Astro Modem over IP

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Lotus54
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Astro Modem over IP

Post by Lotus54 »

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

Post by d119 »

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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Re: Astro Modem over IP

Post by Lotus54 »

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

Post by d119 »

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

Post by Lotus54 »

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

Post by 515 »

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

Post by Lotus54 »

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

Post by kossuth »

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

Post by 515 »

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

Post by chartofmaryland »

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
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Re: Astro Modem over IP

Post by MotoFAN »

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

Post by MotoFAN »

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.
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MotoFAN
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Re: Astro Modem over IP

Post by MotoFAN »

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.
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MotoFAN
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Re: Astro Modem over IP

Post by MotoFAN »

Hi gius!

Can't explaing this, but analog portion of hybrid link fails or can't be established when g711ulaw is used. Link come up and stay reliable when you issue these commands:

Code: Select all

dial-peer voice xxx voip
codec clear-channel
voice-port x/y/z
shut
no shut
On the both routers.

When analog link fails due to G711 usage, station still can be keyed via V.24, but in Analog mode you hear nothing or not loud noise. So, analog voice is not going horough network. Analog voice might appear for some short periods of time, but quickly disappears for long periods of time.

Who can explain this???
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alex
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Re: Astro Modem over IP

Post by alex »

Easy: It's the Codec. Just like P25 is optimized for voice, so is G711ULAW. This is the same reason why when you buy Vonage or some other cirucits that are voice over IP they charge "extra" for Fax. It's a different codec which has a "cost" tied to it in the form of bandwidth.

Two pieces:

1) Think of an audio wave form and then take a 2" pipe and place the middle on center of the waveform. That's G711ULAW. It basically chops whatever falls outside of that 2" pipe range and shoots everything in the middle down the pipe. Voice range and most sound is well reproduced in this example because the 2" pipe covers the frequency range nicely. You take a modem that wants a 3" pipe and makes noises that are outside of what we humans would normally hear or be able to understand as sound and it basically cuts off some of the top end.

2) The other issue is going to be delay. G711ULAW takes time to compress/decompress voice. It might be milliseconds, but, it still takes time. That might knock the modems off course just enough where someone is sending when they expect to be receiving. I believe I read a document on Cisco's site that it takes roughly 200ms. From friends who make this stuff work everyday on other circuits they say the maximum that an AstroTac wants to see is roughly 100ms at the most. So you could be making it work, but, the delay can't be understood by the comparator.

Ok - Maybe 3rd point - G711ULAW and Modems should never be used with "VAD" (aka VOX) because that also introduces delay in detection and would chop off bits of audio (potentially).

Clear Channel must do something much more efficient and allow that full amount of data go point to point with very little interference from the router compressing/decompressing the sound. It's also likely more bandwidth intensive and maybe doesn't support VAD.

Alex
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MotoFAN
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Re: Astro Modem over IP

Post by MotoFAN »

Hi Alex!

Thanks for detailed response. All things are pretty clear, but I still can't explain how it works for others. Because a lot of Cisco samples shows G711 - this is the most interesting thing for now. I am intended to leave clear-channel anyway, but just interested.

About delay. This is definitely not the case, because I still run in LAN. 1 ms delay or something.

VAD might be the point, but actually is not. I tried "no vad" elsewhere, including dial peers and voice ports, but nothing (of course I shut down and unshut all ports after applying these parameters). Analog link might have lit, but voice not passing. Or links is not lit, but voice is passing for some periods of time.

Looks like clear-channel is only good option here.
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alex
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Re: Astro Modem over IP

Post by alex »

You do need to have no vad on both the dial peer and the voice-port configuration. The shut/no shut is good after any chance to a voice-port or dial peer setting. I don't have a good answer on why it works in some cases and not in others. I know I had tried it a while ago and it would sync up for a minute and then it would go out of sync just as quick with G711. I think the spec was something like 300-3000hz, and a astro modem needs up to 3400 hz to work properly (?).

