Computer Networks

In information technology, a network is a series
of points or nodes interconnected by
communication paths.
In a network, a node is a connection point. In
general, a node has programmed or
engineered capability to recognize and
process or forward transmissions to other
A network is an interconnected system of
things or people
Business contacts
Snail Mail
Social Media
Broadcasting - NBC, CBS, ABC, PBS
Transportation (highways & rail)
Cellular phone service
…and of course computer based (internet)
The Internet is a worldwide system of
computer networks - a network of networks
in which users at any one computer can, if
they have permission, get information from
any other computer.
◦ An organizations restricted computer network
◦ Private, yet using WWW software
◦ Part of a organization‘s intranet that is extended to
users outside the organization – usually via WWW.
◦ Customer access
◦ A worldwide computer network using TCP/IP
protocol to transmit and exchange data.
 (TCP/IP is a set of communication protocols used by
Simultaneous Access
◦ Software/Programs
◦ Data
Device Sharing
◦ Printers
◦ NAS – Network Access Storage
◦ Email
◦ VOIP – Voice over internet protocol (Skype)
◦ Backups of multiple clients by a single server
In communication networks, a topology is a
usually schematic description of the
arrangement of a network, including its
nodes and connecting lines. There are two
ways of defining network geometry: the
physical topology and the logical (or signal)
◦ Physical connectivity
 Nodes and Addressing
Geographical Distribution
◦ Where are the nodes?
Work Load
◦ Server networks use the nodes to disperse the
Network topology is the physical
interconnections of the elements (Links,
Nodes, Clients, etc.) of a computer network
Main Types
Star topology is the most common topology used in
today’s workplace.
North Greenville University in Tigerville uses star
Bus topology is where in a computer
network, a bus is a transmission path on
which signals are dropped off or picked up
at every device attached to the line. WAP
(wireless access points) are not necessary
A ring is a network topology or circuit
arrangement in which each device is attached
along the same signal path to two other
devices, forming a path in the shape of a ring.
A wireless Internet service provider (WISP) is an
Internet service provider (ISP) that allows
subscribers to connect to a server at designated
hot spots (access points) using a wireless
connection such as Wi-Fi.
Standards – IEEE 802.11
802.11n has a higher frequency and
transmits fastest and the longest range
Coax cable is the kind of copper cable used
by cable TV companies between the
community antenna and user homes and
◦ Benefit is one wire for all
Ethernet is the most
widely-installed local area
network (LAN) technology.
◦ One wire per node/client
Ethernet twisted pair cable is faster
than Wireless and is very
commonly used in businesses
Fiber optic (or "optical fiber")
refers to the medium and the
technology associated with
the transmission of
information as light impulses
along a glass or plastic wire
or fiber.
◦ WIMAX (Worldwide Interoperability for Microwave
◦ Satellite (Dish Network/Direct TV)
 High transmission rate (has to be) & latency
Each node needs antenna to connect
◦ Low frequency – reliable but slower transmission
◦ High frequency – less reliable but higher speed
Fiber is the fastest - pricey
Ethernet twisted pair – cheaper and faster
COAX – still needed
Wireless – price greater than Ethernet twisted
Node – Client
Network storage devices
Anything that can connect to a network
 Cell phone
 GPS device
 IPOD/PSP/XBOX/PS3/Tivo/DVR/Slingbox…
How does the network identify a node?
◦ NIC MAC address – every node’s is unique
 Format: 01-23-45-67-89-ab, 01:23:45:67:89:ab
 Each vendor has a pool of addresses
 Linksys
 D-Link
 Etc.
 Hardware address
 Translated into a software address (IP address)
 Two standards for Internet Protocol (IP)
 IP V4
 IP V6
IP Addresses
◦ IP addresses are four octets of the form and range
 (0-255).(0-255).(0-255).(0-255)
◦ Data is routed between nodes based on IP addresses
◦ Each domain name translates to a unique IP address
 translates to
 i.e. try Ping from DOS prompt
 is in charge of DNS
 Maintains to provide info about domain names
◦ A profound shortage of addresses with IP V4
 4.3 billion addresses with some reserved
 Usefulness of static addresses
 How many nodes in the world?
