QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/tcp/940149.txt

Internet Message Format | 1994-11-13 | 15KB

Date: Fri, 15 Jul 94 04:30:02 PDT
From: Advanced Amateur Radio Networking Group <[e-mail]>
Errors-To: [e-mail]
Reply-To: [e-mail]
Precedence: Bulk
Subject: TCP-Group Digest V94 #149
To: tcp-group-digest


TCP-Group Digest            Fri, 15 Jul 94       Volume 94 : Issue  149

Today's Topics:
              800 mHz Trunked HT - To Person Interested
                     Bridge vs. Repeater (2 msgs)
                      Bridge vs. Repeater (fwd)
                      DAMA v. Repeaters (4 msgs)
                         PI/PI2 driver update

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We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party.  Your mileage may vary.  So there.
----------------------------------------------------------------------

Date: Thu, 14 Jul 94 11:35:39 CDT
From: [e-mail] (System Administrator)
Subject: 800 mHz Trunked HT - To Person Interested
To: [e-mail]

I know this is off the topic..bt..

To the persn interested in my 800 mHz Trunked HT, and wanted them. I hav
lost your address so I'm unable to FedEx them to you. If you will email
me your address at [e-mail]

Thanks,
N9TOL De Greg

------------------------------

Date: Thu, 14 Jul 1994 09:12:06 -0400
From: [e-mail]
Subject: Bridge vs. Repeater
To: [e-mail]

>Well, isn't there a bit more than that?  Even if two nearby users don't
care about routing, a router can keep two local users from sucking up
bandwidth... I'll share this with the group...

Routers and repeaters solve different problems.  When you maintain
your car, do you change the oil or the check the tires?  Waddayamean
both?  What kind of religious war are we having if we have two different
correct answers?

A repeater -- operating in the physical layer -- is VITAL to solving the
hidden transmitter problem.  I personally think DAMA's impractical for
most ham use, for various reasons including the crappy radios we glue
on to, but a repeater WILL get rid of HTS.  When you have Hidden
Transmitter Syndrome, the actual channel capacity degrades to about
18-20% of bit rate, since it's effectively Aloha technology.  When you
have a repeater and everyone hears everyone else when they're NOT
transmitting, then you have CSMA and the channel capacity increases
dramatically, MORE than doubling, though the actual efficiency depends
on various timing factors.  When you have a repeater and everyone else
is ALSO full duplex, then you have CSMA/CD and the channel capacity
increases even more.  I've seen Ethernets run over 90% capacity, even
though the theory says that you can't run over say 60% or so -- the
theory assumes WORST CASE with everyone at maximum distance in a huge
star.

So a repeater uses two frequencies but will get MORE bps/Hz than the
crappy Aloha digis we have now.  It's insane that we don't use them
on 2 meters more; haven't the old yakkers died off yet :-)?  The old
first-come first-serve policy is enough to warrant giving the band
over to commercial  users, almost, since it guarantees the obsoete old
stuff will forever prevent more efficient newer users.

A router works at a higher layer, between users who do NOT have any
physical layer connectivity (or at least that's it's main functiom).
That's just not the same function as a repeater.  Now if the router
were atop a mountain, it might choose not to pass along stuff that
didn't need tocross the mountain.  But what does that solve?  The
presence of one user's packets crossing the mountain will cause
bits to be present on both sides, and local users will get clobbered
anyway.  The mountaintop should probably have a repeater for the
local users AND a router to go to OTHER mountaintops.
   fred k1io

------------------------------

Date: Fri, 15 Jul 1994 12:24:20 +1000
From: [e-mail] (Carl Makin)
Subject: Bridge vs. Repeater
To: [e-mail]

At 10:57 AM 13/7/94 -0500, David Rush wrote:

> Because traffic between two stations on the left side of the mountain would
> generate useless traffic (thru the regen) on the right side of the mountain.
> (Sucking up bandwidth.)  A router could decide which packets need to cross
> over the mountain, but otherwise stay quiet.

Whether you want to route or repeate depends on the traffic flow on the
network and the topography of the surrounding terrain.

Canberra (Australia) is quite hilly and the BBSs are at the north and south
ends of the city.  The biggest problem is hidden transmitters.  The terrain
means even in the same "valley" many stations can not hear everyone else in
the same "valley" and the majority of the traffic on frequency is going to
or from the next "valley" anyway.  In this case a bit regen repeater solves
a number of problems and as the traffic is mainly crossing between
"valleys" then we don't lose bandwidth.  We also don't have enough local
traffic to justify the expense of isolating the "valleys" and linking them
via routers (yet).  We've chosen to make the entire ACT one "LAN" (for 4800
baud traffic anyway).

