Re: Lost Packets

Dennis J. Streveler (strev@mobius.net)
Thu, 30 May 1996 09:19:51 -0700


At 10:50 PM 5/29/96 -0700, jim wrote:
>I've been using White Pine 2.01 and Windows 95 on several different
>reflectors at varying times of day. When I check the packet loss window
>on various senders I'm frequently seeing packet losses of 60%, sometimes
>more. I've got a 28.8 modem and have the receive set for about 24kbs
>which is a little slower than normal connect. But this setting doesn't
>seem to make much difference.
>
>Where are these packets going? Is this an ISP problem or is it just the
>state of the net these days? Color doesn't work at all well with half
>the packets lost!

Hello,

Yes, it most certainly is the state of the Net these days. Packet loss of
60% is not all that uncommon. When this happens forget about audio
altogether because you are going to lose so much as to make the conversation
nearly unintelligible.

Where do these packets go? Well, to cyberspace heaven of course! Seriously,
the Net is fundamentally a maybe-my-packet-will-get-there arrangement.
Protocols on the Net include UDP which is a protocol which requires no
acknowledgement that a packet ever arrives. TCP/IP is a protocol which
requires an acknowledgement and resends a packet if one gets lost, but
requires considerably more net overhead.

So, most video and audio applications on the Net use primarily UDP to
communicate. This is because UDP is more suitable to "real-time"
applications, where you can't wait all day for all packets to arrive.

Thus, with CUSeeMe, as with its competitors, video information can get lost.
This is not such a big deal, really, since you lose part of a frame. But
with audio information, and even for information in the Chat/Talk window, if
substantial information gets lost, it can render a conversation worthless.

Regarding color, believe it or not, given the state of the developoment of
color compression algorithms these days, COLOR uses less bandwidth to
transmit than b&w. This is counter-intuitive, and I suspect it springs from
the fact that more research has been done in color image compression these
days. But go figure, reportedly the Color QuickCam can outperform the B&W
version on CUSeeMe because of this.

Regards,
Dennis

--------------------------------------+------------------------------
Dennis J. Streveler, Ph.D., | Internet: strev@mobius.net
Systems Consultant | CIS: 71036,1645
| CUSeeMe: strev.mobius.net
-Future Technologies in Medicine | web: www.usr.mobius.net/strev
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