Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 9 Troubleshooting Cisco Media Gateways
Troubleshooting the Gateways
deldchan Command Fails
The deldchan command deletes the specified D-channel. This command could fail if:
1. Specified D-channel is not added.
2. Specified parameters are out of range/illegal.
3. Logical slot specified in the command is not ACTIVE.
D-Channel Is Down
The lsdlsapstatus command displays the DLSAP status. If the status displays dataXfer, the D-channel
is up and is ready to send and receive Q.931 PRI messages. Any other state indicates the D-channel is
down. The reasons the D-channel could be down include:
1. The soft switch has not “ESTABLISH”ed the D-channel.
The D-channels on MGX8260 are controlled by the soft switch. Once the D-channels are added, the
soft-switch needs to send a backhaul ESTABLISH_REQ channel message on each D-channel
configured on the MGX before using it for transferring Q.931 PRI signalling messages. Until
MGX8260 receives a backhaul ESTABLISH_REQ message, the D-channel MAC layer is shut to
prevent peer from setting up the D-channel. Once soft-switch attempts to setup D-channel, the MAC
is opened to send and receive SABME and UA messages.
2. The remote side is not up.
When soft switch issues an ESTABLISH_REQ messages on a D-channel which is not in “dataXfer”
state,
LAPD sends out a Q.921 SABME message on D-channel. To setup the D-channel to “dataXfer”
state, the remote side should respond back with a Q.921 UA message on the same channel. The
initiating end retries by sending SABME few more times (default of 3) periodically (default is every
second) and if it does not get a response, LAPD sends backhaul RELEASE_IND message to
soft-switch indicating that LAPD can not setup the D-channel.
3. TEI mismatch.
If LAPD is receiving ESTABLISH_REQ messages and the remote side is also up, one possible
reason why the remote side is not responding to SABMEs is that the remote sideis getting SABMEs
on the wrong SAPI/TEI. The MGX8260 always uses SAPI 0. The TEI is user-configurable and
should match on both ends. It is the last parameter dlsapNumTEI in the DLSAP profile configuration
on the MGX8260.
4. User-Network mismatch.
Another possible reason for failing to establish a D-channel is when both the sides are either
configured as User or both sides are configured as Network. Each message carries a C/R
(command/response) field. User and Network devices use this field differently, so if the remote side
is a Network device and it receives messages from a Network device, it drops all messages.
Similarly, if the remote side is a User device and it receives messages from a User device, it drops
all messages.
To fix this, change one of the end-points. The User/Network configuration is part of the MACSAP
profile on MGX8260.