DTMF Receivers, CT1 and PRI

[KrisBoutilier]

I have a MICS 4.1 with one T1, one 6 port fiber (non-combo) and one services cartridge in the KSU. There are also two LS/DS cartridges in the system, one in the KSU and one in a M12x0 cabinet.

The T1 is running as 24 E&M wink tie lines to another pbx, the KSU is driving 64 stations and the system was cold-started with the DID template. I have four digit DNs.

Occasionally during heavy traffic I'm getting alarm 63 (no more DTMF receivers). I understand the DTMF receivers to be dynamically allocated from a resource pool on the services cartridge and that this alarm means there are more requests than resources. I also understand that I can increase the resource pool by upgrading the non-combo fiber card to a combo model which will work in addition to the existing services cartridge.

The questions are:

- Are the LS trunk cartridges contributing to the DTMF resource pool for the T1 at the moment - if I remove them will I exacerbate my problem?

- Exactly how many receivers are there on the services cartridge? I need to know my what my concurrent incoming DID call limit is with this arrangement.

- If I switch to PRI, then all DID signalling is out of band on the D channel. Am I correct that DTMF receivers would only be allocated for DISA calls once PRI is in service?

Thanks for any input.

Kris Boutilier
Information Systems Coordinator
Sunshine Coast Regional District

 

[BagsNYC]

Your call traffic dictates your need for services. Change to Combo card to add additional receivers.

 

[KrisBoutilier]

Ahhh... but what is the provisioning ratio? All the Norstar Handbook says on the topic is:

Provides the clocking service necessary for digital networks. ... One services cartridge supports all clocking required, regardless of the number or mixture of DTIs and/or ISDN-BRI Interface cartridges.

and Googling on the topic hasn't produced anything more quantitative except to indicate that there is also a DTMF receiver resource pool on the card.

Put another way, if I wanted to be able to handle 24 concurrent inbound DID starts over CT1, exactly what hardware would I need with MICS 4.1? If I did the same thing with PRI instead of CT1, would I need the same hardware?

I don't want to be in the position where I end up adding add another DTI card and have a 48 line system that can only handle, say, 12 concurrent DID starts.

tks.
k.

 

[KrisBoutilier]

To answer part of my own question:

Once you move to PRI then the DTMF resource pool is only used for interpreting DTMF passed after a call has been established to, say, the DISA or Auto Answer DNs.

 

[KrisBoutilier]

And to answer the rest (taken from

http://www.tek-tips.com/viewthread.cfm?qid=918266):

"In a fully expanded system using 72 digital channels, consider installing two service cartridges to prevent blocking of incoming calls due to lack of DTMF resources, as there are only four DTMF tone receivers per cartridge."

So with 24 E&M trunks on a RBS T1 (all Auto Answer) you're limited to 4 concurrent call starts with one Services Cartridge. 5 or more will cause alarm 63 on the overflow trunks and those calls will be disconnected/dropped.

I would guess the Combo card has the same size resource pool.

 

[rconn]

I believe (I did read this in Norstar documentation somewhere) there are 5 DTMF receivers in a combo card and if you put 2 combo cards in the cabinet then you would have 10 DTMF receivers. Further to that you can add E&M cards in a trunk module which have 2 DTMF receivers in each card.

Rob

 

[mroberts]

Okay, what??? You cannot tell me that on a full 24 channel T-1 that I can only get 4 or 5 calls at a time?? You mean that the receivers are only used during call set up and then are released to be used for the next incoming call??

Second question: Why would it be any different with a PRI? Where is the back up Nortel documentation on this?

Thanks

MRoberts

http://www.a1teletronics.com

 

[KrisBoutilier]

On the first: I don't know if the DTMF recievers are released back into the pool after the call is established or are held until the end of the call, but I can report from personal experience that with MICS v4.1, a Services Cartridge, a 6 port (non-combo) expansion card and a DTI card I was getting substantial DTMF starvation errors with 24 RBS E&M trunks which were all set to Auto Answer. I would hope that the limit is on the number of concurrent starts (ie. the resources are released after the call is signalled as 'up') however that would need someone with inside knowledge to answer.

On the second: PRI signalling uses one of the twenty four available timeslots as a data channel and all signalling is done there, using a hexidecimal data stream, rather than having to push each digit down the channel as in-band DTMF tones. Thus it doesn't need a DTMF receiver on the MICS end to translate the DTMF back into useful information. So, PRI might still break in the same way if lots of people dialed the Auto Answer or DISA DN at the same time, but it wouldn't break just because of an inrush of concurrent starts.

 

[rconn]

I will see If I can find the information next week as I am a little short of time right now. The receivers are required to handle the incoming digits to route the call to the correct set. They are then free for another call. They are not used at all for outbound. 4 or 5 receivers would likely not create much of a problem for 24 lines incoming because of the number of calls being routed at one time would not exceed the number of receivers. It may be different if it is an inbound call centre application.

The problem that Kris is having is related to having two switches tied together (MICS/PBX) With 64 stations tied to a PBX it could be problem setting up many calls at one time. It sounds like there is a lot of traffic between the two switches. Another combo card or a couple of E&M cards in the TM would likely fix his problem.

Rob

 

[jerryreeve]

MRoberts,
DTMF Receivers are only used during start of calls on incoming T1,DID,E&M, or DISA. most of these calls only use the DTMF Receiver for a second before releasing them. Disa being the most use intensive since it is waiting for manual dialing. once the number of expected digits is received the DTMF Receiver is released back to the system. a DID trunk won't give wink until a DTMF Receiver is available. (I can't find real docs for norstar but that is the way it was set up on other systems that I worked with) PRI dosen't use DTMF receivers since the info comes on the D channel.

If voting could really change things, it would be illegal.

JerryReeve
Communications Systems Int'l
com-sys.com

 

[mroberts]

Thanks Jerry!
That's the answer I was looking for..... 'preciate it.

Melissa

MRoberts

http://www.a1teletronics.com

 

[aragon]

To confirm according to Nortel docs:
5 DTMF receivers per services card.
jerryreeve is correct in his description of D channel signalling on PRI (this is done on the 24th channel and in the case of Meridian 1, one D channel can control all signalling for 16 PRI spans).
In band signalling is for the birds.

Kris you could do site to site with PRI if you enable MCDN and PRI on both switches. You will also need to upgrade to MICS 6.1 (and I suggest MICS 6.1 MR and XC if you require more than 128 stations on a local cabinet).

 

[mroberts]

Is this Nortel doc something that can forwarded to me to read over?? Also the 6 port combos are the same 5 receivers?

Thanks Guys. I've been terribly curious about this issue for some time and just haven't had time to work it out.



MRoberts

http://www.a1teletronics.com

 

[mroberts]

Hummph, answered my own question. According to the MICS 6.1 installers guide (pg196) there are only four DTMF receivers per card, be it services or 6 port combo card.

Can't believe I missed that......

MRoberts

http://www.a1teletronics.com

 

[hawks]

There are 4 receivers on the services cart not 5 according to page 196 of the 6.1 Installers Guide.

 

[aragon]

I stand corrected

 

[KrisBoutilier]

Thanks all for the good information and the followups.