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Astro Modem over IP

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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Lotus54
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Astro Modem over IP

Postby Lotus54 » Fri May 20, 2011 6:40 am

I'm not back to working on this.

We are trying to run Astro Modems across a Cisco IP system (with microwave).

System:
Astro-Tac 3000 (astro modems).
VG-6 4-wire phone line to Cisco box.
E&M cards in Cisco
Copper at far end to Quantar (astro modem).

The link delay on the A-Tac shows about 111 (I'm guessing in ms).
From what I've read anything over 100 is a no go.

The ping time is short, so it may be the E&M cards, or perhaps QoS or packet size.
We dont' own the cisco/microwave system, but can request changes.

Anyone know someone to ask about this? Or someone that has done it?

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d119
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Re: Astro Modem over IP

Postby d119 » Fri May 20, 2011 11:39 am

If the Cisco has E&M cards in it, you should be able to run your ASTRO Modems into that and bypass that 4-wire to Cisco thing or whatever it is. I'm not familiar with the Cisco equipment, but E&M trunks should carry the ASTRO modem audio just fine.

You could also do away with the ASTRO modems and just use a subrate unit to transport the V.24 data directly.

Lotus54
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What radios do you own?: XTL5000, XTS5000, Quanar, A-ta

Re: Astro Modem over IP

Postby Lotus54 » Fri May 20, 2011 2:05 pm

thanks for the ideas.

There is no '4-wire to Cisco thing'.
The microwave is at a remote site from the Astro-Tac- so there is a VG-6 phone line going to that site.

So far, the E&M cards will not properly pass it.

Yes, if we had loads of money, and even MORE phone lines we could do V.24.
But if you use V.24, you need TWO 4-wire lines (we are using analog and digital RF).
So we would have to buy a bunch of V.24 cards, install another phone line at each end and have to pay recurring costs.

Yes, we are running Astro Modems across the E&M cards on our own microwave (it uses T-1 format) with no issues.
I think it is all do do with the IP 'carrier' of the Cisco gear.

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d119
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Re: Astro Modem over IP

Postby d119 » Fri May 20, 2011 4:24 pm

Is this completely IP microwave, or what?

What I'm saying is that there is the possibility of passing the V.24 data via your microwave using a subrate unit in the channel bank. We do this with SRU cards in our Motorola TeNSr channel banks all the time. Does Cisco make an equivalent product that will take serial input on one end and spit it out on the other, and vice versa?

If so, you simply plug the V.24 of your Quantar in one end, and the other end into your AstroTAC. Let the analog audio ride over your E&M.

I'm just not a big fan of unnecessary media conversion (V.24 to Astro Modem to E&M to IP etc etc). It just makes more sense to try and go V.24 -> IP.

We had a situation where one of our former employees engineered and sold a system that took 4-wire audio, converted it to T-1, then converted T-1 to IP and back on the other end. It was a f___ing nightmare. Unreliable as all hell. Once we set them up with equipment that took 4-Wire directly to IP, no more trouble.

Lotus54
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Re: Astro Modem over IP

Postby Lotus54 » Tue May 24, 2011 7:43 am

We do not have any V.24 cards in the A-Tac or Quantars. The option on those is either V.24 OR Astro modem.

If we had the funding to buy a bunch of V.24 cards, we would still need to buy *another* 4-wire circuit to the microwave site, plus get another channel on the microwave.
It is not our microwave either, so we have limited use.

Thanks for the ideas, we just can't do V.24 in our case (I do know it would work though)

Mark

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515
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Re: Astro Modem over IP

Postby 515 » Tue May 24, 2011 12:57 pm

I agree that if you have to run mixed mode, the Astro Modems do simplify things as they allow the analog audio to use the same voice circuits as the digital modem data. As d119 said, if the system were digital-only, V.24 with subrate MUX cards is the best way to do it.

I'd look into what options you have on the IP equipment for configuring packet size. In general, the smaller the packet size, the lower the link latency will be.

If the total link latency is over 100ms, the system should still work to some extent. If the signals from the receivers/Quantars don't arrive at the AstroTAC within 100ms, it simply votes on the first one it receives, and ignores the rest--even if they are less noisy or have fewer errors.

Are you sure your links are good? Are you getting solid "V.24/Modem" green lights on your Quantar's and Astro TAC?

Lotus54
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Re: Astro Modem over IP

Postby Lotus54 » Wed Jun 01, 2011 8:51 am

The modems never finish connecting.
We have run analog over it for a year with no issues at all- so I know the link itself is fine.

