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

ISDN Loopback Test Call
- In a loopback call, a router dials the ISDN number of its own BRI. The call is proceed to the
ISDN switch, which then being switched to the 2nd BRI channel. The call is seen by the router as
an incoming call on the 2nd channel. Therefore, the router both sends and receives an ISDN call
on different B channels and act as both the called and calling routers.
- Loopback call tests the ability of a router to initiate and accept ISDN calls. It can also provide an
indication that the physical links to the ISDN switch along with the ISDN switch are functioning.
Q.931 ISDN Layer 3 Disconnect Cause Codes
- This section explains how to interpret the ISDN disconnect cause codes which appear in the
output of the debug isdn q931 privileged command to indicate the reason for ISDN call
disconnection or failure.
- The ISDN Layer 3 disconnect cause code the has the following format:
Cause i = 0xAABBCC - reason.
AA Cause Code Origination Point
BB Disconnect Cause Code
CC Optional Diagnostics Field
- Below lists all the Cause Code Origination Points:
80 Router
81 Private network near the local router (possibly a local private branch exchange – PBX)
82 Public network near the local router (local Telco switch)
83 Transit network in the ISDN cloud
84 Public network near the remote router (remote Telco switch)
85 Private network near the remote router (possibly a remote private branch exchange – PBX)
87 International network
8A Network beyond the internetworking point
- Below lists all the standard ITU-T Q.931 Disconnect Cause Codes:
80 Normal Disconnect. The ISDN call disconnects normally.
81 Unallocated or unassigned number. The ISDN switch receives the ISDN number in the
correct format. However, the number is not in the ISDN switch’s routing table or it has no
path across the ISDN network. Check the routing table to see whether the number is
available; and check the correct digits were dialed and it is a valid number.
82 No route to specified transit network. The ISDN switch receives a request to route the call
through an unrecognized intermediate (or transit) network – the ISDN switch has no route to
the transit network. This problem can be due to either the transit network does not exist, or
the transit network exists but does not serve the ISDN switch. This cause is supported on a
network-dependent basis.
83 No route to destination. The dialed number is in the ISDN switch’s routing plan, but ehre
is no physical route to the destination and hence the called party is not reachable. This
problem can be due to either the D channel is down at either end, or the span or WAN is not
connected correctly. This cause is supported on a network-dependent basis.
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com