Transcript Computer Networks

In information technology, a network is a series
of points or nodes interconnected by
communication paths.
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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
nodes.
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A network is an interconnected system of
things or people
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Religions
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.
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Intranet
◦ An organizations restricted computer network
◦ Private, yet using WWW software
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Extranet
◦ Part of a organization‘s intranet that is extended to
users outside the organization – usually via WWW.
◦ Customer access
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Internet
◦ A worldwide computer network using TCP/IP
protocol to transmit and exchange data.
 (TCP/IP is a set of communication protocols used by
networks.)
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Simultaneous Access
◦ Software/Programs
◦ Data
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Device Sharing
◦ Printers
◦ NAS – Network Access Storage
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Communication
◦ Email
◦ VOIP – Voice over internet protocol (Skype)
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Archiving
◦ Backups of multiple clients by a single server
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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)
topology.
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Topologies
◦ Physical connectivity
 Nodes and Addressing
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Geographical Distribution
◦ Where are the nodes?
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Work Load
◦ Server networks use the nodes to disperse the
workload
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Network topology is the physical
interconnections of the elements (Links,
Nodes, Clients, etc.) of a computer network
Main Types
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Star
Bus
Ring
Wireless
Hybrid
Star topology is the most common topology used in
today’s workplace.
North Greenville University in Tigerville uses star
topology.
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
needed.
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.
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Standards – IEEE 802.11
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802.11a
802.11b
802.11g
802.11n
802.11n has a higher frequency and
transmits fastest and the longest range
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Coax cable is the kind of copper cable used
by cable TV companies between the
community antenna and user homes and
businesses.
◦ Benefit is one wire for all
computers
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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
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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.
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Types
◦ WIMAX (Worldwide Interoperability for Microwave
Access)
◦ Satellite (Dish Network/Direct TV)
 High transmission rate (has to be) & latency
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Each node needs antenna to connect
◦ Low frequency – reliable but slower transmission
◦ High frequency – less reliable but higher speed
transmission
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Fiber is the fastest - pricey
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Ethernet twisted pair – cheaper and faster
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COAX – still needed
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Wireless – price greater than Ethernet twisted
pair
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Node – Client
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Printers
Desktops
Laptops
Copiers
Network storage devices
Routers
Anything that can connect to a network
 Cell phone
 GPS device
 IPOD/PSP/XBOX/PS3/Tivo/DVR/Slingbox…
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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
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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
 www.google.com translates to 208.67.217.231
 i.e. try Ping www.google.com from DOS prompt
 ICANN.org is in charge of DNS
 Maintains Internic.org 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?
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IP Addresses
◦ Addresses structure:(8 groups of 4 base16 digits)
2001:0db8:85a3:0000:0000:8a2e:0370:7334
◦ 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
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LAN – Local Area Network
◦ Ex. – NGU
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VLAN – Virtual LAN (act as a LAN due to
common set of needs - collaboration)
MAN – Metropolitan Area Network
◦ Ex. - City of Greenville
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WAN – Wide Area Network
◦ Ex. – Internet
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Server Based
◦ Thin client - relies heavily on server processing
◦ Ex. – NGU email server
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Client Server Based
◦ Fat client – shares in the work load with less
expensive server
◦ Ex. – NGU CAMS (clients process the reports)
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Peer to Peer Based
◦ Each computer can act as client or server
◦ Ex. - Home network
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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
happens
 Backups, backups, backups
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Wireless
◦ WEP – Wired Equivalency Protocol
 NOT secure (Google “breaking wep encryption”)
◦ WPA – Wireless Protected Access
 WPA & WPA2 – secure provided you use good pass
phrases
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What do we transmit/exchange?
◦ Text
 Emails
 Print jobs
 Chat
◦ Graphics
 Pictures
◦ Video
 Movies
 Live Streaming
◦ Audio
 Songs
 Voice
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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
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Who owns the internet?
◦ Many companies – Sprint, Verizon, Time-Warner,
etc.
 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?
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TCP/IP – Transmission Control
Protocol/Internet Protocol
◦ Standard network data exchange protocol(standard)
◦ TCP applications
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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
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ISP – Internet service provider
◦ Types of connection for the home
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Cable Modem
DSL Modem
ISDN Modem
56K Dial-up Modem
Home satellite
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Cable Modem – higher capacity than home
DSL Modem – “
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DS1/T1 High speed line (DS3 /T3 even better)
Satellite
◦ Types of connection for business
◦ Businesses concerned with throughput
◦ Become a node on ISP’s network
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Domains
◦ Common
 .com, .net, .org, .edu, .gov
◦ Not so common
 .uk, .us, .tv, .biz, info (checkout godaddy.com)
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Sub Domains
◦ Part of the larger domain
◦ Ex. www.ngu.blackboard.com
 Domain is www.blackboard.com
 Sub domain is ngu
 Accessed via ngu.blackboard.com
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Websites are designed using html (hypertext markup
language)
◦ 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.
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Data specific Websites are encoded using XML
(Extensible Markup Language)
Example – see notes
Standard for data exchange
◦ MS Access can import XML
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Microsoft Office 2007 file naming
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Word “Document.docx”
Excel “Spreadsheet.xlsx”
PowerPoint “Presentation.pptx”
Access – “Database.accdb” ?????
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http://wordnetweb.princeton.edu
http://compnetworking.about.com
http://en.wikipedia.org/
http://www.emailclients.net/