Subject: Re: LINK (Advice for Internet Subnetwork Designers)

From: Joe Touch <[email-masked]>
Date: Fri, 02 Mar 2001 13:51:53 -0800

"Lai, Wai S (Waisum), ALSVC" wrote:
> 
> Joe,
>   Regarding "Cartwheels to overcome design flaws are not necessarily
> techniques to recommend" as you mentioned below, the question is:
>    Are you going to throw out the installed base and ask all your
> existing subscribers to spend money to upgrade to use your service?

No. The question is whether the LINK document tells people how to design
a new LINK or to fix an old one. The latter is a huge can of worms that
we might be better staying out of.

>    Furthermore, this is NOT a design flaw.  At the time when DOCSIS 1.0
> was developed, the market was for data.  Now we have enhanced the
> protocol to support for voice also.  Isn't this similar to upgrading
> the best-effort Internet to support Intserv, Diffserv, ...?

Yes - but LINK doesn't say how to upgrade; it says what to include from
the start.

Joe

---

From: "Lai, Wai S (Waisum), ALSVC" <[email-masked]>
Date: Fri, 2 Mar 2001 16:48:52 -0500

Joe,
Thanks, Waisum.

-----Original Message-----
From: Joe Touch [mailto:[email-masked]]
Sent: Friday, March 02, 2001 4:39 PM
To: Phil Karn
Cc: Lai, Wai S (Waisum), ALSVC; [email-masked]; [email-masked];
[email-masked]; [email-masked]; [email-masked];
[email-masked]; [email-masked]
Subject: Re: LINK (Advice for Internet Subnetwork Designers)

Phil Karn wrote:
> 
> >Can this text be condensed to its generalities? I think PILC already
> >deals with upstream BW and QOS issues in link design. What is the new
> >aspect here?
> 
> That's exactly what I've done. My text reads:
> 
> Another example of link-layer multiplexing is the Data Over Cable
> Service Interface Specifications. [DOCSIS1] [DOCSIS2] [DOCSIS3] DOCSIS
> version 1.1 introduces an internal fragmentation and reassembly
> procedure so that real-time voice packets can avoid undue delay when
> sharing the relatively slow upstream channel of a cable modem with
> large data packets.

Yes, but is it relevant to mention DOCSIS if this principle is more
general and already mentioned?

Lai, Wai S (Waisum) wrote:
> 
>    My purpose of introducing the text is two-fold:
> (1) DOCSIS is a widely used protocol and hence I think it should be
>     mentioned in LINK.

LINK should avoid mentioning specific link layers unless there are
general issues. Specific issues should be listed in the DOCSIS specs.

> (2) There are two aspects to DOCSIS regarding its treatment of large
>     MTU. (A) DOCSIS 1.1 uses internal fragmentation/reassembly, just
>     like other protocols.  So, in terms of protocol feature,
>     you are right that there's nothing new here, other than mentioning
>     that DOCSIS is another example.

As in "ATM and DOCSIS", but that's about it, right?

>     (B) The new twist is the need to provide backward compatibility
>     under the co-existence of both DOCSIS 1.0 and DOCSIS 1.1 where
>     some cable modems will not be able to do fragmentation.
...
>     In this case, it has been demonstrated the use of special bandwidth
>     allocation algorithm and careful capacity engineering can make it
>     to work.

Cartwheels to overcome design flaws are not necessarily techniques to
recommend. :-)

Joe