比特派钱包链接|ethernet interface testing

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks

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 ON THIS PAGEChecklist for Using Loopback Testing for Fast Ethernet and

Gigabit Ethernet InterfacesDiagnose a Suspected Hardware Problem with a Fast Ethernet

or Gigabit Ethernet InterfaceCreate a LoopbackVerify That the Fast Ethernet or Gigabit Ethernet Interface

Is UpConfigure a Static Address Resolution Protocol Table EntryClear Fast Ethernet or Gigabit Ethernet Interface StatisticsPing the Fast Ethernet or Gigabit Ethernet InterfaceCheck for Fast Ethernet or Gigabit Ethernet Interface Error

StatisticsDiagnose a Suspected Circuit Problem 

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet

Interfaces

Checklist for Using Loopback Testing for Fast Ethernet and

Gigabit Ethernet Interfaces

Purpose

Action

PurposeTo use loopback testing to isolate Fast Ethernet and

Gigabit Ethernet interface problems.

ActionTable 1 provides links and

commands for using loopback testing for Fast Ethernet and Gigabit

Ethernet interfaces.

Table 1: Checklist

for Using Loopback Testing for Fast Ethernet and Gigabit Ethernet

InterfacesTasks

Command or Action

Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface

Create a Loopback

Create a Physical Loopback for a Fiber-Optic Interface

Connect the transmit port to the receive port.

Create a Loopback Plug for an RJ-45 Ethernet Interface

Cross pin 1 (TX+) and pin 3 (RX+) together, and pin 2

(TX-) and pin 6 (RX-) together.

Configure a Local Loopback

[edit interfaces

interface-name (fastether-options | gigether-options)]

set loopback

show

commit

Verify That the Fast Ethernet or Gigabit Ethernet

Interface Is Up

show interfaces (fe-fpc/pic/port | ge-fpc/pic/port)

Configure a Static Address Resolution Protocol Table

Entry

show interfaces ge-fpc/pic/port [edit interfaces

interface-name unit logical-unit-number family inet address

address]

set arp ip-address mac mac-address show

commit

run show

arp no-resolve

Clear Fast Ethernet or Gigabit Ethernet Interface

Statistics

clear interfaces statistics fe-fpc/pic/port | ge-fpc/pic/port

Ping the Fast Ethernet or Gigabit Ethernet Interface

ping remote-IP-address bypass-routing

interface (fe-fpc/pic/port |

ge-fpc/pic/port

count 100 rapid

Check for Fast Ethernet or Gigabit Ethernet Interface

Error Statistics

show interfaces (fe-fpc/pic/port | ge-fpc/pic/port ) extensive

Diagnose

a Suspected Circuit Problem

Perform Steps 2 through 8 from Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface.

Diagnose a Suspected Hardware Problem with a Fast Ethernet

or Gigabit Ethernet Interface

Problem

Solution

ProblemDescriptionWhen you suspect a hardware problem, take

the following steps to help verify if there is a problem.

SolutionTo diagnose a suspected hardware problem

with the Ethernet interface, follow these steps:

Create a Loopback

Verify That the Fast Ethernet or Gigabit Ethernet

Interface Is Up

Configure a Static Address Resolution Protocol Table

Entry

Clear Fast Ethernet or Gigabit Ethernet Interface

Statistics

Check for Fast Ethernet or Gigabit Ethernet Interface

Error Statistics

Create a Loopback

You can create a physical loopback or configure a local

loopback to help diagnose a suspected hardware problem. Creating a

physical loopback is recommended because it allows you to test and

verify the transmit and receive ports. If a field engineer is not

available to create the physical loopback, you can configure a local

loopback for the interface. The local loopback creates a loopback

internally in the Physical Interface Card (PIC).

Create a Physical Loopback for a Fiber-Optic Interface

Create a Loopback Plug for an RJ-45 Ethernet Interface

Configure a Local Loopback

Create a Physical Loopback for a Fiber-Optic Interface

Action

To create a physical loopback at the port, connect the transmit

port to the receive port using a known good fiber cable.

