Subject: Re: Guessing the link speed.

From: Vernon Schryver <[email-masked]>
Date: Tue, 20 Jul 1999 12:16:05 -0600 (MDT)

> From: "John R. Martz" <[email-masked]>
> To: <[email-masked]>

> Over the next few weeks we have to start wrestling with addressing how
much "usage" a PPP line is
> getting relative to it's "capacity". My first thought is that I'm not sure
I really know what these
> terms mean. Or how to algorithmically take a guess at what these values
are for an active link.
>
> Can anyone point me towards code or text that discusses these topics in
the context of managing a
> PPP link? Would like to get some idea what others have done rather than
reinvent the proverbial
> wheel. (Or worse, implement a square wheel :) In particular, I was
wondering how the transmission
> speed of a link is usually determined.

How do the capacity and usage of a low speed point to point link differ
from the capacity and usage of a higher speed link?
I don't see how whether you run PPP, SLIP, or one of the old proprietary
protocols makes an interesting difference.
Aren't questions of raw capacity vs. usable bandwidth very old and still
very active topics elsewhere, including in the differential services, RSVP,
End-to-End, and TCP implementors working groups?

The only special thing I can see about low speed PPP is compression (both
modem v.42bis and PPP CCP), which effectively makes the raw bandwidth of
a link appear to vary from about 90% to more than 400% of the nominal bit
rate.

(Isn't 64K ISDN now always available, and 56K used only for DOV?)

Why do you care?  Wouldn't the most useful operational answer be short,
long, and medium term bit rates compared to either 30 kbit/sec (lumping
all modems) or 64 kbps (any ISDN B channel)?   If the need is to fill a
meaningless slot in a MIB used only by people who don't understand the
inevitable inaccuraces of any single answer (e.g. comopression), why not
just report the nominal bit rate?

Vernon Schryver    [email-masked]