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					Foundations: Addressing
        Barry Wessler
       October 1, 2004
             The Postal Letter
•   Variable length
•   Subaddressing
•   Descriptive
•   Field oriented
•   Redundancy (zip code)
•   Limited automation (OCR, ZIP)
•   Global Standard
             Circuit Switch
• Telex, telephone, X.25 (virtual circuits)
• Numeric
• Variable length (but fixed maximum)
• Limited Huffman coding (country codes and
  area codes in some countries)
• Historically geo-coded numbering but some
  breakdown today due to mobile services
           Message Switching
• Telex store-and-forward
• Generally hybrid addressing:
  – Part numeric to a distribution center
  – Part physical address to the final recipient or
    functional area
• Addressing was local
            Packet Services
• Three original ARPANet application models:
  – Person-to-person (RWT)
  – Computer-to-computer (LGR)
  – Person-to-computer (BDW)
Basic Justification: LGR Analysis
    Unit cost




                                   Transmission

                Computing




                            Time
             Original Scale
• 30 to 50 nodes planned
• 50 Kbs lines between nodes
• Less than 100 bytes average packet size
• ARPA IPT contractors and selected defense
  establishments
• R&D money used not implementation or
  operation money
           ARPANet Addressing
• Specified in BBN 1822
  interface document
   – Fixed length (6 bits) node
     addressing
   – Subaddressing (2 bits)
   – Total of 256 addressable
     points
• Later changed to 16 bit
  node addressing and 8 bit
  subaddressing (~1976)
Early ARPANet Map
Later Map
Later Map
             System Complexity
Complexity




                       Time
      Addressing for Internet 0
• Always use existing protocols if rational and
  possible
• If not, try to predict end point complexity and
  plateaus and design accordingly

				
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posted:1/9/2012
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