the rate at which bits are transmitted over a communication path, normally expressed in bps.

bits per second, the basic unit of data communication rate measurement, Usually refers to rate of
information bits transmitted

a standard for IMUX where any IMUX circuit can communicate with any other IMUX circuit that conforms to the same standard. BONDING splits outgoing messages from one client or host across several low speed telephone lines and combines incoming message from
several telephone lines into one circuit so that the client or host "thinks" it has a faster circuit.

transmitting a simple sound wave through the circuit

used in divisions of multiplexing; it is a sperate logical circuit and the devices connected to them are unaware that their circuit is multiplexed.

has 2 very different meanings:
1. referring to "physical circuit"
the actual wire used to connect
2 devices. 2. referring to a
"logical circuit" used to connect
two devices which refers to the
transmission characteristics of
the connection (T1)

the basic physical layout of the circuit. There are
2 types of configurations, 1. point to point 2. multipoint

a type of guided media that is quickly disappearing. It has copper core, with an outer cylindrical shell for insulation.

a device used to translate analog voice data into digital form for transmission over digital computer circuits. There are 2 codecs, one at senders end and one at receivers.

the language that computers use to represent data

is installed in the customers home or office and another DSL modem is installed at the
telephone company switch closet to the customers home or office

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can increase throughput of data over a communication link bu literally compressing the data.

AKA as bit rate, is calculated by multiplying the number of bits sent
on each symbol by the maximum symbol rate.

one approach to changing the way data are transmitted in the local loop to provide higher speed data transfer. DSL is a family of techniques that combines analog transmission and FDM to provide a set of voice and data circuits.

transmission of binary electrical or light pulses in that it only has two possible state, a 1 or a 0. All transmissions require a
set of symbols and symbol rate.

uses high speed streams of light pulses from lasers or LEDs that carry information inside hair then strands of glass called optical fibers.

second characteristic of a wave, is the length, usually expressed as the number of waves per second. Our ears detect frequency as the pitch of the sound. It is the inverse of the length of the sound wave.

can be described as dividing the circuit "horizontally" so that many signals can travel a single communication circuit simultaneously. It is divided into a series of seperate channels, each transmitting on a different frquency, much like series of different radio or TV stations

AKA frequency shift keying (FSK), is a modulation technique whereby each 0 or 1 is represented by a number of waves per second.

AKA frequency modulation (FM), is a modulation technique whereby each 0 or 1 is represented by a number of waves per second.

can transmit in both directions simultaneously
with no turnaround time

are the unused portions of the circuit that separate these frequencies from each other

media in which the message flows through a physical media such as a twisted pair wire, coaxial cable or fiber optic cable

is two way transmission, but you can transmit in only one direction at a time. This type of link is similar to a walkie talkie link. Only one at a time.

measure of symbol rate (64 Hz is
64,000 symbols per second.

uses low frequency light waves to carry the data through the air on a direct line of sight path between two points.

combines several low speed circuits to make them appear as one high speed circuit to the user. One of most common IMUX is to provide T1 circuits for WANs.

another commonly used coding scheme which is standardized by the International Standards
Organization. It is an 8 bit code that includes ASCII code plus non English letters used by many European languages.

builds a dictionary of two-, three- and four character combinations that occur in the message.

sometimes call "last mile";
the wires that run from
your home or business to
the telphone switch that
connect your local loop
into the telephone network

other circuit meaning referred to connection/transmission characteristics of two devices

a special type of bipolar signaling in whcih the signal is changed from high to low or from low to high in the middle of the signal. It is less susceptible to having errors go undetected because if there is no transition in midsignal the receiver knows that an error must have occurred.

an extremely high frequency radio communication beam that is transmitted over a direct line of sight path between any two points. It has extremely short wavelength.

an acronym for modulator/demodulator, takes the digital data from a computer in the form of electrical pulses and converts them into the analog signal that is needed for transmission over an analog voice-grade circuit

also called "shared circuit". Many computers are connected on the same circuit. This means that each must share the circuit with the others. The disadvantage is that only one computer can use the circuit at
a time.

means to break one high speed physical communication circuit into severak kower speed logival circuits so that many different devices can simultaneously use it but still "think" that they have their own separate circuits.

the way the internal transfer of binary data takes place inside a computer. 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
CPU simultaneously on 8 separate connections.

third characteristic of a wave, refers to the direction in which the wave begins. It is measured in terms of degrees.

AKA phase key shifting (PSK); is the most difficult to understand. Phase refers to the direction in which the wave begins. One phase symbol is defined to be a 0 and the other phase symbol is define to be a
1.

AKA Phase Modulation (PM); is the most difficult to understand. Phase refers to the direction in which the wave begins. One phase symbol is defined to be a
0 and the other phase symbol is define to be a 1.

the actual wire used to connect 2 devices

the telephone system enables voice communication between any two telephones within its network, converts sounds waves into electrical signals.

a circuit configuration in which it goes from one point to another (1 computer to another computer). Sometimes called "dedicated circuits". This is
used when computers generate enough data to fill the capacity of the communication circuit.

the plus (+) or minus (-) measurements of an electrical current

North American telephone network uses this. With PCM, the input voice signal is sampled 8000 times oer second. Each time the input voice signal is sampled, 8 bits are generated. Therefore the transmission speed on the digital circuit must be 64,000 bps to transmit a voice signal when it is in digital form.

popular technique in combining modulation techniques. It involves splitting the symbol into 8 different phases (3 bits) and two different aptitudes (1 bit) for a total of 16 different possible values. Thus one symbol in QAM can represent 4 bits.

the difference between two (original/digitized) signals

one of most commonly used forms of wireless media. It uses the same basic principles as standard radio transmission

amount of time half duplex communication takes to switch between sending and receiving. AKA turnaround time or relocking time

similiar to microwave transmission except instead of transmission involving another nearby microwave dish antenna, it involves a satellite many miles in space

means that a stream of data is sent over a communication
circuit sequentially in a bit by bit fashion

is one way transmission such as that with radios and TVs

is the exception to the rule that the capacity of the multiplexed circuit must equal the sum of the circuits it combines. STDM allows more terminals or
computers to be connected to a circuit than does FDM or TDM.

contains the codec that converts the analog signal from your phone into a digital signal

the number of symbols that will be sent over the circuit per second

shares a communication circuit among two or more terminals by
having them take turns, dividing the circuit "vertically" so to speak.

amount of time half duplex communication takes to switch between sending and receiving. AKA retrain time or relocking time

one of most commonly used guided media is this. Insulated pairs of wires than can be packed quite close together. The wire are usually twisted to minimize the electromagnetic interference between one pair and any other
pair in the bundle.

the other commonly used coding scheme. Many different types. UTF 8 - 8 bit version similar to ASCII, UTF 16- 16 bits that can represent many more character beyond the usual English or Latin characters

one of four types of digital transmission techniques; this is always positive or negative.

commonly used to transmit phone conversations over digital networks. Relatively new standrd that uses digital telephones with built in codes to convert analog voice data into digital data

is a version of FDM used in fiber optic cables. WDM works by using lasers to transmit different frequencies of light through the same fiber optic cable. Each logical circuit is assigned a different frequency and the devices attached to
the curcuit dont "know" they are multiplexed over the same physical circuit

media in which the message is broadcast through the air such as infrared, microwave, or satellite.

the ISO standard for data compression, uses Lempel-Ziv encoding.

more commonly called ASCII, is the most popular code for
data communications and is the standard code on most microcomputers. There are two types of ASCII, one is 7 bit code, the other is 8 bit code.