Note: Make sure you use single-mode fiber for a

single-mode port and multimode fiber for a multimode port.

Meaning

When you create and then test a physical loopback, you are testing

the transmit and receive ports of the PIC. This action is recommended

if a field engineer is available to create the physical loop as it

provides a more complete test of the PIC.

See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces

Create a Loopback Plug for an RJ-45 Ethernet Interface

Action

To create a loopback plug, cross pin 1 (TX+) and pin 3 (RX+) together, and cross pin

2 (TX-) and pin 6 (RX-) together. You need the following equipment to create the

loopback:

A 6-inch long CAT5 cable

An RJ-45 connector

A crimping tool

Figure 1 illustrates how to create a loopback plug for an RJ-45 Ethernet

interface.

Figure 1: RJ-45 Ethernet Loopback Plug

Meaning

When you create and then test a physical loopback, you are testing the RJ-45

interface of the PIC. This action is recommended if a field engineer is available to

create the physical loop as it provides a more complete test of the PIC.

See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces

Configure a Local Loopback

Action

To configure a local loopback without physically connecting

the transmit port to the receive port, follow these steps:

In configuration mode, go to the following hierarchy level:

Configure the local loopback:

Verify the configuration:

For example:

Commit the change:

For example:

When you create a local loopback, you create an internal loop

on the interface being tested. A local loopback loops the traffic

internally on that PIC. A local loopback tests the interconnection

of the PIC but does not test the transmit and receive ports. On an

Ethernet interface, you cannot create a remote loopback, therefore

there is no option to use a local or remote statement.

Simply including the loopback statement at the [edit

interfaces interface-name (fastether-options

| gigether-options] hierarchy level, places the interface into

local loopback mode.

Note: Remember to delete the loopback statement

after completing the test.

See AlsoCreate a Loopback

See AlsoVerify That the Fast Ethernet or Gigabit Ethernet Interface Is Up

Configure a Static Address Resolution Protocol Table Entry

Clear Fast Ethernet or Gigabit Ethernet Interface Statistics

Ping the Fast Ethernet or Gigabit Ethernet Interface

Check for Fast Ethernet or Gigabit Ethernet Interface Error Statistics

Verify That the Fast Ethernet or Gigabit Ethernet Interface

Is Up

Purpose

Action

Meaning

PurposeDisplay the status of the Fast Ethernet or Gigabit

Ethernet interface to provide the information you need to determine whether the physical link is up

or down.

ActionTo verify that the status of the Fast Ethernet or Gigabit

Ethernet interface is up, use the following Junos OS command-line

interface (CLI) operational mode command:

Sample Output

Meaning

The sample output shows that the link is up and there are no

alarms in this loopback configuration. When an internal loopback is

configured, the physical loopback should come up without an alarm.

Sample Output

When you see that the physical link is down, there may be a

problem with the port. The following output is an example of the show

interfaces fe-fpc/pic/port command when the physical link is down:

MeaningThe sample output shows that the physical link is down

and there are active alarms and defects.

Table 2 presents problem

situations and actions for a physical link that is down.

Table 2: Problems

and Solutions for a Physical Link That Is Down Problem

Action

Cable mismatch

Verify that the fiber connection is correct.

Damaged

and/or dirty cable

Verify that the fiber can successfully loop a known good

port of the same type.

Too much or too little optical

attenuation

Verify that the attenuation is correct per the PIC optical

specifications.

The transmit port is not transmitting within the dBm

optical range per the specifications

Verify that the Tx power of the optics is within range

of the PIC optical specification.

Mismatch between the cable type and the port

Verify that a single-mode fiber cable is connected to

a single-mode interface and that a multimode fiber cable is connected

to a multimode interface. (This problem does not always cause the

physical link to go down; errors and dropped packets are sometimes

the result.)

Configure a Static Address Resolution Protocol Table Entry

Purpose

Configure a static Address Resolution Protocol (ARP) entry to

allow a packet to be sent out of a looped Ethernet interface.

Note: Remove the static ARP entry at the end of

the loop test after you have completed the tests and monitored interface

traffic.

