KVM switch for DVI

Anyone used the Addlogix PowerReach KVM-201DVU-2AC?

Supposedly it supports independent switching of USB 2.0 devices. Which
is a very attractive feature to me since I was looking at having to get
a seperate USB switch for this purpose anyway. I'm just wondering how
slick the interface is on the Addlogix. I hate switchboxes (or any
devices really) that don't give you seperate buttons for seperate
functions and instead make you press the same button repeatedly for
different functions. From the small photos the Addlogix seems to only
have two buttons on the front so I wonder how the user actually uses
this to do all this "independent switching".

I'm also wondering how good the video quality is. I'm currently using
my monitor connected directly to the DVI port on my video card and the
quality is incredible - noticeably better than the quality on the VGA
side. But now I want to use two PCs with DVI so I'm trying to decide
whether to get a DVI KVM or just get another monitor and use it with a
seperate keyboard and mouse. My concerns are that the advantages of the
KVM would be space savings and possibly energy savings of not powering
up two monitors. But I'm not sure that I'm willing to accept degraded
video quality and/or inconvenient/awkward operation associated with a
KVM.


_DD wrote:
On Tue, 04 Apr 2006 19:44:36 GMT, stanmc
wrote:

_DD wrote:
I'm looking for a 2-channel or 4-channel KVM switch for use with DVI
video. 1600x1200 resolution would be good. 1920x1200 would be even
better.

Any recommendations for models or brands?


You might want to look at the 20 switches offered by newegg

http://www.newegg.com

search for kvm and then refine it with dvi and you will find several
itneresting units.

This search on Newegg (http://tinyurl.com/oxql5) turned up quite a few
switches, but I've heard mixed reviews on StarTech and Linkskey. Not
sure about Addlogix.

Problems often encountered with badly designed switches: Very high
delay (10 seconds?) when switching between monitors. Keyboard and/or
mouse hang after switching, requiring reboot or KVM power-down. Stuff
like that.

I'll pay a bit more if I need to, but some, like Gefen, are just way
too much ($800!?).

* _DD:

I'm looking for a 2-channel or 4-channel KVM switch for use with DVI
video. 1600x1200 resolution would be good. 1920x1200 would be even
better.

Any recommendations for models or brands?

I'm using an ATEN CS-1764 4-port USB/DVI KVM which atm is connected to
two PCs, one Mac and one workstation (HP i2000 Itanium workstation) on
the computer side and a Dell 2005FPW 20" TFT at the monitor side. I have
this KVM for 2.5yrs now and I'm very satisfied with it. Changing
between input channels is just ~0.5s. The ATEN also switches sound
(which I don't use). It also has an integrated USB hub with two USB
ports (additional to the 2x USB for keyb/mouse) which can be switched to
any computer independently of keyb/mouse/video.

I had an analog (VGA and PS/2 keyb/mouse) 8-port Avocent KVM before
which was really good and didn't compromise image quality but also was
extremely expensive. Avocent makes great KVMs but for home use it's just
overkill and too expensive. I also tried some cheaper KVM switches but
they all suffered from one or more problems.

Benjamin

* HockeyTownUSA:

1600x1200 - 1920x1200 would be very expensive, if you can even find one.

Nope. Every better DVI KVM does 1920x1200 without any problems. Going
higher which also means Dual-Link DVI is a different story, though.

Benjamin

* Benjamin Gawert:

I'm using an ATEN CS-1764 4-port USB/DVI KVM which atm is connected to
two PCs, one Mac and one workstation (HP i2000 Itanium workstation) on
the computer side and a Dell 2005FPW 20" TFT at the monitor side.

A little remark: the Dell 2005FPW has a resolution of 1680x1050. I also
had a Dell 2405FPW which runs at 1920x1200 for a few days connected to
this KVM switch and it ran fine.

Benjamin

Benjamin Gawert wrote:
* _DD:

I'm looking for a 2-channel or 4-channel KVM switch for use with DVI
video. 1600x1200 resolution would be good. 1920x1200 would be even
better.

Any recommendations for models or brands?

I'm using an ATEN CS-1764 4-port USB/DVI KVM which atm is connected to
two PCs, one Mac and one workstation (HP i2000 Itanium workstation) on
the computer side and a Dell 2005FPW 20" TFT at the monitor side. I have
this KVM for 2.5yrs now and I'm very satisfied with it. Changing
between input channels is just ~0.5s. The ATEN also switches sound
(which I don't use). It also has an integrated USB hub with two USB
ports (additional to the 2x USB for keyb/mouse) which can be switched to
any computer independently of keyb/mouse/video.

I had an analog (VGA and PS/2 keyb/mouse) 8-port Avocent KVM before
which was really good and didn't compromise image quality but also was
extremely expensive. Avocent makes great KVMs but for home use it's just
overkill and too expensive. I also tried some cheaper KVM switches but
they all suffered from one or more problems.

Benjamin

Benjamin, how is the image quality via your ATEN vs. directly
connecting the DVI cable to the monitor? Can you tell a difference?

Also, how does the independent USB switching work? Are there buttons
for that? Does it support USB 2.0?

* toronado455:

Benjamin, how is the image quality via your ATEN vs. directly
connecting the DVI cable to the monitor? Can you tell a difference?

There is no difference, and there never can be a difference. Unlike
analog signals like VGA DVI is a fully digital transmission and thus
there is no image degradation when using a KVM switch or extension cables...

