Binary: Computer language

1
Binary Computer language

• Machines understand a basic on signal.
• On represented by 1
• No signal present, Off represented by 0
• 2 signals, hence the name BI nary.
• When finding how many signals are needed to
  represent a certain number of characters using
  binary, use Log base 2, as 2 is either a 1 or a 0.

2
Open System Interconnection

• The OSI model
• 7 Application
• 6 Presentation
• 5 Session
• 4 Transport
• 3 Network
• 2 Data link
• 1 Physical

3
How the OSI model works

• Each layer, a program or program segment on a
  host computer, passes a 'message' to the layer
  below it
• The receiving layer adds control information and
  sends on the 'message'
• At the lowest layer, the message is passed to the
  lowest layer on another host computer
• At the receiving computer, each layer strips the
  relevant control information and passes it to the
  layer above
• At the topmost layer, the message is read and
  acted upon (e.g., email)
• Most of the functionality in the OSI model exists
  in all communications systems, although two or
  three OSI layers may be incorporated into one.

4
Rationale for the OSI model

• Lower layer adds value to services provided by
  layer above it
• Logical decomposition of complex system into more
  comprehensible parts
• Standard interface between layered functions
• Symmetry in functions performed at each layer
  between systems
• A means to predict and control changes made to
  logic (modularity)

5
Standardization

• Why standards? The concept of open systems
• Can connect physically to other systems
• Can work with other systems
• Issues in standardization
• The need to get the timing just right
• Examples OSI, early ISDN (too quick) late ISDN
  (too long) TCP/IP (just right?)
• Standards confer power
• Examples EDI, MS-DOS, GOSIP
• Extensions subvert and enhance standards
• Example AT commands on modems

6
Who makes the standards?

• Some better known standards making bodies
• International Telecommunications Union (ITU)
• Formerly CCITT
• ITU-T (Telecommunications Standardization
  Sector) also ITU-R (Radiocommunication), ITU-D
  (Development)
• Institute of Electrical and Electronics Engineers
  (IEEE)
• Electronics Industries Association (EIA)
• Formerly RS standards
• American National Standards Institute (ANSI)
• Internet Engineering Task Force (IETF)
• International Standards Organization (ISO)
• Vendors (IBM DEC Novell Microcom etc.)