Action

To configure a static ARP table entry for a Gigabit Ethernet

interface, follow these steps. You can follow the same procedure to

configure a static ARP entry for a Fast Ethernet interface.

Find the Media Access Control (MAC) address for the Gigabit

Ethernet interface:

user@host> show interfaces ge-fpc/pic/port

In configuration mode, go to the following hierarchy level:

Configure the static ARP entry:

Commit the configuration:

Verify that the static ARP entry is installed:

Meaning

The sample output is for Step 1 through Step 6 and shows that

a static ARP entry was configured on Gigabit Ethernet interface ge-4/0/6.

Clear Fast Ethernet or Gigabit Ethernet Interface Statistics

Purpose

You can reset the Fast Ethernet and Gigabit Ethernet interface

statistics. Resetting the statistics provides a clean start so that

previous input/output errors and packet statistics do not interfere

with the current diagnostics.

Action

To clear all statistics for the interface, use the following

Junos OS CLI operational mode command:

Sample Output

Meaning

This command clears the interface statistics counters

for the Gigabit Ethernet interface only.

Ping the Fast Ethernet or Gigabit Ethernet Interface

Purpose

Action

Meaning

PurposeUse the ping command to verify the loopback connection.

ActionTo send ping packets from the Ethernet interface, use

the following Junos OS CLI operational mode command:

Sample Output

MeaningThe sample output shows that the time to live (TTL)

expired, indicating that the link is receiving the frames from the

ping test. The MAC address used is the same as the physical address

of the port being tested because this allows the port to accept the

frames from the ping test. As the packet is looped over the link,

you expect to receive a TLL exceeded message for each ping sent. These

messages are generated because the ping packets are repeatedly looped

between the router and the physical loopback. When the packet is sent

to the other end of the link, which does not exist, the loopback returns

the packet back to the same interface, where it is again subjected

to the Packet Forwarding Engine fabric for routing. After the route

lookup, the TTL is decremented, and the packet is again sent out of

the looped interface. This process repeats until the packed is either

lost, or the TLL expires with subsequent TTL expired message displayed.

Should any errors occur, the packet is discarded and a time-out error

is displayed, rather than the expected TTL expired message. Note that

the default TTL for ICMP echo packets in Junos OS is 64. This means

a given test packet must be successfully sent and received 63 times

before a TTL expired message can be generated. You can alter the TTL

value to adjust the tolerance for loss, for example, a value of 255

is the most demanding test because now the packet must be sent and

received error free 254 times.

Check for Fast Ethernet or Gigabit Ethernet Interface Error

Statistics

Purpose

Action

Meaning

PurposePersistent interface error statistics indicate that

you need to open a case with the Juniper Networks Technical Assistance

Center (JTAC).

ActionTo check the local interface for error statistics, use

the following Junos OS CLI operational mode command:

Sample Output

MeaningCheck for any error statistics. There should not be

any input or output errors. If there are any persistent input or output

errors, open a case with the Juniper Networks Technical Assistance

Center (JTAC) at support@juniper.net, or at 1-888-314-JTAC

(within the United States) or 1-408-745-9500 (from outside the United

States).

Diagnose a Suspected Circuit Problem

Purpose

Action

PurposeWhen you suspect a circuit problem, it is important

to work with the transport-layer engineer to resolve the problem.

The transport-layer engineer may create a loop to the router from

various points in the network. You can then perform tests to verify

the connection from the router to that loopback in the network.

ActionAfter the transport-layer engineer has created the loop

to the router from the network, you must verify the connection from

the router to the loopback in the network. Follow Step 2 through Step

8 in Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface. Keep in mind that

any problems encountered in the test indicate a problem with the connection

from the router to the loopback in the network.

By performing tests to loopbacks at various points in the network,

you can isolate the source of the problem.

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Physical Layer Compliance Testing for 1000BASE-T Ethernet

Physical Layer Compliance Testing for 1000BASE-T Ethernet

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Engineers designing or validating the 1000BASE-T Ethernet physical layer on their products need to perform a wide range of tests, quickly, reliably and efficiently. This application note describes the tests that ensure validation, the challenges faced while testing multi-level signals, and how oscilloscoperesident test software enables significant efficiency improvements with its wide range of tests, including return loss, fast validation cycles, and high reliability.

