Updated by Gio Wiederhold, 10 Jan, 16, 23, 24 Jan, 8 Feb 2003.
Do: Suggestions for topics, glossary, ...
Resource sharing for ARPA (the Defense Department's Advanced Research Projects Agency) and its Contractors, academic and industrial.
(o ARPA more focus on benefits , influence on industry and technology-- populist, dominant in Democratic administrations
o DARPA - more isolation - more
science - elitist - dominant in Republican administrations)
Robustness: redundant linking over multiple paths
Limited loss on failure, load balancing: packeting of messages
Motivation for changes in the communication infrastructure: reliability in
the presence of threats through redundant paths, nodes; then access for all
academics, commercial operation and participation for viability.
1. three level naming
2. mapping from names to IP
addresses, performed by Domain Name Servers (DNSs)
Packets with headers: from, to, number
Nodes with forwarding information tables
Later: four level adresses: 171.64.64.64. (what is yours?)
Because address tables got too large - Now cached at designated nodes: Domain
Name Servers (DSN>.
Three level addresses: cs.stanford.edu, ranslated by domain name servers (DSN)
Shared resource use required:
Provided a real population on which stuff could be tested -- without realistic use and feedback the net would have been a pipedream.
Email was not thought of initially, first accomplished via multiple FTPs and TELNET operations. Later a simplified protocol for email: SMTP
HTTP: HyperText Transmission Protocol
HTML: HyperText Markup Language -- an instance of SGML
SGML: Structured Graphic MarkUp Language
from 1970ies - for paper document formatting on computers, also motivated by military, designed by IBM
SGML
is a Meta language - HTML is one choice, others could be the format for the
Journal of Psychology, for AirForce reference manuals, for McGraw-Hill College
books etc.
Hypertext: a document with links to more relevant stuff-- look at a document <A HREF= "something else, somewhere else">what</A>
Sharing among major backbone providers {MCI, SPRINT, Worldcom, UUnet,
AT&T }
LANs often use the Ethernet protocol for locally wired networks with
developed originally for satelite networks (Aloha net in Hawaii).
The ethernet protocol is a broadcast protocol, versus a point-topoint protocol.
How did we get into this topic?
Unit testing: programmers test their own stuff: Easy to miss errors, because the testing assumptions will match the authoring assumptions
Alpha testing: components (or units) are integrated to become a product, and tested by a specialized group, unaware of the assumptions.
Beta testing- Software released to selected customer. Now actual practice, not assumptions dominates.
After delivery - error reports come in, have to be filtered because they are likely redundant -- or trivial. But what's distilled from them can be used to fix the software, maybe in a later version.
Specify layout, type of print, bold, italic, size, headers, paragraph boundaries, tables, etc.
with otherwise invisible Commands as <B>boldface
stuff</B>.
Hyper (multi-linked) Text (documents) Markup (with format annotations) Language, Used to markup documents so they can be easily shown on a variety of computer devices, and reference ( HREF ) local and remote documents and images. Remote documents require a computer address (http://www.somewhere.xxx ) so they can be found.
Paper: arbitrarily structured/unstructured;
physical order.
Books: somewhat structured/unstructured; layout order; metadata: ToC, index.
Tables: very structured. Exceptions awkward -- footnotes
Databases: very structured. Machine processable, queryable. Exceptions awkward.
relational: tabular based, links by references,
join operator; unordered. student|><|course-info
object-oriented: tree-based, structural (and optional reference) links; ordered
(often)
SGML: for document printing, hierarchically
structured; ordered
HTML: for document transmittal, varied presentation, hierarchically structured
+ links; ordered
Three older inventions combined:
Two Technologies:
and a business requisite
A community of high-energy physicists who
Browser competition [Clark-Netscape] [Gates-Microsoft]
Reading: Bring in a simple HTML web document (like this one), and see what it looks like
If you look at a `commercial' web page you will
find many markups that we won't have to care about. Make notes about the ones that
puzzle you and discuss them in class. The essential ones are listed in our CS99I HTML notes.
Doing, indirectly: Create a document with, say, Microsoft Word, save it
as HTML, and look at it.
Doing, directly: Create a document with HTML markups yourself, as shown
in the notes, and then save it as text. May be easiest to use a dumb editor, as
Wordpad, Notepad on PCs or vi, Emacs on UnIX.
Change (rename) the postfix from .txt to .html, and then look at what you have created.
Advantages and Limits
Reliability
Readability
Processability
Granularity
-- (structure: word, line, paragraph, chapter, book )
-- (object: value, name-value pair, item, person, group, community ) with
alternatives (family vs dorm)
Multiple levels of providers:
Backbone linkages -- wide, transcontinental links (leased from the phone
companies, as MCI etc.). Trade bandwidth, portal demands inormally. {MCI,
SPRINT, Worldcom, UUnet, AT&T }
Reading: CS99 chapter about the Internet.
Heilmeyer's Catechism:
What is the problem,
why is it hard?
[George Heilmeyer, ex ARPA director, then TI, GE Aero, then at Bellcore,
retired?]
Expectation versus reality: Powerpoint Figures or HTM Figures, some slides from 1998.
Excessive expectations at the point of visibility.
Insufficient realization of the concomitant speed of social change -- 10-20 year -- generational -- cycle
Primary effect - many high risk-taking startups -- much upside promise, little downside risk of failure.
Secondary effect (Not recognized in 1998); orders brought to infrastructure
companies were in the aggregate in excess of what a realistic market could
absorb, but its very hard to say no to your salesmen.