Technology Infrastructure

1
Technology Infrastructure

• Internet

2
Learning Objectives

• In this lecture, we will learn about
• The origin, growth, and current structure of the
  Internet
• How packet-switched networks combined to form the
  Internet
• Internet protocols and Internet addressing

3
Technology Overview

• Computer networks and the Internet form the basic
  technology structure for what is now the WWW.
• The computers in these networks run such software
  as
• Operating systems, database managers, encryption
  software, multimedia creation and viewing
  software, and the graphical user interface

4
Technology Overview

• The Internet includes
• The hardware that connects the computers together
  
• the hardware that connects the networks together
• Rapid change in these technologies requires
  businesses to be flexible

5
Packet-Switched Networks

• A local area network (LAN) is a network of
  computers close together.
• A wide area network (WAN) is a network of
  computers connected over a great distance.
• Circuit switching is used in telephone
  communication.
• The Internet uses packet switching
• Files are broken down into small pieces (called
  packets) that are labeled with their origin,
  sequence, and destination addresses.

6
Internet Protocols
http// World Wide Web mailto E-mail
address ftp// File Transfer Protocol telnet Te
lnet
7
Top Level Domain Names
.edu Educational Institution (in
US) .ca Country Codes (two letters such as .ca,
.de, .mx, .jp) .gov Governmental
Agency .mil Military Entity .com Commercial
Entity .net Internet Service Provider .org Non-P
rofit Organization
8
When Computers Communicate

• When two or more computers communicate, they must
  have a common way in which to communicate.
• To do this computers use protocols
• A protocol is an agreement by which two or more
  computers can communicate.
• Transmission Control Protocol/Internet Protocol
  (TCP/IP) is the underlying protocol for the
  Internet.

9
How TCP/IP Works
10101010100110101001101001101021010101010101101011
11010101110111011101101100001011101101010101010011
10101001010111101000

• 1) Transmission Control Protocol (TCP) breaks
  data into small pieces of no bigger than 1500
  characters each. These pieces are called
  packets.

101010101001101010011010011
101010101001101010011010011
101010101001101010011010011
10
How TCP/IP Works(II)

• 2) Each packet is inserted into different
  Internet Protocol (IP) envelopes. Each
  contains the address of the intended recipient
  and has the exact same header as all other
  envelopes.

101010101001101010011010011
101010101001101010011010011
101010101001101010011010011
11
How TCP/IP Works

• A router receives the packets and then determines
  the most efficient way to send the packets to the
  recipient.
• After traveling along a series of routers, the
  packets arrive at their destination.

Packet 101010101001101010011010011
Router 1
Router 3
Packet 101010101001101010011010011
Router 2
Router 4
12
Packets

• Everything you do on the Internet involves
  packets. For example, every Web page that you
  receive comes as a series of packets, and every
  e-mail you send leaves as a series of packets.
  Networks that ship data around in small packets
  are called packet switched networks. On the
  Internet, the network breaks an e-mail message
  into parts of a certain size in bytes. These
  collections of bytes are the packets. Each packet
  carries the information that will help it get to
  its destination
• the sender's IP address,
• the intended receiver's IP address,
• something that tells the network how many packets
  this e-mail message has been broken into and
• the sequence number of this particular packet.

13
Packets Purpose

• The packets carry the data in the protocols that
  the Internet uses Transmission Control
  Protocol/Internet Protocol (TCP/IP). Each packet
  contains part of the body of your message. A
  typical packet contains perhaps 1,000 or 1,500
  bytes.
• Each packet is then sent off to its destination
  by the best available route -- a route that might
  be taken by all the other packets in the message
  or by none of the other packets in the message.
  This makes the network more efficient. First, the
  network can balance the load across various
  pieces of equipment on a millisecond-by-millisecon
  d basis. Second, if there is a problem with one
  piece of equipment in the network while a message
  is being transferred, packets can be routed
  around the problem, ensuring the delivery of the
  entire message.

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Packet Design

• Most packets are split into three parts
• Header - The header contains instructions about
  the data carried by the packet. These
  instructions may include
• Body - Also called the payload or data of a
  packet. This is the actual data that the packet
  is delivering to the destination. If a packet is
  fixed-length, then the payload may be padded with
  blank information to make it the right size.
• Footer - sometimes called the trailer, typically
  contains a couple of bits that tell the receiving
  device that it has reached the end of the packet.
  It may also have some type of error checking.

