Troubleshooting E1 interface

Common E1 interface issue troubleshooting methods

Common E1 interface issue troubleshooting methods include:

·     Troubleshoot the hardware.

·     Troubleshoot the cable.

·     Troubleshoot the configuration.

·     Troubleshoot the clock.

·     Troubleshoot grounding.

·     Troubleshoot through looping.

Troubleshooting the hardware

1.     Examine the external power supply connection.

Perform an independent power supply test for the faulty device to verify that the power supply is operating correctly.

2.     Perform a local loopback test:

a.     Execute the loopback local command on the E1 interface or the fe1 loopback local command in E1-F interface view.

b.     Identify whether the interface comes up physically, and verify local loopback on the logical serial interface.

-     If local loopback succeeds, the card has no hardware issues.

-     If local loopback fails, proceed with the following steps.

3.     If local loopback succeeds after the card is installed in another slot, the device has hardware issues. In this case, proceed with the device component analysis process.

4.     Replace the card.

If local loopback succeeds after the card is replaced, the card has hardware issues. In this case, proceed with the card component analysis process.

5.     Replace the device.

If local loopback succeeds after the device is replaced, the device has hardware issues. In this case, proceed with the device component analysis process.

Troubleshooting the cable

1.     Examine the cable quality.

¡     Verify that the cable is an H3C standard cable.

¡     Replace the cable.

¡     Connect the Tx and Rx ends of the cable. Identify whether the interface can perform self loopback. If self loopback succeeds, the cable has no problems. For information about configuring self loopback, see "Troubleshooting through looping."

2.     Identify whether the cable impedance matches the interface impedance.

¡     Execute the display controller or display fe1 command to view the interface impedance.

<Sysname> display controller e1 2/3/0

E1 2/3/0

Current state: UP

Description: E1 2/3/0 Interface

Last clearing of counters: Never

Current system time:2020-01-14 15:51:05

Last time when physical state changed to up:2020-01-14 15:51:00

Last time when physical state changed to down:2020-01-14 15:50:51

Basic Configuration:

  Work mode: E1 framed, Cable type: 75 Ohm unbalanced.

¡     Replace the cable to make sure the cable impedance matches the interface impedance.

3.     Identify whether the cable length matches the configuration.

An E1 interface has a limit on the cable length. Typically, the maximum cable length cannot exceed 500 m (1640.42 ft). A longer cable indicates higher signal attenuation.

Troubleshooting the configuration

1.     Verify that the local end and peer end have the same configuration.

The configuration includes the operating mode (framed or unframed), framing format, CRC mode, coding format, line idle code, and interframe filling tags.

 

NOTE: The Cisco E1 interfaces use the CRC4 framing format by default. The H3C E1 interfaces use the no-CRC4 framing format by default. When you connect Cisco and H3C E1 interfaces, make sure they use the same framing format.

 

2.     Troubleshoot AIS alarm issues.

If the line correctly transmits all-one bit streams and the idle code is FF, AIS alarms are generated when no service data is transmitted over the line and the line transmits only all-1 idle codes.

To resolve this issue, change the interframe filling tags to 7E.

Troubleshooting the clock

1.     Select a standard clock scheme.

Depending on whether the transmission network provides a clock, an E1 interface has the following clock schemes:

¡     When the transmission network provides a clock, the transmission network provides the master clock, and both local and peer E1 interfaces use the slave clock mode.

Figure 1 Clock scheme when the transmission network provides a clock

 

¡     When the transmission network does not provide a clock, the transmission network transparently transmits packets. Set the clock mode to master on one end and slave on the other end.

Figure 2 Clock scheme when the transmission network does not provide a clock

 

2.     Measure the frequency deviation.

If the clock configuration is incorrect, frequency deviation will occur on the transmission line. The normal frequency deviation on an E1 interface is in the range of –50 ppm to +50 ppm. If the frequency deviation exceeds the range, normal packet forwarding cannot be guaranteed. The frequency deviation continues to increase over time. Accordingly, error packets will occur on the E1 interface, and finally the E1 interface will become unavailable. To restore the frequency deviation to the initial value, shut down and then bring up the interface.

Typically, you can use the ETEN meter to measure the frequency deviation of lines. Connect the ETEN meter to the Tx or Rx line of the E1 interface in serial, and measure the Tx or Rx frequency deviation of the line, respectively.

Troubleshooting grounding

Typical poor grounding and common grounding

·     The device is installed in a 19-inch rack, but the grounding cable of the device is not connected to the grounding system of the rack.

·     The device and its peer device are in the same equipment room. Both devices are grounded, but they are not commonly grounded.

Influence of poor common grounding

Poor common grounding causes different reference voltages on the two devices. As a result, the Rx/Tx and other signals are not detected on the same voltage platform. Then, the data transmitted on the local end differs from the data received on the peer end, and error packets occur. More seriously, the protocol might come up and go down. Additionally, the normal signals transmitted on the local end might fail to be detected or incorrectly detected on the peer end. As a result, alarms occur on physical links, and physical E1 interfaces come up and go down.

