Networking
What is a Network?


A group of Computers and devices
connected together for the purpose of
sharing resources and services.
It may be as simple as two computers or as
complex as the Internet.
Why Networking?
• Sharing information — eg. data communication
• Do you prefer these?
• Or this?
3
• Sharing hardware or software
• eg. print document
• Centralize administration and support
• eg. Internet-based, so everyone can access the same
administrative or support application from their PCs
4
What is a LAN?
Local Area Network
 A group of computers in a single location
 Limited by no. of computers and distance
covered
 Example: Our school network

What is a WAN?
Wide Area Network
 Two or more LANs connected together
using a telecommunication service
 Example: NYC Dept. of Education

• Example of WAN: Broadband Cable Network
• Cable TV services have been extensively developed in most
modern cities
• Cable TV companies try to make use of their coaxial cable
installed (that are supposed to carry TV signals) to deliver
broadband data services
• Many cable network wiring has been replaced with hybrid
fiber-coax (HFC) ― i.e. use of fiber-optic cable to connect to
the subscribers’ buildings, and then the original coaxial
cable to connect to each household
7
PC
TV
Coaxial
Cable
The connection is shared by a
number of subscribers, hence
may raise performance and
security problems
Cable
Drop
Cable company
8
What is a WLAN

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
Wireless LAN
This is a LAN that uses Radio Frequency
technology to allow for communication
among computers and devices
Example: wireless home network
Role of Computers in a Network


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Client- computer or device that specializes in
knowing how to ask for services in a network.
Example: Workstation in a network
Server- Computer or device that specializes in
knowing how to provide services in network.
Example: Print Server in a network
Peer- Computer or device that may be able to be
both a server or a client at the same time.
Example: Workstation in a simple network (peerto-peer network …. P2P Network)
How many kinds of
Networks?
• We can classify networks in different ways
• Based on network medium: Wired (twisted pair, coaxial
cables, fiber-optic cables) and Wireless
• Based on network size: LAN and WAN
• Based on management method: Peer-to-peer and
Client/Server
• Based on topology (connectivity): Bus, Star, Ring, Mesh
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What is the Network Medium?

Cabled/Wired
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STP – shielded twisted pair
UTP – unshielded twisted pair(cat 5, 5E, 6, 7)
Coaxial
Fiber Optic (single mode, Multi mode)
Wireless


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Microwave - Microwaves are electromagnetic waves
with wavelengths ranging from as long as one meter
to as short as one millimeter
Infrared - Infrared radiation (IR) is electromagnetic
radiation with a wavelength between 0.7 and 300
micrometers
Radio - Radio waves transmit music, conversations,
pictures and data invisibly through the air, often over
millions of miles - wavelengths in the
electromagnetic spectrum longer than infrared light
Twisted-Pair Cables
 If
the pair of wires are not twisted,
electromagnetic noises from, e.g., motors, will
affect the closer wire more than the further one,
thereby causing errors
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Unshielded Twisted-Pair (UTP)

Typically wrapped inside a plastic cover (for
mechanical protection)

A sample UTP cable with 5 unshielded twisted pairs of
wires
Insulator
Metal
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Categories of UTP Cables
UTP cables are classified according to the quality:

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Category 1 ― the lowest quality, only good for voice, mainly found in
very old buildings, not recommended now
Category 2 ― good for voice and low data rates (up to 4Mbps for lowspeed token ring networks)
Category 3 ― at least 3 twists per foot, for up to 10 Mbps (common in
phone networks in residential buildings)
Category 4 ― up to 16 Mbps (mainly for token rings)
Category 5 (or 5e) ― up to 100 Mbps (common for networks targeted for
high-speed data communications)
Category 6 ― more twists than Cat 5, up to 1 Gbps
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Shielded Twisted-Pair (STP)

STP cables are similar to UTP cables, except
there is a metal foil or braided-metal-mesh
cover that encases each pair of insulated wires
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Coaxial Cables


In general, coaxial cables, or coax, carry signals of
higher frequency than UTP cables
Outer metallic wrapping serves both as a shield
against noise and as the second conductor that
completes the circuit
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Fiber-Optic Cables

Light travels at 3108 ms-1 in free space and is the
fastest possible speed in the Universe

An optical fiber consists of a core (denser material)
and a cladding (less dense material)

Simplest one is a multimode step-index optical fiber

Multimode = multiple paths, step-index = refractive
index follows a step-function profile (i.e. an abrupt
change of refractive index between the core and the
cladding)

Common light sources: LEDs and lasers
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Network Types

Peer to peer

Client/server
Advantages of Peer-to-Peer

Easy to install and configure


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Most Client OS already have the components required to set the
computer as part of a peer to peer network
Individual machines do not depend on the presence of a
dedicated server
Individual users control their own shared resources
Inexpensive to purchase and operate
Need no additional equipment or software beyond a
suitable operating system.
Best for networks with less than 10 users
Disadvantages of Peer-to-Peer

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Security applies to a single resource at a time
Users may be required to use as many passwords
as there are shared resources.
Each machine must be backed up individually to
protect all shared data.
The machine that shares resources suffers
reduced performance
There is no centralized organizational scheme to
locate or control access to data
Advantages of Client/Server


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Centralized User Accounts, Security, and access
controls simplify network administration
More powerful equipment means more efficient
access to network resources
A single password for network logon delivers
access to all resources
Server based networking makes the most sense
for networks with 10 or more users or any
network where resources are used heavily.
Disadvantages of Client/Server


