| Author |
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Walter Roberson
Guest
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 Posted:
Wed Feb 02, 2005 12:28 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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In article <ctojk7027n6@news4.newsguy.com>,
J. Clarke <jclarke@nospam.invalid> wrote:
:In a switched architecture the only time collisions occur is when something
:is misconfigured.
Switched != "full duplex".
If you have a host connected to a switch port with nothing
inbetween (no hubs or whatever) and both ports are running full
duplex, then Yes, no collisions. However, if the ports are
running half-duplex then transmissions from the host to the switch
can collide with transmissions from the switch to the host.
:?????? If it's a 100 MB/sec backbone feeding into 10 at the desktop then
:it's necessarily a switched architecture of some sort and collisions should
:not be an issue.
As best I recall, it was only fairly recently that there has
been anything approaching a "standard" for 10 Mb full duplex.
Thus the existance of 10 Mb devices makes it quite likely that
some (many) of the links are running half duplex, for which see above.
--
*We* are now the times. -- Wim Wenders (WoD) |
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jpd
Guest
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| Posted:
Wed Feb 02, 2005 5:29 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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Begin <ctm00e$st4$1@canopus.cc.umanitoba.ca>
On 2005-01-31, Walter Roberson <roberson@ibd.nrc-cnrc.gc.ca> wrote:
[snip!]
| Quote: | :>I'd start with putting him on netnanny or something suitably annoying
:>to see if that doesn't reduce the traffic to something reasonable. :-)
As the OP of that statement, I can say that it would not be an
appropriate solution to the situation.
|
If you're sure. You didn't say so, so the possibility was left open.
(See other people making alike suggestions for alike possibilities.)
| Quote: | :It would be worth the time to see if he's got a virus or spyware.
:Then you should try to understand his business and what makes him
:special.
You ass-u-me'd that I don't understand his business and what makes him
^^^^^^^^
special. I have a fairly good idea of what makes him special.
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Que? _You_ didn't specify, or didn't even give a hint you knew what
this one anomaly makes so special. And given that as often as not
people don't even know an ISDN cable from an ethernet cable, let alone
understand why they're not interchangeable, it was, and still is, basic
prudence to not disallow the possibility.
[snip: sensible advice]
| Quote: |
Again you have ass-u-me'd. You failed to look at my email address
and take a step such as visiting our web site. We aren't -in-
business: we are public sector biomedical research.
|
Excuse me? Why should anyone want to go out of their way to give you
free advice? Just because you're in academentia? Furrfu.
If it's true what you claim (and no, I haven't checked, why should I),
you've been among them doktores too long. Time to sniff some fresh air,
and see the colour of your sky fade to blue again.
--
j p d (at) d s b (dot) t u d e l f t (dot) n l . |
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Rich Seifert
Guest
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| Posted:
Wed Feb 02, 2005 6:27 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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In article <ctol8f$cvm$1@canopus.cc.umanitoba.ca>,
roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote:
| Quote: |
As best I recall, it was only fairly recently that there has
been anything approaching a "standard" for 10 Mb full duplex.
Thus the existance of 10 Mb devices makes it quite likely that
some (many) of the links are running half duplex, for which see above.
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The standard for 10 Mb/s Full Duplex operation was approved/published in
1997 (going on 8 years, now). Even before that, there were products
(non-standard or "pre-standard"). That said, there are lots of legacy
10 Mb/s devices that may not be able to (or ever need to) operate in
full-duplex mode.
--
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 |
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Walter Roberson
Guest
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| Posted:
Wed Feb 02, 2005 6:33 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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In article <36al78F50lcojU1@individual.net>,
jpd <read_the_sig@do.not.spam.it.invalid> wrote:
:Que? _You_ didn't specify, or didn't even give a hint you knew what
:this one anomaly makes so special.
I certainly didn't give any hint that I -didn't- understand why that
one user was producing masses of data. I did, though, give useful
hints to the OP based upon our experiences -- hints that would
tend to lead people to understand that I have done non-trivial
network traffic analysis.
:And given that as often as not
:people don't even know an ISDN cable from an ethernet cable, let alone
:understand why they're not interchangeable, it was, and still is, basic
:prudence to not disallow the possibility.