> And when we say "bit regenerator", it's functionally equivalent to an
> Ethernet repeater, aren't we?

Yes.

--
Carl Makin (VK1KCM)          "Speaking for myself only!"
[e-mail]      'Work [phone]'      Canberra, Australia
'The best book on programming for the layman is "Alice in Wonderland";
 but that's because it's the best book on anything for the layman.'

------------------------------

Date: Thu, 14 Jul 1994 09:05:19 -0500 (CDT)
From: Kurt Freiberger <[e-mail]>
Subject: Bridge vs. Repeater (fwd)
To: [e-mail] (TCP-Group Mailing List)

[e-mail] said:
> Well, isn't there a bit more than that?  Even if two nearby users don't
> care about routing, a router can keep two local users from sucking up
> bandwidth... I'll share this with the group...

First of all, one needs to determine the topology of what one is trying to do.
You have to define "local".  In most cases, "local" means LAN.  The audience
is considered peers in one group, with one shared media.  It'd be nice if
we had one channel for one path, but physics ain't with us.  A router inter-
connects subnets.  A bridge interconnects LANs as peers within subnets.

> I said:
> >> Yeah, presumably cross- or multi-banding would probably make the most
> >> sense (easiest).  All of the stations in a "mutually hearable area"
> >> would share one freq on one band.  The stations in a different
> >> "mutually hearable area" (on the other side of the mountaintop
> >> router) would share a different freq on a different band.
>
> Then Gerry said:
> >So, why not use a wide area machine on 2 in-band frequencies, using the
> >regen? It's a "repeater" to the FM guys, simple to maintain, simple to
> >build, simple to install.  Find a good {tower/building top/mountain top}
> >and put it up to cover as much of the are as possible.  If you THEN have
> >an area that's not adequately covered, put up another regen in that area
> >on the reverse channel, or route over to that remote area.
>
> Because traffic between two stations on the left side of the mountain would
> generate useless traffic (thru the regen) on the right side of the mountain.
> (Sucking up bandwidth.)  A router could decide which packets need to cross
> over the mountain, but otherwise stay quiet.

It depends on whether you need the other side of the mountain to be a
different subnet.  The decision to use a single regenerator (repeater)
on the top vs two regenerators with an interconnect is one of economics.
Obviously, two radio sites with interconnects is more expensive.
If you have two regenerators, then you can decide whether to route or
bridge according to the LAN topology.  To subnet or not to subnet, that
is the question?

> Assuming that nobody even cares about routing in this case, what I'm
> really proposing is a bridge (to use Ethernet terminology) between
> the two sides of the mountain, rather than bit regenerator.
> And when we say "bit regenerator", it's functionally equivalent to an
> Ethernet repeater, aren't we?

You have it exactly.

I've been mulling over the design of a bridge for AX.25, and how that could
work in our environment.  There are some DEFINITE gotchas, especially with
regard to bridging loops.  I didn't really want to deal with spanning-tree
at all!!!!

73/Kurt
--
# Kurt Freiberger, WB5BBW   Dept. of Computer Science, TAMU              #
# Internet: [e-mail]      |  "Even MY hypocrisy has its limits." #
# AuralNet: 409/847-8607          |                                      #
# AMPRNet: [e-mail] |        - "Doc" Holliday, Tombstone   #
# Disclaimer: Not EVEN an official document of Texas A&M University      #

------------------------------

Date: Thu, 14 Jul 1994 11:50:09 -0500 (CDT)
From: [e-mail] (Steve Sampson)
Subject: DAMA v. Repeaters
To: [e-mail]

[e-mail] writes:
> I personally think DAMA's impractical for most ham use, for various reasons
> including the crappy radios we glue on to, but a repeater WILL get rid
> of HTS.

Well I think a crappy radio will not perform either DAMA or Repeater duty, so
I guess I don't understand your logic.  Why DAMA won't succeed in most
Western societies is because we are raised to always seek power in our sphere.
That means every Ham will want to be the Master Node, and not submit to being
a Slave.  Here in Oklahoma City we have more Nodes than users because that's
how people are.  If you ask them if they want to create a network the answer
is: NO!     They just want to beacon their Callsign and own a frequency.

