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A local area network (LAN) is a data
communication system connecting a number
of devices to each other.
The size of a LAN is limited to the radius of a
few miles.
Its physical size is usually limited to a
building, campus, or site.
Local Area NetworkLocal Area Network
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A local area network is a combination of
hardware and software.
The hardware is the part of the network that
is tangible.
The software is a collection of programs that
allows the use of the physical components of
the network.
Local Area NetworkLocal Area Network
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The hardware used in a LAN can be divided into
three categories :
Stations
Transmission media
Connecting devices
HArdWAREHArdWARE
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STATIONS
The purpose of LAN is to connect stations such
as computers, printers, and modems.
These stations are sometimes referred as nodes.
A station needs extra hardware and software
tools to be capable of being connected to the
network to perform tasks such as sending and
receiving data and monitoring the network.
HArdWAREHArdWARE
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The hardware used is generally a Network
Interface Card (NIC), which is commonly installed
inside the station.
It contains the necessary circuitry ( in the form
of chips) to perform network functions.
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TRANSMISSION MEDIA
It is the path that allows communication
between stations.
LANs can either use guided or unguided
transmission media.
Wired LANs can use guided media such as
twisted pair cable, coaxial cable, and fibre optic
cable.
HArdWAREHArdWARE
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CONNECTING DEVICES
Two categories of connecting devices are used in
LANs.
One category consists of devices that connect
transmission media to the stations.
(Transceivers and transceiver cables)
The second category consists of devices that
connect segments of a network together.
( Repeaters and Bridges)
HArdWAREHArdWARE
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SOFTWARESOFTWARE
Software run on LAN can be divided into two large
groups :
Network operating system software
Application programs
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NETWORK OPERATING SYSTEM (NOS)
A network operating system is a program that
allows the logical connection of stations and
devices to the network.
It enables users to communicate and share
resources.
Eg. Novell Netware, UNIX, Linux, Windows 2000
SOFTWARESOFTWARE
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APPLICATION PROGRAMS
Application programs allow users to solve special
problems.
They are not specific to LANs; they are also used
by the stand alone computers.
Eg. Program to calculate taxes.
SOFTWARESOFTWARE
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From a users point of view, a LAN can be
configured either as a client -server LAN or a
peer-to-peer LAN.
LAN MODELSLAN MODELS
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LAN APPLICATIONSLAN APPLICATIONS
Some of the common applications of local area
networks are :
Office networks
Industry networks
Backbone networks
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OFFICE NETWORKSOFFICE NETWORKS
The most commonly used application of a local
area network is in the office environment.
LANs are used in the office for three purposes :
Sharing
Interoffice communication
Internet communication
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Some LAN architectures are suitable for
automated manufacturing and production.
For eg, a LAN can be used in the automobile
industry to coordinate activities such as
controlling robots, material handling, or
warehouse inventory.
INDUSTRY NETWORKSINDUSTRY NETWORKS
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ADVANTAGES
It would be too expensive to use one high
speed LAN to connect each individual user.
It improves the reliability of the system i.e if
one of the LAN fails, the rest will continue to
function.
It isolates the load on one network from others.
BACKBONE NETWORKSBACKBONE NETWORKS
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LAN & WAN are the technologies used for the
internet.
However, internet is not made of a single LAN or a
single WAN & there must be a way to join these
LANs & WANs together.
These joining tools are known as connecting
devices.
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Connecting devices include: RepeatersHubs
Bridges
Routers
Switches
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Operates only in the physical layer.
Receives a signal, & before it becomes too weak or
corrupted, it regenerates the original bit-pattern.
Can extend the physical length of a network.
The cable can be divide into segments to extend the cable
length and repeaters can be installed between them.
Portion of the network between repeaters are called
segments.
A repeater acts as a two interface node & forwards every
packet but has no filtering capability.
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Is actually a multi-port repeater which is
normally used to create connection
between stations in a physical startopology.
