Dear vergita-ga,
Good day!
In the following paragraphs, I have supplied the answers to your
questions.
Q1.) Describe and illustrate with the aid of diagram/s wherever
possible, the role of the following LAN components:
a.) Clients
Clients refer to the computers on a network that let users access the
servers' information and resources. They are also called workstations.
b.) Servers
A server is a computer or a device on a network that manages the
network resources. For example, a file server is a computer dedicated
to storing files; any user on the network can store files on the
server.
Servers are often dedicated, meaning that they perform no other tasks
besides their server tasks. On multiprocessing operating systems,
however, a single computer can execute several programs at once. A
server in this case could refer to the program that is managing
resources rather than the entire computer.
There are various types of servers available in the market:
Server platforms – engine (underlying hardware or software) that
drives the server
Application servers – also known as middleware, sit between the
database server and the client and connect the two
Audio/video servers – enable the websites to broadcast streaming
multimedia content
Chat servers – offer real-time discussion facilities to a large number
of users
Fax servers – manage the receipt and delivery of faxes on a computer
network
FTP servers – allows transfer of one or more files between computers
in a secure manner
Groupware servers – let users collaborate, regardless of location, via
Internet or intranet
IRC servers – allow to serve information to a large number of users in
an environment with real-time discussion capabilities
List servers – help manage Internet mailing lists
Mail servers – move and store mail over the Internet or the intranet
News servers –distribute and deliver news over the Usenet news network
Proxy servers – sit between the client and the server to filter
requests, improve performance and share connections
Telnet servers – enable users to log on to a host computer and perform
tasks as if they're working on the remote computer itself
Web servers – serve content to a browser by loading a file from a disk
and serving it across the network
c.) NIC
The network interface card (NIC) provides the physical connection
between the network and the computer workstation. Each node uses the
NIC (generally internal) to connect to the network media and control
the flow of data. This is the reason why NICs are a major factor in
determining the speed and performance of a network.
The NIC takes data from the node, puts it into the appropriate format,
and sends it over the cable to another NIC across the LAN. This card
receives the data, puts it into a form the node understands, and sends
it to the node. NICs must use a common network technology to
communicate. The three most common network interface connections are
Ethernet cards, Token Ring cards, and LocalTalk connectors, in that
order.
d.) Networking cables
Cable is the physical medium through which information usually moves
from one network device to another. There are three major types of
cable available in the market – unshielded twisted pair (UTP),
coaxial, and fiber-optic. The network's topology, protocol, and size
will determine the type of cable chosen.
Unshielded twisted pair (UTP) is the cheapest and the most popular
cable. The quality of UTP may vary from telephone-grade wire to
extremely high-speed cable. There are four pairs of wires inside the
jacket of UTP cable. Each pair is twisted with a different number of
twists per inch to help eliminate interference from adjacent pairs and
other electrical devices. The standard connector for unshielded
twisted pair cabling is an RJ-45 connector. Five categories of UTP
wire are available in the market:
Category 1 – Voice Only (Telephone Wire)
Category 2 – Data to 4 Mbps (LocalTalk)
Category 3 – Data to 10 Mbps (Ethernet)
Category 4 – Data to 20 Mbps (16 Mbps Token Ring)
Category 5 – Data to 100 Mbps (Fast Ethernet)
The segment length (maximum length allowed between two points) for UTP
varies from 100 – 200 meters.
A coaxial cable has a single copper conductor at its center. A plastic
layer provides insulation between the center conductor and a braided
metal shield that helps to block any outside interference from
fluorescent lights, motors, and other computers. This construction
makes it highly resistant to signal interference. It also allows
greater cable lengths between the network devices ranging from 200 –
500 meters. The most common type of connector used with coaxial cables
is the Bayone-Neill-Concelman (BNC) connector. Apart from high cost,
another disadvantage of coaxial cable is that it does not bend easily
and is difficult to install.
Fiber optic cabling consists of a center glass core surrounded by
several layers of protective materials. It transmits light (using the
principle of total internal reflection) rather than electronic signals
and thereby eliminates the problem of electrical interference. This
makes it ideal for certain environments that contain a large amount of
electrical interference.
Fiber optic cable can transmit signals fastest and farthest as
compared to coaxial and twisted pair. This capacity broadens
communication possibilities to include services such as video
conferencing and interactive services. The cost of fiber optic cabling
is comparable to copper cabling; however, it is more difficult to
install and modify.
e.) Hubs and switches
Please see answers provided in Q. 3 – 3.a and 3.c
f.) NOS
A network operating system (NOS) is the group of programs that causes
a collection of independent computers to act as one system. It is
analogous to a desktop OS except that it operates over more than one
computer. A NOS controls the operation of the network system,
including who uses it, when they can use it, what they have access to,
and which network resources are available.
