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Introduction to Computer Systems
Networking Fundamentals
Dr. E.C. Kulasekere
University of Moratuwa
IESL – Information Technology Part I
Network Technology
Connectivity to other computers.
Expands the capability of a PC.
Satisfies sharing of resources.
Expands human communication.
Increases security threats.
Concurrency effects.
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Modem for Home Connectivity
Most common mode of HAN connection.
Some issues related to modems.
Speed: maximum speed 56K
Needs dial up for connection.
Telephone line usage while on modem.
Price is not to high compared to other
services.
Needs reconnection when the link dies.
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Other Methods of Connectivity
Cable modem.
DSL
Wireless
Satellite-based services.
ISDN
Leased Lines
All of these are categorized as broadband.
Data rates exceeding 128kbps.
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Home Connection Infrastructure
Modem/NIC/DSL
Modem interface.
ISP/POTS.
Switch/Router.
Internet/PSTN
Then the sequence is inverted.
The links maybe digital or analog.
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Cable Modems (Using CATV Services)
This is a piggyback on a cable TV
service.
Faster than ISDN (128 Kbps).
Uses a crossover cable with RJ45
connector.
The fiber-coax cable configuration (fig)
Not found in Sri Lanka.
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Digital Subscriber Line (DSL)
Uses existing POTS to provide a high speed
connection.
Low cost alternative to ISDN.
The connection sharing is more efficient than
cable modems. (fig19.2)
Common types ADSL and SDSL.
Advantageous and disadvantages of DSL/SDSL
Low-pass filters are used to isolate the TP
signal from DSL signal.
..\webDocs\DSL.htm
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Wireless Broadband
Used for home users that are out of
reach from POTS.
Should not be confused with wireless
internet services provided for PDAs and
mobile phones.
Uses microwaves (fig 19.3)
Uses routers and modems (fig 19.4)
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IESL – Information Technology Part I
Integrated Services Digital network (ISDN)
Uses digital signals on the POTS.
Mostly designed for leased lines.
Configuration allows for multiple type of
terminations (fig 19.7)
Uses a terminal adapter (TA) for
termination and it is not a modem.
Costs more than DSL.
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IESL – Information Technology Part I
Leased Lines
For uses with high bandwidth
requirements such as businesses.
Leased line is 24 hour permanent
connection which can only be changed
by the TP company (what about DSL?)
T1 line 1.5Mbps, T3 line 45Mbps.
The BW is split among users by the ISP.
Used for connection that has high
utilization.
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Sharing Internet Connections
One connection may not be enough for
small-office and home (SOHO) systems.
Windows 98SE, ME, 2K and XP have
built in internet connection sharing
(ICS) gateway software (fig 19.12)
Routers can also be used for internet
sharing (fig 19.13/14)
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IESL – Information Technology Part I
Types of Networks
LAN: The smallest office network is referred
too as a LAN
HAN: LAN in a home environment is called a
HAN. Used for internet connection sharing.
WAN: LANS at different places can be hooked
by a WAN.
The Internet: A network of LAN/WAN
networks.
Intranets: One or more LANs in a SOHO
environment is called an intranet.
Extranets: Intranets that share a part of the
network with customers
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Requirements of a Network
Physical cable or wireless connection.
A common set of communication rules
called network protocols.
A software to enable transactions called
a network operating system.
Resources that can be shared.
Software that enables computers to
access other computers with shared
resources: a network client.
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Components of a network
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Network Components
Local area networks contain three basic hardware
components
Servers (also called hosts or host computers)
Clients
Circuits
Clients and Servers typically work together in clientserver networks. Networks without servers are
called peer-to-peer networks.
Routers are specialized devices responsible for
moving information between networks, are also a
common network component.
Server types: file servers, print servers, Web servers,
e-mail and directory servers.
Dr. E.C. Kulasekere
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Network Categorization According to Distance
A common way of thinking about networks is by the scale of the
network. 3 common network types are:
Local Area Networks (LANs) which typically occupy a room
or building, usually include a group of PCs that share a
circuit.
Backbone Networks, have a scale of a few hundred meters
to a few kilometers. Include a high speed backbone linking
the LANs at various locations.
Metropolitan Area Networks (MANs) which typically have a
scale of a few kilometers to a few tens of kilometers &
connects LANs and BNs at different locations, often using
leased lines or other commercial services to transmit data.
Wide Area Networks (WANs) have a scale of hundreds or
thousands of kilometers. Like MANs, leased circuits or other
commercially available services are used to transmit data.
