10Gbit Ethernet Half-Duplex

Archived from groups: comp.dcom.lans.ethernet (More info?)

Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?
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More about 10gbit ethernet half duplex
  1. Archived from groups: comp.dcom.lans.ethernet (More info?)

    Stephen Brown wrote:

    > Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?

    Or more to the point, why bother. Examine the issues with half duplex, as
    bit rate increases, to find your answer. Then try to come up with some
    reasons why you'd even want HD, when FD is so common.
  2. Archived from groups: comp.dcom.lans.ethernet (More info?)

    James Knott wrote:

    > Stephen Brown wrote:

    >>Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?

    > Or more to the point, why bother. Examine the issues with half duplex, as
    > bit rate increases, to find your answer. Then try to come up with some
    > reasons why you'd even want HD, when FD is so common.

    When gigabit was new, before switches were easily available, I had
    thought it would be useful to have NICs and repeaters that didn't do
    carrier extension for clusters of machines in a single room. Especially
    when a large amount of communication is broadcast (such as loading the
    same code into many machines) it would have seemed useful. Now with
    gigabit prices low, it is hard to argue that, but it might be for 10Gb.

    -- glen
  3. Archived from groups: comp.dcom.lans.ethernet (More info?)

    glen herrmannsfeldt wrote:

    > James Knott wrote:
    >
    >> Stephen Brown wrote:
    >
    >>>Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?
    >
    >> Or more to the point, why bother. Examine the issues with half duplex,
    >> as
    >> bit rate increases, to find your answer. Then try to come up with some
    >> reasons why you'd even want HD, when FD is so common.
    >
    > When gigabit was new, before switches were easily available, I had
    > thought it would be useful to have NICs and repeaters that didn't do
    > carrier extension for clusters of machines in a single room. Especially
    > when a large amount of communication is broadcast (such as loading the
    > same code into many machines) it would have seemed useful. Now with
    > gigabit prices low, it is hard to argue that, but it might be for 10Gb.

    But again, what advantage is there to going with half duplex? With HD,
    you've got all the problems with collision detection, reduced throughput
    etc. While there were techniques developed for gigabit, to allow HD with
    reasonable segment lengths, the problems are 10x worse at 10 Gb.
  4. Archived from groups: comp.dcom.lans.ethernet (More info?)

    "Stephen Brown" <sd_brown@ntlworld.com> writes:

    > Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?

    Surely the real question is why 1 Gbit Ethernet at Half Duplex
    WAS allowed ;-)

    John
  5. Archived from groups: comp.dcom.lans.ethernet (More info?)

    In article <vnmzu7rqje.fsf@kenny.ex.ac.uk>,
    John Rowe <rowe@excc.ex.ac.uk> wrote:

    > "Stephen Brown" <sd_brown@ntlworld.com> writes:
    >
    > > Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?
    >
    > Surely the real question is why 1 Gbit Ethernet at Half Duplex
    > WAS allowed ;-)
    >

    Here is a complete explanation, excerpted from Chapter 10 of my book
    "Gigabit Ethernet" (Addison-Wesley, 1998):

    ----begin excerpt----

    Do we even need a half duplex (traditional) Ethernet MAC at gigabit
    rates? This is a reasonable question, especially since it is clear that
    we had to make some significant changes to the Ethernet design in order
    to support half duplex operation at this speed.

    There is only one advantage of half duplex over full duplex operation:
    Half duplex (shared) LANs can use a repeater hub rather than a switching
    hub, thereby potentially saving some system cost. A switching hub will
    always cost more than a repeater hub (on a per-port basis), however,
    over time the difference shrinks considerably with competition and
    availability of high-integration silicon switching components. The cost
    of the station attachment (NIC) is identical whether using shared or
    switched hubs.

    So, to the extent that the hub constitutes a cost factor for the system
    as a whole, the system cost will be greater when using full duplex vs.
    half duplex operation, since full duplex LANs require switching hubs.
    There is a premium paid to use full duplex mode, but it is not very
    large, and the premium decreases over time. In return for this price
    premium, we can avoid:

    - Changing the Ethernet MAC algorithms,
    - The performance degradation of carrier extension (for short frames),
    - The performance limitations of CSMA/CD in general, and
    - Any need to reduce network extent (distance).

    [So] why did the industry bother to develop a half duplex Gigabit
    Ethernet standard at all?

