Networking resources for IPT


9 Δεκ 2013 (πριν από 3 χρόνια και 8 μήνες)

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Networking resources for IPT

This is a sheet of information for teachers to prepare for the networking components of
System Tools

Transmitting and receiving

Always good for background material:


From Discovering Computers 2001

1. What Components Are Required for Successful Communications?

When referring to computers, communica
tions describes a process in which one computer
transfers data, instructions, and information to another computer(s). Communications require: a device
that initiates the transfer (a sending device); a communications device (such as a modem) that converts
he sent material into signals capable of being carried by a communications channel; a communications
channel over which the signals are sent; a communications device that receives the signals and
converts them into a form understood by the receiving device
; and a device that accepts the sent
material (a receiving device).

2. How Is Communications Used?

mail (electronic mail) is the exchange of text messages and computer files via a
communications network. Voice mail functions much like an answering m
achine but converts an analog
voice message into digital form. A fax (facsimile) machine sends and receives documents via telephone
lines. Smart phones are cell phones that track phone calls and their costs, include PDA functions, and
offer Internet capabi
lities. Instant messaging is a communications service that notifies you when people
are online and allows you to exchange messages or files. Telecommuting allows employees to work
away from the standard workplace and communicate using some communications t
Videoconferencing uses video and computer technology to conduct a meeting between participants at
separate locations. Groupware is a software application that helps people work together and share
information over a network. A global positioning
system (GPS) consists of earth
based receivers that
analyze satellite signals to determine the receiver’s geographic location. An electronic bulletin board
system (BBS) is a computer that maintains a centralized collection of electronic messages. The
net, a worldwide collection of networks, offers the World Wide Web and such popular Web
activities as e
commerce and Internet telephony.

3. What Are Various Types of Transmission Media?

Transmission media consists of materials or techniques capa
ble of carrying a signal. Physical
transmission media, which use tangible (touchable) materials to send communications signals, include
pair cable, coaxial cable, and fiber
optic cable. Twisted
pair cable consists of twisted
pair wires
bundled toge
ther. Coaxial cable consists of a single copper wire surrounded by three layers (insulating
material, braided metal and a plastic outer coating). Fiber
optic cable consists of dozens or hundreds of
thin strands of glass or plastic that use light to transmi
t data. Wireless transmission media, which send
communications signals through air or space, include broadcast radio, cellular radio, microwaves,
communications satellites, and infrared. Broadcast radio distributes radio signals through the air over
long d
istances. Cellular radio is a form of broadcast radio used widely for mobile communications.
Microwaves are radio waves that provide a high
speed signal transmission. A communications satellite
is a space station that receives microwave signals from an ear
based station, amplifies the signals,
and broadcasts the signals back over a wide area to any number of earth
based stations. Infrared
sends signals using infrared light waves.

4. Why Is Communications Software Used?

Communications software manages
the transmission of data, instructions, and information
between computers. For two computers to communicate, they must have compatible communications
software. Communications software usually includes a dialing feature (for storing, reviewing, selecting
d dialing), a file transfer feature (for sending one or more files from one computer to another), a
terminal emulation feature (allows a personal computer to act as a terminal), and an Internet access
feature (for sending e
mail, participating in chat room
s, and visiting Web sites).

5. What Are Commonly Used Communications Devices?

A communications device is any type of hardware capable of transmitting data, instructions, and
information between a sending device and a receiving device. A modem converts
a computer’s digital
signals into analog signals (modulate) so they can be transmitted over standard telephone lines, and
then reconverts the analog signals into digital signals (demodulate) that a computer can understand. A
cable modem is a modem that sen
ds and receives data over the cable television (CATV) network,
which consists largely of coaxial cable. A multiplexer combines input signals from telephone lines or
communications devices into a single stream of data and then transmits it over a transmissi
on medium.
A network interface card is an expansion card inserted into an expansion slot of a PC or other device,
enabling the device to connect to a network. Various devices are used to interconnect networks,
including hubs, repeaters, bridges, gateways,
and routers.

6. How Is a Local Area Network Different from a Wide Area


A local area network (LAN) is a network that connects computers in a limited geographical area,
such as a school computer laboratory, office, or group of bui
ldings. Two popular types of LANs are
peer networks and client/server networks. A wide area network (WAN) is a network that covers
a large geographical area (such as a city or country) using a communications channel that combines
telephone lines, m
icrowave, satellites, or other transmission media.