There's also some settings which might be done automatically - like a dynamic jitter buffer for example - which also can impact timing and maybe the bit order where the modem would freak out but your ear will not.

I think I have mentioned in the past making sure the routers are running the IDENTICAL IOS makes a HUGE difference in issues as well. Even a simple version point might contain a bug fix you or I would never know existed.

This is why newer hardware with support contracts with Cisco is always a good idea for public safety grade circuits (goofing around - who cares) so you can always call up Cisco TAC and ask them why this not that. They have the debugging tools to figure out the why and tell you.
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Re: Astro Modem over IP

Post by MotoFAN »

Hi Alex!

Thanks for answer.

Now I am not run Astro 9600 modem, I run V.24 Hybrid. In case of modem I totally understand why it fails, because it's a modem and it can be very sensitive to signal form, etc. Because it's designed for copper dedicated lines, but not for DAC/ADC over IP channels. But in case of Analog link it looks a bit strange for me.

And of course I run absolutely identical hardware and software at the both ends. 2811 with c2800nm-adventerprisek9-mz.151-4.M12a.bin, the same voice cards and the same cables. And similar configs. And I do all changes at the both ends to keep them identical.

Cisco TAC can be helpful, but not always. Also, they need valid subscription for their support services. Once they allowed me to create a case, but it was an exception (something like trial). My hardware is second hand and they are asked me to talk with partner who sold it to me. But nobody know who is that's partner. Due to ham nature of my experiments, I can’t buy brands new Cisco hardware with premium support services.

Thanks anyway.
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Re: Astro Modem over IP

Post by alex »

Ah ok, So your having issue with the Hybrid link remaining stable, not, an astro modem (which explains my confusion - the topic was Astro Modem over IP...). Hybrid isn't something I have played with so I'm not sure what direction to tell you to go in to attempt a fix.

Alex
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chartofmaryland
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Re: Astro Modem over IP

Post by chartofmaryland »

Evening Motofan,

FWIW the Astro modem is voice band sensitive which means if there is poor frequency roll off in the audio link, the modems will constantly re-train

I have been able to get Astro Modem to work across JPS NXU-2 boxes but it took some work to flatten the voice band response

If you have a set of TIMS and or a signal generator for 300hz to 3800hz and an oscilloscope you can measure the audio bandwidth of your E+M cisco circuit you will want to check the 300 to 3.8k is about flat at a -10 signal level

More you can try if latency and jitter have already been ruled out

CoM
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Re: Astro Modem over IP

Post by MotoFAN »

Hi Alex!

Yes, sorry for confusion. I asked about hybrid link in the old thread, because I shared codec feedback here recently. Same issue for both kinds of link, Hybrid and Astro Modem 9600. Solution is the same, to turn off any codec and use clear-channel. One more advantage of clear-channel is transparent pass of voltage levels. If you supplied 200 mV at local Cisco, you will get 200 mV +-5% at Cisco at remote end. And if you supplied 500 mV at remote end, and you will get 500 mV locally +-5%. So they act like physical copper wire (excluding the delay).
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Re: Astro Modem over IP

Post by MotoFAN »

chartofmaryland wrote:Evening Motofan
Hi there!
FWIW the Astro modem is voice band sensitive which means if there is poor frequency roll off in the audio link, the modems will constantly re-train

I have been able to get Astro Modem to work across JPS NXU-2 boxes but it took some work to flatten the voice band response

If you have a set of TIMS and or a signal generator for 300hz to 3800hz and an oscilloscope you can measure the audio bandwidth of your E+M cisco circuit you will want to check the 300 to 3.8k is about flat at a -10 signal level

More you can try if latency and jitter have already been ruled out
I got working Astro Modem over IP as was stated above. But now I moved off Astro Modems, because they are not compatible with G8000 series.
I am biggest fan of XTS2500 and ASTRO Digital Saber.
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