15
Packet Design

Body
Footer
Header
16
How are Packets Used

• If a message is sent over the internet, it will
  be broken into packets. Each packet's header will
  contain the proper protocols, the originating
  address (the IP address of your computer), the
  destination address (the IP address of the
  computer where you are sending the e-mail) and
  the packet number (1, 2, 3 or 4 since there are 4
  packets). Routers in the network will look at the
  destination address in the header and compare it
  to their lookup table to find out where to send
  the packet. Once the packet arrives at its
  destination, the receiving computer will strip
  the header and footer off each packet and
  reassemble the message based on the numbered
  sequence of the packets.

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Packet Header

• Header (contains instructions about the data
  carried by the packet)
• Length of packet
• Synchronization (a few bits that help the packet
  match up to the network)
• Packet number (which packet this is in a sequence
  of packets)
• Protocol (on networks that carry multiple types
  of information, the protocol defines what type of
  packet is being transmitted e-mail, Web page,
  streaming video)
• Destination address
• Originating address

18
Packet Body and Footer

• Body - Also called the payload or data of a
  packet. This is the actual data that the packet
  is delivering to the destination. If a packet is
  fixed-length, then the payload may be padded with
  blank information to make it the right size.
• Footer - sometimes called the trailer, typically
  contains a couple of bits that tell the receiving
  device that it has reached the end of the packet.
  It may also have some type of error checking.

19
Error Checking

• The most common error checking used in packets is
  Cyclic Redundancy Check (CRC).
• CRC takes the sum of all the 1s in the payload
  and adds them together. The result is stored as a
  hexadecimal value in the footer (trailer). The
  receiving device adds up the 1s in the payload
  and compares the result to the value stored in
  the trailer. If the values match, the packet is
  good. But if the values do not match, the
  receiving device sends a request to the
  originating device to resend the packet.

20
Error checking example (CRC)

• Suppose you have 4 bytes of data of the form
• 10101101 00111000 11001011 10010011
• The sum of all the 1s in this data is 17. This
  value can be represented in binary form as
• 00010001
• The value 17 (00010001) is the CRC value which is
  inserted into the footer (trailer)

21
Packet Construction

• Suppose you send an e-mail to a friend, that the
  e-mail is about 3,500 bits (3.5 kbits) in size,
  and that the network you send it over uses
  fixed-length packets of 1,024 bits (1 kilobit).
  The header of each packet is 96 bits long and the
  footer is 32 bits long, leaving 896 bits for the
  payload. To break the 3,500 bits of message into
  packets, you will need four packets (divide 3,500
  by 896). Three packets will contain 896 bits of
  data and the fourth will have 812 bits.

22
Routing Packets

• The computers that decide how best to forward
  each packet in a packet-switched network are
  called routers.
• The programs on these routers use routing
  algorithms that call upon their routing tables
  to determine the best path to send each packet.
• When packets leave a network to travel on the
  Internet, they are translated into a standard
  format by the router.
• These routers and the telecommunication lines
  connecting them are referred to as the Internet
  backbone.

23
How TCP/IP Works

• Upon arrival at their destination, TCP checks the
  data for corruption against the header included
  in each packet. If TCP finds a bad packet, it
  sends a request that the packet be
  re-transmitted.

24
IP Addresses

• Since computers process numbers more efficiently
  and quickly than characters, each machine
  directly connected to the Internet is given an IP
  Address
• An IP address is a 32-bit address comprised of
  four 8-bit numbers (28) separated by periods.
  Each of the four numbers has a value between 0
  and 255
• Normally, an IP address is is given in dotted
  decimal form 138.73.1.35

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IP Addresses

• Example of an IP Address

http//138.73.1.35
The IP Address of the MtA Web Server
26
IP Addresses vs. URLs

• While numeric IP addresses work very well for
  computers, most humans find it difficult to
  remember long patterns of numbers.
• Instead, humans identify computers using Uniform
  Resource Locators (URLs), a.k.a. Web Addresses.
• When a human types a URL into a browser, the
  request is sent to a Domain Name Server (DNS),
  which then translates the URL to an IP address
  understood by computers.
• The DNS acts like a phonebook.

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Anatomy of a URL
http//www.mta.ca/index.html
http protocol www machine
name mta subdomain ca top level domain name
28
Internet Protocols

• A protocol is a collection of rules for
  formatting, ordering, and error-checking data
  sent across a network.
• ARPANET is the earliest packet-switched
  network.(ARPA Advanced Research Projects
  Agency). ARPA was started by the US govt in the
  1960s, after the Soviet launch of Sputnik in
  October, 1967
• The open architecture of this experimental
  network used Network Control Protocol (NCP) which
  later was modified to become TCP/IP, the core of
  the Internet.

