Transcript View/Open

CHAPTER-3
LAN TECHNOLOGIES
PREPARED BY:
V.C.DANDWANI
1
3.1 TRANSMISSION MEDIA:
 GUIDED MEDIA:uses a "cabling" system that guides the
data signals along a specific path. The data signals are
bound by the "cabling" system. Guided Media is also
known as Bound Media.
 There 4 basic types of Guided Media:
Open Wire
Twisted Pair
Coaxial Cable
Fibre Optical
2
Open Wire
 Open Wire is traditionally used to describe the electrical wire
joined along power poles.
 There is a single wire joined between poles. No shielding or
protection from noise interference is used.
 definition of Open Wire is any data signal path without
shielding or protection from noise interference.
 This can include multiconductor cables or single wires.
 This media is susceptible to a large degree of noise and
interference and consequently not acceptable for data
transmission except for short distances under 20 ft.
3
Twisted pair
 One of the oldest and still most common transmission media is twisted pair. A
twisted pair consists of two insulated copper wires, typically about 1 mm
thick. The wires are twisted together in a helical form, just like a DNA
molecule. Twisting is done because two parallel wires constitute a fine
antenna. When the wires are twisted, the waves from different twists cancel
out, so the wire radiates less effectively.
 Each pair would consist of a wire used for the +ve data signal and a wire used
for the -ve data signal. Any noise that appears on 1 wire of the pair would
occur on the other wire. Because the wires are opposite polarities, they are 180
degrees out of phase (180 degrees - phasor definition of opposite polarity).
When the noise appears on both wires, it cancels or nulls itself out at the
receiving end. Twisted Pair cables are most effectively used in systems that
use a balanced line method of transmission: polar line coding (Manchester
Encoding) as opposed to unipolar line coding (TTL logic).
4
UTP
STP
 The degree of reduction in noise interference is determined specifically by the
number of turns per foot. Increasing the number of turns per foot reduces the
noise interference. To further improve noise rejection, a foil or wire braid shield
is woven around the twisted pairs. This "shield" can be woven around individual
pairs or around a multi-pair conductor (several pairs).
 STP :Cables with a shield are called Shielded Twisted Pair.
 STP or Shielded Twisted Pair is used with the traditional Token Ring cabling or
ICS - IBM Cabling System. It requires a custom connector. IBM STP (Shielded
Twisted Pair) has a characteristic impedance of 150 ohms.
 UTP :Cables without a shield are called Unshielded Twisted Pair.
 Twisting the wires together results in a characteristic impedance for the cable. A
typical impedance for UTP is 100 ohm for Ethernet 10BaseT cable.
 UTP or Unshielded Twisted Pair cable is used on Ethernet 10BaseT and can also
be used with Token Ring. It uses the RJ line of connectors (RJ45, RJ11, etc..)
5
Coaxial cable
 Coaxial Cable consists of 2 conductors. The inner conductor is held inside
an insulator with the other conductor woven around it providing a shield.
An insulating protective coating called a jacket covers the outer conductor.
 The outer shield protects the inner conductor from outside electrical
signals.
 The distance between the outer conductor (shield) and inner conductor
plus the type of material used for insulating the inner conductor determine
the cable properties or impedance.
 Typical impedances for coaxial cables are 75 ohms for Cable TV, 50 ohms
for Ethernet Thinnet and Thicknet.
 The excellent control of the impedance characteristics of the cable allow
higher data rates to be transferred than Twisted Pair cable.
6
Fibre optic cable
 Optical Fibre consists of thin glass fibres that can carry information at
frequencies in the visible light spectrum and beyond.
 The typical optical fibre consists of a very narrow chain(string)of glass
called the Core. Around the Core is a concentric layer of glass called the
Cladding. A typical Core diameter is 62.5 microns (1 micron = 10-6
meters). Typically Cladding has a diameter of 125 microns.
 Coating the cladding is a protective coating consisting of plastic, it is
called the Jacket.
 it provides good combination of high bandwidth and excellent noise
immunity. The bandwidth possible depends on the cable quality, length,
and signal-to-noise ratio of the data signal. Modern cables have a
bandwidth of close to 1 GHz. Coaxial cables used to be widely used within
the telephone system for long-distance lines but have now largely been
replaced by fiber optics on long-haul routes. Coax is still widely used for
7
cable television and metropolitan area networks, however.
