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New Member

DID over PSTN / FXO lines

Hi,

I need PSTN connection for an office of 10 users. What are the possible options for connecting to the PSTN. I need DID for each user. I can buy a block of 20 DIDs this is not a problem. The local provider does not provide a fractional T1. Buying a full T1 is too costly and overkill for an office of 10 user. What are the solutions in this scenario? Anyone any experience with DID over PSTN / FXO? I am thinking of using 20 DIDs over 4 POTS line if there is such offering from Telco. Is this possible? anyone tried it?

Thanks,

rdianat

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Gold

Re: DID over PSTN / FXO lines

DID on BRI is supported all over the world, on the other hand if your SP says they will not, they have the last word. If you want to name someone that knows a thing or two about telephony in the USA, say AT&T.

It is also true that BRI never gained acceptance in the USA and many telco do not even know how (or do not want) to provision it.

Time to look for another SP perhaps. I think you want to avoid analog DID as much as possible, as it's archaic and limited anyway.

Last resort, get a single FXO for 911, and the rest via a reputable ITSP with all the DIDs you want.

10 REPLIES
New Member

Re: DID over PSTN / FXO lines

I have configured whats called a 'DID Trunk Group' which basically are 4 POTS lines that are either defined as incoming or outgoing only. A DID/FXS card can do this. Keep in mind that the if the DID mode is configured on the card you must use H323. No MGCP.

We setup the group as incoming only, and then made our employees just dial all of their outgoing calls as long distance and sent them out a PRI at another office. A regular FXO card could be used to send out the outgoing calls via POTS, but no outgoing masking would happen as a result. When calling out the receipient of the call would see the number of the pots line.

New Member

Re: DID over PSTN / FXO lines

Hi Jose,

What did you order from your provider? was that "analog DID trunk" how many DIDs could you use over 4 POTS line? did you use FXO card? You have mentioned "DID/FXS" card. You meant FXO and NOT FXS. Right?

New Member

Re: DID over PSTN / FXO lines

rdianat,

In Cisco terminology a DID/FXS card is actually 2 different separate features. When the card is configured FXS(default) it connects to edge station devices. But you can configure the VIC card to connect to the telephone carrier when you have purchased a DNIS/DID service for direct inward dialing to extensions.

This is a low cost way to get direct extension dialing from the telephone carrier without purchasing a BRI/PRI ISDN circuit.

Cisco Documentation:

=============================

The 4-port FXS/DID VIC provides both FXS and DID functionality on a single VIC. You can select either FXS or DID mode on a port-by-port basis. The default mode is FXS.

An FXS voice port connects directly to a standard telephone, fax machine, private branch exchange (PBX), or a similar device; the voice port supplies ring, voltage, and dial tone to the station only in loop-start signaling mode.

DID is a service offered by telephone companies that enable callers to dial directly to an extension on a PBX without the assistance of an operator or automated call attendant. This service makes use of DID trunks, which forward only the last three to five digits of a phone number to the PBX. If, for example, a company has a PBX with extensions 555-1000 to 555-1999, and a caller dials 555-1234, the local central office (CO) forwards 234 to the PBX. The PBX then rings extension 234. This entire process is transparent to the caller. In DID mode, a voice-enabled Cisco router can receive calls from a DID trunk and connect the caller to the appropriate extension. Outgoing calls are not allowed on DID voice ports. If an outgoing call is attempted, the caller will get a fast busy signal. Dial tone is not present on DID voice ports.

Ground-start signaling does not provide a dial tone.

==========================

I hope this helps ;)

Hall of Fame Super Gold

Re: DID over PSTN / FXO lines

Ask provider for BRI, eg 2 circuits for 4 calls. That will give you all the advantafes of a digital connection, DID, CLID, and much more.

New Member

Re: DID over PSTN / FXO lines

I asked this question from provider. Provider says DIDs are not supported on BRI, and only one number per channel could be used. Are you sure DIDs are supported on BRI? Could you name the provider? Is this in USA? If I know this is something common and supported by other providers I can go back and check further.

Thanks,

Hall of Fame Super Gold

Re: DID over PSTN / FXO lines

DID on BRI is supported all over the world, on the other hand if your SP says they will not, they have the last word. If you want to name someone that knows a thing or two about telephony in the USA, say AT&T.

It is also true that BRI never gained acceptance in the USA and many telco do not even know how (or do not want) to provision it.

Time to look for another SP perhaps. I think you want to avoid analog DID as much as possible, as it's archaic and limited anyway.

Last resort, get a single FXO for 911, and the rest via a reputable ITSP with all the DIDs you want.

New Member

Re: DID over PSTN / FXO lines

Thanks all Jose, Robert and bevilacqua for your responses. I think I am now clear about the options. I will first try BRI and then DID trunk group depending on the price and the feature. I also agree that one should stay away from analog trunks, but this depends on the budget too. The reason I don't like to go with ITSP, is that it limits my control and I am not sure about reliability, however the ITSP option is great as a backup solution.

Thanks,

rdianat

New Member

Re: DID over PSTN / FXO lines

FYI.

Per AT&T DID is NOT supported on BRI. This is San Francisco, CA.

New Member

Re: DID over PSTN / FXO lines

Yah that's my experience too; no DIDs riding on BRI from AT&T in California. However the analog DID trunk business, althogh very much possible, still sucks because those DID trunks CAN NOT be used for outgoing calls.

The analog trunk hooks into an FXS card and the router provides battery to the CO - totally backwards to what one would expect from an analog POTS. That's why Cisco says never to connect an FXS port to a CO POTS - both provide battery and something will fry.

Anyway back onto the AT&T discussion for California: This is Legacy-S territory, is there NOT a cheaper way to get DIDs going other than of course ordering a full PRI?

For small site deployment this lack of intermediate service just pisses me off. I hate the SIP possibility always being offered; just IMHO of course. It does work I am sure.

~B

Hall of Fame Super Gold

DID over PSTN / FXO lines

Yes, it does. So having feelings to it is purely subjective.

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