Also, how does the independent USB switching work? Are there buttons
for that?

Yes, there are separate buttons for USB routing...

Does it support USB 2.0?

I'm not sure because I rarely use this feature and if I do I only use it
with an old USB 1.1 card reader.

Benjamin

On Tue, 02 May 2006 21:28:02 +0200, Benjamin Gawert
wrote:

* toronado455:

Benjamin, how is the image quality via your ATEN vs. directly
connecting the DVI cable to the monitor? Can you tell a difference?

There is no difference, and there never can be a difference. Unlike
analog signals like VGA DVI is a fully digital transmission and thus
there is no image degradation when using a KVM switch or extension cables...

Untrue.
It may be digital but the signal strength still has to be
strong enough to differentiate the digit(s). Flip a few
bits and it can certainly degrade the image, though it's not
so likely it would work at all if it did it on the scale
that analog did.

* kony:

Benjamin, how is the image quality via your ATEN vs. directly
connecting the DVI cable to the monitor? Can you tell a difference?
There is no difference, and there never can be a difference. Unlike
analog signals like VGA DVI is a fully digital transmission and thus
there is no image degradation when using a KVM switch or extension cables...

Untrue.

Nope, it's not.

It may be digital but the signal strength still has to be
strong enough to differentiate the digit(s). Flip a few
bits and it can certainly degrade the image, though it's not
so likely it would work at all if it did it on the scale
that analog did.

If a KVM switch does influence the signal so that as you said "some bits
flip" then it's defective. Period.

With DVI the image quality remains constant (there is no degradation).
If signal quality decreases over to a point that violates the
specifications (i.e. because of too long extension cables) the you get
display errors or no display at all.

Benjamin

On Wed, 03 May 2006 07:17:52 +0200, Benjamin Gawert
wrote:

* kony:

Benjamin, how is the image quality via your ATEN vs. directly
connecting the DVI cable to the monitor? Can you tell a difference?
There is no difference, and there never can be a difference. Unlike
analog signals like VGA DVI is a fully digital transmission and thus
there is no image degradation when using a KVM switch or extension cables...

Untrue.

Nope, it's not.

It may be digital but the signal strength still has to be
strong enough to differentiate the digit(s). Flip a few
bits and it can certainly degrade the image, though it's not
so likely it would work at all if it did it on the scale
that analog did.

If a KVM switch does influence the signal so that as you said "some bits
flip" then it's defective. Period.

Nonsense, same vague thing could be said about analog cable
and would be equally untrue. The signal level can in fact
degrade and this is WHY there are always (ALWAYS) cable
length limitations for digital signal cables. You must use
a repeater of some sort to overcome the problem at some
length (which may well be longer than the spec calls for, as
it should be, but nevertheless IS necessary at *some*
length). It has nothing to do with the KVM switch (opposed
to not having one), though.

In fact, with ANY digital cable, the signal itself does
ALWAYS degrade. That's just what wire does. The question
is whether this always-present degradation of signal is too
much for the receiver to differentiate the data.

Is there a checksum on the data? That may preserve it (if
enough bandwidth remained for resends), but it does nothing
to prevent the bits flipping in the first place.

* kony:

If a KVM switch does influence the signal so that as you said "some bits
flip" then it's defective. Period.

Nonsense, same vague thing could be said about analog cable
and would be equally untrue.

Nope. With analog transmission image quality is directly proportional to
the various influences over the transmission line. With digital, it's not.

The signal level can in fact
degrade and this is WHY there are always (ALWAYS) cable
length limitations for digital signal cables. You must use
a repeater of some sort to overcome the problem at some
length (which may well be longer than the spec calls for, as
it should be, but nevertheless IS necessary at *some*
length).

Right. So what? Of course you can't use as much extension cords as you
want with DVI. But that doesn't change a thing on the fact that digital
transmission unlike analog transmission has no image quality degradation
due to longer cables or the fact that there is a KVM switch in the line.

In fact, with ANY digital cable, the signal itself does
ALWAYS degrade. That's just what wire does.

Right, the _signal_quality_ degrades. But that doesn't mean the
_image_quality_ degrades, too.

The question
is whether this always-present degradation of signal is too
much for the receiver to differentiate the data.

Is there a checksum on the data?

Yes.

That may preserve it (if
enough bandwidth remained for resends), but it does nothing
to prevent the bits flipping in the first place.

"Bit flipping" as you call it doesn't happen over cables. What happens,
though is that there are various types of influences (crosstalk, wave
effects, reflections, irradiation etc) that are effective in cables (and
any other type of signal transmission). One of the advantages of digital
transmission over analog transmission however is that digital
transmission is way more robust to these influences than analog
transmissions. With analog, the data integrity is directly proportional
to the amount of disturbance. With digital transmission the data
integrity remains constant up to a certain extend where no valid data
can be recovered from the received signal. Since unlike with analog
transmission the data integrity remains constant over a certain area of
noise level the image quality also remains constant, no matter if the
cable is say 1m or 5m or if there is a KVM in the line or not.

Your very basic thinking of degradation because of "flipping bits"
doesn't really fit to DVI because the TMDS signalling used in PanelLink
communications (the technology that is used in DVI) is more than the
plain transmission of a few bits. PanelLink uses quite complex data
words with ecc schemes which makes it even more robust.

Benjamin