PLS 21 Lecture #2

PLS 21 Lecture #2 - Lecture#2NetworksandtheInternet...

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Lecture #2 – Networks and the Internet Computer Networks  What is a computer network? o 2 or more computers connected together Types of computer networks: o LANs: local area networks o WANs: wide area networks o Internet: a network of networks Networking advantages: o Reduce hardware costs o Enable shared applications o Build massive information resources o Connect people Understanding Networks Packet vs. Circuit switching     o Packets: multiple routes     o Circuit: a single route     Technologies and Topologies Protocol, TCP/IP Routing History of the Internet Packet vs. Circuit Switching  In Circuit switching
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o A physical and continuous circuit is established before, and maintained during  communication. In Packet switching o The individual parts (packets) of a message can take different paths from the  source to the recipient where they are reassembled. Circuit vs. Packet Switching
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Numbering Systems A slight digression.     Before we continue to talk about networks and the internet, we have to become  familiar with how data is encoded by computers. Things (apples, people, stars, etc.) that are real and can be counted are  represented by the Natural numbers. One group of natural numbers are the positive integers.
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There are a number of ways (e.g., decimal, binary, hexadecimal) to represent and  manipulate the symbols that we use to code for these natural numbers. A sequential grouping of things     Symbols are used to represent the number of things. The decimal system uses the symbols of 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. Since there are only 10 symbols in the decimal system, a number higher than 9  must be represented by employing place value o For example, the number 12 means 1x10+2x1=12 Computers use a binary system, with the symbols “0” and “1” Some computer applications use a hexadecimal system (16 symbols) Three Numbering Systems A binary number has 2 symbols (base 2):     o 0 or 1 o 101=15 o [(1x2 2 )+(0x2 1 )+(1x1)]=5 o [(1x4)+(0x10)+(1x1)]=5 A decimal number has 10 symbols (base 10):     o 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9 o 101=101
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o [(1x10 2 )+(0x10 1 )+(1x1)]=101 o [(1x100)+(0x10)+(1x1)]=101 A hexadecimal number has 16 symbols (base 16):     o 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, or F o 101=257 o [(1x16 2 )+(0x16)+(1x1)]=257 o [(1x256)+(0x16)+(1x1)]=257 The primary purpose of Hexadecimals is to represent binary code in a format  easier for humans to read. It acts as a shorthand, in which one hexadecimal digit  stands in place of four binary bits (e.g., the decimal numeral 79, whose binary 
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This note was uploaded on 01/26/2011 for the course PLS 21 taught by Professor Lieth during the Spring '08 term at UC Davis.

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PLS 21 Lecture #2 - Lecture#2NetworksandtheInternet...

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