Common network operating systems for PC-based networks include:
Unix
Linux
Microsoft Windows NT (New Technology)
Novell Netware
Q2.) Draw the following LAN topologies and explain the difference
between them in the ways that data flows around the network?
a.) Star
In a star network, all the nodes are directly connected to the “hub”
(see Fig. 2.1). There are no direct connections between the individual
nodes. However, every node is indirectly connected to every other
through the hub.
Node Node
| |
|______Hub______|
| |
| |
Node Node
Fig.2.1 Star Topology
The data on a star network passes through the hub before being
delivered to its destination. An analog for the data flow in a star
network is the working of the postal department. All the posts from
the source (say the various post offices in a city) are sent to the
General (or the Central) Post Office. At the GPO, the mails are
classified and segregated & then they are forwarded to their
respective destinations.
b.) Ring
As the name suggests, in a ring network the nodes are connected in a
closed loop configuration (see Fig. 2.2). Adjacent pairs of nodes are
directly connected. Other pairs of nodes are indirectly connected,
with the data passing through one or more intermediate nodes. In
effect, every device has exactly two neighbors for communication
purposes.
Node-----Node
| |
| |
Node-----Node
Fig. 2.2 Ring Topology
In a ring network, data flow from one node to the next in an ordered
sequence. When the data reach the last node, they are returned to the
originating node. A failure in any cable or device breaks the loop and
can take down the entire network. An analogy for the data flow in a
ring network is the familiar “passing the parcel” game that children
play.
A variation of the ring network topology is known as the token ring.
In this scheme, the signal travels in only one direction (effectively
either "clockwise" or "counterclockwise") or senses around the ring,
carried by a so-called token from node to node.
c.) Bus
The bus topology is the simplest network configuration. Here, each
node is connected to a main cable or link known as the “bus” (see Fig.
2.3). Effectively, each node is directly connected to every other node
in the network.
Node Node Node
| | |
|----------------------------------|
| |
Node Node
Fig. 2.3 Bus Topology
When a device wants to communicate with another device on the network,
it sends a broadcast message onto the bus. This message will be seen
by all the other devices, but only the intended recipient will
actually accept and process the message.
The following table briefly compares the above three topologies:
Features Bus topology Star topology Ring topology
Cost Low Medium High
Reliability Good Excellent Good
Scalability Poor Good Excellent
Ease of troubleshooting Poor Excellent Good
Q3.) Identify and describe with the aid of diagram/s wherever
possible, the basic roles of the following connectivity devices:
a.) Hub
A hub (also known as a concentrator) is a multi-slot device that
provides a central connection point for cables from workstations,
servers, and peripherals. In a star topology, twisted-pair wire
connects each workstation to the hub. Passive hubs allow the signal to
pass from one computer to another without any change. Active hubs, on
the other hand, electrically amplify the signal as it moves from one
device to another in a manner similar to that of repeaters. Hubs may
also possess self-learning and filtering capabilities that are usually
found in bridges.
b.) Repeater
A repeater electrically amplifies the signal (boosts the signal
strength) it receives and rebroadcasts it. This is required since a
signal loses strength as it passes along a cable, a process known as
attenuation. Repeaters can be separate devices or they can be
incorporated into hubs. They are used when the total length of the
network cable exceeds the standards set for the type of cable being
used, e.g., the length limit for unshielded twisted-pair cable is 100
meters. In this case, repeaters will have to be located at a distance
of every 100 meters (from the start of the cable) to allow for the
total length of cable on the network to exceed the 100-meter limit.
c.) Switches
Switches are devices that filter and forward packets between LAN
segments. Switches, in principle, are multi-port bridges. Switches
operate at the data link layer (layer 2) and sometimes the network
layer (layer 3) of the OSI Reference Model and therefore support any
packet protocol. LANs that use switches to join segments are called
switched LANs or, in the case of Ethernet networks, switched Ethernet
LANs.
d.) Bridge
A bridge connects a LAN to another LAN that uses the same protocol
(for example, Ethernet or token ring). A bridge can be thought of as
being a device that decides whether a message from you to someone else
is going to the LAN in your building or to someone on the LAN in the
building across the street. A bridge examines each message on a LAN,
"passes" those known to be within the same LAN, and forwards those
known to be on the other interconnected LAN (or LANs). Bridges have
the ability to learn which addresses are on which network and to
develop a learning table so that subsequent messages can be forwarded
to the right network.
