LIS508 lecture 9: GNU

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LIS508 lecture 9GNU introduction to networks

• Thomas Krichel
• 2002-11-19

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Structure

• open source, and GNU
• General things about networks
• Some concepts
• History of Internet
• LANs

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Software anatomy

• Software can be distributed in two ways
• Binary code
• Source code
• Sometimes both are available

4
Binary code

• Looks like this
• ?ELFAAA_at__at__at__at__at__at__at__at__at_B_at_C_at_A_at__at__at_plt9Agt
  4_at__at__at_XG_at__at__at__at__at_4_at__at_F_at_(_at___at_\_at_F_at__at__at_4
  _at__at__at_4lt80gt4lt80gtÀ_at__at__at_À_at__at__at_E_at__at__at_D_at__at__at_C
  _at__at__at_ô_at__at__at_ôlt80gtôlt80gtS_at__at__at_S_at__at__at_D_at__at__at_
  A_at__at__at_A_at__at__at__at__at__at__at__at_lt80gt_at_lt80gtòÞB_at_òÞB_at_
  E_at__at__at__at_P_at__at_A_at__at__at_øÞB_at_ønønK_at__at_ìÈ_at__at_F
  _at__at__at__at_P_at__at_B_at__at__at_èB_at_xxÐ_at__at__at_Ð_at__at__at_F
  _at__at__at_D

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Binary code

• It will run on a compute with one operating
  system, may not run on a computer with another.
• It can not be modified.
• It is difficult to find out what it does.

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Source code

• / For now, don't try to include termcap.h. On
  some systems, configure finds a non-standard
  termcap.h that the main build won't find. /
• if defined HAVE_TERMCAP_H 0
• include lttermcap.hgt
• else
• extern void tputs P_ ((const char , int, int
  ()(int)))
• extern int tgetent P_ ((char , const char ))
• extern int tgetflag P_ ((char id))
• extern int tgetnum P_ ((char id))
• endif

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Source code

• This is human (geek) readable code.
• May be understood by humans.
• Can be changed.
• Needs a compiler software to translate it to
  translate it to binary code, for every type of
  machine where it needs to run.

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One upon a time

• Early 80s, MIT lab get a printer as a shared
  resource, but with faulty driver software that
  leads the printer to be jammed.
• Richard Stallman tries to get the source code to
  change the driver software, but can not get it.
• Decides to work for software freedom. Founds Free
  Software Foundation FSF.
• Resigns from MIT AI lab to work on a free
  replacement of UNIX.
• Wrote important parts of UNIX replacement.
• Became particularly famous for his text editor
  Emacs

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Stallmans theory of 4 freedoms

• Free software is a matter of the users' freedom
  to run, copy, distribute, study, change and
  improve the software.
• It implies
• The freedom to run the program, for any purpose
  (freedom 0).
• The freedom to study how the program works, and
  adapt it to your needs (freedom 1).
• The freedom to redistribute copies so you can
  help your neighbor (freedom 2).
• The freedom to improve the program, and release
  your improvements to the public, so that the
  whole community benefits. (freedom 3).
• Access to the source code is a precondition for
  freedom 1 and 3. For that reason, some people
  refer to free software as open source software.

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GNU public license

• GNU stands for GNU is not UNIX
• Its license is the most famous among a group of
  licenses for free software.
• License to implement the four freedoms.
• Key idea The licensee is not allowed to impose
  restrictions on the code that (s)he has developed
  from the code that she received.
• Such software is know as copylefted software.

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St IGNUcius the church of Emacs

• Emacs was originally a text editor by Richard
  Stallman, but it became a way of life and a
  religion. To join the Church of Emacs, you need
  only say the Confession of the Faith three times
  
• There is no system but GNU, and Linux is one of
  its kernels.
• Sainthood in the Church of Emacs requires living
  a life of purity. Being holy in our church means
  installing a wholly free operating
  system--GNU/Linux is a good choice--and not
  putting any non-free software on your computer.

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Business case

• Eric Raymond has been pressing the business case
  for open source software.
• Open office is a software suite that is
  available in open source to replace the MS Office
  suite of software.
• Linux could straight away move into business
  environment. Manufacturers and consultants need
  to get their act together.

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networks
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Computer network

• Definition
• A computer network is a collection of autonomous
  computers
• The distributed nature of the system is apparent
  to the user
• Motivation
• Resource sharing
• Increase reliability
• Improve scalability
• Money savings through use of PCs

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Computer networks for communication

• Access to remote information
• Data soucres
• Software
• E-commerce
• Video on demand
• Person to person communication
• Email
• Video conferencing
• Interactive television

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Types of networks

• By technology
• Broadcasting network
• Point-to-point network
• Circuit switched
• Packet switched
• By size
• LAN
• Bounded size, bus or ring
• High speed and reliability
• WAN
• Interconnection of a large number of hosts
• Has transmission lines and routers
• Has an irregular topology, often with subnets
• Internet
• a collection of interoperable networks

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Network modeling

• Usually networks are modeled as layers
• Purpose of layer is to carry out services for the
  higher layer in a way that is transparent to the
  higher layer.
• Layers communicate with their peers according to
  known protocols
• Between layers in the same machine there is an
  interface.

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Service types

• Connection oriented / connectionless
• phone conversation
• datagram
• Reliable / non-reliable
• Online video
• File transfer

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http//openlib.org/home/krichel

• Thank you for your attention!