3.The cable connecting the router to the ISDN network or NTI is faulty. Try a different cable.
4.There is a fault in the ISDN network or the NT1.
If options 1, 2 and 3 do not show any faults on the router, then contact your ISDN network provider and see if they can find the fault on their network.
Step 2: Is the router communicating with the ISDN network at the LAPD level?
Once the router has established a signalling connection with the network, it starts sending LAPD packets. LAPD (Link Access Protocol - D channel) is a protocol whereby the router establishes a logical connection with the ISDN switch. It is via this protocol that the router informs the switch of its presence, and the switch allocates the router a connection ID. An LAPD connection has to be established before the router can make or receive ISDN calls.
To see if an LAPD connection has been established, use the command:
show lapd=n
where n is the number of the BRI interface under consideration. Interfaces are numbered from 0.
The output of this command will be as shown in the following figure.
Interfaces: |
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ISDN | Type | TEI Mode | Debug | TEI |
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BRI0 | TE | automatic | off | 064 |
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SAPs: |
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ISDN | SAPI | T200 | T201 | T202 | T203 N200 N201 | N202 k |
BRI0 | 063 | 000010 | 000010 | 000020 000100 000003 | 000260 | 000003 | 001 |
000000010 000010 000020 000100 000003 000260 000003 001
DLCs:
ISDN SAPI CES TEI State V(S) V(A) rxN(S) V(R) rxN(R)
BRI0 063 | 000 | 127 | bcast | - | - | - | - | - |
000 | 000 | 127 | bcast | - | - | - | - | - |
| 001 | 064 | ALIVE | 0000 | 0000 | 0000 | 0000 | 0000 |
The most important item to look at in this output table is the very last line. If an LAPD connection has been established, then the entry in the State column in this line will be ALIVE. If the connection has not been established, the state will be DEAD.
If the LAPD is alive, then the problem lies at a higher layer. Go to "Step 3: Are ISDN calls connecting successfully?" on page 5.
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