New Reflector 4.0b1

Richard Cogger (
Mon, 10 Jul 1995 17:56:08 -0400

A significantly updated new version of the CU-SeeMe Reflector will be
released in a day or two. This is advance notice, as the distribution will
be changed somewhat from the previous.

Major changes are aimed at being "kinder to the Internet" by not sending a
lot of traffic that the network would lose anyway. Reflector operators
will have more control over (and responsibility for) how pushy CU-SeeMe
traffic will be compared to other Internet traffic. Of course, we
recommend everyone be very polite unless you know you are using only your
own facilities. The effect is that a mix of modem-connected and
lan-connected participants will work much better. Also, audio is given
priority and becomes much more robust.

These changes operate with the current Mac and Windows desktop apps.
However, the control dynamics and accuracy are limited because of the form
of the current loss reports. A new version of the Mac app will be out (in
alpha) in about a week, and beta in another week or so, which will work
much better and also have a bunch of new goodies. The corresponding
Windows version should be just a few days behind. The reflector will be
updated (perhaps more than once) at this time too.

The new reflector is running at Cornell and has been for several days. You
can try it at

Some details on new functionality (more info in a future memo):

* The reflector will now examine loss reports being returned by each
connected participant and will impose a cap on that participant's total
receive-bandwidth. The cap is dynamically adjusted to reduce bandwidth of
total A/V/Control stream sent to that recipient (by dropping video packets)
until reported losses are below a maximum loss criterion configured in the
reflector (current value on Cornell reflector is 5%, same as the desktop
app uses).

* Audio packets will be dropped if a participant does not have enough
bandwidth on the path from the reflector to receive the encoding's rate.
(E.g., someone with a 14.4 Modem connection hasn't enough bw to receive a
32Kbps encoding.) On the other hand, if you have enough bw for the stream,
no audio packets will be dropped, but more video packets will be as needed.
The effect is to make audio much more robust.

* A form of "slow-start is implemented. The reflector operator can
configure, in Kbps, a max, min, and starting point for the dynamic receive
cap. At Cornell, these are now 200 max, 14 min, 40 start. It takes abut
15 Seconds to reduce to min when a connection with a 14.4 modem is
initiated. We're futzing with these and other parameters to determine best

* Some of the way things operate are on the crude side, because of limits
imposed by the characteristics of the currently deployed desktop apps. But
the operation will be vastly better, in terms of impact on the internet,
than the current version. We decided to do what we could this way and
refine in a later phase in order to make a major improvement sooner.
Improvements when we can deploy updated desktop apps will include
measurement of rtt, receive cap parameters set by participants (within
reflector imposed limits), much improved indicators for participants about
bw used, etc.

Changes to distribution are:

* We will no longer provide sources to the reflector code except under
license (i.e., the reflector sources will be provided the same way as the
sources to the desktop apps). We will provide binaries for most Unix

* When a new reflector version is ready for release, binaries for SunOS
4.x.x and for AIX will be provided immediately at Cornell. Within a day or
so, binaries for other platforms will be compiled at White Pine, our Master
Licensee, and posted there and at Cornell. White Pine intends to support
all the popular platforms, but may be interested in assistance for less
common ones.

* Copyright notices are updated to permit, as before, unrestricted use and
copying, but now they will restrict redistribution to "whole and
unmodified" and for non-commercial purposes only.

* You will be able to get sources under an Internal Use Only license or
under a license that permits free redistribution of modified binaries if
you give the mods back to Cornell and White Pine. Both of these licenses
will be free or nominal-cost (administrative charge). You can also get a
commercial license from White Pine.

Cheers, -Dick