| |
ZL3AI > APRDIG 26.07.03 09:18l 223 Lines 11124 Bytes #999 (0) @ WW
BID : 1670-ZL3AI
Read: GUEST
Subj: TAPR Digest, Jul 23, 2/8
Path: DB0FHN<DB0RGB<DB0MRW<OK0PKL<OK0PPL<DB0RES<DB0EEO<PI8DAZ<PI8WFL<PI8WFL<
WB0TAX<VE7RXD<W7NTF<KD4GBA<ZL2BAU<ZL3VML
Sent: 030725/1326Z @:ZL3VML.#80.NZL.OC #:4978 [Chch-NZ] FBB7.00i $:1670-ZL3AI
From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: Reality check needed re uptimes and a soapbox rant, like it or
not.From: "Gregg G. Wonderly" <gregg@skymaster.cytetech.com>
Date: Tue, 22 Jul 2003 23:50:32 -0500
X-Message-Number: 3
>I disagree. Regarding #1, the application is using TCP's ability to
>handle buffering. The problem is that certain TCP/IP stacks do not
>execute the timeout property properly (a simple search will bear this
>out concerning numerous bugs in various stacks).
Which is why I discussed application maintained leasing/timeouts...
>Regarding #2,
>understanding how to build a fault tolerant distributed system and
>implementing a compatible system are two different issues...
In the case of my suggestion, the proxy servers are on the same machine as or
are very near to the existing TCP/IP clients. They will completely hide the
new transport infrastructure from the clients. At anytime, we can change the
behavior of that transport to fix problems, optimize particular cases or add
features to the transport system in realtime. My proposal included the use of
Java's dynamic class loading facilities to automatically update the proxy's
codebase to facilitate this. Security features available today would allow
the right code to be guarenteed to be running.
>IMO, servers should not flush queues. This causes data loss without the
>client being aware of a problem.
Dropping the connection doesn't guarentee anything. If the network has become
partitioned because of connectivity problems, the receiving software will
never, ever receive a TCP close, unless keep alive is enabled.
>One problem stated many times in the
>past is "why doesn't my packet show up".
This is only because the existing mechanism does not include any out of band
signalling facility. When you look at the network layers, you see that there
are all kinds of things underneath TCP that facilitate it actually being able
to provide a stream between nodes on the network. Each of these underlying
notions of control and routing need to be considered when designing an
application. You should never consider TCP to provide more than a way to get
data from one place to another in the correct order. That fact that it may or
may not arrive is the primary issue. But, what does arrive will be in the
order it was transmited. You must design your application to use control
means to let you know what got to the other side, and what the otherside might
still need, if that is important to your application.
>Finally, relying on ICMP means that the clients and servers can handle
>ICMP messages (many firewalls and NAT routers have ICMP blocked).
ICMP ECHO is typically what is denied. Other ICMP packets must be able to
traverse the network or we wouldn't have a working network for many common
control operations.
>Your recommendation for proxy server applications on every client and a
>fully distributed, fault tolerant system are commendable. However, I
>believe (and have stated in the past) that any recommendations such as
>this should be addressed as looking at APRS-IS V2, with consideration
>given not only to the best network solution but also things like how
>easily it can be implemented, how well and quickly will it be accepted,
>what is the impact on the RF APRS networks, etc.
Should there be some kind of formal proposal process then? I have not heard
of any design or review board/group that might be 'in charge' of what will
happen to the future APRS-IS system. What's the best way to make this happen?
A sourceforge project? What about an ARRL sponsored working group?
>It is easy to diss an
>existing design as "ill designed" but the question then becomes "Does
>what you recommend as a replacement meet all of the requirements that
>the current design does?" The question is valid. As Sony found out
>many years ago, sometimes the best design doesn't meet an important
>requirement causing its rejection by the masses (Beta vs. VHS).
What I purposed provides a TCP connection to the client that is identical to
what they see today. That is the only 'standard' that has been kept. All the
various ports that have been adopted (and none of the oddball ones are
reserved with IANA for our user last I knew) may seem standard, but only
complicate the application and the users experience because these numbers are
so arbitrary. In my proposal, I discussed an application that included a GUI
interface that could provide a full blown subscription based service that the
user could user to save configurations for certain types of data streams that
they are interested in. The filtering would always be done on the sending
side and this would provide the reduced bandwidth desired by some, but would
also standardize how this works by making facilities similar to AFilter be an
integral part of the system with documented interfaces at the transport layer.
>This is simply to say "progress can be made without disparaging
>developments made previously". It also goes the other way, "Current
>designs can always be improved upon." As users, sysops, and authors, we
>each make the decision whether the pain demands the gain or the gain
>isn't worth the pain.
I realize that "Ill designed" was not a great term to use. I did not mean to
disparage the efforts of those that have succeeded in getting the system to
work as well as it does today! I am interested in creating more refined
system that guarantees data transport reliability. The current system mostly
works. Steve's numbers provide an indication of that. So, as you ask, is
there any gain that will be worth the pain?
