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Wide Area Networks

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Wide Area Networks The Internet and the World Wide Web Eric Cozzi eric (at) cozzi (dot) us Agenda History of the Internet In the 1960 s there was great concern that ... – PowerPoint PPT presentation

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Title: Wide Area Networks


1
Wide Area Networks
The Internet and the World Wide Web
  • Eric Cozzi
  • eric (at) cozzi (dot) us

2
Agenda
History of the Internet
Transmission Control Protocol / Internet Protocol
Modern Day Internet
Questions
3
History of the Internet
  • In the 1960s there was great concern that a
    nuclear strike would render all traditional
    communications useless.
  • As a result, the US Department of Defense funded
    the ARPAnet in the development of a
    decentralized, resilient, and self-configuring
    communications network.

1960s
4
First ARPANet Connections
The first ARPANET links were between UCLA and the
Stanford Research Institute in November 1969. A
month later links to the University of Utah and
the UC Santa Barbara were added.
Len Kleinrock standing next to the first Inter
Message Processor (IMP) at UCLA
1960s
5
Creation of the NSFNet
  • Recognizing the potential of the ARPANet, the
    National Science Foundation funded the
    non-military NSFNet.
  • The NSFNet initially interconnected six
    universities Boulder, Champaign, Ithaca,
    Pittsburg, Princeton, and San Diego. A gateway to
    the ARPANet was provided by Carnegie Mellon
    University.

1960s
1970s
6
Commercialization of the Internet
  • While both the ARPANet and NSFNet were funded by
    the United States government, both networks were
    for the sole purpose of supporting research.
  • In the 1980s, the Internet started to be
    commercialized by Telephone Providers and
    privately owned Internet Service Providers.

1960s
1970s
1980s
7
Exponential Growth of the Internet
After widespread commercialization of the
Internet in the 1980s, Internet use grew and
continues to grow at an exponential rate.
1960s
1970s
1990s
1980s
8
Agenda
History of the Internet
Transmission Control Protocol / Internet Protocol
Modern Day Internet
Questions
9
TCP/IP
TCP/IP defines a set of rules to enable computers
to communicate over a network, specifying how
data should be packaged, addressed, shipped,
routed and delivered to the right destination.
The specification defines protocols for different
types of communication between computers and
provides a framework for more detailed standards.
Application Layer
Transport Layer
Network Layer
Data Link Layer
10
Application Layer
Network communication starts and ends at the
Application Layer. The application layer
interfaces directly to and performs common
application services for the application
processes in order to send and receive data. The
application layer also issues receives requests
to/from the transport layer.
Data
Application Layer
Data
TCP Data
Transport Layer
TCP Data
IP Data
Network Layer
IP Data
Frame Data
CRC
Data Link Layer
11
Transport Layer
The transport layer validates the application
layer request, segments the data, encapsulates it
with a transport layer header containing the
correct port numbers and sequence count. The
packet is then and passes down to the network
layer. The transport layer also has the tricky
task of dealing with transfer problems. In the
event of a TX/RX failure, the transport layer (in
the case of TCP) will send and request duplicate
packets in order to maintain application layer
data integrity.
Data
Application Layer
Data
TCP Data
Transport Layer
TCP Data
IP Data
Network Layer
IP Data
Frame Data
CRC
Data Link Layer
12
TCP Header
13
Handling Errors and Flow Control
Here you can see the error handling that is
performed by TCP. Whenever a packet is correctly
received by the receiver, an ACK is sent to the
sender acknowledging the packet. If the sender
does not hear an acknowledgement within a certain
timeout, the sender will automatically resend any
unacknowledged packets. This is known as a
Sliding Window Flow Control Protocol.
14
Network Layer
The network layer translates the source and
destination IP addresses into physical MAC
addresses. A MAC address is a quasi-unique
identifier that acts like a name for a particular
network adapter. The resolution of an IP
address into a MAC address is performed through
an ARP (Address Resolution Protocol) lookup.
Data
Application Layer
Data
TCP Data
Transport Layer
TCP Data
IP Data
Network Layer
IP Data
Frame Data
CRC
Data Link Layer
15
IP Header
16
Data Link Layer
The data link provides data transfer across the
physical network link. That transfer may or may
provide reliable communications as many data link
protocols do not provide a means to test the
correctness of a received frame. In these cases,
higher-level protocols (such as TCP at the
Transport Layer) must provide flow control, error
checking, and acknowledgments and retransmission.
Data
Application Layer
Data
TCP Data
Transport Layer
TCP Data
IP Data
Network Layer
IP Data
Frame Data
CRC
Data Link Layer
17
Ethernet Header Footer
18
Packet Routing over the Internet
  • For a packet to get to its intended recipient, it
    needs to find a route through the network.
  • The most common way for this to happen is hop by
    hop. The originating machine will deliver the
    packet to the best next-hop toward the ultimate
    destination. The packet will continue to move 1
    hop closer to its destination until either the
    hop count dies or the packet reaches its intended
    destination.