A bridge can be likened to a traffic cop at a busy intersection during
rush hour. It keeps information flowing on both sides of the network,
but it does not allow unnecessary traffic pass through.
e.) Gateway
A gateway is a network point that acts as an entrance to another
network. In the network for an enterprise, a computer server acting as
a gateway node is often also acting as a proxy server and a firewall
server. A gateway is often associated with both a router, which knows
where to direct a given packet of data that arrives at the gateway,
and a switch, which furnishes the actual path in and out of the
gateway for a given packet.
f.) Router
On the internet, a router (either a physical device or a software)
translates information from one network to another; it is like a super
intelligent bridge. Routers determine the next network point to which
a packet should be forwarded toward its destination and then select
the best path to route a message, based on the destination address and
origin. The router can direct traffic to prevent head-on collisions,
and is smart enough to know when to divert traffic along back roads
and shortcuts.
While bridges know the addresses of all computers on each side of the
network, routers know the addresses of computers, bridges, and other
routers on the network. Routers can even "listen" to the entire
network to determine which sections are busiest -- they can then
redirect data around those sections until they clear up.
A router is located at any gateway (where one network meets another),
including each Internet point-of-presence. A router is often included
as part of a network switch.
Q4.)
a.) Distinguish between the Internet and WWW
In one sentence - the Internet is a network whereas the WWW is an
application available on the Internet.
The Internet is a network of networks in which users at any one
computer can, if they have permission, get information from any other
computer (and sometimes talk directly to users at other computers).
The World Wide Web (“WWW” or “the web”) is the most widely used
application on the Internet. It has been defined as the universe of
network-accessible information, an embodiment of human knowledge.
b.) Describe a range of services provided by the Internet and WWW
The major applications provided by the Internet and WWW are outlined
in the following paragraphs.
E-mail
Electronic mail (e-mail) is one of the most popular uses of the
Internet. It refers to the exchange of computer-stored messages by
telecommunications. E-mails can be distributed to individuals as well
as to groups of people. To create, send, and receive e-mail messages,
you need an e-mail program and an account on an Internet mail server
with a domain name. To use e-mail, a user must have an e-mail address,
which you create by adding your user name to the e-mail server's
domain name. E-mail programs use a protocol called Post Office
Protocol (POP).
News
This Internet-based service includes tens of thousands of newsgroups.
Each newsgroup hosts discussions on a specific topic. A newsgroup's
name indicates its users' special topic of interest, such as
alt.food.cake. To participate in a newsgroup, you need a newsreader
program that lets you read articles that have been posted on a news
server. You can post articles for others to read and respond to. The
protocol used is the Network News Transfer Protocol (NNTP).
File Transfer
File Transfer Protocol (FTP) is the Internet tool used to copy files
from one computer to another. Using a special FTP program or a Web
browser, you can log into an FTP host computer over the Internet and
copy files onto your computer. FTP is handy for finding and copying
software files, articles, and other types of data. Universities and
software companies use FTP servers to provide visitors with access to
data.
Remote Login
Telnet is a specialized service that lets you use one computer to
access the contents of another computer – a Telnet host. A Telnet
program creates a "window" into the host so you can access files,
issue commands, and exchange data. Telnet is widely used by libraries,
to allow visitors to look up information, find articles, and so on.
Chat
Internet Relay Chat (IRC) is a service that allows users to
communicate in real time by typing text in a special window. Like
news, there are hundreds of IRC "channels," each devoted to a subject
or user group. You can use a special IRC program to participate in
chatroom discussions, but many chat rooms are set up in Web sites,
enabling visitors to chat directly in their browser window.
Online Services
An online service is a company that provides access to e-mail,
discussion groups, databases on various subjects, and the Internet.
America Online, CompuServe, and Prodigy are examples of popular online
services.
Additional links:
http://www.whatis.com
http://www.networkmagazine.com/tutorials/mile.html
http://www.cyber.ust.hk/handbook3/hb3main.html
http://fcit.coedu.usf.edu/network/default.htm
http://www.cyber.ust.hk/handbook3/hb3main.html
http://www.commweb.com/article/COM20020820S0005
http://webopedia.internet.com/TERM/S/server.html
http://www.webopedia.com/quick_ref/servers.asp
Search Strategy:
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