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LAN Topologies
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Bus Topology
These are the earliest networks.
Single cable (coaxial) is used with
terminations at end.
If some part of the cable malfunctioned,
since the termination is lost the
connections are lost.
Adding a new computer was
troublesome.
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Ring Topology
This is a bus with the two ends connected.
No termination necessary.
Examples are fiber distributed data interface
(FDDI) used for large high speed networks.
Token ring (IBM) is another example.
Is SeaMeWe an example?
Signals go in a ring and get absorbed at the
sender terminal.
Malfunction of ring results in failure (solution:
Fig 20.11)
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Star Topology
Most popular type used today.
Uses UTP cables to patch panel.
Example implementation is a hub.
Failure in one link is not catastrophic.
For fast Ethernet this is the most
commonly used type of configuration.
CAT3 (10MB) or CAT5 (100MB) cables
are used.
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High Speed Networking
Switched Ethernet
Fast Ethernet
100Base-T
Gigabit Ethernet: Used with fiber optic
cables. Can use CAT5 cable. Also
referred to as 1000Base-T.
ATM
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Switched Ethernet
Switched Ethernet relies on centralized
multiport switches to provide a physical
link between multiple LAN segments
The switch is intelligent and switches
between segments with maximum BW
allocation.
It’s a cost-effective technique for
increasing the overall network
throughput and reducing congestion on
a 10-Mbps network.
The infrastructure is the same as usual.
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100Base-T
100BASE-T retains the familiar
CSMA/CD media access technique used
in 10-Mbps Ethernet networks. Hence
network management system need not
be rewritten.
Supports a broad range of cabling options.
CAT5 UTP, Type 1 STP or duplex multimode
fiber cable.
It can easily be integrated into existing
10-Mbps Ethernet LANs, so your
previous investment is saved
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ATM
cell-based fast-packet communication
technique that supports data-transfer
rates ranging from sub-T1 speeds (less
than 1.544 Mbps) up to 10 Gbps
An ATM network can be treated as a
single network, whether it connects
points in a building or across the
country
The fixed cell length signaling method offers
predictable performance.
Can be integrated into the existing network.
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IESL – Information Technology Part I
Gigabit Ethernet
The Gigabit Ethernet standard was
approved in June 1998, and its speed of 1
Gbps is a tenfold increase over Fast
Ethernet.
two basic types: shared and switched.
Shared Gigabit Ethernet is a higher-speed
version of 10/100BASE-T using CSMA/CD
Medium Access Control
Switched Gigabit Ethernet uses Logical
Link Control (LLC)
Its primary use is for backbones. The
medium is fiber or Category 5e 100-ohm
cable.
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IESL – Information Technology Part I
More on Wireless Networking
Advantages
Flexibility in installing
Flexibility in usage (movement of PCs)
Disadvantages
Security is not so good.
Interference from other devices.
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Adhoc Wireless Networks
Inexpensive and flexible.
Each workstation relates on a peer-topeer basis with the other PCs.
You can add a wireless router to gain
access to the internet if required.
Only suitable for small networks where
security is not an issue.
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Adhoc Wireless network
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Infrastructure Mode Wireless Network
Larger installations in larger buildings.
Depends on access points connected
together.
Each workstation communicates with
the access point rather than directly
with another workstation.
May not offer BW for networks with
heavy traffic.
Security is still a concern.
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Infrastructure mode wireless network
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Completely wired network
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IESL – Information Technology Part I
Integrated Network
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Fiber Optic Networks
Fiber optic cable is used in
applications that require high BW,
long distances, and complete
immunity to electrical interference.
A common application for fiber
optic cable is as a network
backbone
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Fiber Optic Networks (Cont …)
Greater BW. Eg. two million telephone
conversations have been simultaneously
transmitted over a single fiber using
Wavelength-Division Multiplexing
(WDM).
Low attenuation, longer distances: less
repeaters are used so cost effective.
Security:It’s very easy to monitor taps. If
tapped, the cable leaks light, causing
the entire system to fail.
Immunity to interference.
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IESL – Information Technology Part I
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IESL – Information Technology Part I
Cables
Most commonly used are the
(unshielded twisted pair) UTP cables.
The need for better cabling is tied down
to the increase in speeds and BW that
is required for todays' applications.
