Foundations:%20Addressing

1
Foundations Addressing

• Barry Wessler
• October 1, 2004

2
The Postal Letter

• Variable length
• Subaddressing
• Descriptive
• Field oriented
• Redundancy (zip code)
• Limited automation (OCR, ZIP)
• Global Standard

3
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

4
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

5
Packet Services

• Three original ARPANet application models
• Person-to-person (RWT)
• Computer-to-computer (LGR)
• Person-to-computer (BDW)

6
Basic Justification LGR Analysis
Unit cost
Transmission
Computing
Time
7
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
• RD money used not implementation or operation
  money

8
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)

9
Early ARPANet Map
10
Later Map
11
Later Map
12
System Complexity
Complexity
Time
13
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