19
Routing Protocols
  • There are a number of different routing protocols
    that are employed to correctly route a packet
    through the Internet. Some of the most common
    include
  • Static Routes
  • Routing Information Protocol (RIP)
  • Spanning Tree
  • Border Gateway Protocol (BGP)

20
DNS - The Big Phone Book in the Sky
  • When trying to connect to a remote machine, often
    all we know is the machines name and not its IP
    address.
  • The Domain Name Service (DNS) can be thought of
    like a giant phone book in the sky, that
    automatically maintains a mapping between Domain
    Names and IP Addresses.
  • The DNS system maintains a hierarchy of redundant
    DNS servers starting with the Root Name Servers.
    When looking up a domain name, a DNS host
    resolves the name against this hierarchy until
    the ultimate host IP is found.

21
The OSI Model
  • The OSI Model is an idealized networking model
    that can be closely correlated to the TCP/IP
    model.
  • The OSI Model defines 7 layers, where the TCP/IP
    model defines 4 (or 5 depending).
  • Roughly the first three layers of the OSI model
    map to the Application layer of the TCP/IP model.
    Further, the last two layers of the OSI model
    roughly map to the Data Link layer of the TCP/IP
    model.
  • Each layer in between directly maps with its
    couterpart.

22
Comparison of the TCP/IP and OSI Models
TCP/IP Model
OSI Model
Application Layer
Application Layer
Presentation Layer
Session Layer
Transport Layer
Transport Layer
Network Layer
Network Layer
Data Link Layer
Data Link Layer
Physical Layer
23
Agenda
History of the Internet
Transmission Control Protocol / Internet Protocol
Modern Day Internet
Questions
24
The World Wide Web
  • The World Wide Web (WWW) was developed by Sir
    Timothy Berners-Lee while working at the CERN
    laboratories.
  • While at CERN, Berners-Lee proposed a method of
    using a HyperText Transmission Protocol (HTTP),
    along with HyperText Markup Language (HTML) to
    facilitate the sharing of ideas among
    researchers.
  • To view an HTML page, a browser application would
    reformat and display the HTML encoded page in a
    way appropriate for the users display. In this
    way, hypertext documents are not tied to any
    particular capability or functionality.

25
HTML
  • HTML consists of a series of formatting commands,
    known as HTML tags, which can be embedded into
    the text content of a page.
  • These tags are used to describe properties of the
    page including how the page should be formatted
    and presented.
  • Some Example Tags include
  • ltBgt lt/Bgt - embolden font
  • ltIgt lt/Igt - Italicize font
  • ltA HREFURLgtlt/Agt - Define a hyperlink\
  • ltIMG SRCURLgt - Insert an image

26
Hello World in HTML
  • lthtmlgt
  • ltheadgt
  • lttitlegtHTML Hello Worldlt/titlegt
  • lt/headgt
  • ltbodygt
  • ltH1gtHeading of Hello World!lt/H1gt
  • This is where we say ltpgtHello Worldlt/pgt
  • lt/bodygt
  • lt/htmlgt

27
Server and Browser side Enhancements
  • Since the inception of the WWW, new technologies
    and language extensions have been developed that
    have enhanced both the server and browser sides
    of the web experience.
  • Some of these include
  • Server Side Scripting
  • PHP, Java, ASP, CGI, Perl,
  • Client Side Scripting
  • JavaScript, Flash, AJAX

28
HyperText Transfer Protocol (HTTP)
  • HTTP is a client-server protocol intended for use
    when retrieving documents from the World Wide
    Web.
  • Some examples of HTTP commands include
  • PROXY ltURLgt
  • HEAD ltURLgt HTTP/1.0
  • GET ltURLgt HTTP/1.0
  • POST ltURLgt HTTP/1.0

29
Uniform Resource Locators (URLs)
  • A Uniform Resource Locators (URLs) are used to
    address web pages on the World Wide Web. These
    can be thought of like a file path to a file on
    your hard drive.
  • A URL can be split into a minimum of three
    different parts
  • Protocol Most commenly, HTTP
  • Machine Name The DNS name or IP address of the
    server machine where the HTTP page lives
  • File Path The relative file path to the file on
    the server machine.
  • Example http//www.cs.sjsu.edu/lee/index.html

30
WWW Search Engines
  • Without the modern day search engines, like Yahoo
    and Google, the World Wide Web would long ago
    have become unmanageable.
  • Search Engines work by crawling the Internet to
    find, sort, rank and index pages. This results in
    an extremely large database which essentially
    holds the entire Internet.
  • When performing a user search, the search engine
    uses this local database to locate presumptive
    matches before presenting them to the user.

31
Agenda
History of the Internet
Transmission Control Protocol / Internet Protocol
Modern Day Internet
Questions
32
Thank You!
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