    The answer is more political than technical. Gigabit Ethernet was
    developed under the auspices of the IEEE 802.3 Working Group. By
    definition [at that time], 802.3 networks must include the capability of
    CSMA/CD operation. If Gigabit Ethernet offered a full-duplex-only
    solution, it would have been difficult to justify its development within
    the IEEE 802.3 Working Group. This would have resulted in some important
    political difficulties:

    (1) A new Working Group would have to have been formed within IEEE
    802; this takes considerably more time than a new project within an
    existing Working Group and would have delayed the development of the
    standard.

    (2) The resulting standard would have had difficulty calling itself
    "Ethernet", since it would neither use CSMA/CD (even as an option), nor
    would it have been developed as part of IEEE 802.3, the recognized
    "owner" of the Ethernet name.

    So, rather than fight the system, the IEEE 802.3z committee chose to
    work on both half duplex and full duplex Gigabit Ethernet, making
    modifications to the CSMA/CD algorithm to support reasonable distances
    in half duplex mode. The real rationales for the specification of half
    duplex Gigabit Ethernet are standards-committee machinations and market
    positioning. Few industry observers believe[d] that there will be much
    (if any) half duplex Gigabit Ethernet deployment.

    ----end excerpt----

    (C)1998, Addison-Wesley Longman and Networks & Communications Consulting.
    All rights reserved.


    --
    Rich Seifert Networks and Communications Consulting
    21885 Bear Creek Way
    (408) 395-5700 Los Gatos, CA 95033
    (408) 228-0803 FAX

    Send replies to: usenet at richseifert dot com
  6. Archived from groups: comp.dcom.lans.ethernet (More info?)

    John Rowe <rowe@excc.ex.ac.uk> wrote:
    > "Stephen Brown" <sd_brown@ntlworld.com> writes:

    >> Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?

    > Surely the real question is why 1 Gbit Ethernet at Half Duplex
    > WAS allowed ;-)

    "It ain't Ethernet if it don't do CSMA/CD?" :)

    rick jones
    --
    oxymoron n, Hummer H2 with California Save Our Coasts and Oceans plates
    these opinions are mine, all mine; HP might not want them anyway... :)
    feel free to post, OR email to raj in cup.hp.com but NOT BOTH...
  7. Archived from groups: comp.dcom.lans.ethernet (More info?)

    In article <1l6Qd.8$X46.6@news.cpqcorp.net>,
    Rick Jones <foo@bar.baz.invalid> writes:
    >John Rowe <rowe@excc.ex.ac.uk> wrote:
    >> "Stephen Brown" <sd_brown@ntlworld.com> writes:
    >
    >>> Any reason why 10Gbit Ethernet at Half Duplex is dis-allowed?
    >
    >> Surely the real question is why 1 Gbit Ethernet at Half Duplex
    >> WAS allowed ;-)
    >
    >"It ain't Ethernet if it don't do CSMA/CD?" :)

    The VG-AnyLan trauma? ;-)

    SCNR

    --
    Manfred Kwiatkowski kwiatkowski@zrz.tu-berlin.de
  8. Archived from groups: comp.dcom.lans.ethernet (More info?)

    >>"It ain't Ethernet if it don't do CSMA/CD?" :)

    > The VG-AnyLan trauma? ;-)

    Nah, I think I'm mostly over that one by now. Just feeling irreverant
    today :)

    rick jones
    --
    a wide gulf separates "what if" from "if only"
    these opinions are mine, all mine; HP might not want them anyway... :)
    feel free to post, OR email to raj in cup.hp.com but NOT BOTH...
  9. Archived from groups: comp.dcom.lans.ethernet (More info?)

    James Knott wrote:

    > glen herrmannsfeldt wrote:

    (snip)

    >>When gigabit was new, before switches were easily available, I had
    >>thought it would be useful to have NICs and repeaters that didn't do
    >>carrier extension for clusters of machines in a single room. Especially
    >>when a large amount of communication is broadcast (such as loading the
    >>same code into many machines) it would have seemed useful. Now with
    >>gigabit prices low, it is hard to argue that, but it might be for 10Gb.

    > But again, what advantage is there to going with half duplex? With HD,
    > you've got all the problems with collision detection, reduced throughput
    > etc. While there were techniques developed for gigabit, to allow HD with
    > reasonable segment lengths, the problems are 10x worse at 10 Gb.

    But I am specifically interested in the case where the segment lengths
    are known to be short. That is, even 10Gb without carrier extension.

    And yes, in a fairly short time 10G switches will be cheap, but that day
    isn't here yet.

    How many clusters of machines packed together as close as they can be
    exist today that could use faster network interconnects? How much
    faster would 10Gb half duplex be than 1Gb full duplex?

