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Packet Loss Occurred Due to Impedance Mismatch

Publication Date:  2013-09-22 Views:  58 Downloads:  0
Issue Description
Two routers connected to each other through E1 lines provided by E1-F modules. The packet loss rate in ping tests was 30%.
Handling Process

To address the issue, Huawei performed the following operations and observed the following information:

1. Verified that the two routers used the framed mode.

2. Verified that the two routers were enabled with no crc-4.

3. Verified that the transmission side provided clocks.

4. Verified that the two routers used the consistent E1 line and timeslot.

5. Checked cables.
The routers used 120-ohm cables but the E1-F module impedance was 75 ohms.

6. Replaced the 120-ohm cable with a75-ohm cable.
No packet loss occurred.
Root Cause
The impedance of cables did not match that of the E1-F module.
Solution
120-ohm cables were replaced by 75-ohm cables.
Suggestions

To diagnose a problem related to packet loss on E1 lines or the link layer down, perform the following operations:

1. Check whether the farming modes are consistent at the local and remote ends. By default, Huawei E1-F modules work in framed mode.

2. Check whether CRC-4 is consistently configured at the local and remote ends.

3. Check whether timeslots are consistently configured if CE1 mode is used.

4. Check whether the transmission side provides clocks. If not, configure the clock on one router as the master clock to provide a clock for the line.

5. Check whether impedance of cables and modules match.

END