Help with concurrent calls

Hi there,

I wonder if someone can tell me how conncurrent calls work with asterisk?

What I would like to know is if I connected my telephone line to an analogue card on asterisk then how many external calls could made at the same time.

Also would this then effect other people calling in?

Much appreiciated!


That is true whether or not you have a PABX.

EDIT - Sorry I didnt see the “1” :/.

So what would be the best way to have multiple calls in/out without using a VOIP provider? Multiple analogue lines?

This has already been answered within the last few days, although it may have been on the wrong forum.

The answer depends on your exact requirements. Most medium to large businesses will use digital (ISDN) trunks to their PSTN operator. I think you can safely say that all ITSPs do that for their network side interface.

I just joined this site today so I do apologise for my stupidity :smiley:

Basically it is a small business with only 3 - 5 people using the phones. The line is provided by BT which I am assuming is ISDN (Phone and ADSL). They won’t all be calling/receiving calls at the same time but it would be nice to be able to have atleast 2 concurrent calls: 1 incoming + 1 outgoing or 2 outgoing or 2 incoming.

Would I require 2 lines from BT to acheive this?

This needs not to be correct - especially if You know, that BT is using ANNEX A for ADSL which means ADSL over POTS.
However, You should check Your requireements with BT: One thing is the amount of channels (and the technology used) and the other thing is the amount of callnumbers/extensions BT assigns to You (I don’t know if You’ll have the need to distinguish incoming calls by different incoming extensions).

After all I would suggest to require a single BRI (ISDN Basic Rate Interface with two B-channels allowing 2 concurrent calls) from BT (

Ok so I would need to talk to BT and see if I can get a BRI ISDN line with 2 links.

Is this the only way to have multiple calls other than VOIP?

No, alternatively You may use more than one analog (POTS) line. But: usually You’ll have different phone numbers on these different lines. This will lead to a situation where You have two lines (with the possibility of two concurrent calls) but: If You talk (in- or outbound) on one line the callnumber, associated to this specific line will signal a busy to an additional caller from outside. Thus the caller needs to try the other number to get through …

That’s why ISDN is easier to operate: Even if BT assigns more than one number to the two channels evry single number may use both channels so all numbers are busy (if both channels have active calls) or no one (if at least one channeel is free).

ADSL, by its very nature, is only ever provided over copper pairs. Although those can be used for basic rate ISDN, it think it unlikely that it would co-exist with ADSL, so I think it rather unlikely that you currently have ISDN. Basic rate ISDN is now even more of a legacy product than analogue lines, as its main users now use ADSL.

Although I’m not that familiar with BT low end business products, I would hope you can still get analogue lines as hunt groups, so that they share a single directory number. I don’t know if they will allow ADSL over one member of a hunt group.

ADSL - when provided with either Annex-B or Annex-J is typically combined with ISDN (but could also be combined with POTS) as it is typically installed in Germany or Luxembourg.
ADSL provided as Annex-A (like in UK) is typically combined with analog POTS but may be combined with ISDN (typically in installations in Austria or Switzerland).
In all these countries we still have copper-pairs which provide ADSL (or even SDSL) and ISDN or analog services over the same (copper) cable by diverting/splitting the frequency bands.