7. What Are Communications Protocols?

A protocol is a set of rules and procedures for exchanging information among computers. Using
the same protocols, different types and makes of computers can commun
icate with each other.
Ethernet is a LAN protocol that allows personal computers to contend for access to a network. A token
ring protocol controls access to a network by requiring that a special signal called a token is shared or
passed among network devi
ces. TCP/IP (Transmission control protocol/Internet protocol) is a set of
protocols used to manage data transmission by breaking it up into packets.

8. How Are Intranets and Extranets Used?

Intranets are internal networks that use Internet and Web techn
ologies. Intranets make
company information accessible to employees and facilitate working in groups. An extranet is an
intranet that extends to authorized users outside the company. Extranets facilitate communications
among a company’s customers or suppli
ers. A firewall denies intranet and extranet access to outsiders.

Syllabus Topics with some support

IPT looks at transmitting and receiving as the process that transfers information/data within
and between information systems

Communications concepts

serial and parallel


the next generation

From Computer World

Data stored on disk is made up of long strings (called tracks and sectors) of ones and zeroes
. Disk
heads read these strings one bit at a time until the drive accumulates the desired quantity of data and
then sends it to the processor, memory or other storage devices. How the drive sends that data affects
overall performance.

Years ago, all data
sent to and from disks traveled in serial form

one bit was sent right after another,
using just a single channel or wire.

With integrated circuits, however, it became feasible and cheap to put multiple devices on a single
piece of silicon, and the parallel

interface was born. Typically, it used eight channels for transmission,
allowing eight bits (one byte) to be sent simultaneously, which was faster than straight serial
connections. The standard parallel interface used a bulky and expensive 36
wire cable.

So why are vendors dropping parallel interfaces in favor of serial ones, when we need to get data to
and from disks faster than ever?

or example, most printers don't even come with parallel ports anymore. Laptops have dropped
traditional parallel and ser
ial ports in favor of higher
speed Universal Serial Bus and IEEE 1394 ports.
QuickLink 29332

for more about these technologies.] We now see this same migration in the
interfaces that connect disk dr

At first glance, this seems counterintuitive. Isn't parallel more efficient than serial, with more capacity?
Not really, and certainly not anymore. At current speeds, parallel transmission has several

Processing Overhead

First, remembe
r that data is stored and retrieved one track at a time, one bit at a time. We talk about
bytes for convenience, but a byte is just a line of eight bits in a row, and ultimately, we have to process
each bit separately.

Thus, before we can send a byte in pa
rallel to a disk drive, we have to get those eight bits and line them
up, funneling each to a different wire. When we've done all the processing and moving to get them all
ready, we fire off that byte.

At the other end of the cable, when the drive receives

the bits, it must go through the reverse process to
convert that byte back into a serial bit stream so the disk drive write heads can write it to the disk.

To visualize this another way, think about what's almost precisely the reverse process

arallel to serial for transmission and back again. This is what happens in sending Morse code over a
telegraph line. The message starts out as written words (think parallel) on a sheet of paper. A processor
(i.e., the operator's brain) has to convert each
letter into a series of dots and dashes (serial) and then
send these over the wire.

At the receiving end, another processor has to listen to these serial dots and dashes, then convert them
back into letters and words. A lot of overhead is required because
the transmission medium doesn't
match the original input or desired output.

Signal Skewing

As a signal travels over a wire or an integrated circuit trace, imperfections in the wires or integrated
pad drivers can slow down some bits.

In a parallel c
onnection, the eight bits that leave at the same time don't arrive at the other end at the
same time; some will get there later than others. This is called skew. To deal with this, the receiving end
has to synchronize itself with the transmitter and must w
ait until all bits have arrived. The sequence of
processing is this: read, wait, latch, wait for clock signal, transmit.

The more wires there are and the longer the distance they span, the greater the skew and the higher
the delay. This delay limits the ef
fective clock rate as well as the length and number of parallel lines that
are feasible to use.


The fact that parallel wires are physically bundled
means that one signal can sometimes "imprint" itself
on the wire next to it. As long as the signal
s are
distinct, this doesn't cause problems.

