IST220 Networking and Telecommunications

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IST220 Networking and Telecommunications

• Chapter 20 IP Datagrams and Datagram Forwarding
• Fall 2007

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TCP/IP Protocol

• Connection-oriented service
• Similar to phone communication
• Connection must be established between two
  computers before data can be transferred
• Connectionless service
• Similar to postal mail
• Computer places data into a frame
• Attach the receivers address
• Pass the frame to the network

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Traveling packets
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What is the format of Internet packet?

• Internet packet ? IP Datagram
• What is the size of IP datagram?
• What kind of information needed to be in the
  header?

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Traveling packets
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IP Datagram Format
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(No Transcript)
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How does a packet travel across the Internet?
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What kind of service IP offers?

• Best-effort service
• What does this mean?
• Datagram duplication
• Delayed or out-of-order delivery
• Corruption of data
• Datagram loss

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IST220 Networking and Telecommunications

• Chapter 21 IP Encapsulation, Fragmentation, and
  Reassembly
• Fall 2007

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Encapsulation
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Traveling Datagrams
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Scenario Networks with different MTU values
What is the potential problem in this scenario?
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Solution Fragmentation

• Router divides the datagram into smaller pieces
  called fragments and send each fragment
  independently.
• Example Original Datagram has the totl length of
  5140 bytes. This datagram has to pass through
  Ethernet LAN.

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Fragments
FRAGMENT OFFSET
FLAGS
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Problem Fragment Loss

• A sender starts a timer when the first fragment
  arrives.
• If all fragments arrives before the timer
  expires, the receiver cancels the timer and
  reassembles the datagram.
• If the timer expires before all fragment arrives,
  the receiver discards those fragments that
  arrived.