Document when "D-Chan RX Bad checksum" is not a problem.

Merged revisions 4109 via svnmerge from 
http://svn.digium.com/svn/zaptel/branches/1.2


git-svn-id: http://svn.digium.com/svn/zaptel/branches/1.4@4110 5390a7c7-147a-4af0-8ec9-7488f05a26cb

1 files changed, 29 insertions, 0 deletions

diff --git a/kernel/xpp/README.Astribank b/kernel/xpp/README.Astribank
index e3c6070..37af95b 100644
--- a/kernel/xpp/README.Astribank
+++ b/kernel/xpp/README.Astribank
@@ -559,6 +559,35 @@ This is a normal part of the shutdown of the USB connection.
 Ignore them. Unless the USB should not have disconnected at that time.
 
 
+BRI Layer 1 Down
+^^^^^^^^^^^^^^^^
+.Symptoms:
+With the BRI module only, and not in the middle of an active call, you
+notice that suddenly the line goes down. The LED of the port stops
+blinking, layer1 not listed as "active" in the bri_info file in
+/proc/xpp, and the span is in RED alarm in Zaptel.
+
+You may also see an error message such as:
+
+  NOTICE-xpd_bri: XBUS-00/XPD-02: D-Chan RX Bad checksum: [2A:01=FC] (252)
+
+from the exact time of the disconnecting.
+
+.Cause:
+This is expected with most european BRI PtMP providers. If they support
+PtMP, they are normally also expected to support ISDN phones, that get
+the power from the provider. And thus they shut down the line whenever
+there's no active call. 
+
+Sometimes the line is shut down in the middle of a layer 2 message. In
+the BRI driver the HDLC decoding/encoding is done in the card. In that
+case we may get the above error.
+
+.Fix:
+Normaly this is not a problem. The driver will re-establish a connection
+once a new call needs to be made.
+
+
 Reference
 ---------
 LEDs Indication