Subject: Re: Previous discussions

From: "Hattig, Myron" <[email-masked]>
Date: Thu, 1 Mar 2001 09:33:12 -0800

There were ideas written on the white board during IP/1394 interoperability
testing. To work it would have to do things differently than a normal 802.3
to 802.3 link layer bridge. It has to be IP aware to a minor degree, but the
IP devices would not be aware of the presence of this bridge. I'm not sure
if any of these bridges have been built or not. This would make an excellent
informational RFC. We talked about writing it up a long time ago, but it
fell to a very low point on the priority list - sigh.

-myron

> -----Original Message-----
> From: Erik Nordmark [mailto:[email-masked]]
> Sent: Thursday, March 01, 2001 9:16 AM
> To: Hattig, Myron
> Cc: [email-masked]
> Subject: Re: Previous discussions
>
>
>
> > Changing the MTU size has huge ramifications that we were
> not aware of when
> > we chose 1500 bytes. Luckily it was a good decision. Specifically it
> > improves the ability to bridge to other important link
> layer technologies
> > that were not available 4 years ago that also have an MTU
> of 1500 bytes.
> > These include  802.11b, HomeRF, HomePNA 1.0, and HomePNA 2.0.
>
> Just a curious side comment not related to the current thread.
>
> Are there bridge devices in existence that bridge 1394 to these
> other technologies?
> Seems like a bridge would need to do quite a bit of work for
> multicast packets.
>
>   Erik
>
>

---

From: Mike Teener <[email-masked]>
Date: Tue, 6 Mar 2001 15:36:04 -0800

Hmm. I don't remember these "facts", so I would appreciate understanding the
reasoning.

Myron says:
        >Facts:
        >1) Memory mapped model has more interrupts per IP packet due to the
need to
        >lock and unlock memory packets necessary before and after
transfers. There
        >are 3 interrupts per IP packet. In addition, there must be some
mechanism to
        >agree on whether the memory transfer uses reads or writes.
        >2) Msg passing has fewer interrupts per IP packet because there is
only a
        >single interrupt per IP packet.

I can understand your position if you really believe this is true, so I'd
like to understand .... I think the position of the OS vendors is that #1 is
not accurate, and that, indeed, other higher layer protocols running on 1394
have *less* than one interrupt per "packet" when they are doing longish
transfers.

BTW, like Peter, Eric (Anderson) and others in the 1394 community, I don't
think memory-based transfers must be used all the time for all purposes ....
rather that they are very efficient for point-to-point uses, which is a very
interesting and common thing to do. The RFC2734 approach to multicast and
the like is probably just fine. The unicast transfer of RFC2734 is also
acceptable for some embedded applications where we have the freedom to
design custom silicon just to support IP traffic.

=============================================================
Michael D. Johas Teener
Chief Technical Officer, Zayante, Inc.
269 Mt. Hermon Rd. #200, Scotts Valley, CA 95066-4000, USA
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