3.1 TRANSMISSION MEDIA:
 UNGUIDED MEDIA: It transports electromagnetic waves
without using physical conductor. It is also known as wireless
communication. The data signals are not bound to a cabling
media and as such are often called Unbound Media.
 Signals are broadcast to air and thus are available to anyone
who has a device capable of receiving them.
They are
 Radio wave transmission(freq between 3kzh and 1ghz)
 Microwave transmission(1ghz to 300ghz)
 Infrared transmission (300ghz to 400 thz)
 (terrestrial,satellite,point to point and broadcast)
8
Radio transmission
 Radio waves are easy to generate, can travel long distances, and can
penetrate buildings easily, so they are widely used for communication,
both indoors and outdoors.
 Radio waves also are omni directional, meaning that they travel in all
directions from the source, so the transmitter and receiver do not have to
be carefully aligned physically.
 There are 3 types of RF (Radio Frequency) Propagation:
 Ground Wave, Ionospheric and Line of Sight (LOS) Propagation.
 Ground Wave Propagation follows the curvature of the Earth. Ground
Waves have carrier frequencies up to 2 MHz. AM radio is an example of
Ground Wave Propagation.
9
fig.: Ionospheric
Propagation
 Ionospheric Propagation: It bounces off of the Earths Ionospheric Layer
in the upper atmosphere. It operates in the frequency range of 30 - 85
MHz. Because it depends on the Earth's ionosphere, it changes with
weather and time of day. The signal bounces off of the ionosphere and
back to earth. Ham radios operate in this range.
fig.: LOS Propagation
Line of Sight Propagation: transmits exactly in the line of sight. The
receive station must be in the view of the transmit station. It is sometimes
called Space Waves or Tropospheric Propagation. It is limited by the
curvature of the Earth for ground based stations (100 km: horizon to
horizon). Reflected waves can cause problems. Examples of Line of Sight
10
Propagation are: FM Radio, Microwave and Satellite.
microwave
transmission
 Microwave communication is so widely used for long-distance telephone
communication, mobile phones, television distribution,etc.
 It has several significant advantages over fibre. The main one is that by
buying a small plot of ground every 50 km and putting a microwave tower
on it, one can bypass the telephone system and communicate directly.
Microwave is also relatively inexpensive.
 Microwave transmission is line of sight transmission. The Transmit station
must be in visible contact with the receive station. This sets a limit on the
distance between stations depending on the local geography.
 Microwaves carry large quantities of data due to the large bandwidth.
11
Infrared
transmission
 Signals with frequencies from 300ghz to 400thz
 Prevents interference between one system and other.
 Short range communication system in one room cannot be
affected by another system in other room.
 Band is almost 400thz.an excellent for data transmission .can
be used to transmit digital data with very high data rate.
 By using these signal for communication between devices
such as keyboard,mic,pc and printers.
 These signals transmits through LOS.
 Used for short range in a close area using LOS propogation.
12
3.2 Network devices:
Repeater(layer-1 physical layer)
Network adapters(NIC-network interface
card) (layer-2 data link layer)
Bridge (layer-2 data link layer)
Hubs /Switches (layer-2 data link layer)
Routers (layer-3 network layer)
Gateways (all seven layers)
Access points
connectors
13
REPEATER
A repeater is an electronic device that receives a signal and
retransmits it at a higher power level, or to the other side of an
obstruction, so that the signal can cover longer distances
without degradation.
14
REPEATER
A repeater connects segments of a LAN. both
segment of network must have the same
media access, protocol and transmission
techniques.
A repeater forwards every frame; it has
no filtering capability.
A repeater is a regenerator,
not an amplifier.
15
Function of a repeater
In most twisted pair Ethernet configurations, repeaters are
required for cable, which runs longer than 100 meters.
16
REPEATER
Advantage: It can easily extend the length of network.
 Connect segments from same network type that use different types of
cable.(can join dissimilar media such as unshielded twisted pair. but
can’t join dissimilar network architecture. For example can’t join
802.3 LAN and 802.5 LAN)
Disadvantage: Can not connect segments of different network types. and different
access methods. (e.g. CSMA/CD and token passing)
 Can not be used to reduce traffic and congestion.
17
NIC(network interface
card)/network adapter card
 Network adapter card commonly known as NIC.
