CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- Below lists all the possible Q.931 messages during call establishment and termination:
Message Description
SETUP Indicates that a device would like to establish an ISDN Layer 3 call.
CALL_PROC The SETUP message is received and is being processed by the network
and/or the remote device.
ALERTING Informs the network that the router is alerting the user, which would
normally be the case for a telephone and the alert would ring the handset.
This message is normally associated with equipment using a handset, eg:
an ISDN telephone or TA and is not usually seen for data calls.
CONNECT Call is accepted.
CONNECT_ACK Connect Acknowledge. The device has received the CONNECT
message. Higher layer protocols (eg: PPP) should now begin the
negotiation process.
DISCONNECT The router initiated a DISCONNECT message, which usually indicates
that an operational ISDN call is disconnected due to some higher layer
issues (eg: DDR, PPP, etc). The 3-way Disconnect Handshake will be
accompanied by a RELEASE message, a Disconnect Cause Code, and a
RELEASE_COMP message.
RELEASE Acknowledges the DISCONNECT message and continues the circuit
termination process. The RELEASE message is sent between the
DISCONNECT and RELEASE_COMP messages.
RELEASE_COMP Release Complete. The call termination is completed. This message is
often seen during a normal call termination initiated by one of the
routers; in response to a SETUP message from the calling party when
there is a mismatch of bearer capability between the ISDN switch and the
router; or due to protocol error if the coding of the SETUP message does
not comply with the Q.931 standard or the configuration of the ISDN
switch.
- If the calling router does not send a SETUP message to the ISDN switch, the problem is likely
related to ISDN Layer 1, 2, or DDR issues, and is not ISDN Layer 3 related. Perform the
following troubleshooting tasks on the calling and called routers:
i) Verify that the ISDN switch types on both routers are configured correctly.
ii) Verify that the ISDN Layers 1 and 2 on both routers are functioning.
iii) Perform ISDN loopback test calls on both routers to verify they are able to initiate and
accept calls.
iv) Verify the ISDN network of the called side is functioning by making a test call to the
called router with a regular analog phone, in which the router should receive a SETUP
message, although the call would eventually fail as it is not an ISDN call.
v) Verify that the calling router has a route to the destination with the show ip route
EXEC command.
vi) Verify that the interesting traffic on the calling router is identified correctly.
vii) Verify that the appropriate dialer string or dialer map interface subcommand on the
calling router refers to the correct number to the called router.
viii) Check the DDR configuration and use the debug dialer privileged command to verify
that the calling router is able to initiate calls.
ix) If the called router does not send a CONNECT message, check if the call is rejected due
to the misconfiguration of the isdn caller {incoming-number} interface subcommand.
x) Contact the Telco and determine whether the long distance call service is activated.
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com