I am a relative newcomer to comp.dcom.lans.ethernet, having posted
only 142 messages here during the last year, about 100 of which were
in the last 6 months. That's only about 2 a week during that time, so
I can understand why you might not have recognized my name. These days
I'm mostly three newsgroups further over, in comp.dcom.sys.cisco,
answering about 35 questions a week.
:Excuse me? Why should anyone want to go out of their way to give you
:free advice? Just because you're in academentia? Furrfu.
If you re-examine my posting that started this subtree, you will see
that I wasn't asking for advice, I was giving it.
:If it's true what you claim (and no, I haven't checked, why should I),
:you've been among them doktores too long. Time to sniff some fresh air,
:and see the colour of your sky fade to blue again.
The weather's been quite strange here this winter. Normally at this
time of year it is clear and cold (-42 overnight is pretty common here
for the first week of February); instead we've had a mix of deep cold
and abnormal highs... and very little sunshine. It's a choice between
grey skies and greyer skies.
--
Beware of bugs in the above code; I have only proved it correct,
not tried it. -- Donald Knuth |
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Fred Marshall
Guest
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| Posted:
Thu Feb 03, 2005 3:05 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
news:utKdnRxYd6hAz2LcRVn-qw@comcast.com...
| Quote: | Fred Marshall wrote:
(snip)
Compared to 10Mb, if everything is 100Mb, will that necessarily increase
the volume of data? Probably not. It would only increase the peak data
rate - and reduce the time accordingly. Thus reduce the possibility of
collisions.
Depending on the topology of the servers and switches there should be
less opportunity for collisions anyway - until multiple workstations vie
for service on the same server.
Ask this: why would it matter if the network elements limit data rate to
10Mb on the clients or if network loading limits data rate to <100Mb on
occasion?
There is a possibility that a 100Mb network could be slower, but
not so likely.
If a switched 100Mb network with all links full duplex and
no flow control saturates the uplink, it can be slower than
10Mb links, full or half duplex, to a 100Mb uplink.
That should be relatively unlikely, but it is possible.
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Glen,
I'm not sure I understand...
What is the basis of comparison?
You said:
"If a switched 100Mb network with all links full duplex and
no flow control saturates the uplink, it can be slower than
10Mb links, full or half duplex, to a 100Mb uplink."
Let me paraphrase:
"Comparing:
a LAN of N clients using 100Mb links each, full duplex, no flow control
with:
a Lan of N clients using 10Mb, full or half duplex
with a 100Mb uplink for both then:
The 100Mb links can demonstrate lower throughput compared to the 10Mb links,
given the same traffic demand."
So, the traffic demand can be no greater than what will be presented with
the 10Mb links - although the peaks will be higher with the 100Mb links. If
that's the case how can the 100Mb links cause lower throughput? There must
be some system overhead issue eh?
On the other hand if somehow one allows the 100Mb linked clients to demand
more throughput than their 10Mb cousins then are you saying that THEN the
100Mb linked clients will actually provide lower throughput than the 10Mb
clients *or* lower throughput than some other idealized situation that's not
under discussion (yet)?
Fred |
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glen herrmannsfeldt
Guest
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| Posted:
Thu Feb 03, 2005 8:00 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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Fred Marshall wrote:
| Quote: | "glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote
(snip) |
| Quote: | If a switched 100Mb network with all links full duplex and
no flow control saturates the uplink, it can be slower than
10Mb links, full or half duplex, to a 100Mb uplink.
That should be relatively unlikely, but it is possible.
|
| Quote: | I'm not sure I understand...
What is the basis of comparison?
You said:
"If a switched 100Mb network with all links full duplex and
no flow control saturates the uplink, it can be slower than
10Mb links, full or half duplex, to a 100Mb uplink."
Let me paraphrase:
"Comparing:
a LAN of N clients using 100Mb links each, full duplex, no flow control
with:
a Lan of N clients using 10Mb, full or half duplex
with a 100Mb uplink for both then:
The 100Mb links can demonstrate lower throughput compared to the 10Mb links,
given the same traffic demand."
So, the traffic demand can be no greater than what will be presented with
the 10Mb links - although the peaks will be higher with the 100Mb links. If
that's the case how can the 100Mb links cause lower throughput? There must
be some system overhead issue eh?