 NIC are responsible for moving data from the computer to the
transmission media.
 NIC transforms data into signals that are carried across the
transmission media to its destination.
 Once signal reach to its destination device, it translate the
signals back into information, computer can process.
 The Network Interface card allows computers to communicate
with each other through the network.
 NIC work at data link layer of OSI.they provide the
MAC(media access control) and LLC(logical link control)
18
sublayer function of that layer.
NIC(network interface
card)/network adapter card
 When NIC transmits data, it first receives the data from the
computer.it attaches its header containing a checksum and the
network card’s address. The data is then converted to signals
that are passed over network media.
 During the conversion data changed to 5v e current signal
transmitted over coaxial cable and to change to pulses of light
when sent over fiber optic cable.
 When it is correctly installed and configured ,it can work
correctly.
19
NIC(network interface
card)/network adapter card
Adapter settings:
 Adapter cards such as sound and video cards. Most network
cards require setting some combinations of the parameters.
 IRQ(INTERRUPT REQUEST):
 IRQ sends request to computer’s processor to interrupt it’s
processing when it needs to send information.
 When a modem has finished sending data, it may interrupt the
processor so that CPU can give it something else to send.
 I/O ADDRESS:
 After a network card has interrupted the CPU with IRQ, it
needs a way to communicate with main board.
20
 Most card us I/O address to do this.
NIC(network interface
card)/network adapter card
DMA:
 Direct memory access, enables your cards to work directly
with computer’s memory.
SHARED MEMORY ADDRESS:
 It is an option to I/O address. Network card and software
driver use shared RAM address in high memory range to
communicate.
 Shared memory is slower than I/O address method. so you
must be sure to block out assigned range from any memory
management software, so it does not try to use that area at
same time.
21
BRIDGE
It uses data link layer addresses (e.g. MAC addresses) to make
data forwarding decisions.
Layer 2 of the “OSI model”
22
BRIDGE
 Repeaters can not handle or filter the traffic pass through it.
while bridge has filtering capability. they are used to extend the
network.
• Has one input and one output
• It can examine incoming packet source and destination
addresses, But cannot interpret higher-level information.
• Hence cannot filter packet according to its protocol.
23
BRIDGE-
How Bridges Work
• Bridges work at the Media Access Control Sub-layer of the OSI
model. It can be used at both segments to join dissimilar media
like UTP and fiber optic.
• Bridge can support SNMP.Repeters just copy the bits, while
bridges are intelligent. Routing table is built to record the segment
no. of address.
• If destination address is in the same segment as the source address,
stop transmit ,Otherwise forward to the other segment.
24
3 types of bridges.
 (1) Internal bridge: modification in existing network system
on file server to transmit signals between network segments.
so file server act as internal bridge.
 (2)Remote bridge: used to create WAN. It can link between
LAN.they are used in large network. segment are joined by
telephone line.
(3) wireless bridge: also used to join LAN.
Used a link networking building without cables.
Range up to 3 miles.
AIRLAN is an example of wireless bridge.(radio technology)
25
BRIDGE
 ADVANTAGES:
 Extends networks segments by connecting them together to make one
logical network.
 Filtering capabilities.
 Connect similar network types with different cabling.
 It can also connect different network types together.
 DISADVANTAGES:
 Cost is more then repeater due to extra intelligence.
 Bridges work best where traffic from one segment of a network to other
segments is not too great. when traffic between network segments becomes
too heavy, the bridge can become a bottleneck and actually slow down
communication.
HUB
 Multi-port repeaters are often called hubs. Hubs are very common
internetworking devices.
 Generally speaking, the term hub is used instead of repeater when referring
to the device that serves as the center of a star topology network.
 A hub is a small rectangular box, often constructed mainly of plastic.
 It includes a series of ports that each accepts a network cable. they contain
4 or 5 ports.
 Large Hub contains 8,12,16,31 ports.
 A hub joins multiple computers together to form a single network segment.
On this segment, all computers can communicate directly with each other.
27
TYPES OF HUB
ACTIVE HUB:
Amplify or regenerate the signal
Also connect segments to ensure all the nodes see the signals.
They have their own power supply.
PASSIVE HUB:
Connect the network segments together only. can't amplify the
signal.
They are not used in Ethernet network.
SMART HUB:
Provide same facility as active hub.
Provide management and monitoring capabilities.