29
Internet Protocols

• This open architecture has four key rules that
  have contributed to the success of the Internet.
• Independent networks should not require any
  internal changes to be connected to the network.
• Packets that do not arrive at their destinations
  must be retransmitted from their source network.
• Router computers act as receive-and-forward
  devices they do not retain information about the
  packets that they handle.
• No global control exists over the network.

30
Internet Protocols

• The Transmission Control Protocol (TCP) and the
  Internet Protocol (IP) are the two protocols that
  support the Internet operation (commonly referred
  to as TCP/IP).
• The TCP controls the disassembly of a message
  into packets before it is transmitted over the
  Internet and the reassembly of those packets when
  they reach their destination.
• The IP specifies the addressing details for each
  packet being transmitted.

31
IP Addresses

• IP addresses are based on a 32-bit binary number
  that allows over 4 billion unique addresses for
  computers to connect to the Internet.
  (138.73.27.246 is Art Millers office machine)
• Ping 138.73.27.246
• IP addresses appear in dotted decimal notation
  (four numbers separated by periods).
• Each number is in the range 0255
• Hex notation (aside)
• IP Addresses in decimal form
• IP addresses are assigned by three not-for-profit
  organizations (ARIN, RIPE, and APNIC).
• Organization of IP numbers

32
IP Addresses

• Approximately two billion IP addresses are either
  in use or unavailable for use.
• Private IP addresses are a series of IP numbers
  that have been set aside for subnet use and are
  not permitted on the Internet.
• IPv6 is a possible solution that uses a 128-bit
  hexadecimal number for addresses.
• A number written using 128 bits can be in the
  range from 12 128
• Since 2 10 is approximately 103 1,000, it
  follows that
• 2 128 (2 10) 12 (10 3) 12 10 36
• 1,000,000,000,000,000,000,000,000,000,000,000,000

33
Domain Names

• To make the numbering system easier to use, an
  alternative addressing method that uses words was
  created.
• An address, such as www.google.com, is called a
  domain name.www.mta.ca 138.73.1.35
• The last part of a domain name (i.e., .com) is
  the most general identifier in the name and is
  called a top-level domain (TLD). The TLD for
  for MtA is .ca

34
Top-level Domain Names
35
History Before the Web

• History of the Internet
• Before the creation of the World Wide Web (1989,
  Tim Berners-Lee) there was a set of technologies
  which constituted the internet
• telnet
• ftp
• Gopher
• History of the Web
• Early browsers for the Web were not as capable as
  those of today

36
Web Page Delivery

• Hypertext Transfer Protocol (HTTP) is the set of
  rules for delivering Web pages over the
  Internet.
• HTTP uses the client/server model
• A users Web browser opens an HTTP session and
  sends a request for a Web page to a remote
  server.
• In response, the server creates an HTTP response
  message that is sent back to the clients Web
  browser.
• In particular, this same action can be
  accomplished without a browser by using the (DOS
  command prompt)
• TELNET www.mta.ca 80 (port 80) and once connected
  using the case sensitive command GET / (followed
  by two carriage returns) This will return the
  same thing that is returned by your web browser
  when you enter http//www.mta.ca
• The combination of the protocol name and the
  domain name is called a uniform resource locator
  (URL).

37
SMTP, POP, MIME, and IMAP

• E-mail sent across the Internet must also be
  formatted to a common set of rules, otherwise
  e-mail created by one company (or Web site) could
  not be read by a person at another company.
• Simple Mail Transfer Protocol (SMTP) specifies
  the exact format of a mail message and describes
  how mail is to be administered at the Internet
  and network level.

38
SMTP, POP, MIME, and IMAP

• An e-mail program running on a users computer
  can request mail from the companys main e-mail
  computer using the Post Office Protocol (POP).
• Multipurpose Internet Mail Extensions (MIME)
  allow the user to attach binary files to e-mail.
• The Interactive Mail Access Protocol (IMAP)
  performs the same basic functions as POP, but
  includes additional features.

39
Internet Connection Options

• The Internet is a set of interconnected
  networks.
• Large firms that provide Internet access to other
  businesses are called Internet Service Providers
  (ISPs).

40
Connectivity Overview

• The most common connection options that ISPs
  offer to the Internet are telephone, broadband,
  leased-line, and wireless.
• The internet grew quickly in North America
  because local telephone calls were free, as
  opposed to Europe, where local calls were charged
  by the time unit
• Bandwidth is the amount of data that can travel
  through a communication line per unit of time.

41
Voice-Grade Telephone Connections

• The most common way to connect to an ISP is
  through a modem connected to your local telephone
  service provider.(or cable provider)
• POTS uses existing telephone lines and an analog
  modem to provide a bandwidth of 28-56 Kbps.
• DSL protocol offers high speed bandwidth over
  standard phone lines.