1 Reply Latest reply on Dec 2, 2015 3:31 PM by Leon Adato

    Feedback and Questions on Lesson 3


      Here is some feedback on lesson 3 of the DPI online course.  Below you will find my thanks, three possible small corrections and two questions



      Thanks for all your hard work creating this course.  The information is interesting.



      The 4th paragraph says: "High network latency can cause loss of lip-synchronization because the relatively small voice packets may be delivered in a different timeframe than the larger voice content packets. "  I was wondering if perhaps the 3rd word from the end was supposed to be video instead of voice.  So it would read:  "High network latency can cause loss of lip-synchronization because the relatively small voice packets may be delivered in a different timeframe than the larger VIDEO content packets. "


      The last sentence of the fourth paragraph under the section "Effects Of Network Delay" says: If there are 35 files required to load one page over a 72 millisecond RTT path, the total time incurred from App Turns alone is: 35 x .075 = 2.625 seconds".  I was wondering if the equation was supposed to show 72 milliseconds instead of 75 milliseconds.  And if the answer should then be 2.520 seconds.  I am wondering this because the set up for the equation says its a 72 millisecond RTT path not a 75 millisecond path. If not perhaps you could tell me where the extra 3 milliseconds are coming from.


      Two thoughts on the 2nd sentence of the 6th paragraph under the same section "Effects Of Network Delay" says: "In addition, current Web browsers can now employ as much as 6-8 simultaneous connections to a Web server, enabling the completion of multiple requests in a relatively short time frame. "  The graph below the paragraph seems to imply 6-13 simultaneous connections not 6-8.  For some reason it sounds better to me to say as MANY as 6-13 connections instead of as MUCH as 6-13 connections.



      Could you elaborate on why more connections allows faster downloading of a web page? If I understand correctly connections are logical and all the connections would exist over the same physical medium and thus be limited to the maximum speed of that medium.  No matter how many connections I have over a single T1 all the connections must share the 1.554 Megabits per second.  It does not help to put more cars over a one lane road with a 25 mile per hour speed limit. If I put one package in three cars or 3 packages one car, they all take just as long to get there.  And with three cars I have to open and close three doors instead of one door.  So three cars actually takes me a little longer.  I suspect there is a flaw in my logic.  I just don't know where.


      Could you give an example of when you can use CSS instead of an image?






        • Re: Feedback and Questions on Lesson 3
          Leon Adato

          First, I apologize for the long delay in responding. You can thank jeffpaul for mentioning your post.


          I'm going to forward your corrections to the content team and see if we can get some of this updated. If it's audio/video issues we might not be able to do much. but we'll do what we can.


          And I'm going to re-review the course content so I can answer your other questions a little more authoritatively.