Also used to locate and identify problems on the network. 28
ADVANTAGES:
They needs almost no configuration.
Active hub can extend maximum network media distance.
No processing is done at the hub to slow down performance.
DISADVANTAGES:
Hubs have no intelligence to filter traffic, so all data is sent
out all ports whether it is needed or not.
It act as repeater, network using them must flow the same
rules as repeater.
29
Switches:
• A switch is a small device that joins multiple computers
together at a low level network protocol layer.
• Switches operate at the Data Link layer (layer 2) of the OSI
model.
• Switch look like hub, but a switch generally contains more
intelligence than hub. because it is capable of inspecting the
data packets ,determining the source and destination device of
that packet, and forwarding that packet appropriately.
• Switches are considered as multiport bridges.
• By having multiport, can better use limited bandwidth and
prove more cost-effective than bridge and hub.
30
Switches:
Switches divide a network into several isolated channels.
Packets sending from 1 channel will not go to another if not
specify.
Each channel has its own capacity and need not be shared with
other channels.
Switches are primary available for ethernet,comes in a range of
port configurations starting with 4 and 5 port model. it support
10 mbps ethernet,100 mbps Ethernet or both.
31
Advantages of Switches
• Switches divide a network into several isolated channels.
Reduce the possibility of collision.
Each channel has its own network capacity.
Suitable for real-time applications, e.g. video conferencing.
Since isolated, hence secure.
Data will only go to the destination, but not others.
 Higher link bandwidth:-Point to point electrically simpler than
bus.
32
Disadvantages of Switches
Although contains buffers to accommodate bursts of traffic,
can become flooded by heavy traffic.
Device cannot detect collision when buffer is full.
Some higher level protocols do not detect error E.g. UDP
When data packets are continuously pumped to the switch it
may introduce more problems.
33
ROUTER:
Routers work at the OSI layer 3 (network layer).
It is used to connect different types of network, such as those
using different architecture and protocol.
They use the “logical address(like MAC or IP address)” of
packets to handle data routing. And routing tables to determine
the best path for data delivery.
34
ROUTER:
How Routers Work
 Routers are used to connect two or more networks. For
routing to be successful, each network must have a unique
network number.
• As packets are passed from routers to routers, Data Link layer
source and destination addresses are identified and then
recreated.
• Only packets with known network addresses will be passed hence reduce traffic.
• Routers can listen to a network and identify its busiest part.
• Will select the most cost effective path for transmitting
packets.
35
ROUTER:
Router can provides,
 Filtering and isolating traffic.
 It can access more information then bridges, and use this
information to improve packet deliveries.
 They are used in complex network situation because they
provide better traffic management than bridge.
 It contains internal routing table, so it can keeps track of all
known network address.
36
ROUTER:
 ADVANTAGES:
 Use the highest level of intelligence to route data.
 It can also act as a bridge to handle nonroutable protocol.
 DISADVANTAGES:
 Higher level intelligence takes more processing time.
 Installation and maintenance are difficult than repeater.
37
Comparison of bridges and routers
38
Comparison of bridges and routers
 both store-and-forward devices
routers: network layer devices (examine network layer
headers)
bridges are Link Layer devices
 routers maintain routing tables, implement routing algorithms
 bridges maintain filtering tables, implement filtering, learning
and spanning tree algorithms
39
GATEWAY:
 It is a network component that allows communication between
different networking architectures and different protocols.
40
GATEWAY:
 It operates at higher level of OSI model. they are commonly
used to provide connectivity between two different protocol
stacks that might be running on different system.E.g. mail
gateway that receives simple mail transfer protocol (SMTP)
email, translate it into a standard x400 format and forward it
to its destination.
 A gateway is usually a dedicated device or set of services
running on a dedicated computer.
 They are task specific, which means that they are dedicated to
a particular type to transfer.
 They use all the layers of OSI models but they typically
perform protocol conversion at the application layer.
 Levels of functionality varies between types of gateways.
Access point
 In computer networking, a wireless access point (WAP) is a
device that allows wireless devices to connect to a wired
network using Wi-Fi, Bluetooth or related standards.
 The WAP usually connects to a router (via a wired network),
and can relay data between the wireless devices (such as
computers or printers) and wired devices on the network.
