martinyoung

You only get an Interworking Message option with ISDN PRI T1s.

Out of curiousity (and I had some time to kill), I checked all the T1s in all six switches that I deal with today. They are all across the country from Oahu to Norfolk, and all 346 T1s are PROGress. There is obviously a reason to change it because you get the option to do so. But I do not recall ever changing one from PROGress.

So, yes, I do look at your one odd one with one eyebrow raised.

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Marty
Retired Avaya DSIC tech

oozenoz

This is because ISDN is the only north america protocol that supports transmitting this infromation from the premise equipment to the network. If a call is delivered over E&M trunks, the inbound call is considered answered (from the network side) as soon as the trunk seizure completes, independent of whether it is transferred externally or answered by a switchboard operator.

The option exists to allow forced answer supervision on the network trunks when interworking is at play, and the answer supervision on the tandem call is going to take longer than the duration of the T303 timer on the network switch (times 2). There is nothing wrong with this, but it nails up the call on the network side and opens the speech path from the originating party to the premise switch. Completion of the voice path end-to-end will not occur until the premise switch considers the tandem call is delivered and answered. If the call does not finally complete, network resources have been utilized unnecessarily.

The premise switch has the duration of the network switch's T303 timer (twice) to respond with either a CALL PROCEEDING, ALERTING, or CONNECT message - regardless of whether a PROGRESS message is sent; the purpose of the message is not to delay answer supervision, but to announce to the network that interworking is occuring.

In cases where calls are being delivered directly to stations (or an ACD system, modem pool, voice mail, etc.) the immediate response will be either an ALERTING or CONNECT message (depending on the device at the destination and whether auto-answer is turned on). So unless there are calls being rerouted, the default of PROGress for Interworking Message on the DS1 is never going to have any effect. In cases where calls are being rerouted and the premise switch considers that as interworking, as long as the calls are answered before the second expiration of T303, the use of PROGress will result in interworking being announced back to the SS7 network, and the voice path will not be opened until the call completes.

In your original configuration the calls are being dropped due to the length of time it takes for the tandem call to complete. You may actually have a problem with that transfer, but we have been so involved in looking at the network switch, AT&T, the programming, etc. that we've completely overlooked the reason the calls are being torn down in the first place.

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- calvin

PBXtech.info

 

martinyoung

I printed your response in case I ever encounter this situation.

You obviously have a Central Office background, my CO experience ended early in 1971 when I stopped being a frameman and became a station installer.

I disagree that changing the Interwork Message from PROGress to Alerting should be a normal activity.

Having to make that change on one T1 out of 12, to me, falls into the same category as rolling the send and receive pair on an incoming T1 because a tech made an error in a B-box. If the cross connect eventually gets fixed, your T1 will break.

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Marty
Retired Avaya DSIC tech

oozenoz

I started out in specials, then moved to an ISDN maintenance center. (It was a lot more interesting than setting decibel levels on analogue data circuits.)

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- calvin

martinyoung

After I had been on the frame for a couple of years, they asked me if I wanted to be a switchman. I worked in a SXS office (Crossbar was the latest and greatest technology), what I saw the switchmen do all day long was sit on platforms on the rolling ladders and lube connectors all day. Occasionally an alarm would come in to break the routine.

I figured there had to be something more interesting to do than that, so I went outside. The first PBX I worked on was a 701, same technology.

As an aside, on the frame I worked the 4 to Midnight shift and New Years Eve was always interesting. We always had a bet as to how many call block indicators would light up. You have never heard a noise like a SXS office when all the connectors come up at the same time.:D

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Marty
Retired Avaya DSIC tech

oozenoz

I had an instructor back at Bell who worked as a switchman on crossbar and step by steps... he used to love to tell us about the fun he used to have scrubbing contacts. Made me really appreciate digital switch technology!

I'm in short-time mode today, I leave Friday for a much needed vacation:D .

Not having much to do beyond catching up with the latest world cup scores and reading my horoscope, I did some more research and found that an interworking PROGRESS message is intended to tell the network to complete the voice path back to the originating caller, to allow inband messaging (such as ringback or busy) on the non-ISDN (interworking) path to be heard.

Apologies for that innacuracy.:shame:

__________________
- calvin

PBXtech.info

 

martinyoung

Enjoy your vacation.:D :D

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Marty
Retired Avaya DSIC tech