10Base-T vs. 100Base-T (discussion)

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I curious to know what peoples thoughts were on 100Base-T in embedded
systems applications. In my experience, many embedded systems that are
network enabled aren't necessarily very high throughput devices and
don't really take advantage of the extra throughput available in
100Base-T. I.e. how many embedded processors can really transfer
packets at 10Mbytes/sec between memory and the NIC, and still get
useful work done ?

Also, it seems like running at 10Base-T on CAT5 would give you some
extra noise margins and perhaps extended range over 100Base-T. Is this
important ? 100Base-T gives a lower packet latency, is this important
to real time response in application ?

Are there benefits to using 100Base-T in applications where your
throughput is known to be low ? Do systems intergrators really worry
about noise margins in cabling ? Do most network enabled devices just
plug into a 10/100 Hub anyway ? Is 10Base-T effectively dead/legacy ?

See ya, -ingo
--
/* Ingo Cyliax, snipped-for-privacy@ezcomm.com, Tel: 812-391-0895 */


Re: 10Base-T vs. 100Base-T (discussion)

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For most embedded systems, 100BT is purely a marketing gimmick.

Once upon a time in the days of yore, it was not unusual to
find a hub that would force all ports to 10M whenever any port
was connected to a 10M device.  These-days "hubs" are almost
always switches and can run ports at different speeds.

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Probably.


That depends on the application.

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That depends on the application.

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Marketing feature list.

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Only after things fail.

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Probably.


Yup.

What's up with the extra space before the question marks?

--
Grant Edwards                   grante             Yow!  What UNIVERSE is
                                  at               this, please??
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Re: 10Base-T vs. 100Base-T (discussion)

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10Mbps can only run half duplex except on managed switches with operator
configuration.  If your application is well below 10Mbps requires then you
will probably be fine.  However, there are non related things like multicast
and broadcast packets that can infringe on your usable bandwidth, or worse
completely use up your bandwidth.  100Mbps is extra protection for network
issues that may be beyond your control.



Re: 10Base-T vs. 100Base-T (discussion)
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Hi Ingo,

I assume you're trying to gather data to decide whether or not ZWorld
should add 100 Mbps to some new Rabbit products?

I have the same questions with 100 Mbps versus gigabit on the products I
work on.  Even though our hardware can't sustain passing gigabit
traffic, we decided to use gigabit NICs for connectivity rather than
performance.  In our market, it turns out upstream from our product is a
T-1 or two - that's such a small pipe (1.5) that the difference between
100 and 1000 is totally moot.

I have had many more problems with auto-negotiating correct speed and
duplex using (cheap) embedded systems and (cheap) hub/switches than I've
had problems running out of bandwidth.

To put it another way, very few users tend to performance test their
installed systems and utilize them near their maximum capacity.  But
anyone can look at the link speed LED and make a snap decision.

My advice: make sure that when the user plugs it in, the little LED
comes on.  If that means ditching 10 Mbps only controllers, then do it.

Kelly

Re: 10Base-T vs. 100Base-T (discussion)

100Base-T gives a lower packet latency, is this important
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Please note that 100Base-T has extended delays
between frames to extend the collision domain to
an useful value. Simply scaling 10Base-T by
10 would give a maximum cable length of 18 meters,
which is deemed to be on the short side. This
also translates the other way that 100 Mbit/s
does not cut the delays of 10 Mbits/s by a factor
of 10.

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They should, but pretty many are fallen victims of
marketing push of 100 Mbits/s.

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Currently it's nearly always a dual-speed switch. It is
somewhat difficult to get plain hubs - I tried to get one
for network sniffing purposes.

Is 10Base-T effectively dead/legacy ?

Maybe, but I hope that it still has many years ahead.

One point in embedded devices is that 100 Mbit/s
chips are much more power-hungry than plain 10 Mbits/s.

Tauno Voipio
tauno voipio (at) iki fi


Re: 10Base-T vs. 100Base-T (discussion)

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This is a excellent reason to keep 10BT, at least so long 100TX does not
meet this point.

Furthermore, there are now many 10BT DSL modems and 10BT NICs spread around
the world which are working fine and provide a correct service to end users
(Internet access, most of 512k).
How do you think all those parts (plastics, lead, chemicals, ...) will be
recycled?



Re: 10Base-T vs. 100Base-T (discussion)

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You're assuming there are only two devices on the wire -- the
unit in question and "something else" talking to it.  I.e. if you have
several devices sharing the wire -- in one or more applications -- then
the load any one device sees may be considerably less (yet still
bang the network pretty hard overall).

Smaller processors using older technology NICs are usually bandwidth
limited in themselves.  But, smarter NICs can offload almost
all of this overhead from the processor, cutting down on bcopy()'s,
even checksum generation, etc.  NIC's with klunky implementations
("programmed I/O", 8 bit data paths, etc.) are more of a hassle than
the 10 vs 100 issue.