42
Access point
 An access point is different from a wireless router, in that it does not have
a firewall and therefore is not appropriate to protect your local network
against threats from the Internet. A basic wireless setup may not have an
access point, but just a router (or a modem) and an adapter. An access
point extends the coverage within your network — it's put in a "dead spot",
a place that's distant from the router, perhaps in a different room, or on a
different floor.
 In a wireless network, an access point sends and receives signals to any
number of other, local wireless devices. These are usually adapters and
routers.
 Prior to wireless networks, setting up a computer network in a business,
home, or school often required running many cables through walls and
ceilings in order to deliver network access to all of the network-enabled
devices in the building. With the creation of the Wireless Access Point,
network users are now able to add devices that access the network with
few or no cables.
43
connectors
Connectors may join two lengths of flexible wire or cable, or may connect a wire
or cable or optical interface to an electrical terminal.
An electrical connector is an electro-mechanical device for joining electrical
circuits as an interface using a mechanical assembly. The connection may be
temporary, as for portable equipment, or may require a tool for assembly and
removal, or may be a permanent electrical joint between two wires or devices.
There are hundreds of types of electrical connectors. In computing, an electrical
connector can also be known as a physical interface. (compare Physical Layer
44
in OSI model of networking).
connectors
Plug and socket connectors
Blade connector
4-conductor hermaphrodite connector
for token-ring attachment.
A blade connector is a type of single wire connection using
a flat blade which is inserted into a blade receptacle.
Usually both blade connector and blade receptacle have
wires attached to them either through soldering of the wire
to the blade or crimping of the blade.
8P8C connector(8 position 8 conductor.
most famous for its use in Ethernet and widely
used on CAT5 cables.
Detail of mating surfaces of
hermaphrodite connector.
45
connectors
Wiring
Ethernet crossover cable, showing wiring at each end.
Transistor switch module with large screw connectors
and small fast-on connectors.
46
The D-subminiature electrical connector is commonly used for
the RS-232 serial port on modems and IBM compatible
computers.
A male DE-9 plug
The Universal Serial Bus is a serial bus standard to interface
devices. It is currently widely used among PCs, Apple Macintosh
and many other devices.
47
3.4 -SERVERS:
What is server:
 Computer networks can range from a simple peer-to-peer network to a
more complex client-server network.while a complicated network can
generally perform more advanced functions, it requires more involved
planning,particularly regarding the server application.
 TYPES OF SERVERS
 File
 Print
 Mail
 Proxy
 web
48
File server
49
File server
 In computing, a file server is a computer attached to a network that has the
primary purpose of providing a location for shared disk access, i.e. shared
storage of computer files (such as documents, sound files, photographs,
movies, images, databases, etc.) that can be accessed by the workstations
that are attached to the computer network.
 The term server highlights the role of the machine in the client–server
scheme, where the clients are the workstations using the storage.
 A file server is usually not performing any calculations, and does not run
any programs on behalf of the clients. It is designed primarily to enable the
rapid storage and retrieval of data where the heavy computation is
provided by the workstations.
 File servers are commonly found in schools and offices and rarely seen in
local internet service providers using LAN to connect their client
computers.
50
Print server
 A print server, or printer server, is a computer or device that is connected
to one or more printers and to client computers over a network, and can
accept print jobs from the computers and send the jobs to the appropriate
printers.
 It is simply a device that allows computer workstations to interface with one
or more printers that are shared on a network. Each station has the ability to
designate one of the printers on the network as its default printer, but may
always choose to send a print job to any of the other printers recognized by
the print server.
51
Print server







The three most popular print servers are,
Microsoft windows NT 4
Microsoft windows 2000
Novell netware 5.1
Advantages
Allows any number of users to share the same printer.
Avoids having to move files to a computer that is the only way to reach a
printer that's connected directly to it.
 Disadvantages
 Most of the features of multi-function printers (such as FAX and
photocopying) are not supported by print servers.
 Some printers, such as GDI printers, use proprietary commands which
make them unusable by print servers.
52
Mail server
 It transfers and stores mails over corporate networks through LANs, WANs
and across the Internet.
 A mail server is a computer that serves as an electronic post office for email.
 Mail exchanged across networks is passed between mail servers that run
specially designed software. This software is built around agreed-upon,
standardized protocols for handling mail messages, the graphics they might
contain, and attachment files.
 Internet Service Providers (ISPs) each have a mail server for handling their
clients’ mail messages, sometimes referred to as private mail servers.
