RE: small, grey squares

Mark A. Thornton (
Wed, 14 Sep 1994 17:00:43 -0400

Actually I had this problem using CUSM over CSLIP with Trumpet B6 and
CUSM .33. The UDP packets were getting broken up over CSLIP and
the bandwidth was too low to effectively refresh the screen. Switching to
CUSM .34.4 and Trumpet B14 has cured the problem. If you are using SLIP
make sure your MTU is at least 512 because most of the UDP packets sent
seem to top this. If the packets are larger than your MTU (or rather MSS) then
these packets will be lost because SLIP doesn't handle fragmentation. The
refresh packet would also presumeably be appx. the same size, hence you would
never see that particular area filled with video.
>The small grey squares you see are areas of the picture that have not been
>updated since
>you began your session. The reflector only transmits areas of the image
>which have changed.
>The reflector does this by breaking the image up into these squares and
>comparing each square to the square from the previous image. If the pixels
>in that block are equal, then that block is not transmitted. This is a
>simple form of image compression. The blocks you see are normal. If every
>frame was transmitted in its entirety, there would be no bandwidth left for
>other users, or
>the frame rate would be too low to recognize as motion video.
>Hope this helps,
>Byron Jones
>Office of Admission
>University of Miami
> -- Generation-X will be the first generation unable to afford
> -- .sig files better than their parents...
> ----------
>From: cu-seeme-l
>To: Multiple recipients of list
>Subject: small, grey squares
>Date: Tuesday, September 13, 1994 11:12PM
>Can anyone tell me why, when I recieve video from reflectors (I cannot send,
>yet), the image is covered, in places by small, grey squares??? Sometimes,
>they coelesque and block out large areas of video, other times they stand
>alone. Every time, however, they are there.
>Mark E. Berkman
>The Ohio State University
>(614) 688-7532

Mark Thornton	"Let the Good Times Roll!"