Grid Computing, B. Wilkinson, 20042.1 Reading Assignments Since there is no assigned textbook, there...

Grid Computing, B. Wilkinson, 2004 2.1

Reading Assignments

Since there is no assigned textbook, there will be a few reading assignments.

Purpose is to consolidate your understanding.

Materials posted on home page from link “reading/on-line materials” at end of section on lecture materials.


First Reading Assignment

"The Anatomy of the Grid: Enabling Scalable Virtual Organizations"

by

I. Foster, C. Kesselman, and S. Tuecke

Int. J. Supercomputer Applications, 2001.


• We said that grid computing is now based upon Internet protocols and interconnections.

• So let’s first review some well-known Internet technologies.


Networked Computers, Internet and World Wide Web

Technology - Basics

Some really basic stuff!


Network Protocol

• TCP/IP (Transmission Control Protocol/Internet Protocol) - standard that establishes basic low level rules for networked computers to communicate and pass data.

• Higher level protocols build on top of TCP/IP.


Network InterfacesComputers connect to the Internet through a network interface (mostly Ethernet).

Each network interface has a unique 48-bit address called a MAC (Media Access Controller) address, which is assigned during manufacture of the interface.

Allocation of addresses controlled by IEEE Registration Authority.


Internet Protocol (IP) AddressSlightly higher level - assigned to interfaces and hence computers.

Example

129.49.82.1

(IP version 4). Divided into fields to allow various network decoding arrangements.

IP address can be static or dynamically changing. Mapped to MAC address with a software table.


Some Network Protocols(on top of TCP/IP)

TelnetAn insecure Internet protocol that allows you to connect to another computer on the Internet.

FTP(File Transmission Protocol)

Standard insecure Internet protocol to exchange files.


FTPtelnet HTTP

TCP

IP

Ethernet driver

Network interface

Network

20/21

23 80

“port” numbers 06

0800


Network services(servers)

Implementation of a protocol with a set of capabilities.

Example - FTP server

FTP protocol Telnet protocol

TCP protocolIP protocol

FTP server


Secure Connections

• Secure connections needed in many computer related activities, including e-business and grid computing.

• Telnet and FTP are very insecure - information is transmitted in clear text.


SSL Protocol(Secure Socket Layer)

• Proposed by Netscape Communications and adopted widely - Latest version SSL 3.0.

• Uses Public Key Cryptography - see later in course.

• Can be used with FTP (SFTP) and other protocols (e.g. HTTTPS).

• Transport Layer Security protocol (TLS) subsequently proposed to SSL - no major differences.


World Wide Web

• Started in earnest in early1990’s when HTTP developed at CERN and Mosaic browser at NCSA.

• HTTP (Hypertext Transfer Protocol) - basic way of accessing web pages.

• World wide web expanded at an amazing rate (1 million hosts in 1993 to 200 million+ hosts in 2004.


Domain Name

• For ease of use by humans, names are used rather than IP addresses.

Example

cs.wcu.edu

• Conversion between IP address and name done by a domain name service, a distributed name database.


URL(Uniform Resource Locator)

• Way of identifying and accessing a web page:

Example

http://www.cs.wcu.edu/~abw/index.html

“how”Type of transaction

(protocol)

“where”Address or name of server

“what”Resource requested

Mark-up Languages

• A way of describing information in a document.• Standard Generalized Mark-Up Language (SGML)

- a specification for a mark-up language ratified in 1986.

• Key aspect - using pairs of tags that surround information - a begin tag <tag_name> and a matching end tag </tag_name> .

Example

<title> CS 493 home page </title>


HyperText Markup Language (HTML)

A mark-up language used in web pages.

“Hypertext” refers to the text’s ability to link to other documents.

“Markup” refers to providing information to tell browser how to display page and other things.

HTML page format

<HTML>

<HEAD>

</HEAD>

<BODY>

</BODY>

</HTML>

Signifies an HTML document

Head section includes information about document - “metadata”

Body section contains text and references to images to be displayed

End of document

HTML Tags

• Tags specify details such as type of text.

Example

 to start bold text

 to end bold text

 to start italic text

 to end italic text

HTML page<HTML>

<HEAD>

</HEAD>

<BODY>

Hello world

 My name is Barry 

</BODY>

</HTML>


QuestionWhat does the previous HTML page display?

Answer

Hello World My name is Barry

HTML page<HTML>

<HEAD>

</HEAD>

<BODY>

 

Hello world 

 My name is Barry 

</BODY>

</HTML>

Line break tag - some tags in HTML are not in pairs

Attributes

Many tags can have attributes which specify something about the body between tag pair.

Example

This text is displayed in red in Times font, about 12 pt.

Attributes


More information about HTML

See WCU course CS 130 (also includes JavaScript).

http://www.cs.wcu.edu/~abw/CS130F04/


Extensible Mark-up LanguageXML

• Ratified in 1998 - very important standard mark-up language - a “simplified” SGML.

• Developed to represent textual information in a structured manner that could be read and interpreted by a computer.

• A foundation for web services and grid services.


Some key aspects of XML

• Tags always used in pairs delineate information to make it easy to process. (There is an exception, when the body between the tags holds nothing.)

• Tags can be nested. They can have attributes.

• Names of tags can be defined broadly at will. (In HTML, tags are predefined.)


XML Application Areas

• Used for two applications areas:

– Document-centric XML

– Data-centric XML


Document-Centric XML

• Documents usually meant for humans, although could be processing by computers.

• Semi-structured - some tags can be placed more-or-less anywhere, similar to HTML tags.

Sample document-centric XML

<H1>Prerequisites for grid computing course</H1>

Fall 2004

<LIST>

<ITEM>CS 150 Programming I or equivalent</ITEM>

<ITEM>CS 151 Programming II or equivalent desirable</ITEM>

<ITEM>Able to program in Java or learn quickly.</ITEM>

<ITEM>Able to program in C/C++ or learn quickly.</ITEM>

<ITEM>Able to use Linux system or learn quickly.</ITEM>

</LIST>

 For more information look at <LINK HREF=“outline.xml”>Outline</LINK>.


Data-Centric XML

• Usually generated and meant to be read by computer programs.

• Structured.

• Nesting useful to create a clearly structured and computer-readable document.

Sample data-centric XML<po id=“53912” submitted=“2004-08-05”>

<billTo>

<name>Department of Mathematics and Computer Science</name>

<company>Western Carolina University</company>

<street></street>

<city>Cullowhee</city>

<state>NC</state>

<postalCode>28723</postalCode>

</billTo>

<shipTo>



<street></street>


<state>NC</state>


</shipTo>

<order>

<item sku=“456-CS” quantity=“7”>

<description>computer system type 1234 </description>

</item>

<item sku=“135-GS” quantity=“12”>

<description>Unmanaged 16 port GigE switch.</description>

</item>

</order>

</po>

Sample data-centric XML

<po id=“53912” submitted=“2004-08-05”>

<billTo>



<street></street>


<state>NC</state>


</billTo>


Quiz

1. (Test of any prior knowledge - answer not in slides.) Where exactly is the file stored with the URL given as

www.cs.wcu.edu/~abw/CS493F04and what is its name (be careful) ?

Answer


Quiz

2. Why are the FTP and telnet protocols insecure?

Answer


Quiz

3. How are tags defined in HTML?

Answer


Quiz

4. How are tags defined in XML?

Answer

Quiz

5. A pair of XML tags with empty contents:

<tag_name></tag_name>can be written as

<tag_name/>

Under what circumstances would such a construction make sense?

Answer

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