    Those are the questions. I am not interested in carrier extension and
    long segments.

    -- glen
  10. Archived from groups: comp.dcom.lans.ethernet (More info?)

    glen herrmannsfeldt wrote:

    >> But again, what advantage is there to going with half duplex?  With HD,
    >> you've got all the problems with collision detection, reduced throughput
    >> etc.  While there were techniques developed for gigabit, to allow HD with
    >> reasonable segment lengths, the problems are 10x worse at 10 Gb.
    >
    > But I am specifically interested in the case where the segment lengths
    > are known to be short.   That is, even 10Gb without carrier extension.
    >
    > And yes, in a fairly short time 10G switches will be cheap, but that day
    > isn't here yet.
    >
    > How many clusters of machines packed together as close as they can be
    > exist today that could use faster network interconnects?  How much
    > faster would 10Gb half duplex be than 1Gb full duplex?
    >
    > Those are the questions.  I am not interested in carrier extension and
    > long segments.
    >

    But again, why bother? What possible advantage is there, that you'd want to
    go backwards? If you want faster, why waste time with HD? You'd be back
    to the overhead of collision detection, collisions, cutting the bandwidth
    in half etc. If you want to maximize bandwidth, FD is the way to go.
  11. Archived from groups: comp.dcom.lans.ethernet (More info?)

    James Knott wrote:

    > glen herrmannsfeldt wrote:
    >
    >>> But again, what advantage is there to going with half duplex?  With HD,
    >>> you've got all the problems with collision detection, reduced throughput
    >>> etc.  While there were techniques developed for gigabit, to allow HD
    >>> with reasonable segment lengths, the problems are 10x worse at 10 Gb.
    >>
    >> But I am specifically interested in the case where the segment lengths
    >> are known to be short.   That is, even 10Gb without carrier extension.
    >>
    >> And yes, in a fairly short time 10G switches will be cheap, but that day
    >> isn't here yet.
    >>
    >> How many clusters of machines packed together as close as they can be
    >> exist today that could use faster network interconnects?  How much
    >> faster would 10Gb half duplex be than 1Gb full duplex?
    >>
    >> Those are the questions.  I am not interested in carrier extension and
    >> long segments.
    >>
    >
    > But again, why bother? What possible advantage is there, that you'd want
    > to
    > go backwards? If you want faster, why waste time with HD? You'd be back
    > to the overhead of collision detection, collisions, cutting the bandwidth
    > in half etc. If you want to maximize bandwidth, FD is the way to go.

    I think perhaps that his reasoning is that 10G HD would be cheaper to
    implement than FD but still give higher performance than gigabit. Which,
    while it might be true, is mostly a matter of degree--10G right now is
    going to cost you whether it's full or half and using a repeater instead of
    a bridge wouldn't be likely to save that much. I suspect that the same
    performance level as 10G HD would provide can be achieved for less cost
    with trunked gigabit.

    --
    --John
    Reply to jclarke at ae tee tee global dot net
    (was jclarke at eye bee em dot net)
  12. Archived from groups: comp.dcom.lans.ethernet (More info?)

    Hi John,

    On Wed, 16 Feb 2005 10:13:14 -0500,
    J. Clarke <jclarke@nospam.invalid> wrote:

    > I think perhaps that his reasoning is that 10G HD would be cheaper to
    > implement than FD but still give higher performance than gigabit. Which,
    > while it might be true, is mostly a matter of degree--10G right now is
    > going to cost you whether it's full or half and using a repeater instead of
    > a bridge wouldn't be likely to save that much. I suspect that the same
    > performance level as 10G HD would provide can be achieved for less cost
    > with trunked gigabit.

    On the other hand the cost of half duplex (collission detection) will
    follow you even if only full duplex will be deployed. So in the long
    term it will be more expensive.
    Although i have no real idea of the relative costs of collision
    detection to rest.
    But another interesting point is the delay, an repeater will introduce.
    A switch is allowed to have a delay greater than the time of a collision
    domain...

    Ciao
    --
    Rainer Nagel
    Rainer.Nagel@tashrah.com
    Duesseldorfer Linux User Group - http://www.dlug.de
  13. Archived from groups: comp.dcom.lans.ethernet (More info?)

    I think the size of the padding in each frame would be detremental to using
    half duplex
    especially at the distances it would be implemented over. The cost thing
    might be only
    partly responsible for it. But both seem worth commenting on.

    - Thanks everyone.


