20-11
Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide
OL-14127-08
Chapter 20 Troubleshooting the Serial SPAs
Performing Basic Interface Troubleshooting
Ta b l e 20-5 Serial Lines: Troubleshooting Serial Line Input Errors
Input Error Type
(Field Name) Possible Problem Solution
CRC errors
(CRC)
CRC errors occur when the CRC
calculation does not pass
(indicating that data is
corrupted) for one of the
following reasons:
• The serial line is noisy.
• The serial cable is too long,
or the cable from the
CSU/DSU to the router is
not shielded.
• Serial clock transmit
external (SCTE) mode is not
enabled on the DSU.
• The CSU line clock is
incorrectly configured.
• A ones density problem has
occurred on the T1 link
(incorrect framing or coding
specification).
1. Ensure that the line is clean enough for
transmission requirements. Shield the
cable, if necessary.
2. Make sure that the cable is within the
recommended length (no more than 50 feet
[15.24 meters], or 25 feet [7.62 meters] for
a T1 link).
3. Ensure that all devices are properly
configured for a common line clock. Set
SCTE on the local and remote DSU. If your
CSU/DSU does not support SCTE, see the
“Configuring Invert Data” section on
page 17-14 to invert the transmit clock
signal.
4. Make certain that the local and remote
CSU/DSU are configured for the same
framing and coding scheme as that used by
the leased-line or other carrier service (for
example, Extended Superframe
Format/binary eight-zero substitution
[ESF/B8ZS]).
5. Contact your leased-line or other carrier
service, and have it perform integrity tests
on the line.
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