MAKING THE CONNECTION

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MAKING THE CONNECTION
chapter3

• The Basics of Networking

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Key communication concepts

• Synchronous- Sender and receiver communicate
  instantaneously (ex telephone)
• Asynchronous- Sender and receiver communicate at
  different times (ex walkie-talkie)

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Key communication concepts

• Broadcast- Single sender many receivers (ex
  radio)
• Multicast- Single sender a subset of receivers
  (ex videoconference)
• Point-to-point- One sender one receiver (ex
  telephone)

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Networking Terminology

• LAN Local Area Network
• A discrete network linked by a single cable or
  pair of wires
• Typically serves a single building (home or
  office)
• WAN Wide Area Network
• Networks that communicate over greater distances
  where the computers are not directly connected
• Internet is a collection of networked WANS
• Intranet A LAN that enables communication
  within the network and that allows connection to
  the internet via a gateway

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Internet Capabilities

• Internet is asynchronous but so fast it appears
  synchronous
• Internet is an all-purpose communication network
• Synchronous -gt phone service
• Multicasting -gt chatrooms
• Broadcasting -gt web pages

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Figure 3.1. A diagram of the Internet.
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World Wide Web

• Web Servers Internet computers that send files
  to browsers
• WWW web servers files
• Lots of useful information that can be easily
  found and retrieved
• Internet the physical infrastructure (wires
  routers) that connects computers
• WWW is a subset of the internet

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Figure 3.3a. Two diagrams of domain hierarchy.
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Figure 3.3b. Two diagrams of domain hierarchy.
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Figure 3.2. Computers connected to the Internet
are given IP addresses.
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Internet Protocol Addresses

• Every computer must have a destination address
  (IP address)
• Currently, IP address is a series of 4 numbers
• Ex 128.95.1.207
• Each number ranges from 0-255
• Can handle 2564 computers (4.3 billion) -gt not
  enough!
• IPv6 will handle 25616 (340 trillion trillion
  trillion)
• Domain is a related set of networked computers w/
  hierarchical structure
• Each computer has a name that corresponds to an
  IP address
• Domain Name Servers translate names into IP
  addresses

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Figure 3.4. Hosts like Spiff make requests to a
local DNS server.
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World Wide Web

• URL Uniform Resource Locator uniquely
  identifies each resource on the WWW, it has 3
  parts
• Protocol (http//) specifies how browser and web
  server communicate
• Web servers name (www.pitt.edu, for example)
• Pathname for file requested from the server
• WWW is based on client-server model
• Browser is the client who requests resource from
  server
• Server sends resource to client, then serves next
  request

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Internet TCP/IP Protocol

• Protocol- An agreed upon format for exchanging
  information between parties
• Specifies data structure, error checking, when
  sender is finished, confirmation of receipt, etc.
• All parties must know the protocol and follow it
• Example protocols
• TCP/IP (Transmission Control Protocol/Internet
  Protocol)
• HTTP (Hypertext Transfer Protocol)
• FTP (File Transfer Protocol)
• A common protocol is required for communication
  via the internet
• TCP/IP is the fundamental internet protocol

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Figure 3.5. The TCP/IP postcard analogy.
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Figure 3.6. The Internet makes use of whatever
routes are available to deliver packets.
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Internet TCP/IP Protocol

• Transmission Control Protocol/Internet Protocol
• TCP/IP breaks a message into a numbered series of
  IP packets.
• Packet contains message, destination IP address,
  sequence number
• Each packet may travel a different route
• Reassembled in order at destination
• Packets hop from WAN to WAN via various physical
  media (wire, fiber optic, satellite, etc.)

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Figure 3.7. A ping from the authors machine to
eth.ch.
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World Wide Web

• Web pages usually stored in HTML format
• Hypertext Markup Language describes document
  layout
• Browser displays document based on the HTML tags
  embedded in document
• HTML is the next topic in the course

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Figure 3.9. A Web page and the HTML source that
produced it. Notice that an additional image
file, alto.jpg, is also required to display the
page.
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Figure 3.9 (continued). A Web page and the HTML
source that produced it. Notice that an
additional image file, alto.jpg, is also required
to display the page.
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Figure 3.10. A hierarchy diagram showing the path
between xerox-alto.jpg and the desktop.
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Figure 3.11. The pathname hierarchy ending in
pioneer.html.
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Ethernet

• Dominant network technology for LANs
• Uses broadcast to achieve point-to-point
  communication
• Only 1 communication at a time on the network
• OK since LAN carries local traffic
• If you want to talk, follow these rules
• If no one is talking, then talk
• If someone is talking, listen until they stop,
  then start talking
• If someone else starts talking at the same time,
  stop talking
• Wait a random amount of time, then try to start
  talking

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Ethernet

• Sends bits by varying the voltage in the wire
• A voltage increase 1, voltage decrease 0
• Well talk about bits later in the course
• Bits are combined into data bundles called Frames
• A protocol defines the data structure of each
  Frame
• Frames are transmitted through the network

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Figure 3.8. Robert Metalfes original drawing of
the Ethernet design the unlabeled boxes,
computers, tap onto the wire that Metcalfe has
labeled The Ether.