Day: August 12, 2010

Grid Computing, week 3, saw another jam-packed lecture that left me with a great deal of questions. I think this is a good thing as it forces students to do required readings or simply be left behind in the lectures. Unfortunately I have not been keeping up with readings on this subject and am feeling the pressure now.

The lecture focused on a possible real life example of a butterfly grid. When developing such a grid, the key considerations must be identified:

• Latency
• Downtime
• Security (cheating)
• Physical scalability
• Specific stakeholder needs (Production company, vendors, ISP, gamers, etc)

The butterfly grid add 7 major tiers in the architecture… There was no diagram in the lecture to assist in understanding where these layers fit, a simplified representation can be seen above.

The layers listed in the lecture slide were:

• Object Management System [OMS]
• Network Protocol Stack (UPD/IP instead of TCP/IP for reduced latency)
• Gateway Servers
• Daemon Controllers
• Game Servers
• Data Store and Grid Service – existing layers
• Globus Toolkit Services

Some news article relating to butterfly grids from early 2000s:

http://www.gridcomputingplanet.com/news/article.php/1107421/IBM-Butterflynet-Announce-Video-Game-Grid.htm

https://www-304.ibm.com/easyaccess/ukcomms/gclcontent/gcl_xmlid/91353

There is however very little recent  information on Butterfly grids to be found on the web.

Data Communication’s third lecture review in more detail the Physical Layer (Application -> Transport -> Network -> DataLink -> Physical).

Analogue vs Digital

Dataflow transmissions (Simplex, Half Duplex, Full Duplex, Multiplex)

Multiplexing Division methods:

• Frequency Division multiplexing [FDM]
• Time Division multiplexing [TDM]
• Statistical Time Division Multiplexing [STDM]
• Wavelength Division Multiplexing [WDM]

Communication Medias

Physical

• • Twisted Pair Cables
  • Coaxial Cable
  • Fiberoptic
• Wireless
  • Radio
  • Infrared
  • Microwave
  • Satellite

Interestingly, as satellites need to orbit the earth at quite a high distance to maintain stable service (ideally geostationary appx. 36,000kms) the delay due to the speed of light makes fibre optic a much faster option.

Internet Application development week 3 extended on the subject of XML from last week. As we learned the basics in week 1 and the XML schema (.xsd) in week 2, next up was stylesheets (XSLT). Stylesheet start to give evidence to the value of XML in dynamic web design. HTML code can be generated through the ‘transformation of XML files and XSLT files.

Initially this is not very exciting but when considering that style sheet processing can be done on the fly, it present a wide range of possibilities.

Some simple processing can be done in the XSLT, although it must be noted that it is certainly not a fully fledged programming language and is not enjoyable to write in!

A snippet of code from an XSLT doc illustrates this fact:

<td>
 <xsl:variable name="assTot" select="sum(assignments/assignment)"/>
 <xsl:variable name="unitTot" select="sum(assignments/unitTest)"/>
 <xsl:variable name="count" select="count(assignments/assignment) + count(assignments/unitTest)"/>
 
 <xsl:value-of select="format-number((($assTot + $unitTot) div $count), '##0.00')" />
 </td>
 <td>
 <xsl:variable name="assTot" 
 select="sum(/units/unit[unitCode='FIT5432']/class/studentMarks/student[@id=$curID]/assignments/assignment)"/>
 <xsl:variable name="unitTot" 
 select="sum(/units/unit[unitCode='FIT5432']/class/studentMarks/student[@id=$curID]/assignments/unitTest)"/>
 <xsl:variable name="count2" select="count(/units/unit[unitCode='FIT5432']/class/studentMarks/student[@id=$curID]/assignments/assignment) + 
 count(/units/unit[unitCode='FIT5432']/class/studentMarks/student[@id=$curID]/assignments/unitTest)"/>                
 <xsl:value-of select="format-number((($assTot + $unitTot) div $count2), '##0.00')" />
 </td>

After spending a lot of time this week working on the first assignment I feel quite comfortable with the topics covered in the first 3 weeks:

• XML
• XML Schema Language
• XSLT (Extensible Stylesheet Language Transformations)