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]

---

From: Andy Koscinski <[email-masked]>
Date: Tue, 20 Jul 1999 11:49:03 -0700

> Andy Koscinski writes:
> > again the question was about usage, not the speed.
> 
> ? Knowing the usage is trivial, once you know the speed (ie, 
> capacity).
> You just count the bits moved each second and divide by the capacity
> to get a percentage. Or am I missing something.

1. what about a multi segment PPP link with different speeds on each
segment?:

    home               CO/LAC                    ISP/LNS
      |<---------PPP-link---------------------------->|
      |----ISDN---------|--------ATM------------------|

2. what about metering the data at wirespeed in hardware
without afecting the throughput?
(when you meter in software, you slow down)

3. what about policing and shaping of bursty real time data coming over
PPP
to make them comply with a Service Level Agreement?

4. what about collecting statistics about all that,
especially the number of IP packets dropped because commited 
peak burst rate exceeded?
     
/andy

---

From: "mike winslow" <[email-masked]>
Date: Tue, 20 Jul 1999 15:21:41 -0400

I don't think that the actual modem transmission speed needs to be
considered, unless it is a synchronous connection, and the modem actually
can change the clock speed. In most cases, a compressing modem is Async, and
the clock speed of the interface is fixed.

If you are SCC connected (eg < T1 speeds) set the chip up for passing data
transparently, and see how many characters that you clock in (rcv) in a time
period. Of course, do this only after a boot and not while the link is up.

The transmission time method as recommended before should be pretty valid in
most cases if you have a good HW clock.

As a protocol analyzer vendor, I'd have to recommend that you need one
(protocol analyzer) per circuit..

(If wishes were horses the poor would ride, and if pigs could fly, we'd all
carry steel umbrellas)

Mike Winslow
Director of Products, North America
Radcom Equipment Inc
1-800-RADCOM4 ext. 304
(pager) 1-800-609-9283
(car)  201-220-3218
(text page) [email-masked]
www.radcom-inc.com

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of Karl Fox
Sent: Tuesday, July 20, 1999 2:03 PM
To: John R. Martz; Archie Cobbs
Cc: [email-masked]
Subject: Re: Guessing the link speed.

At 10:38 AM 7/20/99 -0700, Archie Cobbs wrote:
>For a modem (if you have scripting
>that is capable of this) you can set the modem to reflect actual
>carrier baud rate and then have your script match the CONNECT message.

Of course, compressing modems are hard, as their actual throughput varies
from moment to moment depending on the compressibility of the data being
sent.

Karl Fox <[email-masked]>
Key fingerprint = 5B15 7260 D55E D680 0B93  4953 8A3B AB0E C05D 77A3