On the other hand if somehow one allows the 100Mb linked clients to demand
more throughput than their 10Mb cousins then are you saying that THEN the
100Mb linked clients will actually provide lower throughput than the 10Mb
clients *or* lower throughput than some other idealized situation that's not
under discussion (yet)?
|
Well, traffic demand and traffic allowed are different. If many
hosts are able to send somewhere close to 100Mb, the switch will
be forced to discard packets. Without flow control there is no
way for the switch to slow down the traffic coming in.
On half duplex links, some switches will do flow control by forcing
collisions on incoming packets, so at least the sending host knows
that the packets aren't getting through.
This problem will only occur when there is enough traffic to more
than fill the 100Mb uplink, which should be relatively rare.
Maybe a group of machines all trying to backup data to a server
at the same time would do it.
Somewhat similar to traffic meters on freeway onramps that limit
the rate traffic can enter the freeway to allow the freeway to
run faster. People aren't good at doing flow control without
an external signal and the threat of a ticket.
-- glen |
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Fred Marshall
Guest
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| Posted:
Sat Feb 05, 2005 8:02 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
news:2MKdnZlw7uASTpzfRVn-sA@comcast.com...
| Quote: | Fred Marshall wrote:
"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote
(snip)
If a switched 100Mb network with all links full duplex and
no flow control saturates the uplink, it can be slower than
10Mb links, full or half duplex, to a 100Mb uplink.
That should be relatively unlikely, but it is possible.
I'm not sure I understand...
What is the basis of comparison?
You said:
"If a switched 100Mb network with all links full duplex and
no flow control saturates the uplink, it can be slower than
10Mb links, full or half duplex, to a 100Mb uplink."
Let me paraphrase:
"Comparing:
a LAN of N clients using 100Mb links each, full duplex, no flow control
with:
a Lan of N clients using 10Mb, full or half duplex
with a 100Mb uplink for both then:
The 100Mb links can demonstrate lower throughput compared to the 10Mb
links, given the same traffic demand."
So, the traffic demand can be no greater than what will be presented with
the 10Mb links - although the peaks will be higher with the 100Mb links.
If that's the case how can the 100Mb links cause lower throughput? There
must be some system overhead issue eh?
On the other hand if somehow one allows the 100Mb linked clients to
demand more throughput than their 10Mb cousins then are you saying that
THEN the 100Mb linked clients will actually provide lower throughput than
the 10Mb clients *or* lower throughput than some other idealized
situation that's not under discussion (yet)?
Well, traffic demand and traffic allowed are different. If many
hosts are able to send somewhere close to 100Mb, the switch will
be forced to discard packets. Without flow control there is no
way for the switch to slow down the traffic coming in.
On half duplex links, some switches will do flow control by forcing
collisions on incoming packets, so at least the sending host knows
that the packets aren't getting through.
This problem will only occur when there is enough traffic to more
than fill the 100Mb uplink, which should be relatively rare.
Maybe a group of machines all trying to backup data to a server
at the same time would do it.
Somewhat similar to traffic meters on freeway onramps that limit
the rate traffic can enter the freeway to allow the freeway to
run faster. People aren't good at doing flow control without
an external signal and the threat of a ticket.
-- glen
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Ah, OK. The links act as a throttle - which is not the same thing as saying
that the clients work "OK" with those slower links. Even if the clients
work "OK", they will demand more given the opportunity. The former is a
perspective of the user and the latter is the perspective of the
applications.
Fred |
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glen herrmannsfeldt
Guest
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| Posted:
Sun Feb 06, 2005 8:01 am Post subject:
Re: 100mb network and 100mb backbone, good bad or indifferen |
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Fred Marshall wrote:
(snip)
| Quote: | Ah, OK. The links act as a throttle - which is not the same thing as saying
that the clients work "OK" with those slower links. Even if the clients
work "OK", they will demand more given the opportunity. The former is a
perspective of the user and the latter is the perspective of the
applications.
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The important point being that with 10Mb half duplex links, the
sending hosts either can't send faster than the uplink can take
the data, or get collisions as flow control.
The data from 10 links of 10Mb/s each should fit into a 100Mb/s
uplink, so even full duplex it should be fine.
-- glen |
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