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From my experience, the biggest win is a well engineered protocol
stack.  Look at the time from *application* generating a message
to the time it appears on the wire.  In many stacks, you'll find that
this isn't (realistically) bounded at all!  Does the stack provide
any QoS guarantees/features?  Is it "real time" (no, not *real fast*)?
Or, does it have a more traditional "desktop/mainframe" structure?

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Depends on your application domain and operating environment.
In the past few years, I have been deploying 10Base*2* designs
as they are more appropriate to the applications I was addressing.
The design in progress currently (totally different market) deliberately
offboards the NIC so the consumer can opt for whatever is
appropriate for *their* needs.

If you are designing for a "PC" type market, then you'll probably chase
100Mb "commodity" parts.  And, probably faster processors (streaming
audio, video, network infrastructure, etc.).  If you're doing
process control, you'll probably stick to other technologies (even
EIA485, et al.) more appropriate to that market and or that
*environment*.

--don



Re: 10Base-T vs. 100Base-T (discussion)


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That's pretty much a requirement for 10BaseT and 100BaseT.
They are both point-to-point connections.

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That's only going to be a consideration if you're using a dumb
hub rather than a switch, and dumb hubs are really hard to find
these days.

--
Grant Edwards                   grante             Yow!  Yow! It's a hole
                                  at               all the way to downtown
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Re: 10Base-T vs. 100Base-T (discussion)
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The point was, the *network* may have more than two nodes
in/on it.

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I don't care how smart your switch is.  If 30 nodes all want
to talk to "node 0", the bandwidth of the radial out to node 0
sets the performance of the entire network.  And, the reverse
(my comment above) is true -- if node 0 is driving the performance
of the network, then the load that any of the other (30, in this example)
nodes sees is correspondingly throttled by that node.

In many of the distributed applications that I have encountered,
this is often the case.  "Node 0" might be a SCADA device
(e.g., often, a "PC" watching / controlling a network of field devices).
Those devices are often dumb and slow.  Yet, with enough of
them on the wire, the "PC" ends up as the bottleneck despite the
fact that other nodes are transfering data at ridiculously low rates.

That SCADA function may sit behind a "gateway" (explicit or
otherwise) and, AFTER-THE-FACT impose limits on the traffic by its
mere presence.

Also, there seems to be a steady trend towards replacing
wired networks with wireLESS technologies.  Suddenly,
the fact that a switch could give *apparent* bandwidth
multiplication disappears as the "network" reverts to more
of a true star topology -- with, potentially, other UNEXPECTED
devices competing for bandwidth.  Sure you can design with
the *expectation* of a particular communication technology;
but, eventually find yourself faced with the aspect of that
"communication subsystem" being increasingly treated like
a commodity item -- swapped out by marketeers for whatever
is "en vogue" down the road.

So, unless you want to "special case" the *types* of traffic you
are going to tolerate and the *virtual* topology of the network
(a function of the application domain), expecting a switch to
magically alter the apparent available bandwidth is wishful thinking.

And, unless you are designing a *truly* distributed application
with roughly level network loads, you are going to find some
node(s) drive the overall performance of the network.  And,
indirecly, *limit* the effective data rates for all other nodes
regardless of the technology and topology used.

--don






Re: 10Base-T vs. 100Base-T (discussion)
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[... lots snipped...]

Done, you're missing the point.  The rest of the network is quite
irrelevant to the question being discussed here, which was about the
connections between some embedded device and its neighboring node in
the network, under the premise that a 10BaseT would be sufficient for
the bandwidth needs of that device.  

If some "central" node's link to the network becomes the bottleneck,
exchanging the link of the embedded device we're discussing here will
help quite exactly nothing at all to solve that problem --- it's
strictly the link between that central node and its peer (e.g. the
switch) that has to be discussed then, and possibly the internal
throughput of the switch.

The only case where a 10BaseT device's link could, theoretically,
become a bottleneck would be for traffic patterns dominated by
broadcasts transmissions.  But if that's the case, you have much worse
problems to worry about than the link type of that individual device.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: 10Base-T vs. 100Base-T (discussion)
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[... lots snipped...]

Don, you're missing the point.  The rest of the network is quite
irrelevant to the question being discussed here, which was about the
connections between some embedded device and its neighboring node in
the network, under the premise that a 10BaseT would be sufficient for
the bandwidth needs of that device.

If some "central" node's link to the network becomes the bottleneck,
exchanging the link of the embedded device we're discussing here will
help quite exactly nothing at all to solve that problem --- it's
strictly the link between that central node and its peer (e.g. the
switch) that has to be discussed then, and possibly the internal
throughput of the switch.

The only case where a 10BaseT device's link could, theoretically,
become a bottleneck would be for traffic patterns dominated by
broadcasts transmissions.  But if that's the case, you have much worse
problems to worry about than the link type of that individual device.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: 10Base-T vs. 100Base-T (discussion)

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Or multicast.



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