overlap receiving in Q.931 1

[Ihjaz]

Hi All,
I have this question...ITU-T's Q.931 recommendation says

Overlap Receiving

When a user determines that a received SETUP message contains either:
a) no called number information; or
b) incomplete called number information; or
c) called number information which the user cannot determine to be complete; and

when the user:
d) is compatible with other call characteristics (see Annex B); and
e) implements overlap receiving,
the user shall start timer T302; send a SETUP ACKNOWLEDGE message to the network and enter the Overlap receiving state.

Taking case a) no called number information how does the SETUP message gets routed to called user if there is no number.

Thanks

 

[ISDNman]

The digits are each sent in additional INFO messages. This is more complex, but after the call setup is received with no, or only some, digits dial tone is returned.

With "Enbloc" they are sent (literally in french" en bloque or as a block.

 

[Ihjaz]

Thanks ISDNman,

But my question is called user returns SETUP ACKNOWlEDGE when SETUP contains no or some number..but how does the SETUP message reach the called user when there is no number for the network to route the SETUP message.

Hope you got my question.

Eagerly wiating for your reply.

 

[ISDNman]

Got it.

ISDN messaging is between the Terminal and the local switch.

ISDN signaling is not end-to-end per se, since it is SS7 in the middle.

In this case, the local switch does not send a SETUP to the far end until it has collected all digits. Just like a pots call where there is a digit collection interval and there is no call setup on the SS7 network until all digits are collected.

I hope this helps

 

[Ihjaz]

Thanks again.

Let me see whether I have got it right.....is it that the numbers are collected at the local switch and routed to the destination network.....and then the destination network sends a SETUP message to the called user which,gets the ACK and then sends the remaining INFORMATION messages.

Please correct me if am wrong.

 

[ISDNman]

Originating device sends SETUP to local switch

Originating switch waits for digits (and based on a timer or a timer plus pre-translation determines when to stop collecting digits)

Originating Switch determines a network route sends an SS7 message to terminating switch with the route and terminating phone number.

OR

If there is no route the originating switch ends the call with an appropriate cause code.

Originating Switch sends PROCeeding to Originating device.

If the terminating line is POTS, the terminating switch applies ringing and sends back an ALERTing to the Originating switch.

OR

If terminating device is ISDN, the terminating switch sends an SETUP to the terminating device. Terminating device replies with ALERTing. Terminating switch sends the ALERTing message to the originating switche which sends an ALERTing message to the originating device.

To summarize, the ISDN messages per se don't travel over the SS7 network. Each ISDN device talks to its local switch. Each local switch talks to the local device as appropriate based on the local protocol (POTS, ISDN of various flavors, etc etc)

I hope this helps. What are you working on?

 

[Ihjaz]

Thanks ISDNman it was really helpful.

You said If terminating device is ISDN, the terminating switch sends an SETUP to the terminating device. Terminating device replies with ALERTing. Terminating switch sends the ALERTing message to the originating switche which sends an ALERTing message to the originating device.

But in the case of overlap I beleive Terminating switch sends a SETUP to the Terminating device,gets a SETUP ACK from device and then sends the numbers in the following INFORMATION messages...and once all info has been attained by the terminating device it sends the ALERT message to the terminating switch which inturn sends it to the originating switch and then to the originatin device.

What are you working on?

My current project is to implement overlap send/receive in ISDN.

 

[ISDNman]

Ihjaz

As far as I am aware, there is no overlap receiving by an ISDN terminal. As you correctly wonder, how could this be possible?

Yes, the originating CO Switch has to deal with overlap receiving, but it never sends the SETUP to the destination switch until it has collected all the digits.

So, from the originating switch it looks like

On ISDN Orig side it gets

Setup + Info (digits)

On the SS7 it sends

SS7 en bloc call setup to terminating switch

This is the same as POTS. There is no SS7 activity until all digits have been collected.

So, if you are working on a terminal you have only have the work to do! If you are on a PBX, then you have half your work to do on the LT side (overlap receive) and half you work to do on the NT side (overlap send).

best of luck.

 

[ISDNman]

I hope this helped. Best of luck on your software.