The Basics of 1000BASE-T Testing

Popularly known as Gigabit Ethernet, 1000BASE-T has been experiencing rapid growth. With only minimal changes to the legacy cable structure, it offers 100 times faster data rates than 10BASE-T Ethernet signals. Gigabit Ethernet, in combination with Fast Ethernet and switched Ethernet, offers a cost-effective alternative to slow networks.

1000BASE-T uses four signal pairs for full-duplex transmission and reception over CAT-5 balanced cabling.The transmission occurs at a data rate of 250 Mbps over each pair, operating at 80% efficiency. It employs a four-level, PAM5 encoding signaling scheme as in Figure 1.

Figure 1. 1000BASE-T Multi-level PAM5 encoded signal.

1000BASE-T Physical Layer Compliance Standards

To ensure reliable information transmission over a network, industry standards specify requirements for the network's physical layer. The IEEE 802.3 standard defines an array of compliance tests for 1000BASE-T physical layer. These tests are performed by placing the device under test in test modes specified in the standard.

While it is recommended to perform as many tests as possible, the following core tests are critical for compliance:

Test Mode

Test

IEEE 802.3 Reference

Test Mode-1

Peak Droof Template

40.6.1.2.140.6.1.2.240.6.1.2.3

Test Mode-2 Test Mode-3

Master JitterSlave Jitter

40.6.1.2.5

Test Mode-4

DistortionMDI Return LossMDI Common Mode Voltage

40.6.1.2.440.8.3.140.8.3.3

Table 1. Core 1000BASE-T tests.

1000BASE-T Test Modes

For conformance testing, test modes are enabled in the Device Under Test (DUT) to allow for testing transmitter waveform characteristics like transmitter distortion, and transmitted jitter. These test modes determine the data symbols provided to the transmitter circuitry and do not alter the electrical or jitter characteristics of the transmitter and receiver from those of normal operation. Testing a device with standardized test signals ensures the DUT will inter-operate with other Ethernet devices under normal (non-test mode) conditions.

Test Mode 1 is used to test for Template, Peak and Droop conformance tests. When Test Mode 1 is enabled, the PHY transmits a sequence of data symbols continually from all four transmitters. This sequence is repeated continuously without breaks between repetitions. The typical transmitter output is shown in Figure-2.

Sequence

Signal Level

Symbol Count

Points/Regions

Sequence-1

1x +2

127 x 0's

A

Sequence-2

1x -2

127 x 0's

B

Sequence-3

1x +1

127 x 0's

C

Sequence-4

1x -1

127 x 0's

D

Sequence-5

128x +2, 128x -2, 128x +2, 128x -2

127 x 0's

E, F, G, H, J, K

Sequence-6

1024 x 0's

M

Table 2. Data signals transmitted in Test Mode 1."Points/Regions" refer to Figure 2.

Figure 2. Single cycle of 1000BASE-T Test Mode 1 signal.

When Test Mode 2 is enabled, the transmitter sends out a data symbol sequence of levels +2 and –2 repeatedly on all four channels. The transmitter controls the symbols from a 125 MHz clock in the master timing mode. The typical transmitter output in Test Mode 2 looks like a clock and is shown in Figure 3.

Figure 3. Test Mode 2 for 1000BASE-T alternates between +2 and -2.

Test Mode 3 follows the same data symbol sequence as Test Mode 2 except that the transmitter controls the symbols from a 125.00 MHz clock in the slave timing mode.

When Test Mode 4 is enabled, the transmitter sends out a sequence of symbols generated by a scrambler generator polynomial, with bit generation and level mappings as defined in the IEEE spec. The maximum-length shift register used to generate the sequences defined by the polynomial is updated once per symbol interval (8 ns) resulting in a scrambled signal output, as shown in Figure 4.

Figure 4. 1000BASE-T Test Mode 4 transmits a scrambled signal.