Grounding requirements

·     The devices must be reliably grounded.

·     If the device and its peer device are in the same equipment room, both devices must be grounded and commonly grounded.

·     Use a copper cable for grounding the device to reduce high-frequency impedance. Make sure the grounding cable is as thick and short as possible. Do not use an aluminum cable as the grounding cable.

·     Make sure both ends of the grounding cable have good electric contact and are treated with corrosion and rust protection.

·     Do not use other devices for electric contact of the grounding cable.

·     The grounding cable cannot be parallel to or twisted with signal cables.

·     Do not install connectors, on-off switches, or fuse protectors on the grounding cable.

·     Use a yellow-green plastic-insulated copper cable as the grounding cable.

·     The grounding cable cannot exceed 30 m (98.43 ft) and must be as short as possible. If the cable exceeds 30 meters, place the grounding strip nearby.

·     If an UPS is used for power supply, the UPS must also be grounded.

Reliably grounding the device is crucial to lightning, electrical shock, and EMI protection. It guarantees the long-term reliability and stable operation of the device.

Grounding the device in different environments

IMPORTANT: Method 3 is simple, but the ground resistance might be very high. Use method 3 only when method 1 or method 2 cannot be used.

 

Grounding the device when a grounding strip is available at the installation site

If a grounding strip is available at the installation site and is reliably grounded, connect one end of the yellow-green grounding cable to the grounding post on the grounding strip, and then fasten the nut. (See Figure 3.) The sectional area of the grounding cable must be no smaller than 4 mm2 (0.0062 in2). Make sure the cable is as short as possible, and do not twist the cable.

Figure 3 Grounding the device when a grounding strip is available in the equipment room

 

When the device is installed in a 19-inch rack, you can connect the yellow-green grounding cable to the grounding terminal of the rack. Make sure the grounding terminal of the 19-inch rack is reliably connected to the grounding strip in the equipment room.

Grounding the device when no grounding strip is available and the grounding conductor cannot be buried in the earth at the installation site

When no grounding strip is available and the grounding conductor cannot be buried in the earth at the installation site, follow these guidelines:

·     If the device uses a 220 V AC power supply, you can use the PE wire of the AC power supply for grounding, as shown in Figure 4. Make sure the PE wire of the AC power supply is reliably grounded in the electric distribution room or the AC power transformer. Additionally, make sure the PE terminal of the device is reliably connected to the PE wire of the AC power supply. The power cable of the device must be a three-core cable that has a PE wire. If the PE wire of the AC power supply is not grounded in the electric distribution room or the AC power transformer, submit the rectification requirement to the customer as soon as possible.

Figure 4 Grounding the device by using the PE wire of the AC power supply

 

·     If the device uses a –48 V (or +24 V) DC power supply, you can use the RTN or PGND wire of the DC power supply for grounding, as shown in Figure 5. Make sure the RTN or PGND wire of the DC power supply is reliably grounded at the DC egress of the DC power cabinet. If the RTN or PGND wire does not meet the requirement, submit the rectification requirement to the customer as soon as possible.

Figure 5 Grounding the device by using the PGND of the power cabinet

 

 

Grounding the device by using a grounding conductor buried in the earth ground

If the installation site does not have grounding strips, but earth ground is available, hammer a 0.5 m (1.64 ft) or longer angle iron or steel tube into the earth ground to act as a grounding conductor. The dimensions of the angle iron must be a minimum of 50 × 50 × 5 mm (1.97 × 1.97 × 0.20 in). The steel tube must be zinc-coated and its wall thickness must be a minimum of 3.5 mm (0.14 in). Weld the yellow-green grounding cable to the angel iron or steel tube and treat the joint for rust protection. The sectional area of the grounding cable must be no smaller than 4 mm2 (0.0062 in2). Make sure the cable is as short as possible, and do not twist the cable, as shown in Figure 6.

Figure 6 Grounding the device by burying the grounding conductor into the earth ground

 

Grounding resistance

Determine the grounding resistance of grounding strips based the equipment room environment requirements. For the central telecom equipment room, determine the grounding resistance according to YDJ26-89 (which requires the grounding resistance to be less than 1 ohm). For non-central telecom equipment rooms, the grounding resistance must be less than 5 ohms. For angle irons hammered into the earth, the grounding resistance must be less than 10 ohms. For locations with high soil resistivity, sprinkle some saline water or resistance reducer to reduce soil resistivity.

Commonly grounding devices

The interconnected devices must be commonly grounded and reliably grounded.

·     If the interconnected devices are both installed in a 19-inch rack, connect the grounding cables of these devices to the grounding strip of the rack for common grounding.

·     If the interconnected devices are placed in the same equipment room and not far from each other, you can connect the grounding cables of the interconnected devices and then connect the cables to the ground. See Figure 7.

Figure 7 Commonly grounding devices

 

·     If the interconnected devices are not in the same equipment room, make sure all interconnected devices are reliably grounded.

