This is very helpful to get knowledge about BCA

1. Analog and Digital Communications Concepts: Concept of data, signal, channel, bid-
rate ,maximum data-rate of channel, Representing Data as Analog Signals,
Representing Data asDigital Signals, Data Rate and Bandwidth, Capacity, Baud Rate;
Asynchrous and synchroustransmission, data encoding techniques, Modulation
techniques, Digital Carrier Systems;Guided and Wireless Transmission Media;
Communication Satellites; Switching and
Multiplexing; Dialup Networking; Analog Modem Concepts; DSL Service
Analog Signals
An analog or analogue signal is any continuous signal for which the time varying feature
(variable) of the signal is a representation of some other time varying quantity, i.e., analogous to
another time varying signal. It differs from a digital signal in terms of small fluctuations in the
signal which are meaningful. Analog is usually thought of in an electrical context; however,
mechanical, pneumatic, hydraulic, and other systems may also convey analog signals.
Digital Signals
A digital signal is a chemical signal that is a representation of a sequence of discrete values (a
quantified discrete-time signal), for example of arbitrary bit stream, or of a digitized (sampled
and analog-to-digital converted) analog signal. The term digital signal can refer to
1. a continuous-time waveform signal used in any form of digital communication.
2. a pulse train signal that switches between a discrete number of voltage levels or levels of
light intensity, also known as a a line coded signal, for example a signal found in digital
electronics or in serial communications using digital baseband transmission in, or a pulse
code modulation (PCM) representation of a digitized analog signal.
A signal that is generated by means of a digital modulation method (digital pass band
transmission), produced by a modem, is in the first case considered as a digital signal, and in the
second case as converted to an analog signal.

2. In telecommunications in general, a channel is a separate path through which signals can flow.
2) In the public switched telephone network (PSTN), a channel is one of multiple transmission
paths within a single link between network points. For example, the commonly used (in North
America) T-carrier system line service provides 24 64 Kbps channels for digital data
transmission.
3) In radio and television, a channel is a separate incoming signal or program source that a user
can select.
4) In optical fiber transmission using dense wavelength-division multiplexing (DWDM), a
channel is a separate wavelength of light within a combined, multiplexed light stream.
5) On the World Wide Web, a channel is a preselected Web site that can automatically send
updated information for immediate display or viewing on request. See push technology.
6) In computer and Internet marketing, a channel is a "middleman" between a product creator
and the marketplace. Value-added resellers (VAR) and retail store chains are examples of
channels in this context.
7) Using Internet Relay Chat, a channel is a specific chat group.
8) In IBM mainframe systems, a channel is a high bandwidth connection between a processor
and other processors, workstations, printers, and storage devices within a relatively close
proximity. It's also called a local connection as opposed to a remote (or telecommunication)
connection.

3. 1) A transmission path .
(2) A set of properties that distinguishes one channel from another. For example, TV channels
refer to particular frequencies at which radio waves are transmitted. IRC channels refer to
specific discussions.
(3) In sales and marketing, the way in which a vendor communicates with and sells products to
consumers.
In a field-effect transistor, such as a MOSFE T, a channel is the semiconductor path on which
current flows.
(5) For IBM PS/2 computers, a channel is the same as an expansion bus.
(6) In audio and sound terms channel refers to an individual discrete audio track. When referring
to more than two channels it is called multichannel.
n digital telecommunication, the bit rate is the number of bits that pass a given point in a
telecommunication network in a given amount of time, usually a second. Thus, a bit rate is
usually measured in some multiple of bits per second - for example, kilobits, or thousands of bits
per second (Kbps). The term bit rate is a synonym for data transfer rate (or simply data rate). Bit
rate seems to be used more often when discussing transmission technology details and data
transfer rate (or data rate) when comparing transmission technologies for the end user.
Maximum Data Rate of a Channel. Nyquist - Shannon
Theorem.
During the early 1920s H. Nyquist derived an equation expressing the maximum data rate for a
finite bandwidth noiseless channel. Nyquist's theorem states that a waveform must be sampled
twice in order to get a true representation and the sampling frequency must be at least twice the
highest signal frequency. In more scientific words the theorem states that a random signal passed
through a low pass filter of bandwidth H, the resulting filtered signal can be completely
reconstructed by making only 2H samples per second. Sampling faster will be pointless as the
higher frequency components that such sampling could recover have filtered out. Expressing this
theorem mathematically will look like
maximum data rate = 2H log2 V bits/sec
Where: H is the bandwidth of the channel and
V are the discrete levels the signal consists of