Also used to create multiple levels of
hierarchy. The hierarchical use of hubs removes the
length limitation of 100 mts.
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Operates in both the physical & data link layer.
As a physical layer device, it regenerates the
signals it receives.
As a data link layer device, the bridge can check
the physical addresses contained in the packet.
Has no physical address & acts only as filter, i.e.,
not as an original sender to a final destination.
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A bridge has filtering capability, i.e., can
check the destination address of a packet and
decide if the packet should be forwarded or
dropped. If the packet is to be forwarded, the decision
must specify the interface.
A bridge uses a table in filtering decisions. Connects segments of a LAN together.
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A Router is a three layer device:
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Router is an inter-networking device. It can connect :
LANS together
WANS together
LANS and WANS together
Two networks (LANS or WANS) connected by a
router becomes an internetwork or an internet
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A two-layer switch is a bridge with many
interfaces and better(faster) performance.
Due to having many interfaces , it may beable to allocate a unique interface to each
station, with each station on its own
independent segment. This means no traffic and no collision .
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A three-layer switch is a router with an
improved design to allow better
performance. It can receive , process and dispatch a
packet much faster than a traditional router
even though the functionality is the same.
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Backbone networkallows several LANs to
be connected together.
No station is directly connected to the
backbone.
Stations are part of LAN and backbone
connects LANs.
Uses a LAN protocol like Ethernet
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Logical topology of the backbone is a bus.
Physical topology can be a bus or a star.
Protocol that supports the logical bus are 10BASE5,
10BASE2, 10BASE-T OR 100BASE-T
Normally used as a distribution backbone to connectdifferent buildings in an organization.
Each building can be comprised of either a single LAN or
another backbone. (normally a logical star backbone)
To connect logical bus backbone uses:-
Bridge based
Router based
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LANs are connected to the backbone through
bridges.
Delivery of the frame uses the Data Link layer
address of the frame.
Each bridge connected to the backbone has a table
that shows the station on the LAN side of the
bridge. The blocking or delivery of a frame is based on the
contents of this table.
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LAN
LAN
LAN
LAN
BRIDGE
BRIDGE
BRIDGE
BRIDGE
BACKBONE
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LANs are connected to the backbone through
routers.
Delivery of the frame uses the network layer
(IP) address of the packet encapsulated
inside the frame.
System is viewed as several sub-networks
with each LAN and the backbone each
forming a subnet.
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Each router connected to the backbone has a routingtable that shows how to route the frame to the
appropriate router.
The blocking or delivery of the frame is based on the
content of this table.
After the router finds the IP address of the destination
router, it uses either static or dynamic mapping to find
the data link layer address of the destination router.
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LAN
LAN
LAN
LAN
ROUTE
R
ROUTER
ROUTE
R
ROUTE
R
BACKBONE
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Also called as collapsed or switched backbone
Logical topology of the backbone is a star.
The backbone is just one switch that connects the
LAN together.
No need of bridges or routers.
Switch-acts as backbone as well as connects LANs
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Delivery of frames can be based on the data link layer ornetwork layer addresses.
If the backbone switch is a two layer switch, delivery is
based on the data link layer address, means wholesystem is still one single network.
If the switch is a three layer switch acting a multiport
router, the delivery is based on the network layer
addresses, means each LAN acts as a subnet.
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Mostly used as a distribution backbone
inside a building.
In a multi-floor building, one LAN serves the
whole floor.
Logical star backbone connects these LANs
Switch can be set at one place and separate
cables can run from the switch to each LAN.
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LAN
LAN
LAN
LAN
BACKBONE
SWITCH
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Two token rings are provided for possible backup
in case the primary ring fails.
The primary ring offers up to 100 Mbps capacity.
When a network has no requirement for the
secondary ring to do backup, it can also carry
data, extending capacity to 200 Mbps.
The secondary ring makes FDDI self-healing.
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NODE
NODE
NODENODE
PRIMARY RING
SECONDARYRING