Identifying whether the devices are commonly grounded reliably

As shown in Figure 8, use the grounding cable to lead out the grounding terminals of the interconnected devices, and use the multimeter to measure the voltage and resistance between the two grounding terminals.

·     If the devices are reliably grounded, the resistance between the two terminals quickly returns to zero and the voltage is lower than 1 V.

·     If the devices are not reliably grounded, the resistance between the two terminals is not zero or slowly returns to zero, or the voltage is higher than 1 V.

Figure 8 Identifying whether the devices are commonly grounded reliably

 

Troubleshooting through looping

Common looping points

Figure 9 Common looping points

 

·     Looping point 1:

Method: Execute the loopback local command on the E1 interface of the router.

Purpose: Verify that the interface on the router can correctly send and receive packets.

·     Looping points 2 and 3:

Method: Perform a short connection on the E1 Rx and Tx cables between Router 1 and transmission device 1 or form a leftwards loop on the transmission device.

Purpose: Verify that the line between Router 1 and transmission device 1 is normal.

·     Looping point 4:

Method: Form a leftwards loop on transmission device 2.

Purpose: Verify that the transmission network is normal.

·     Looping point 5:

Method: Perform a short connection on the E1 Rx and Tx cables between Router 1 and transmission device 1.

Purpose: Verify that the whole physical link between Router1 and Router 2 is normal.

·     Looping point 6:

Method: Execute the loopback remote/loopback payload command on the E1 interface of Router 2.

Purpose: Verify that the whole link and Router 2 are normal.

Troubleshooting lines after looping

·     Use the self-loopback test feature of the router to troubleshoot lines.

a.     Enable PPP encapsulation on the interface.

b.     Display the interface information.

-     If the command output shows that the number of received packets evenly increases by 12 packets, loopback is detected, and no error packets occur, the link is normal.

-     If the command output does not show the above information, the link has failed.

<Sysname> display interface serial 2/1/0

Serial2/1/0

Current state: UP

Line protocol state: UP

Description: Serial2/1/0 Interface

Bandwidth: 1984 kbps

Maximum transmission unit: 1500

Hold timer: 1500 seconds, retry times: 15

Physical layer is E1-F, baudrate is 1984000 bps

fe1 timeslot-list 1-31

Internet protocol processing: Disabled

Link layer protocol: PPP

LCP: initial

Output queue - Urgent queuing: Size/Length/Discards 0/1024/0

Output queue - Protocol queuing: Size/Length/Discards 0/500/0

Output queue - FIFO queuing: Size/Length/Discards 0/75/0

Last link flapping: Never

Last clearing of counters: Never

Current system time:2023-08-07 11:41:13

Last time when physical state changed to up:-

Last time when physical state changed to down:2023-08-06 18:44:40

Last 300 seconds input rate 0.00 bytes/sec, 0 bits/sec, 0.00 packets/sec

Last 300 seconds output rate 0.00 bytes/sec, 0 bits/sec, 0.00 packets/sec

    Input: 0 packets, 0 bytes, 0 no buffers

           0 errors, 0 runts, 0 giants

           0 CRC, 0 align errors, 0 overruns

           0 aborts, 0 no buffers

    Output:0 packets, 0 bytes

           0 errors, 0 underruns, 0 collisions

           0 deferred

·     Use the error code meter to troubleshoot lines.

c.     Replace the router with an error code meter.

d.     Connect the Rx and Tx cables previously connected to the router to the error code meter.

e.     The error code meter can display whether error codes exist on the line.

Locating E1 interface issues

Common E1 interface issues include the following types:

·     Physical interface anomaly, for example, LOS, LFA, AIS, or RAI alarms exist on the controller interface and the controller interface stays down or flaps.

·     The physical interface is up, and has no alarms. However, it sends or receives data incorrectly. For example, error packets exist on the local and peer interfaces, or the link layer protocol comes up and goes down.

Physical interface anomaly

Symptom

The physical interface is abnormal, for example, LOS, LFA, AIS, or RAI alarms exist on the controller interface and the controller interface stays down or flaps.

Solution

To resolve this issue:

1.     Troubleshoot the hardware.

2.     Troubleshoot the cable.

3.     Troubleshoot the configuration.

4.     Troubleshoot the clock.

5.     Troubleshoot grounding.

6.     Troubleshoot through looping.

Data transmission anomaly

Symptom

The physical interface is up, and has no alarms. However, it sends or receives data incorrectly. For example, error packets exist on the local and peer interfaces, or the link layer protocol comes up and goes down.

Solution

To resolve this issue:

1.     Troubleshoot the hardware.

2.     Troubleshoot the cable.

3.     Troubleshoot the configuration.

4.     Troubleshoot the clock.

5.     Troubleshoot grounding.

6.     Troubleshoot through looping.

Collecting information

If the issue persists, execute the following commands to collect information and contact H3C Support.

·     display diagnostic-information

·     display device verbose

·     display controller

·     display interface serial (If the number of inbound or outbound error packets increases, execute this command multiple times at intervals.)