still confused after all these years

Robert Hsiung (dr-bob@uchicago.edu)
Mon, 14 Apr 1997 18:45:00 -0600


Hi,

I still don't understand these transmit and receive parameters. Let me
spell out my questions, and maybe one of you helpful gurus can set me
straight. (Just typing this all out has helped a little already.)

1. What the settings do in the first place. I think I understand the "max
transmission" setting. If you try to transmit more than your connection
allows, information is lost and the recipient doesn't get the whole
picture, so to speak. Likewise, I suppose the max reception setting keeps
the other person from flooding you with more information than you can
handle, so you get their whole picture yourself.

But then there's this "max transmission without audio" setting. If you're
not saying anything, why not just let your video be transmitted at the
regular max transmission rate? Or is the idea to reserve some bandwidth for
audio by capping the non-audio transmission, in which case a more accurate
name might be "max non-audio transmission"? If so, how much should be
reserved for audio, ie, what should the difference between the regular max
transmission and the max transmission without audio be? (See also #3 below.)

Next, what's the point of min settings? Is the idea to transmit a certain
amount to make sure the other person's picture of you is refreshed (and to
receive a certain amount to make sure your picture of them is refreshed)?
In which case it wouldn't have anything to do with audio? Or are you not
actually transmitting or receiving at a minimum rate, but only reserving
that amount of bandwith for transmitting or receiving? (Hmm, that sounds
right.)

2. I heard that transmitting and receiving are independent. So how much I
transmit doesn't influence how much I receive? In other words, having a
higher max transmission setting doesn't leave less room (bandwidth) for
receiving?

If they are independent, and I have a 28.8 modem, does that mean I can
simultaneously receive at 28.8 *and* transmit at 28.8? Or is the limit at
any one time 14.4 receiving + 14.4 transmitting = 28.8 total?

I thought the general idea was to apportion your pipe (bandwidth). But if
transmitting and receiving are independent, then it's not like you have to
make choices, you just transmit as much as you can and receive as much as
you can.

Say you want a two-way audio and video connection. I guess you would set
your min transmission to reserve enough bandwith for audio + a little more
for a bit of video, so the other person can hear (and kind of see) you, and
your min reception to the same thing, so you can hear (and kind of see)
them. If transmitting and receiving are independent, then you set each max
to your bandwidth minus the above min. If you're transmitting and receiving
with the same pipe, though, you have to lower each max further, to
accommodate the "other" min (eg, you have to lower the transmission max to
leave room for the reception min).

Well, I'm sure that's as clear as mud. Moving on...

3. The different audio options, delta-mod, linear, et al. The number (eg,
16 kbps for delta-mod) presumably is how much bandwidth the option takes
up? So if I choose delta-mod, then my min transmission setting has to be at
least 16 for my audio to go out (and the other person's max reception
setting has to be at least 16 for them to get it)?

Also, is it right that bandwidth is more of an issue here than computing
power, ie, if the computer has to work harder to compress the audio into
fewer kbps, then that's OK?

4. I've heard both that each party has to choose the same audio option and
that they don't (the latter would mean CUSM figures out for itself what
kind of audio it's receiving). Which is really true?

Help? Sorry to have gone on for so long, but I wanted to try to make clear
to you what isn't clear to me. :-/

Bob