-----
gregg@cytetech.com (Cyte Technologies Inc)
----------------------------------------------------------------------
Subject: Re: Running aprs in the car with a laptop
From: Bill Herrmann <bherrman@spro.net>
Date: Tue, 22 Jul 2003 23:22:22 -0600
X-Message-Number: 4
At 09:35 PM 7/23/2003 +1000, Andrew VK4TEC wrote:
>I would like suggestions. DC-DC converter or inverter ?
The DC-DC converter is going to be a little more efficient, but as others
have pointed out you can use the inverter for other things. I've done both
and each has their advantages. One thing to think of - because I had the
inverter we were able to use my buddies laptop when he was running APRS. My
DC-DC converter wasn't compatible.
One caution that I haven't seen mentioned (someone did mention watching
potentials) - Make sure of the grounding in your laptop. Some laptops used
positive ground. (I know older HP Omnibooks are in this group. I think
there are others.) It works find as long as the power supply provides
isolation. A DC to DC convertor will do that as will an inverter with the
AC power supply. The cheaper voltage convertors will not. I did actually
use one in that mode by running the TNC on an internal battery but I was
only reconfiguring it so I was able to disconnect from the radio. The
easiest way to guess which way the laptop is wired is by checking the
polarity of the coaxial power plug. The outer barrel is most likely the
ground. If it's positive you'll need to be careful.
Bill
----------------------------------------------------------------------
Subject: Re: Internet feed settings???
From: "Curt Mills, WE7U" <archer@eskimo.com>
Date: Tue, 22 Jul 2003 22:20:16 -0700 (PDT)
X-Message-Number: 5
On Sun, 20 Jul 2003, Dick C. Reichenbach wrote:
>I know you run Xastir, so just put "filter t/mn"
>on the filter properties line in the Interfaces - Properties dialog box.
Skip the "filter" part. Xastir adds that automatically if the input
field has anything in it.
Curt, WE7U. archer@eskimo.com
http://www.eskimo.com/~archer
Lotto: A tax on people who are bad at math. - unknown
Windows: Microsoft's tax on computer illiterates. - WE7U.
The world DOES revolve around me: I picked the coordinate system!"
----------------------------------------------------------------------
Subject: Re: Running aprs in the car with a laptop - Use DC-DC conv!
From: WA8LMF2@aol.com
Date: Wed, 23 Jul 2003 02:10:13 EDT
X-Message-Number: 6
In a message dated 7/22/2003 1:48:12 PM Pacific Daylight Time,
sparkfel@qwest.net writes:
>My only objections to running an inverter is that it adds to the "python"
>of wiring already in the vehicle.
AGREED! More uneccessary boxes plugged into other boxes is exactly what you
don't need in a mobile installation.
Not to mention the reduced efficiency. If you plug the laptop's original
AC-powered "brick" into a DC-to-AC inverter you are essentially placing TWO
switching mode power supplies in series. If each one is 80% efficient, the
net conversion efficiency from the car to the laptop is .8 x .8 or only
about 64%.
Another consideration: The DC-to-AC inverter by necessity runs at 60 HZ
producing a 60 Hz squarewave output loaded with harmonics that extend well
into the audio frequency range. The 12 VDC input of the inverter is being
switched on and off at a 120-hertz rate and causes 120-hz ripple to back up
into the car's electrical system. This can result in 120/240/360/etc Hz
audible buzz or hum in other audio devices and transmitted audio (similar
to alternator whine) if the other devices don't have adequate DC power
filtering at their inputs.
Most DC-DC converters (such as laptop adapters) operate at ultrasonic
switching rates ( typically 20-200 KHz -- makes for smaller inductors in
the converter) so any ripple produced by these devices will be beyond the
audio range and therefore inaudible.
Most of the low-power ( under 100 W or so types that one might use for a
laptop or camcorder charger) DC-to-AC inverters I have tried also produce
massive amounts of squarewave harmonic hash that goes clear up into the MF
and lower HF range, blanketing the AM broadcast band and 160/80/40M ham
bands with broadband trash. [ Since the fundamental is 60 Hz, you get a
birdie every 60 Hz across these bands or in other words, effectively
continously! ]
The DC-DC converters also produce MF/HF harmonics but because the
fundamental frequency is much higher, the birdies are spaced 20-200 KHz
apart allowing you to tune around large spreads of freqs between them if
they present a problem.
Finally, I would NEVER think of connecting a laptop directly to a car's 12
VDC system, even if it would run directly on 12 VDC, because of the
horrendous voltage surges and spikes running to hundreds or even thousands
of volts created when starter motors, power lock solenoids, etc drop out.
At the least you should have some sort of power conditioning in the cable
between the computer and the power source such as series inductors and
18-20 VDC transorbs or MOVs.
Stephen H. Smith wa8lmf (at) aol.com
Home Page: http://wa8lmf.com
Ham Radio/Mobile SSTV page: http://members.aol.com/wa8lmf/ham
APRS Stuff
http://members.aol.com/wa8lmf/aprs
----------------------------------------------------------------------
Read previous mail | Read next mail
| |
