Chapter Three Key Concepts OSI and TCPIP Layers

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Chapter Three Key ConceptsOSI and TCP/IP Layers
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Indirect Communication through Encapsulation

• Upper layer program passes messages down to next
  layer
• Lower layer encapsulates message by placing it in
  a data field and adding a header
• Communication occurs indirectly between the
  layers as packets flow down the source stack and
  up destination stack

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Review of Terms

• Domain Name Services (DNS)
• Maps host names to IP addresses
• Dynamic Host Configuration Protocol (DHCP)
• Dynamically leases IP addresses (and more) to
  network hosts

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Windows Networking

• Setting up Windows Networking
• Right-click Network Neighborhood to modify
  settings
• Setup requires identification of adapters, and
  protocols, plus some services.
• Bindings are automatic
• Focus on TCP/IP protocol settings

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Chapter 3 Objectives

• How do HTTP, TCP, IP, and PPP work
• Describe IP addresses and subnet masks
• Discuss router forwarding tables, dynamic routing
  protocols, and router forwarding decisions
• Define Connection-oriented vs connectionless
  service
• Define Reliable vs unreliable service

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The TCP/IP Protocol Suite

• A standards architecture
• Defines standards at all layers
• HTTP, FTP, Telnet at Application layer
• TCP and UDP at Transport layer
• IP and others at Internet layer

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Transport Layer Protocols

• TCP
• Connection-oriented
• Provides for flow control
• Is reliable
• Correctly received segments are acknowledged by
  receiver
• Unacknowledged segments (lost or in error) are
  retransmitted by sender
• Lower layer errors are corrected

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Transport Layer Protocols

• User Datagram Protocol
• An alternative to TCP
• Connectionless and unreliable
• Useful if occasional data loss is tolerable
• Useful when error correction delays are
  intolerable (real-time voice)

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Network Protocol

• Internet Protocol (IP)
• Connectionless and unreliable to minimize router
  processing and costs
• Errors are corrected by TCP
• Hop-by-Hop (router to router) protocol

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IP Protocol Versions

• IPv4
• 32 bit address fields
• Very few of these addresses are unused
• IPv6
• Next version under development
• 128-bit addresses

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IP addresses Key Terms

• Host ID part of IP address that identifies
  computer
• Network ID part of IP address that identifies
  network where computer resides
• Subnet Mask Used to hide or mask host ID
  from network ID

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Simple Subnet Mask Example

• Given IP address 132.178.16.4
• Given Subnet mask 255.255.0.0
• Convert both to binary equivalent
• AND subnet mask to IP address
• For A1 and B 1, A AND B 1
• Otherwise A AND B 0

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Router Forwarding Decisions

• Consider Source and Destination hosts on
• The same subnet
• Different subnets
• Destination on same subnet
• Destination different subnet

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Solutions

• Same subnet
• Message is delivered directly to destination host
• Different subnets
• Message sent to Default Gateway (Router)
• Router table used to look for destination subnet

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Solutions (continued)

• Destination found on next subnet
• If destination is not found, then send to next
  router (using information in route tables) until
  destination host is found

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Point-to-Point Protocol

• Data-Link layer protocol
• Source negotiates how data will be delivered to
  destination
• PPP uses a protocol field to tell whether
  information field is supervisory or a packet to
  be delivered
• Unreliable. CRC discards error frames