But as bits get closer together, signal strength
attenuates over distance (especially at higher
frequencies), and spurious reflections accumulate
because of intermediate connectors. As a result, the
for error grows significantly, and the disk
controller may not be able to differentiate between a
one and a zero. Extra processing is needed to prevent

Serial buses avoid this by modifying signals at the time of transmittal to compensate for such los
s. In a
serial topology, all the transmission paths are well controlled with minimum variability, which allows
serial transmission to run reliably at significantly higher frequencies than parallel designs.

The Newer, Smaller Serials

We've already seen seri
al connections displace parallel ones for printers and other peripherals. Now,
inside computers, we're replacing parallel connections to disk drives and arrays, both SCSI and
Advanced Technology Attachment (ATA), with a new serial architecture called Seria
l Attached SCSI
and Serial ATA .

Other storage
related serial system interfaces include Serial RapidIO, InfiniBand and Fibre Channel.

Kay is a

contributing writer in Worcester, Mass. You can reach him at

Further Syllabus topics (less information)


Communications concepts (cont)

simplex, half duplex and full duplex

Question: What are examples of each type of hardware? Television

simplex. Printer

duplex .

duplex, however generally used as half
duplex so we can hear the other speaker..
Some networks are able to transmit a message to all nodes which are connected to the network (this is
common in LANs). This is known as

transmission. In additio
n to broadcast, some networks
also allow simultaneous transmission to a specific group of users, this is known as

transmission. An example of multicast transmission is the use of the
IP network protocol

to support
packet video allowing remote par
ticipation in conferences across the Internet.

synchronous and asynchronous

Group ware used in course will be asynchronous. Video conferencing is synchronous

measurements of speed

When you want to conect to the internet, you need to consider h
ow much data you want to
transmit/recieve. If this is a lot of data, you will want to transmit at high speed to reduce waiting time at
each end. However the technology for high speed costs.

analog to digital conversion

Can consider how a varying sou
nd is coded as a digital record. Start with how the numbers 1

15 are
coded into binary. Then you can code a sound with a volume value of 1
15, and a wave frequency of
1500 hz, etc. The description of the binary representation of the wave then becomes
a string of
binary descriptors. If software knows the first 4 digits are volume, next 4 are frequency, etc.


hardware for transmitting and receiving

Really Good video from how stuff works

mmunications within a computer between peripheral devices and the CPU via buses

Within the computer the components must send messages to each other. Eg CPU send data to printer
port for instructing printer what to draw. The bus is a wide wire track to red
uce losses.

the role of modems, including:

a. modulation demodulation

Information is carried around the internet as packages or data streams. The modem codes this
information onto the data stream eg inserts packages at correct intervals, in a process
modulation. This is the same as a radio modulates the radio wave to code the audio signal onto the
wave, except we are now dealing with digital “waves”

b. other features such as fax, scanner, automatic answer

local area networks and wide area n


software for transmitting and receiving

a. communications packages to interface with hardware

b. transmitting and receiving text, numeric, image, audio and video

c. electronic mail, its operation

4. encoding and decoding

a. non
computer t
ools for transmitting and receiving, such as :



fax and

radio and

television (transmit only)

5. social and ethical issues associated with transmitting and receiving

a. accuracy of data received from the Internet

b. security of data b
eing transferred

c. net

d. acknowledgment of data source

e. global network issues, time zones, date fields, exchange rates

f. changing nature of work for participants, such as work from home and telecommuting

g. current developments and future tr
ends in digital communications, radio and television

the impact of the Internet on traditional business.

New Areas


Virtual Private Networking

for private communicati
on within a
socially closed network, using open hardware linkages such as internet cabling.

Also open source software to do this at

Computer to telephones

From : IP Telephony Basics: Technology, Operation, Economics, and Services by Au
thors: Lawrence
Harte, David Bowler, and Robert T. Flood

IP Telephony Communication Servers

This figure shows the different types of servers in some IP Telephony communication systems. This
example shows that a call manager (proxy server) receives and pro
cesses call requests from
communication units (IP telephones). The administrator server coordinates accounts to the system. A
unit manager (location server) functions as a location server by tracking the IP address assigned to the
communication units. The
gateway manager identifies and coordinates communication through the
available gateways. The system manager coordinates the communication between the different servers
and programs available on the system.

Gateway Manager Software

This figure shows how
gateway manager software can be used to configure and manage gateways that
connect the SIP network to other networks such as the public switched telephone network. This
example shows how the gateway manager contains the configuration information for the ga
including IP address, capabilities such as speech coders, protocols, and access control information.