Now that I'm getting back into it, I may take a unit to the microwave side of a VG-6 circuit we have getting there. That would take the VG-6 out of it.
I'll work on one block at a time.
Just hoping someone has done it!

kossuth
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Re: Astro Modem over IP

Postby kossuth » Wed Jun 15, 2011 6:50 am

So coming in on this alittle late, but here are a few thoughts. You are essentially using the VG6 to produce an analog leased line for the analog Astro modem which is converted to IP going to the Cisco router. Now, my knowledge on the Astro modem is alittle dated (haven't worked on them in 3+ years) so please confirm what I'm thinking. The Modem does it's signaling in the typical PSTN voice band (300-3300 hz) or is it higher or lower than that? I think it's the same as the voice band but just want to confirm. Because if it's above or below that range you could be experiencing packet loss due to part of the spectrum being cut off. Most VG devices are only designed to work from 300-3300 hz FYI. That's one thought. Another thought is that if everything checks out as far as the signaling frequency goes I'd ask what type of codec they are using on the VG6 to convert the analog audio to digital IP. You should be using G711 which is completely uncompressed and is a 64k channel per audio stream. In my experience you gotta use the larger codecs on things like faxes and so on. There are other codecs out there used for VOIP that are much smaller, but they compress the audio using techniques like silence suppression which can cause the first few milliseconds of a transmission to be dropped (we don't notice it as a person, but a device has a hard time with this obviously). These are a couple of thoughts to work with.

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515
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Re: Astro Modem over IP

Postby 515 » Thu Jun 16, 2011 6:23 am

The Astro Modems are 9600 bps, so the should work on most voice grade circuits.

Are you sure the modem inputs/outputs are wired correctly? That is, the modem output of one station is wired to the modem input of the comparator? Here's a pic of the back of the comparator, with some of the wiring labeled 'IN' and 'OUT'.
Image

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chartofmaryland
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Re: Astro Modem over IP

Postby chartofmaryland » Thu Jun 30, 2011 7:19 am

First off,

The 4 wire circuits coming out of the Astro Tac receivers, you have 1 & 2 and 4 & 5 wired into your 4 wire circuit, these setups are not 4 & 5 and 3 & 6.

Do you have a TIMS, if so what is the frequency response of your lines and are they bi-directional or hybrid meaning transmit one way receive the other?

Last to check is the MODEM levels in the CPS for each receiver and the comparator. If you neglect to transmit the IMBE at a high enough rate then the receiving modem cannot "hear" the talking end.

Check these out and as long as the audio circuits, wiring and levels are proper, then this should be happy with solid V.24 / modem lights.

CoM
If the lights are out when you leave the station and then come on the second you key up, you know you have enough power.

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MotoFAN
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Re: Astro Modem over IP

Postby MotoFAN » Thu Nov 02, 2017 2:58 pm

Guys, who can confirm that it's possible at all? I mean subject, Astro Modem over E/M? Who got it working in real life?
I am biggest fan of XTS2500 and ASTRO Digital Saber.

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MotoFAN
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Re: Astro Modem over IP

Postby MotoFAN » Fri Nov 03, 2017 9:20 am

Hi all!

I can confirm, it's possible. You can transfer Astro modem's data stream via E&M and IP. But you must use no codec! In case of Cisco, go to dial-voice peer and issue this command:

Code: Select all

codec clear-channel

G711 family will NOT work even in LAN (with 1 ms latency)! In case of G711 modems will establish connection for 1-2 seconds and will lose it for ~30 seconds. And this situation repeats in cycle.
I am biggest fan of XTS2500 and ASTRO Digital Saber.

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MotoFAN
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Re: Astro Modem over IP

Postby MotoFAN » Fri Nov 03, 2017 11:05 am

And one very very interesting thing

If you're using some traditional codec, like G711, voice port input gain and output attenuation "softpots" works fine. And by default Cisco E/M --- Network -- Cisco E/M setup provides 6 dB gain (by voltage). It's true even when both input gain and output attenuation "softpots" set to 0. To compensate this gain, you must issue a command on each side. For example:

Code: Select all

output attenuation 6

But!!! If you're working with codec clear-channel, input gain and output attenuation "softpots" have no any effect on channel gain/loss! Appropriate commands still can be issued, but actually they don't change anything. Port shut/no shut changes nothing. So, looks like no codec = no channel gain/loss control. And in this case, you must work with I/O ranges on Motorola side :o

This statement is true for VIC2-2EM.
I am biggest fan of XTS2500 and ASTRO Digital Saber.


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