MSIT 194

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MSIT 194

• Internet Technologies
• Engr. Gerardo S. Doroja, M.Sc.
• Professor

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TCP / IP

• Reporters
• Ms. Ma. Leonisa Reyes
• Ms. Melanie Cadavos
• Mr. Surendra Shakya

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Overview

• In the late 1980s and early 1990s there was a
  significant increase in the number and overall
  size of networks. However, many of the early
  networks were built using different
  implementations of hardware and software. This
  resulted in many of the networks being
  incompatible and communication between networks
  was quite difficult. To address this problem, the
  International Organization for Standardization
  (ISO) researched many network schemes. The ISO
  recognized that there was a need to create a
  network model that would help network builders
  implement networks that could communicate and
  work together (interoperability). As a
  consequence, the OSI reference model was released
  in 1984.

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The OSI Reference Model

• The OSI reference model is the primary model for
  network communications. Although there are other
  models in existence, most network vendors, today,
  relate their products to the OSI reference model,
  especially when they want to educate users on the
  use of their products. They consider it the best
  tool available for teaching people about sending
  and receiving data on a network.

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Encapsulation

• All communications on a network originate at a
  source, and are sent to a destination. The
  information sent on a network is referred to as
  data or data packets. If one computer (host A)
  wants to send data to another computer (host B),
  the data must first be packaged by a process
  called encapsulation.

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• Encapsulation wraps data with the necessary
  protocol information before network transit.
  Therefore, as the data packet moves down through
  the layers of the OSI model, it receives headers,
  trailers, and other information.

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• In order for data to travel from the source to
  the destination, each layer of the OSI model at
  the source must communicate with its peer layer
  at the destination. This form of communication is
  referred to as Peer-to-Peer Communications.

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• Data packets on a network originate at a source
  and then travel to a destination. Each layer
  depends on the service function of the OSI layer
  below it. To provide this service, the lower
  layer uses encapsulation to put the PDU from the
  upper layer into its data field then it adds
  whatever headers and trailers the layer needs to
  perform its function.

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The Importance of TCP/IP

• The TCP/IP reference model and the TCP/IP
  protocol stack make data communication possible
  between any two computers, anywhere in the world.

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• The TCP/IP model has historical importance, just
  like the standards that allowed the telephone,
  electrical power, railroad, television, and
  videotape industries to flourish.

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• The U.S. Department of Defense (DoD) created the
  TCP/IP reference model because it wanted a
  network that could survive any conditions, even a
  nuclear war. To illustrate further, imagine a
  world at war, crisscrossed by different kinds of
  connections including wires, microwaves, optical
  fibers, and satellite links. Then imagine that
  you need information/data (in the form of
  packets) to flow, regardless of the condition of
  any particular node or network on the
  internetwork (which in this case may have been
  destroyed by the war). The DoD wants its packets
  to get through every time, under any conditions,
  from any one point to any other point. It was
  this very difficult design problem that brought
  about the creation of the TCP/IP model, and which
  has since become the standard on which the
  Internet has grown.

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• The TCP/IP model has four layers the application
  layer, the transport layer, the internet layer,
  and the network access layer. It is important to
  note that some of the layers in the TCP/IP model
  have the same name as layers in the OSI model. Do
  not confuse the layers of the two models, because
  the application layer has different functions in
  each model.
• Application Layer
• The designers of TCP/IP felt that the higher
  level protocols should include the session and
  presentation layer details. They simply created
  an application layer that handles high level
  protocols, issues of representation, encoding,
  and dialog control. The TCP/IP combines all
  issues related to application into one layer, and
  assures this data is properly packaged for the
  next layer.

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• Transport Layer
• The transport layer deals with the quality of
  service issues of reliability, flow control, and
  error correction. One of its protocols, the
  transmission control protocol (TCP), provides
  excellent and flexible ways to create reliable,
  well-flowing, low-error network communications.
  TCP is a connection-oriented protocol. It
  dialogues between source and destination while
  packaging application layer information into
  units called segments. Connection-oriented does
  not mean that a circuit exists between the
  communicating computers (that would be circuit
  switching). It does mean that Layer 4 segments
  travel back and forth between two hosts to
  acknowledge the connection exists logically for
  some period. This is known as packet switching.

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• Internet Layer
• The purpose of the internet layer is to send
  source packets from any network on the
  internetwork and have them arrive at the
  destination independent of the path and networks
  they took to get there. The specific protocol
  that governs this layer is called the Internet
  protocol (IP). Best path determination and packet
  switching occur at this layer. Think of it in
  terms of the postal system. When you mail a
  letter, you do not know how it gets there (there
  are various possible routes), but you do care
  that it arrives.

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• Network Access Layer
• The name of this layer is very broad and
  somewhat confusing. It is also called the
  host-to-network layer. It is the layer that is
  concerned with all of the issues that an IP
  packet requires to actually make a physical link.
  It includes the LAN and WAN technology details,
  and all the details in the OSI physical and data
  link layers.

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• FTP - File Transfer Protocol
• HTTP - Hypertext Transfer Protocol
• SMTP - Simple Mail Transfer protocol
• DNS - Domain Name System
• TFTP - Trivial File Transfer Protocol

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If you compare the OSI model and the TCP/IP
model, you will notice that they have
similarities and differences. Examples include

• Similarities
• Both have layers
• Both have application layers, though they include
  very different services
• Both have comparable transport and network layers
  
• Packet-switched (not circuit-switched) technology
  is assumed
• Networking professionals need to know both

• Differences
• TCP/IP combines the presentation and session
  layer issues into its application layer
• TCP/IP combines the OSI data link and physical
  layers into one layer
• TCP/IP appears simpler because it has fewer
  layers, however this is a misconception. The OSI
  reference model, with its less complex and
  multiple layers, is simpler to develop and
  troubleshoot.
• TCP/IP protocols are the standards around which
  the Internet developed, so the TCP/IP model gains
  credibility just because of its protocols. In
  contrast, typically networks are not built on the
  OSI protocol, even though the OSI model is used
  as a guide.

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