    "Rainer Nagel" <rainer@angor.de> wrote in message
    news:slrnd17j1s.9rv.rainer@ramoth.angor.de...
    > Hi John,
    >
    > On Wed, 16 Feb 2005 10:13:14 -0500,
    > J. Clarke <jclarke@nospam.invalid> wrote:
    >
    >> I think perhaps that his reasoning is that 10G HD would be cheaper to
    >> implement than FD but still give higher performance than gigabit. Which,
    >> while it might be true, is mostly a matter of degree--10G right now is
    >> going to cost you whether it's full or half and using a repeater instead
    >> of
    >> a bridge wouldn't be likely to save that much. I suspect that the same
    >> performance level as 10G HD would provide can be achieved for less cost
    >> with trunked gigabit.
    >
    > On the other hand the cost of half duplex (collission detection) will
    > follow you even if only full duplex will be deployed. So in the long
    > term it will be more expensive.
    > Although i have no real idea of the relative costs of collision
    > detection to rest.
    > But another interesting point is the delay, an repeater will introduce.
    > A switch is allowed to have a delay greater than the time of a collision
    > domain...
    >
    > Ciao
    > --
    > Rainer Nagel
    > Rainer.Nagel@tashrah.com
    > Duesseldorfer Linux User Group - http://www.dlug.de
  14. Archived from groups: comp.dcom.lans.ethernet (More info?)

    Stephen Brown wrote:

    > I think the size of the padding in each frame would be detremental to using
    > half duplex
    > especially at the distances it would be implemented over. The cost thing
    > might be only
    > partly responsible for it. But both seem worth commenting on.

    I would be interested in one where the maximum link distance was 2m.

    Consider clusters of machines, MPI or PVM, for example. You can put a
    lot of machines within a 2m radius of a repeater.

    -- glen
  15. Archived from groups: comp.dcom.lans.ethernet (More info?)

    Rich,

    I hope you agree that this is a very minor comment. From
    what I have read on this and other newsgroups your work
    seems to me to be utterly outstanding.

    Rich says:
    "A switching hub will
    always cost more than a repeater hub (on a per-port basis), however,
    over time the difference shrinks considerably with competition and
    availability of high-integration silicon switching components"

    As far as I know (which is not far at all) the cost of LSI components
    is strongly related to the production volume and is much less closely
    related to the complexity of the chips (until the yield falls off
    anyway).

    So:-
    I contend that your comment "A switching hub
    will always cost more than a repeater hub"
    is only the case for equal production volumes
    and since GBE repeater hubs are practically non
    existent, your comment is not strictly applicable.

    It would clearly be applicable if neither switching
    hubs nor repeater hubs were yet in production.

    I have only made this comment since I was hoping for a
    second edition:)

    Thanks.
  16. Archived from groups: comp.dcom.lans.ethernet (More info?)

    In article <1110396995.536971.174770@o13g2000cwo.googlegroups.com>,
    anybody43@hotmail.com wrote:

    > I contend that your comment "A switching hub
    > will always cost more than a repeater hub"
    > is only the case for equal production volumes
    > and since GBE repeater hubs are practically non
    > existent, your comment is not strictly applicable.
    >
    > It would clearly be applicable if neither switching
    > hubs nor repeater hubs were yet in production.
    >

    Which was the case in the emerging market for Gigabit Ethernet (which, I
    believe, was the context for the statement); of course, you are correct
    that I am assuming at least comparable, if not equal, volumes.

    > I have only made this comment since I was hoping for a
    > second edition:)
    >

    Not likely to happen anytime soon, I am sorry to say. My work has taken
    a very different direction.


    --
    Rich Seifert Networks and Communications Consulting
    21885 Bear Creek Way
    (408) 395-5700 Los Gatos, CA 95033
    (408) 228-0803 FAX

    Send replies to: usenet at richseifert dot com
  17. Archived from groups: comp.dcom.lans.ethernet (More info?)

    > anybody43@hotmail.com wrote:
    > > I have only made this comment since I was hoping for a
    > > second edition:)


    Rich Seifert wrote:
    > Not likely to happen anytime soon, I am sorry to say. My work has
    > taken a very different direction.


    That's too bad (the book part, not your work part! :)

    It's hard to find good technical books.

    --

    hsb


    "Somehow I imagined this experience would be more rewarding" Calvin
    **************************ROT13 MY ADDRESS*************************
    Due to the volume of email that I receive, I may not not be able to
    reply to emails sent to my account. Please post a followup instead.
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