System information

Troubleshooting Serial Line Problems 15-321
Serial Lines: Troubleshooting Serial Line Input Errors
Framing errors
(frame)
A framing error occurs
when a packet does
not end on an 8-bit
byte boundary for one
of the following reasons:
• Noisy serial line
• Improperly designed
cable; serial cable is too
long; the cable from
the CSU or DSU to the
router is not shielded
• SCTE mode is not enabled
on the DSU; the CSU line
clock is incorrectly
configured; one of the
clocks is configured for
local clocking
• Ones density problem
on T1 link (incorrect
framing or coding
specification)
Step 1 Ensure that the line is clean enough for
transmission requirements. Shield the
cable if necessary. Make certain you are
using the correct cable.
Step 2 Make sure the cable is within the
recommended length (no more than
50 feet [15.24 meters], or 25 feet [7.62
meters] for T1 link)
Step 3 Ensure that all devices are properly
configured to use a common line clock.
Set SCTE on the local and remote DSU.
If your CSU/DSU does not support
SCTE, see the section “Inverting the
Transmit Clock” later in this chapter.
Step 4 Make certain that the local and remote
CSU/DSU is configured for the same
framing and coding scheme as that used
by the leased-line or other carrier
service (for example, ESF
1
/B8ZS
2
).
Step 5 Contact your leased-line or other carrier
service and have it perform integrity
tests on the line.
Aborted transmission
(abort)
Aborts indicate an illegal sequence
of one bits (more than seven in a
row)
The following are possible reasons
for this to occur:
• SCTE mode is not enabled on
DSU
• CSU line clock is incorrectly
configured
• Serial cable is too long or cable
from the CSU or DSU to the
router is not shielded
• Ones density problem on T1 link
(incorrect framing or coding
specification)
• Packet terminated in middle of
transmission (typical cause is an
interface reset or a framing error)
• Hardware problem—bad circuit,
bad CSU/DSU, or bad sending
interface on remote router
Step 1 Ensure that all devices are properly
configured to use a common line clock.
Set SCTE on the local and remote DSU.
If your CSU/DSU does not support
SCTE, see the section “Inverting the
Transmit Clock” later in this chapter.
Step 2 Shield the cable if necessary. Make
certain the cable is within the
recommended length
(no more than 50 feet [15.24 meters], or
25 feet [7.62 meters] for T1 link).
Ensure that all connections are good.
Step 3 Check the hardware at both ends of the
link. Swap faulty equipment as
necessary.
Step 4 Lower data rates and determine whether
aborts decrease.
Step 5 Use local and remote loopback tests to
determine where aborts are occurring
(see the section “Special Serial Line
Tests” later in this chapter).
Step 6 Contact your leased-line or other carrier
service and have it perform integrity
tests on the line.
1 ESF = Extended Superframe Format
2 B8ZS = binary eight-zero substitution
Input Error Type
(Field Name) Possible Problem Solution