-----Ursprüngliche Nachricht-----
Von: UniversalDigitalRadio@yahoogroups.com
[mailto:UniversalDigitalRadio@yahoogroups.com] Im Auftrag von
avignonmimi@...
Gesendet: Mittwoch, 12. Juni 2013 11:29
An: UniversalDigitalRadio@yahoogroups.com
Betreff: [UniversalDigitalRadio] Re: Frequencies, Band Plans and other
annoyances



I was thinking one station could have right-hand, but then to communicate
the next station would need left-hand (two antennas pointed at each
other).

Wimo only sells right-hand, as they sell to the satellite market, where
only the satellite needs to be left-hand.

--- In UniversalDigitalRadio@yahoogroups.com
<mailto:UniversalDigitalRadio%40yahoogroups.com> , M5AKA <m5aka@...>
wrote:

Circular antennas are available from Wimo
http://www.wimo.de/helix-antennas_e.html

73 Trevor M5AKA

Developers,

I'm trying my hardest to spread the word about the UDR56K-4 here in CT, but many hams have adopted the "proof is in the pudding" theory.

Circular antennas are available from Wimo
http://www.wimo.de/helix-antennas_e.html

73 Trevor M5AKA

As we move forward to deployment, it occurs to me that the landscape for operating frequencies is anything but stable.

Here in Western Washington we have 19 - 25kHz simplex channels designated as packet, of which only 3 are contiguous, such that we could use them as a 100kHz high speed channel.

We also have 3 pairs designated as packet repeaters.

What are your thoughts on how to deploy the UDR in your area, particularly once we move past the current 4800 NB and 9600 baud rate limitations.

Bryan - K7UDR

I see the specs for the UDR56K specify "RF Connector: Type N" but is it male or is it female?

Thanks,
Mark KV4I

As we move forward to deployment, it occurs to me that the landscape for operating frequencies is anything but stable.

Here in Western Washington we have 19 - 25kHz simplex channels designated as packet, of which only 3 are contiguous, such that we could use them as a 100kHz high speed channel.

We also have 3 pairs designated as packet repeaters.

What are your thoughts on how to deploy the UDR in your area, particularly once we move past the current 4800 NB and 9600 baud rate limitations.

Bryan - K7UDR

As we move forward to deployment, it occurs to me that the landscape for operating frequencies is anything but stable.

I seem to remember that we were using 1024-byte packets over 9600 baud in the Seattle area on TCP/IP back in the early 90's, and UI frames.

As soon as I get a box in my hand I'll be trying to do the same or better on 56k.

Questions that came in via email. Thanks to John for responding

Is it possible to use TCP-IP over ax25 with large MTU ?

The UDR56K implements the Linux AX.25 stack using a socket interface. Each AX.25 frame may carry a payload of up to 256 octets. (http://www.tapr.org/pub_ax25.html 2.5.5) This comes with an overhead of up to 76 octets, and is exclusive of bit-stuffing (2.2.6) which translates to about 21 frames per second in continuous, unconnected mode under perfect conditions, e.g. no packet loss.

Sometimes when describing TCP/IP or UDP/IP circuits, the MSS (Maximum Segment Size - http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Maximum_segment_size) is mislabeled MTU. The MTU is governed by the transport, in this case AX.25, or 256 octets per frame. However, the Linux protocol stack will allow a larger MSS, which is fragmented over multiple AX.25 frames. (Source code http://www.cs.albany.edu/~sdc/Linux/linux/net/ax25/ax25_out.c). TCP/IP allows a MSS of 65000+ octets, but this number is impractical for any reasonable network. An MSS of 65000 over AX.25 would fragment into 256 frames or more than 10 seconds transmission under ideal 56 kbps conditions and could require a retry on a single bit error. An IP MTU is the MSS + Header (>=20 Octets) and in most AX.25 circuits the IP MTU is kept to a modest 512 octets or 2 AX.25 frames. The optimum IP MTU on the UDR56K-4 may or may not be a higher number and will require experimentation by the amateur community to come up with a specific recommendation.

What is the net throughput in tcp/ip ?

At 1:1 IP to AX.25 MTU (no fragmentation) one would see speeds approaching 31 kbps using UDP over AX.25, this would vary +/- depending on fragmentation (to lower header count under IP) and packet loss, and acknowledgement time for TCP. The radio is specified with a tx/rx turnaround at < 1.5 ms.

If your interest is truly TCP/IP you may also want to consider using the D-STAR Data Mode. It encapsulates Ethernet frames in a D-STAR packet. http://www.jarl.com/d-star/shogen.pdf 2.1 - This would provide 4.3 1430 (MSS) data per second (UDP) or approximately 49 kbps. (58% improvement).

We also believe there is room for a yet to be determined protocol that might have up to a 7000 octet MTU, basically raw IP with a few sync bits, which would approach 56 kbps of UDP on a loss less circuit.