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CAT5 Cabling
Category 5 (CAT5) cabling is good, solid
cable for 100-Mbps LANs
Category 5 standard has been around
since 1991
If you still have a lot of 10-Mbps
equipment, CAT5 cabling will serve your
needs. Also handles 100Mbps fast
ethernet as well.
If you are hitting the limit at 100Mpbs
upgrade to CAT5e.
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IESL – Information Technology Part I
CAT5e Cabling
Enhanced Cat 5, was ratified in 1999.
It’s an incremental improvement
designed to enable cabling to support
full-duplex Fast Ethernet operation and
Gigabit Ethernet.
CAT5e has stricter specifications for PSELFEXT (Power Sum Equal-Level FarEnd Crosstalk), NEXT (Near-End
Crosstalk), Attenuation, and Return
Loss (RL) than those for Category 5
This is also a 100MHz standard.
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IESL – Information Technology Part I
CAT6 Cabling
Features more stringent specifications for
crosstalk and system noise. Ratified in
2002.
to transmit according to CAT6 specs,
jacks, patch cables, patch panels, crossconnects, and cabling must all meet CAT6
standards
all CAT6 components must be backward
compatible with CAT5e, CAT5, and
Category 3.
if CAT6 cable is used with CAT5e jacks,
the channel will perform at a CAT5e level.
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IESL – Information Technology Part I
Cable Standards
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IESL – Information Technology Part I
Cabinets and Racks
A cabinet is an
enclosure with a door
(or doors); a rack is
an open frame
An enclosed cabinet
can be locked with a
simple lock and key
Fans are installed to cool.
Built in power cabling.
Cabling infrastructure
provided.
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Connectors/Data Interfaces
..\webDocs\Connector Guide.htm
Connectors are important for the
cabling infrastructure.
If two types of connectors are mixed.
The lower speed one will set the limit of
operation.
..\webDocs\Data Interfaces.htm
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LAN Hardware
In traditional LANs, only one network
node transmits data at a time while all
other stations listen. This can lead to
timing requirements not satisfied for
video tx etc.
bridges and routers process data
packets on an individual basis, switches
maintain multiple, simultaneous data
conversions among attached LANs
Switched circuits are better since they
are dedicated connections.
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IESL – Information Technology Part I
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IESL – Information Technology Part I
Switch Technologies
The switch you have to buy for the LAN
depends on the type of switching that
have to be carried out.
..\webDocs\Layer 2, 3, and 4 Switching
Overview.htm
In depth analysis of such switches will
be done next year.
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Routers and Bridges
Routers and bridges link two or more individual Local Area
Networks (LANs) to create an extended-network LAN or Wide
Area Network (WAN).
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IESL – Information Technology Part I
Routers
Link networks using different network
identities.
Transmit only the data needed by the
final destination across the LAN.
Examine and rebuild packets without
passing errors on to the next LAN.
Routers are "smarter" than bridges,
because they find the best route for all
the data sent to them by the previous
router or the end station of the LAN.
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IESL – Information Technology Part I
Bridges
Connect two parts of the same LAN network to
make it larger.
Unlike routers, every bridge builds an internal
list of addresses of the attached network
devices on both sides of it.
If the destination address is on the opposite
segment or if the bridge doesn't have the
address logged, it forwards the information.
Bridges operate on MAC-Layer addresses.
They're protocol independent, so they transfer
data between workstations without having to
understand the protocol.
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IESL – Information Technology Part I
Media Converters
interconnects different cable types—
twisted pair, fiber, and Thin or thick
coax—within an existing network
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IESL – Information Technology Part I
Media Converters (Cont …)
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IESL – Information Technology Part I
Wiring
Cable is cable, so buy the
cheapest! – Follow this advice
to fall in trouble.
experts estimate that 70% of
network failures are primarily
caused by cable-related
problems.
So what’s a LAN manager to do?
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IESL – Information Technology Part I
Backbone Wiring
Main wiring between
closet and floors.
Star topology is
used for backbone
wiring.
Starting point for
horizonal wiring.
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IESL – Information Technology Part I
Horizontal Wiring
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Horizontal Wiring (Cont…)
encompasses all cable from a work-area
wallplate or network connection to the
telecommunications closet.
The outlets, cable, and cross-connects
in the closet are all part of the
horizontal wiring, which gets its name
because the cable typically runs
horizontally above ceilings or along the
floor.
..\webDocs\Premise Wiring.htm
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Other Devices
..\webDocs\Routers & Bridges.htm
..\webDocs\USB & FireWire.htm
..\webDocs\Video Connectors.htm
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