1000BASE-T Tests

Peak Tests

A peak test is performed at the peak of the waveform at points A, B, C and D as shown in Figure 5. The criteria for passing the test is that that absolute value of the peak of the waveform at points A and B must fall within the range of 670 mV to 820 mV. These measurements are to be made for each differential pair, observing the signal at the output of the MDI port of the Device Under Test. The specification defines a relationship between points A, B, C and D in terms of the absolute and average values of the peak voltage to ensure all the peaks are within passing limits.

Figure 5. Peak points of 1000BASE-T Signal.

Droop Tests

This test measures the voltage as a magnitude of the negative peak value of the waveform at point G (in Figure 2). For a pass condition, the measured value should be greater than 73.1% of the magnitude of the negative peak value of the waveform at point F. Point G is defined as the 500 ns after point F, where Point F is the point where the waveform reaches its minimum value at the location indicated in Figure 2. The same formula is used to compute Droop test results at points J and H, where point J is defined as the point exactly 500 ns after point H and Point H is defined as the point where the waveform reaches its maximum value at the location indicated in Figure 2 (positive peak). Figure 6 indicates a passing condition of Droop point G, where the measured value was -963.3 mV, which is 97.5% of the peak value of the waveform at point F, -987.5 mV.

Figure 6. Result computed at Droop G point of 1000BASE-T signal shows a passing result.

Template Tests

A template test is like a mask test which specifies the transmitter signal tolerance limits at each of the points A, B, C, D, F, and H. The 1000BASE-T spec defines a template for each of the points and allows for waveforms to be shifted in time, as appropriate to fit within the template. A normalization setting is defined in the spec for each of the points as described in Table 3. Normalization allows peaks A, B, C and D to be evaluated as ratios relative to Peak A. Points F and H are normalized with respect to their own peak voltage levels. Thus, one mask is used for points A, B, C and D and another mask is used for points F and H during compliance testing.

Waveform Points

Normalization Definition

Point A

WaveformA/VpeakA

Point B

WaveformB/VpeakB

Point C

WaveformC/(VpeakA/2)

Point D

WaveformD/(VpeakA/2)

Point F

WaveformF/VpeakF

Point H

WaveformH/VpeakH

Table 3. Normalization for critical points on the Test Mode 1 test signal.

Figure 7 shows the passing results of a template test at point A, and Figure 8 shows the passing results of a template test at point F.

Figure 7. Template test at point A compares the normalized waveform to the mask defined in the standard.

Figure 8. Template test at point F compares the normalized waveform to the mask defined in the standard.

Distortion

This test is performed by putting the device under test in Test Mode 4 and observing the differential signal output at the MDI using a transmitter test fixture, for each pair, with no intervening cable. To pass the test, the peak distortion must be less than 10 mV.

Figure 9. Transmitter Distortion without TX_CLK.

Common Mode Voltage

This test measures the magnitude of the total common-mode output voltage which must be less than 50 mV peak-to-peak when transmitting data at frequencies above 1 MHz.

Return Loss

The return loss test indicates the performance of the transmission system. The standard defines the minimum amount of attenuation the reflected signal should have relative to the incident signal.

To ensure interoperability, the standard also specifies the impedance of the cabling system under which return loss is tested. The environment is specified as 100 Ω ± 15%. As a result, the test needs to be performed over the impedance range of 85 Ω, 100 Ω and 115 Ω.

The test is performed for transmit as well as receive pairs. The device is set to transmit scrambled signals in Idle or Halt Line state.

Figure 10 shows the three plots (85/100/115 Ω) for 1000BASE-T transmit pair.

Figure 10 shows the three plots (85/100/115 Ω) for 1000BASE-T transmit pair.

Test Equipment

To perform the complete suite of tests described previously requires an oscilloscope, differential probes, and an Ethernet test fixture. A software tool may be needed to configure the port under test and place it in test modes.

a. Digital Oscilloscope: To choose an appropriate oscilloscope it is important to consider the rise time, sampling rate and acquisition technique of the oscilloscope. The rise time of the measurement system (right up to the probe tip) must be on the order of 400 ps. This will ensure minimal error in measurements and accurate, reliable test results.

