LIS 508 lecture 9 GNU introduction to networks

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LIS 508 lecture 9: GNU & introduction to networks Thomas Krichel 2002 -11 -19

LIS 508 lecture 9: GNU & introduction to networks Thomas Krichel 2002 -11 -19

Structure • open source, and GNU • General things about networks – Some concepts

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

Software anatomy • Software can be distributed in two ways – Binary code –

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

Binary code • It will run on a compute with one operating system, may

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.

Source code /* For now, don't try to include termcap. h. On some systems,

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 <termcap. h> #else extern void tputs P_ ((const char *, int (*)(int))); extern int tgetent P_ ((char *, const char *)); extern int tgetflag P_ ((char *id)); extern int tgetnum P_ ((char *id)); #endif

Source code • • This is human (geek) readable code. May be understood by

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

One upon a time • Early 80 s, MIT lab get a printer as

One upon a time • Early 80 s, 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

Stallman’s theory of 4 freedoms • Free software is a matter of the users'

Stallman’s 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.

GNU public license • GNU stands for “GNU is not UNIX” • Its license

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.

St IGNUcius & the church of Emacs • Emacs was originally a text editor

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.

Business case • Eric Raymond has been pressing the business case for open source

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.

networks

networks

Computer network • Definition: – A computer network is a collection of autonomous computers

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

Computer networks for communication • Access to remote information – Data soucres – Software

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

Types of networks • By technology – Broadcasting network – Point-to-point network • Circuit

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

Network modeling • Usually networks are modeled as layers • Purpose of layer is

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.

Service types • Connection oriented / connectionless – phone conversation – datagram • Reliable

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

http: //openlib. org/home/krichel Thank you for your attention!

http: //openlib. org/home/krichel Thank you for your attention!