 Some websites also offer public email services, utilizing their own mail
servers. An email client or email program allows a user to send and receive
email by communicating with mail servers. There are many types of email
clients with differing features, but they all handle email messages and mail
servers in the same basic way.
53
Mail server
 A mail server is the computerized equivalent of your friendly neighbourhood
mailman. Every email that is sent passes through a series of mail servers along
its way to its intended recipient. Although it may seem like a message is sent
instantly - zipping from one PC to another in the blink of an eye - the reality is
that a complex series of transfers takes place. Without this series of mail
servers, you would only be able to send emails to people whose email address
domains matched your own - i.e., you could only send messages from one
example.com account to another example.com account.
 Mail servers can be broken down into two main categories: outgoing mail
servers and incoming mail servers. Outgoing mail servers are known
as SMTP, or Simple Mail Transfer Protocol, servers. Incoming mail servers
come in two main varieties. POP3, or Post Office Protocol, version 3, servers
are best known for storing sent and received messages on PCs' local hard
drives. IMAP, or Internet Message Access Protocol, servers always store
copies of messages on servers. Most POP3 servers can store messages on
servers, too, which is a lot more convenient.
54
proxy server
 It acts as a mediator between a client program and an external
server to filter requests, improve performance and share
connections.
 In computer networks, a proxy server is a server that acts as
an intermediary for requests from clients seeking resources
from other servers. A client connects to the proxy server,
requesting some service, such as a file, connection, web page,
or other resource, available from a different server.
 The proxy server evaluates the request according to its filtering
rules.
 A proxy server may optionally alter the client's request or the
server's response, and sometimes it may serve the request
without contacting the specified server.
55
proxy server
A proxy server has a large variety of potential purposes, including:
 To keep machines behind it anonymous(unidetified) (mainly for security).
 To speed up access to resources (using caching). Web proxies are
commonly used to cache web pages from a web server.
 To apply access policy to network services or content, e.g. to block
undesired sites.
 To log / audit usage, i.e. to provide company employee Internet usage
reporting.
 To circumvent regional restrictions.
 A proxy server that passes requests and replies unmodified is usually
called a gateway or sometimes tunneling proxy.
 A proxy server can be placed in the user's local computer or at various
points between the user and the destination servers on the Internet.
56
web server
It provides static content to a web browser by loading a file
from a disk and transferring it across the network to the user's
web browser. This exchange is intermediated by the browser
and the server, communicating using HTTP.
57
web server
 A web server is a computer program that delivers (serves) content, such as
web pages, using the Hypertext Transfer Protocol (HTTP), over the World
Wide Web.
 The term web server can also refer to the computer or virtual machine
running the program. In large commercial deployments, a server computer
running a web server can be rack-mounted with other servers to operate a
web farm. (rack-framework for handling objects)
 The primary function of a web server is to deliver web pages to clients. This
means delivery of HTML documents and any additional content that may be
included by a document, such as images, style sheets and JavaScripts.
 A client, commonly a web browser or web crawler, initiates communication
by making a request for a specific resource using HTTP and the server
responds with the content of that resource, or an error message if unable to do
so.
58
web server
 The resource is typically a real file on the server's secondary memory, but this
is not necessarily the case and depends on how the web server is implemented.
the primary function is to serve content, a full implementation of HTTP also
includes a way of receiving content from clients. This feature is used for
submitting web forms, including uploading of files.
 Web server has an IP address and possibly a domain name. For example, if you
enter the URL http://www.pcwebopedia.com/index.html in your browser, this
sends a request to the Web server whose domain name ispcwebopedia.com.
The server then fetches the page named index.html and sends it to your
browser.
 Any computer can be turned into a Web server by installing server software
and connecting the machine to the Internet There are many web server
software application, including public domain software from NCSA and
Apache, and commercial packages from microsoft,netscape and others.
web server

Common features
 Virtual hosting to serve many Web sites using one IP address.
 Large file support to be able to serve files whose size is greater than 2 GB
on 32 bit OS.
 Bandwidth throttling to limit the speed of responses in order to not
saturate the network and to be able to serve more clients.
 Server-side scripting to generate dynamic Web pages, still keeping Web
server and Web site implementations separate from each other.
 2 most popular web servers are,
 Apache
 Microsoft internet information services(IIS)
60