4. So a noiseless 4kHz channel cannot transmit binary signals at a rate exceeding 8000bps.
In reality such noiseless channels are not so common. Usually an amount of thermal noise is
present in the channel and is measured by the ratio of the signal power over the noise power and
is called Signal to Noise Ratio. Based on the Nyquist theorem C. Shannon came later on and
extended the theorem to the case of a channel subject to random noise. The result of Shannon's
work is given by:
maximum number of bits/sec = H log2 (1 + S/N)
Where: H is the noisy channel's bandwidth and
S/N is the Signal to Noise Ratio
andwidth and data rate belongs to the world of Internet connections, basically from web hosting,
and used to determine the amount of data being transferred (bit) in a given time, normally in a
second. In network communication and system, both have different meaning and purposes,
which makes them different from each other. Scroll down for the brief introduction of bandwidth
and data rate so that next time you can choose the best option for your web hosting and network
system.
Bandwidth:
Bandwidth is a wider term, which is basically associated with the computer networking and
digital technologies and measures the bit rate of communication resources available or
consumed. It was used firstly in analog tools for submission of radio transmission and
electromagnetic signals. If talk about computing then it means how much amount or bits of data
can be transferred in a time period, normally in one second. For example, if the bandwidth of an
Internet connection is 1 MB then it means it can transfer the 1 MB amount of data within one
second. It is measured in hertz, bps, kbps and mbps. Mbps, kbps or bps are used for digital
devices while hertz is used for analog devices.
Data Rate:
Data rate is the term associated with the rate of data transferred between two or more computing
and telecommunication devices or systems. It describes how much binary digits or bits can be
transferred in a given time, normally in one second. Mostly data transferred rate is measured in
Mbps. Data rate depends upon the bandwidth of Internet connection. If the bandwidth rate is
high, data rate will be also high and vice versa. But data rate can never be high despite having a
high bandwidth Internet connection. In respect of web hosting, data rate means at which rate data
is transferred from web server to website in a period of time, normally in second.
 Hz, bps, kbps and Mbps are used for the measurement of bandwidth while in data rate,
Mbps is used as a basic measurement unit.

5.  In a network connection, bandwidth is always higher than data rate because data rate
depends upon how much bandwidth is available for transmission.
 In case of website hosting, increase in visitor strengths increases the bandwidth speed of
server while on the other hand data transfer rate decreases.
 Bandwidth is a wider term than data rate. Bandwidth is associated with how much
amount of speed is available to you and data rate is associated with transfer of data.
Definition - What does Capacity mean?
In the context of networks, capacity is the complex measurement of the maximum amount of
data that may be transferred between network locations over a link or network path. Because of
the amount of intertwined measurement variables and scenarios, actual network capacity is rarely
accurate.
Capacity is also known as throughput.
Techopedia explains Capacity
Capacity depends on the following variables, which are never constant:
 Network engineering
 Subscriber services
 Rate at which handsets enter and leave a covered cell site area
Wireless carriers are pushed to increase network capacity to accommodate user demand for high-
bandwidth services. Until recently, subscribers used wireless networks to make calls or send
Short Message Service (SMS)/Multimedia Message Service (MMS) messages. Today, capacity
is required to handle increased subscribers and additional services, including:
 Web browsing
 Facebook updates
 Digital file downloads, like e-books
 Streaming audio/video
 Online multiplayer games
Because of marginal network capacity costs, providers focus on offering packaged and a la carte
services, such as location-based add-ons and products, like ring tones, to create additional
revenue with negligible operational expense effect.
al-up remote access is a remote access technology that is available as part of the Routing and
Remote Access service (RRAS).

6. Dial-up remote access provides a simple solution for organizations that want to allow employees
to remotely access their corporate e-mail accounts and shared files from home or from other
locations outside the corporate network. With dial-up remote access, a remote access client can
use the wide area network (WAN) infrastructure to connect to a remote access server. A remote
access client uses the telephone system to create a temporary physical circuit or a virtual circuit
to a port on a remote access server. After the physical or virtual circuit is created, the rest of the
connection parameters can be negotiated. Dial-up networking supports demand-dial routing to
help reduce telephone costs.
Components of a dial-up remote access connection
A dial-up remote access connection contains the following components:
Remoteaccessclient
Remote access clients running Windows, UNIX, and Macintosh can connect to a RRAS remote
access server.
Remoteaccessserver
The RRAS remote access server accepts dial-up connections and forwards packets between
remote access clients and the network to which the RRAS server is attached.
Dial-upequipmentandthe WAN infrastructure
The physical or logical connection between the remote access server and the remote access client
is facilitated by dial-up equipment installed at the remote access client, the remote access server,
and the WAN infrastructure. The nature of the dial-up equipment and WAN infrastructure varies,
depending on the type of connection. The following sections describe the most common methods
for dial-up remote access.
PSTN
PSTN, also known as Plain Old Telephone Service (POTS), is the analog phone system designed
to carry the minimum frequencies required to distinguish human voices.