IP Addresses
◦ Addresses structure:(8 groups of 4 base16 digits)
◦ Version 6 provides enough addresses for every
atom in the universe - provided they buy a
computer 
◦ Supports 2128 (about 3.4×1038) addresses.
◦ Currently used at main WWW routing points
◦ Advantages of having your own address?
 Your are known wherever your node physically resides
LAN – Local Area Network
◦ Ex. – NGU
VLAN – Virtual LAN (act as a LAN due to
common set of needs - collaboration)
MAN – Metropolitan Area Network
◦ Ex. - City of Greenville
WAN – Wide Area Network
◦ Ex. – Internet
Server Based
◦ Thin client - relies heavily on server processing
◦ Ex. – NGU email server
Client Server Based
◦ Fat client – shares in the work load with less
expensive server
◦ Ex. – NGU CAMS (clients process the reports)
Peer to Peer Based
◦ Each computer can act as client or server
◦ Ex. - Home network
All networks
◦ Authentication
 User name and password
◦ Encryption
 https – encrypts credit card account #s, email
◦ Firewall Software
 What can network users get to on your machine
◦ Anti-virus Software
 Protect against malware
 Vendors – McAfee, Symantec, AVG, etc…
◦ Finger Print Scanner
◦ Contingency planning – what if the unexpected
 Backups, backups, backups
◦ WEP – Wired Equivalency Protocol
 NOT secure (Google “breaking wep encryption”)
◦ WPA – Wireless Protected Access
 WPA & WPA2 – secure provided you use good pass
What do we transmit/exchange?
◦ Text
 Emails
 Print jobs
 Chat
◦ Graphics
 Pictures
◦ Video
 Movies
 Live Streaming
◦ Audio
 Songs
 Voice
How is it transmitted?
◦ Broken into packets
 Header – Packet 1
 Trailer – Last Packet
 Those in between
◦ Not all packets take the same route
◦ Reassembled on receipt to match that sent
Who owns the internet?
◦ Many companies – Sprint, Verizon, Time-Warner,
 We’re just renting space 
◦ Transmission is not perfect
 Must have schemes for re-sending dropped packets
 What about audio & video – is there any reason to resend?
 What about your debit card atm transmission
 Easier to resend the whole thing or just what’s missing?
TCP/IP – Transmission Control
Protocol/Internet Protocol
◦ Standard network data exchange protocol(standard)
◦ TCP applications
FTP – File transfer protocol (transfer files)
Telnet – Terminal connections
SMTP – email transmission
POP3 – email transmission
◦ IP applications
 HTTP – Hypertext transfer protocol
VOIP – Voice over IP
ISP – Internet service provider
◦ Types of connection for the home
Cable Modem
DSL Modem
ISDN Modem
56K Dial-up Modem
Home satellite
Cable Modem – higher capacity than home
DSL Modem – “
DS1/T1 High speed line (DS3 /T3 even better)
◦ Types of connection for business
◦ Businesses concerned with throughput
◦ Become a node on ISP’s network
◦ Common
 .com, .net, .org, .edu, .gov
◦ Not so common
 .uk, .us, .tv, .biz, info (checkout
Sub Domains
◦ Part of the larger domain
◦ Ex.
 Domain is
 Sub domain is ngu
 Accessed via
Websites are designed using html (hypertext markup
◦ Easy enough for anyone to create
 Write html
 Use applications like Dreamweaver or Microsoft Expression
 Can save MS Office 2007 files as web pages
◦ Store cookies
 Ease of use
 User names
 Passwords (not so good if not secure – https)
◦ Store temporary files
 Faster browsing
 Fills up hard drive
 Fragmentation
◦ Your browser will let you purge cookies and files.
Data specific Websites are encoded using XML
(Extensible Markup Language)
Example – see notes
Standard for data exchange
◦ MS Access can import XML
Microsoft Office 2007 file naming
Word “Document.docx”
Excel “Spreadsheet.xlsx”
PowerPoint “Presentation.pptx”
Access – “Database.accdb” ?????