chapter 3 internet. physical components of the internet servers networks routers
TRANSCRIPT
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Chapter 3
Internet
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Physical Components of the Internet Servers Networks Routers
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Server
Computer Answers requests for services.
– Mail servers– Web servers– List servers (discussed in Ch. 10)– News servers (discussed in Ch. 10)
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Network
A computer system that uses communications equipment to connect two or more computers and their resources.
Actual physical means for transporting data (packets of information)
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Network
Uses:– Copper wires -- electrical impulses. or– Fiber-optic cables - light waves. or– Radio Waves or– Microwaves or– Infrared light -- invisible light that carries a
message through air.
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Router
Special-purpose computer Computer that directs data packets
along the network.
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Local Area Network (LAN)
A network designed to share data and resources among several computers, usually personal computers in a limited geographical area, such as an office or a building. (compare to WAN)
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Wide Area Network (WAN)
A network of geographically distant computers and terminals. (compare to LAN)
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Host
The central computer in a network, to which other computers, and perhaps terminals, are attached.
A personal computer with file-transfer software permits a user to download data files from the host or upload data files to the host.
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Downloading a file means to retrieve it from another computer.
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Uploading a file means to send a file to another computer.
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Node
A device, usually a personal computer, that is connected to a network.
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Star network topology
Hub Computer
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Ring network topology
Computers are connected in a circular fashion
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Bus network topology Network is preserved if one computer fails
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Benefits of a Network
Used as a back up for files Resources, such as printers, can be
shared Promotes an ease of communication
through e-mail, transferring files and videoconferencing
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Benefits of a Network (continued) It costs less to use several small
computers connected to a network than to use a large computer.
And several small computers connected to a network can offer more computing power than just using a single large computer.
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Packet switching
Transmitted data is divided into small packets of information.
Each packet has the same destination but does not necessarily take the same path.
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Advantages of packets
Packets can be rerouted to a less congested area of the network if a particular area is congested.
If the network experiences a failure, packets can be rerouted.
If a packet is corrupted, only the corrupted packet needs to be resent.
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What other information is contained in a packet? Info about the computer that sent it Info about the computer to which it is
being sent A sequence number
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TCP / IP
Software managing the transmission of the individual packets.
TCP / IP - Transmission Control Protocol / Internet Protocol
Consists of many (approx. 100) different protocols
Communication between networks is based on the TCP/IP suite.
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TCP
Places the data into packets and reassembles the packets.
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IP
Handles the addressing and sees to it that packets are routed across multiple computers.
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Connecting to the Internet User connects to the ISP (Internet Service
Provider) using either a modem or an ISDN (Integrated Services Digital Network) – Replaces a modem with a special adaptor.
ISP connects to the NSP (Network Service Provider) networks through leased lines through the local phone company.
TCP/IP then divides the message into packets and sends them over the lines.
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Connecting to the Internet (continued) The router directs the packets to their
destination. The packets are reassembled at their
destination-computer which then responds to any request.
A message is sent from the destination computer to the sending computer in order to request that any missing or corrupt packets be resent.
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Internet
Network of networks Used to:
– View web pages (WWW)– Download files (ftp)
• Files located on a remote computer can be downloaded
– Communicate through e-mail
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Internet (another definition)
Global information system linked together by a unique address space (DNS).
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Domain Name System (DNS)
Used to assign names to host computers.
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Domain Name
Symbolic name used to identify each computer on the Internet.
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IP Address
Numeric name used to identify each computer on the Internet.
Consists of 32 bits (4 bytes)
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Largest 8 bit number is 255. Smallest 8 bit number is 0
11111111 = 28 - 1 = 255
00000000 = 0
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IP Address (continued)
Consists of a network component and a host component.
Ex. 102.150.8.68 01100110 = 102 10010110 = 150 00001000 = 8 01000100 = 68
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Review URL entered
– http://publications.UNL.edu/faculty/index.htm
Browser queries the DNS for the IP Address– Domain Name System
IP address returned– 123.66.102.77
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TCP connection is established with 123.66.102.77
Browser then asks for the “what” part of the URL– index.htm
The server, publications.UNL.edu, sends back the file index.htm.
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TCP connection is then closed Browser renders the text portion of the
HTML code contained in index.htm Steps are repeated in order to retrieve
any in-line images within index.htm.– In-line image -- Image within a document.
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Who can publish on the web?
Anyone
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Some material is monitored for accuracy. Electronic Journals Commercial presentations Reputable authors
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Be a critical judge
Who wrote it? Is the writing quality high? Is the document up to date? Are there obvious errors?
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Note: Pg. 126 Communication Mechanisms
LOL - laughing out loud
TY - thank you
RTFM - Read The Fine Manual• Not all substitute the word “fine” for the letter
“F”.