Subject: Re: Previous discussions

From: Erik Nordmark <[email-masked]>
Date: Thu, 1 Mar 2001 18:16:07 +0100

> 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: Peter Johansson <[email-masked]>
Date: Thu, 1 Mar 2001 17:25:10 -0800

At 06:16 PM 3/1/01, Erik Nordmark wrote:

>Are there bridge devices in existence that bridge 1394 to these other
>technologies?

Draft Standard IEEE P1394.1 specifies bridges that may interconnect two
Serial Bus segments, but in fact it permits bridged interconnection of any
two buses whose behaviors are compatible with the CSR Architecture, ISO/IEC
13213:1994. I am the Chair of the working group; the draft is about to
commence its sponsor ballot.

It is in this latter area that bridge activity is most active at present.
The European Telecommunications Standards Institute (ETSI) has approved a
specification that describes how to bridge a wired IEEE 1394 domain to
HiperLAN 2; it is based upon IEEE P1394.1. The 1384 Trade Association
Wireless working group is developing an analogous document that will
specify a bridge that connects wired IEEE 1394 with IEEE 802.11e.

>Seems like a bridge would need to do quite a bit of work for multicast
>packets.

In so far as multicast traffic is carried on the IEEE 1394 default
broadcast channel, I believe that bridges will not have any extraordinary
work to perform in the forwarding of IP multicast traffic. In fact,
P13934.1 bridges are, for the most part, ignorant as to the content of the
packets they store and subsequently forward. Keep in mind that these
devices bridge Serial Bus atomic transactions (read, write, lock and stream
data) between two buses; they are entirely ignorant of Internet Protocol.

RFC 2734 requires some extension to permit communications between two IP
hosts separated by an IEEE P1394.1 bridge.

Regards,

Peter Johansson

Congruent Software, Inc.
98 Colorado Avenue
Berkeley, CA  94707

(510) 527-3926
(510) 527-3856 FAX

[email-masked]