Oops, I've drifted from technology to behavior again. . . sorry.

--
Steve

------------------------------

Date: Thu, 14 Jul 1994 14:20:11 -0400
From: [e-mail]
Subject: DAMA v. Repeaters
To: [e-mail]

> I think a crappy radio will not perform either DAMA or Repeater duty, so
I guess I don't understand your logic.  Why DAMA won't succeed in most
Western societies is because we are raised to always seek power in our sphere.
That means every Ham will want to be the Master Node, and not submit to being
>a Slave.

Nope, that's not why I think DAMA won't cut it.

First off the average radio doesn't HAVE to do repeater duty; a CSMA
(no /CD) arrangement is probably the happy medium;  tha'ts ONE repeater
and ORDINARY HDX radios.

DAMA itself is based on polling, right?  So in DAMA, you need to make
FAST polls to potential users.  Long Txdelay times make it fail, and
that's the problem.  If there are 50 users on the freq. and only 3 are
active, you avhe to waste time poling 47.  For a wireline tolkien ring
that's no issue; they take microseconds.  But voice-oriented ham
radios take many milliseconds to be polled.  Way way too many.

ALso, the protocols we use are not master/slave; or are they very
happy about waiting long times for a round-robin poll to take place.
Super-fast polling would fix that but I just don't see it.

Other than that, Mrs. Lincoln, how did you like the play?
    fred k1io

------------------------------

Date: Thu, 14 Jul 1994 13:55:45 -0500 (CDT)
From: [e-mail] (Steve Sampson)
Subject: DAMA v. Repeaters
To: [e-mail]

> DAMA itself is based on polling, right?

Yes.

> So in DAMA, you need to make FAST polls to potential users.  Long Txdelay
> times make it fail, and that's the problem.

Well it would be a problem compared to NO txdelay true.

> If there are 50 users on the freq. and only 3 are active, you have to waste
> time poling 47.

Well, as I understand it - When you are polled and respond with IDLE, the Node
will begin backing off on your poll timing.  So the 3 active will get the
channel while the 47 IDLE users will get more and more backoff.  Then if one
more user switches from IDLE to ACTIVE they get back to high priority again.
I guess this is akin to Prioritized Round Robin in Task scheduling.
--
Steve

------------------------------

Date: Thu, 14 Jul 94 14:22 EDT
From: [e-mail] (Russell Nelson)
Subject: DAMA v. Repeaters
To: [e-mail]

   From: [e-mail]
   Date: Thu, 14 Jul 1994 14:20:11 -0400

   DAMA itself is based on polling, right?  So in DAMA, you need to make
   FAST polls to potential users.  Long Txdelay times make it fail, and
   that's the problem.  If there are 50 users on the freq. and only 3 are
   active, you avhe to waste time poling 47.  For a wireline tolkien ring
   that's no issue; they take microseconds.  But voice-oriented ham
   radios take many milliseconds to be polled.  Way way too many.

But if only three are active, why waste time polling 47?  Why not make
a poll priority list, doing an exponential (up to a point) fallback in
priority.

Also, why should the hub be doing any transmitting?  It should just
assign slot times for the users, assigning more slots to more active
users.

Or is DAMA some sub-optimal scheme that someone is pushing as a
universal solution?  I'm afraid I've got my "Answer for every question
regardless of my ignorance" hat on.

-russ <[e-mail]>    http://www.crynwr.com/crynwr/nelson.html
Crynwr Software   | Crynwr Software sells packet driver support | ask4 PGP key
11 Grant St.      | [phone] (9201 FAX)  | What art thou doing about it?
Potsdam, NY 13676 | LPF member - ask me about the harm software patents do.

------------------------------

Date: Fri, 15 Jul 1994 00:00:22 -0400 (EDT)
From: [e-mail]3dp (Dave Perry va3dp)
Subject: PI/PI2 driver update
To: [e-mail]

A driver update is available which improves performance for the B port on
PI and PI2 cards. Depending on the host machine, it should now be capable
of 9600 baud (on 386 class machines). Also included is a bugfix that should
eliminate rx overruns.

This update is for the NOS source code. The Linux driver update will follow.
It is available for ftp from hydra.carleton.ca as:

pub/hamradio/packet/tcpip/pi2/pi.c

Dave
va3dp

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End of TCP-Group Digest V94 #149
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