Description:

This document uses an example trace to document the full processing of an inbound telephone call from call set-up to call termination.

In the interests of readability, the trace has been shortened to a few relevant sections. Traces usually contain some components that have to be skipped as they are not relevant to the analysis.


Scenario:



Trace-Analyse:

1) The provider sends an  INVITE  packet to the LANCOM router.

You can find for the  INVITE  packet in the trace by searching for the character string  INVITE sip . The  INVITE  packet is a part of the  SIP-Packet  trace.

The following important parameters are included in the  INVITE :

2) The number in the  To  field (+49240512345) is replaced by the Internal dest. number in the corresponding SIP line (see Scenario).

3) The router sends the message  100 Trying  to the provider to signal that the call is being forwarded. This is an  outbound packet  ( Sending datagram ).

4) The target number 12345 (see  step 2 ) passes through the Call Routing table. The phone number does not match any call route, so the number is forwarded to the user table, where a match to an ISDN user is found (see  scenario).

For more information on the Call routing table, see  this knowledge base article .

5) The LANCOM router sends a  SETUP  to the ISDN telephone. The  SETUP  indicates the establishment of the ISDN connection.

You can identify this packet precisely by searching the trace for  SETUP . The  SETUP  packet is a part of the  D-channel-dump  trace.

The following important parameters are included in the  SETUP :

6) The ISDN telephone sends the message  CALL PROCEEDING  to signal that the call is ongoing and then that the ISDN telephone is ringing ( ALERTING ). Each of these are inbound packets ( RX ).

7) The router sends the message  180 Ringing  to the SIP provider. This means that the target subscriber’s phone is ringing (see  ALERTING  in  step 6 ).

8) The ISDN telephone sends the message  CONNECT  to inform the router that the call is connected.

9) The router confirms the  CONNECT  with the message  CONNECT ACKNOWLEDGE .

10) The router sends the message  200 OK  to the SIP provider to signal that everything is OK and transmission can begin.

11) The SIP provider confirms the  200 OK  message with the message  ACK.

12) The ISDN telephone ends the call and sends the message  DISCONNECT  to the router.

13) The router ends the call in the direction of the provider with the message  BYE .

14) The router terminates the ISDN connection to the ISDN telephone and releases the ISDN channel ( RELEASE ).

15) The ISDN telephone confirms the release of the ISDN channel with the message  RELEASE COMPLETE .

16) The SIP provider confirms that the call has been ended with the message  200 OK .