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Re: Does Ten-Gigabit Ethernet need fault tolerance? (nonredundant NICs)


Some clarifications below.


Brian MacLeod

-----Original Message-----
From: Joe Gwinn <>
To: <>
Cc: <>
Date: Wednesday, July 28, 1999 12:44 PM
Subject: Re: Does Ten-Gigabit Ethernet need fault tolerance? (nonredundant

>At 8:28 PM 99/7/27, Roy Bynum wrote:
>>You wrote "There is no problem with parts of the segment having
>>NICs,".  With a full duplex, point to point link, there are only two
>>interfaces, one
>>at each end.  It was my understanding that 10GbE was to be a full duplex,
>>point to
>>point implementation only.  Within a data switch, at layer 2 or layer 3,
>>links to multiple systems can be implemented, creating virtual segments;
>>but each
>>10GbE link is itself, full duplex, point to point.  It is the single 10GbE
>>link that
>>I am writing about when I refer to fault tolerance.  I am not writing
>>about fault
>>allowance at the virtual segment level, as in the case of allowing for
>>nodal data
>>switch failures within the virtual segment.  Are we talking about two
>I suspect you are correct.  In my nomenclature, a "link" is bidirectional,
>having two independent fibers, and connects NICs to hubs.  It seems to me
>that when one speaks of a link in GbE, it's the path from NIC to NIC (via
>an unnamed hub); the hub is assumed.  In any case, we will need to arrive
>at a common and self-consistent nomenclature.

802.3 generally defines "link segments" which are symmetrical and are at the
lowest level.  In other words, there is (mostly) no differentiation between
types of link segment.  A link from a NIC to a switch is the same as a link
between two switches and is the same as a link between two NICs by which I
mean a link from NIC A to NIC B without any other device in the middle.
Generally, there is no definition of link as between two NICs with a switch
in the middle.  The definition used in 802.3u was

"1.4.110 link segment:  The point-to-point full-duplex medium connection
between two and only two MDIs.

>Is 10GbE expected to have hubs, or will all links be physically point to
>point between pairs of NICs?  One would expect that there will be hubs in
>10GbE as well, as inability to handle anything but pairs of NICs would be
>pretty limiting.

Up to 1 Gbps speed, there has been two modes of operation written into the
standard: half-duplex and full-duplex.  At the time we started the 1 Gbps
work, there was no standard full-duplex mode of operation (that came in
March 1997 with 802.3x) so we felt compelled to include half-duplex
operation.  Practical experience is that no one (in my personal knowledge)
is building any half-duplex equipment at 1 Gbps.  Since we now have a
full-duplex component to the standard, we could craft a 10 Gbps standard
that is only full-duplex.  I suspect this is what most participants want so
we might save ourselves the bother of the half-duplex work.

Hubs are generally shared devices using half-duplex operation so following
my previous opinion, I expect 10 Gbps to be an all-switched environment with
no hubs.

>So, my mental picture of 10GbE has been a star topology, with a hub in the
>center and the NICs at the points of the star, with duplex fiber-optic
>links connecting each NIC to the hub, one link per NIC.

I agree, except that the hub changes to a switch.

>In RTFC, one has the same number of NICs as before, but there are two (or
>more) hubs, each hub having its own star of links to those NICs.  Each NIC
>now has multiple duplex ports, one per hub.  The whole affair, containing
>NICs and hubs, is called a "segment".  Bridges between segments are
>two-headed NICs, one head per segment, even if the bridge NIC happens to be
>physically colocated with a hub.
>If one of the NICs is connected to only one hub, and nothing is broken,
>rostering will cause that NIC to be included in the segment, and thus to be
>accessible to other NICs.  This behaviour is automatic.  If a NIC having
>only one hub connected breaks or loses contact with that hub, rostering
>will isolate that unfortunate NIC.  This behaviour is also automatic.
>>Joe Gwinn wrote:
>>> Roy,
>>> At 9:12 PM 99/7/24, Roy Bynum wrote:
>>> >
>>> >Does RTFC allow a minimally trained individual to simply plug two fiber
>>> >pairs into the 10GbE interface to implement fault tolerance and if a
>>>second T/R
>>> >pair, parallel to the first, is not plugged in the fault tolerance is
>>> >implemented?  This will be the simplest and most common implementation
>>> Yes, this will work, by design.  The rostering algorithm will just treat
>>> the missing path as broken, and press on.  There is no problem with
>>> of the segment having non-redundant NICs, although those NICs will be
>>> out of the segment if those NICs or their links fail.
>>> Joe