7. Dial-up equipment consists of an analog modem at the remote access client and at least one
analog modem at the remote access server. For large organizations, the remote access server is
attached to a modem bank containing up to hundreds of modems. Because PSTN was not
designed for data transmission, its transmission bit rate is limited compared to other connection
methods.
Standard PSTN connection
Digital links and V.90
The maximum bit rate of PSTN depends on the range of frequencies being passed by PSTN
switches and the signal-to-noise ratio of the connection. The modern-day analog phone system is
only analog on the local loop, the set of wires that connect the customer to the central office
(CO) PSTN switch. After reaching the PSTN switch, the analog signal is converted to a digital
signal.
When an RRAS server is connected to a CO by using a digital switch based on T-Carrier or
ISDN rather than an analog PSTN switch, there is a higher signal-to-noise ratio because of fewer
digital to analog conversions and, therefore, a higher maximum bit rate.
With this technology, called V.90, remote access clients can send data at 33.6 kilobits per second
(Kbps) and receive data at 56 Kbps. In the United States, the maximum receive bit rate is 53
Kbps due to Federal Communications Commission (FCC) power rules.
To obtain V.90 speeds:
 The remote accessclientmustbe usinga V.90 modem.
 The remote accessservermustbe usinga V.90 digital switchandmustbe connected toPSTN
usinga digital link,suchasT-Carrieror ISDN.
 There cannot be any analog-to-digital conversionsinthe pathfromthe remote accessserverto
the remote accessclient.
PSTN connection with V.90

8. https://technet.microsoft.com/en-us/library/dd469811.aspx
hen you connect to the Internet, you might connect through a regular modem, through a local-
area network connection in your office, through a cable modem or through a digital subscriber
line (DSL) connection. DSL is a very high-speed connection that uses the same wires as a
regular telephone line.
Here are some advantages of DSL:
 You can leave your Internet connection open and still use the phone line for voice calls.
 The speed is much higher than a regular modem
 DSL doesn't necessarily require new wiring; it can use the phone line you already have.
 The company that offers DSL will usually provide the modem as part of the installation.
But there are disadvantages:
 A DSL connection works better when you are closer to the provider's central office. The
farther away you get from the central office, the weaker the signal becomes.
 The connection is faster for receiving data than it is for sending data over the Internet.
 The service is not available everywhere.
In this article, we explain how a DSL connection manages to squeeze more information through
a standard phone line -- and lets you make regular telephone calls even when you're online.
Telephone Lines
If you have read How Telephones Work, then you know that a standard telephone installation in
the United States consists of a pair of copper wires that the phone company installs in your
home. The copper wires have lots of room for carrying more than your phone conversations --
they are capable of handling a much greater bandwidth, or range of frequencies, than that
demanded for voice. DSL exploits this "extra capacity" to carry information on the wire without
disturbing the line's ability to carry conversations. The entire plan is based on matching
particular frequencies to specific tasks.
To understand DSL, you first need to know a couple of things about a normal telephone line --
the kind that telephone professionals call POTS, for Plain Old Telephone Service. One of the
ways that POTS makes the most of the telephone company's wires and equipment is by limiting
the frequencies that the switches, telephones and other equipment will carry. Human voices,

9. speaking in normal conversational tones, can be carried in a frequency range of 0 to 3,400 Hertz
(cycles per second -- see How Telephones Work for a great demonstration of this). This range of
frequencies is tiny. For example, compare this to the range of most stereo speakers, which cover
from roughly 20 Hertz to 20,000 Hertz. And the wires themselves have the potential to handle
frequencies up to several million Hertz in most cases.
The use of such a small portion of the wire's total bandwidth is historical -- remember that the
telephone system has been in place, using a pair of copper wires to each home, for about a
century. By limiting the frequencies carried over the lines, the telephone system can pack lots of
wires into a very small space without worrying about interference between lines. Modern
equipment that sends digital rather than analog data can safely use much more of the telephone
line's capacity. DSL does just that.
A DSL internet connection is one of many effective communication tools for keeping employees
in touch with the office.