Chapter 6 Computer Networks from the reference book

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Chapter 6Computer Networks(from the reference
book)

• Introduction to CS
• 1st Semester, 2009 Sanghyun Park

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Outline

• Network Classification
• Bridge and Router
• Internet
• World Wide Web
• Internet Protocols
• Security (will be covered in 12th week)

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Network Classification (1/3)

• Two broad categories
• LAN (Local Area Network)normally consists of a
  collection of computers in a single building or
  building complex, e.g., university campus
• WAN (Wide Area Network) links machines that may
  be in neighboring cities or an opposite side of
  the world
• Ownership
• Public domain ? open network (Internet)
• Private entity ? closed network or proprietary
  network
• Network topology (pattern in which machines are
  connected)
• Ring, bus, star, irregular

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Network Classification (2/3)
The machines are all connectedto a common
communication linecalled a bus
The machines are connectedin a circular fashion
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Network Classification (3/3)
One machine serves as a hub to whichall the
others are connected
The machines are connected in whatappears to be
a haphazard manner
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Bridge and Router (1/2)

• At times it becomes necessary to connect two
  existing networks
• When the networks are compatible, this can be
  done by merely connecting the networks by a
  coupling device called a bridge
• When two networks are connected via a bridge, the
  result is simply a larger single network
• It is often necessary to join two networks whose
  characteristics are not compatible
• In this case, the two networks must be connected
  in a manner that builds a network of networks,
  which is known as an internet
• The connection between two networks to form an
  internet is handled by a machine known as a router

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Bridge and Router (2/2)
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Inter-Process Communication

• Client-server
• One server, many clients
• Server must execute continuously
• Client initiates communication
• Peer-to-peer
• Two processes communicating as equals
• Peer processes can be short-lived

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Client/Server Model
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C/S Model Compared ToPeer-To-Peer Model
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Distributed Systems

• Systems with parts that run on different
  computers
• Infrastructure usually provided by standardized
  toolkits
• Examples include
• Enterprise JavaBeans from Sun Microsystems
• .NET framework from Microsoft

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The Internet

• A network of networks ? internet
• An example of an internet is the Internet
• Originated from a research program initiated in
  1973 by the Defense Advanced Research Projects
  Agency (DARPA)
• Internet is a combination of WANs and LANs
  involving maybe millions of machines

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Internet Topology (1/2)

• The Internet can be viewed as a collection of
  domains, each of which is relatively small
  internet operated by a single organization
• To establish a domain, the entity desiring the
  domain must register with ICANN (Internet
  Corporation for Assigned Names and Numbers)
• A domain is attached to the existing Internet via
  a router that connects a network in the domain to
  a network already in the Internet
• This particular router is called the domains
  gateway
• The gateways of a number of domains can be
  connected to form a regional network of gateways

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Internet Topology (2/2)

• A typical approach to connecting to the Internet

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Internet Addressing (1/2)

• Each machine in the Internet is assigned a unique
  address,called an IP address
• Each IP address is a pattern of 32 bits
  consisting of two parts
• Identify the domain (network identifier)
• Identify the particular machine within the domain
  (host address)
• Network identifier is assigned by ICANN at time
  of domain establishment and registration
  (guarantees uniqueness of network identifier)
• The host address is assigned by the domains
  local authority
• Example
• 192.207.177 (network identifier of Addison-Wesley
  publishing co.)
• 192.207.177.133 (a machine within this company)

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Internet Addressing (2/2)

• ICANN assigns each domain a unique mnemonic
  addressknown as domain name (edu, gov, org, com,
  first-level domains)
• Break domain into sub-domains
• We need a mapping between numeric addresses and
  mnemonic addresses (each local authority
  maintains such directory)
• Directory is implemented within the domain in the
  form of a server called a name server (DNS ?
  Domain Name System)
• Name server provides lookup for mnemonic
  addresses to obtain the corresponding numeric
  addresses

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World Wide Web (1/3)

• Hypertext is a text containing words, phrases, or
  images that are linked to other documents
• When hypertext contains sounds and video, it is
  called hypermedia
• Reader of hypertext documents can explore related
  documents
• A web of related information is formed
• Web that has evolved on the Internet spans the
  entire globe and is known as World Wide Web

Request
Client machine Browser
Server machine Serves web pages
Reply
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World Wide Web (2/3)

• Each document is identified by a unique address
• This unique address is called a URL (Uniform
  Resource Locator)
• The URL allows to identify the server, the
  protocol in use, and a desired document
• Sometimes a URL does not explicitly identify a
  document, in such case a predetermined document
  is often returned(usually a home page)

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World Wide Web (3/3)

• A hypertext document contains several markers
  that describe
• How the document should appear within the browser
• Which items within the document are to be linked
  to other documents
• Systems of markers known as Hypertext Markup
  Language (HTML)
• Finding information on the WWW ? Search Engines

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Layered Approach to Internet Software (1/2)

• A principal task of network software is to
  provide the infrastructure required for
  transferring message from one machine to another
• Package-shipping example

The transportation of the gift would be carried
out by a three-level hierarchy(1) the user
level, (2) the shipping company, and (3) the
airline
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Layered Approach to Internet Software (2/2)

• The Internet software has four layers rather than
  three

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TCP/IP Protocol Suite (1/2)

• The TCP/IP protocol suite is a collection of
  protocols used by the Internet to implement the
  four-level hierarchy just described
• Actually, TCP (Transmission Control Protocol) and
  IP (Internet Protocol) are the names of only two
  of the protocols in this collection
• TCP/IP protocol suite provides two ways of
  implementing the transport layer TCP and UDP
  (User Datagram Protocol)
• The application layer may choose to send data via
  a TCP or UDP
• IP is the Internets standard for the network
  layer

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TCP/IP Protocol Suite (2/2)