| Q. |
Is the SETUP message sent to User B the same one that User A sent to the
network? |
| A. |
No, the SETUP message does not pass through the network. The
network generates a new SETUP message to send to the User B. It may have copied
some of the information that USER A provided. |
| Q. |
How many D channels are shown in the diagram? |
| A. |
The answer is 2. The D channel is not end-to-end. It only connects a user to the network. |
More about the incoming SETUP
The incoming SETUP that indicates that a call is available will contain the
call type (Bearer Capabilities). The called number (destination) and
calling number (origin of call) are optional and may not be supplied.
If the called (destination) number is not supplied in the SETUP message then
the implication is that the call can be answered by any device on the line.
Frequently, delivery of the calling (origin) number is an extra service from
your service provider that you have to pay for. This service is often
called CLIP (Caller Line Identification Presentation) or sometimes just CLI. See the section Managing Inbound Calls for more information on this
subject.