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Server failure renders the network
unusable, or it results in loss of network
resources.
Special purpose server software requires
allocation of expert staff, which increases
expenses.
Dedicate hardware and software add to the
cost.
What are Protocols
Set of rules that allow
communicate with each other
computer
to
Network Protocols

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TCP/IP (Transmission Control Protocol/
Internet Protocol)
Nwlink or IPX/SPX
NetBEUI
Network Software

NOS (Network Operating System)

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Windows Server 2008
Windows 2003 Server
Novell Netware 6.5
Unix
Linux
Network Services
The reason for setting up a network in the first place:
 File and Print
 DHCP (Dynamic Host Configuration Protocol)
 DNS (Domain Naming Service)
 Security
 E-mail
 Application or Database
 Web / Proxy
 Mail/FTP/IM/Chat
 RAS (Remote Access Service)
What are Topologies?
The physical shape computers and devices create
when connected together
The different topologies are:
 BUS
 STAR
 RING
 MESH
 HYBRIDS

Bus (not commonly
found in LANs
anymore)

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Needs termination
Adding devices
disrupts the network
Cable failure hard to
find
Bus Topology
Coaxial
cable
BNC T-Connector
Network Card
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
Star (Most common
topology)

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Requires a
hub/switch
Easy to troubleshoot
Requires more
wiring

Star Topology
Topologies
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Ring
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No beginning and no end
Uses token passing
to communicate
Mesh
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All computers are
connected to each other
More Fault tolerant
Variation of Major Topologies
(Hybrids)
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Star-Bus
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Backbone interconnect two
or more hubs
Star-Ring
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Physical Star, but logical ring
The way the IBM token ring Works.
What are Networking Models?
A model describes the different stages data
needs to go through in order to go from one
computer to another.
When you send an e-mail how does it reach
the destination?
Examples
models
are TCP/IP and the OSI
OSI Networking Model

7 Layers
 Application
 Presentation
 Session
 Transport
 Network
 Data link
 Physical
TCPI/IP Networking model

4 layers
 Application Layer
 Transport
 Internet Layer
 Network Interface Layer
Networking standards

IEEE 802.x Standards

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802.3 Ethernet Networks
802.11 Wireless Networks
 11a,
11b, 11g, 11n
Bluetooth

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an alternative wireless network technology
standard
supports a very short range (approximately
10 meters)
relatively low bandwidth (1-3 Mbps)
Computer/device ID/Addressing
Every
computer or device which is part of a
network includes a network card.
Every network card needs to have:
 Physical
address (MAC address)
 Logical address (IP address)
MAC address

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Media Access Control address
a unique identifier assigned to most
network adapters or NIC by the
manufacturer for identification
a series of 6 groups of two digits, letters
and numbers, separated by dashes

Example: 00-1E-4F-A0-61-69
IP Addressing

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Supports 4.3 billion addresses
32 bit address (Dotted decimal)
4 numbers (0 to 255) separated by dots
The addresses are divided into Class
A, B, C, D, E according to network
size.
Subnet Mask
The subnet mask is used to identify the
network address.
The sending computer needs to know this in
order to decide whether the packet is meant
for the local network or for another network.
Default Subnet masks are:
Class
A 255.0.0.0
Class B 255.255.0.0
Class C 255.255.255.0
Private vs. Public Addresses.
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Private addresses are only valid in a
private network
Public are valid in the Internet
 Ex. Private address. 10.0.0.0/8 ,
172.16.0.0 to 172.31.0.0, and
192.168.0.0/24
IP addressing
Network Class
Number of Hosts
Class A
approximately 16,000,000
Class B
approximately 65,000
Class C
254
IP address Class A

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Class A addresses range from 1.0.0.0 to 126.0.0.0
The Class A range has the possibility of 126
networks
Each network has the capability of 16,777,214
unique hosts
The default subnet mask is 255.0.0.0
IP address Class B

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Class B addresses range from 128.0.0.0 to
191.255.0.0
The Class B range has the possibility of
16,384 networks
Each network has the capability of 65,534
unique hosts
The default subnet mask is 255.255.0.0
IP address Class C
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Class C addresses range from 192.0.1.0 to
223.255.255.0
The Class C range has the possibility of
2,097,152 networks
Each network has the capability of 254
unique hosts
The default subnet mask is 255.255.255.0
IP Address Class D
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Class D addresses are used for multicasting
to a number of different hosts.
Class D addresses range from 224.0.0.0 to
239.255.255.255
Has the potential for 268,435,456 unique
multicast groups.
IP address Class E

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Class E is an experimental address block
that is reserved for future use
Class E addresses range from 240.0.0.0 to
254.255.255.255
Communication types

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Unicast (One to one)
Broadcast (One to all)
Multicast (One to a group)
TCP/IP Protocols

Application layer
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Transport Layer
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Telnet, FTP, HTTP, SMTP
DHCP, DNS, TFTP, SNMP
TCP, UDP
Internet Layer

ICMP, ARP, RARP, IP
Binary to decimal conversion
128
64
32
16
8
4
2
1
0
1
0
0
1
0
1
1
Binary= 01001011
This is equivalent to
 Decimal=64+8+2+1=75

Binary Conversion
Binary
Decimal
_____________________________________
10000000
128
11000000
192
11100000
224
11110000
240
11111000
248
11111100
252
11111110
254
11111111
255