Also, the test limits of duty cycle distortion tests and rise/ fall tests demand high sample rate. It is imperative to have a sampling rate of more than 5 GS/s to offer the resolution required for these measurements. A good fit for such applications is an oscilloscope in the 5 or 6 Series MSO platform that offers at least 1 GHz bandwidth with 400 ps rise time and 10 GS/s sampling speed.

b. Compliance Test Software: Considering the test mode signals discussed so far and the precise areas of signals where measurements need to be performed, an automated test solution is critical for performing the test procedures, allowing the engineer to spend more time on design analysis and less time setting up instruments and referring to the standard.

Tektronix offers Ethernet test automation solutions on several oscilloscope platforms. The precise TekExpress automation software varies based on the oscilloscope.

TekExpress Ethernet Compliance Test Software

5 Series MSO

Option 5-CMENET

6 Series MSO

Option 6-CMENET

DPO/MSO5000, 7000 and 70000

Optioin CMENET3

c. Differential Probe: Gigabit Ethernet testing involves a differential transmission system. Using a pair of single-ended probes to make the measurement requires accurate deskewing and careful matching of the pairs. Failure to do so can lead to undesirable artifacts in the measurement resulting in erroneous test results.

For Gigabit Ethernet testing, either TDP1500 1.5 GHz differential voltage probes, or TDP3500 3.5 GHz differential probes are recommended. To perform return loss tests, two differential probes are required.

d. Arbitrary Waveform Generator: An Arbitrary Waveform Generator, or AWG, is used for return loss tests and as a disturber signal source. An AWG with a sample rate of 250 MS/s or above is well-suited for return loss tests. A 2-channel AWG5200 arbitrary waveform generator is a good source for return loss testing.

e. Test Fixture: The standard describes fixturing requirements for compliance testing. It is important to recognize that the integrity of the fixture directly affects the reliability of the tests. The Tektronix TF-GBE-BTP 1000/100/10BASE-T Basic Ethernet Test Fixture is well-suited for testing the physical layer. Carefully designed interconnects help minimize unwanted exposure to cross-talk and other side-effects. Ideally, the distance between the port under test and the probe-interconnect-point must not be more than one inch.

Generating Test Mode Signals and Performing the Test Setup

There are two predominant methods of generating the test mode signals from the port under test:

1) Configuring the port registers

Port registers are used set the port to transmit test patterns. The registers can be accessed using special software available from the silicon-provider. Contact your siliconprovider for more information on accessing port registers. Most 1000BASE-T tests including Template, Peak Volt, Droop, and Distortion tests require this method to generate the required test mode signals.

Once the port is configured to generate the test mode signal, connect as described in Figure 11.

Figure 11: Test setup without a link partner with access to port registers.

2) Using a link partner

Connecting the port-under-test to another 1000BASE-T device (called a link partner) initiates the sequence generation. 1000BASE-T Master and Slave Jitter tests support this method of signal generation. A link partner could be a computer, a hub or a more sophisticated traffic generator.

The scheme of connections is described in Figure 12.

Figure 12: Test setup with a link partner

3) Test setup for the return loss test

The Tektronix method of implementation employs an oscilloscope-based approach to performing return loss measurements, eliminating the need for additional instruments.

Calibration is performed by using a section of the test fixture specifically designed for return loss calibration. During calibration, the DUT is connected to an open, load and short. The calibration data is then stored and applied during the return loss test.

For this test, the port is configured to generate scrambled sequences. The test setup is described in Figure 13. This test verifies that the return loss of the DUT is below the conformance limit.

For 1000BASE-T, the specification requires the result to be at least 16 dB over the frequency range of 1.0 MHz to 40 MHz and at least 10 - 20log 10 (f /80) dB over the frequency range 40 MHz to 100 MHz (where f is in MHz). Figure 10 shows the limit lines.

Figure 13: Return loss test setup with a link partner

Performing the 1000BASE-T Ethernet Tests

In general, the test process involves four steps:

a. Recalling oscilloscope setups

b. Performing the test and its related measurements

c. Exporting results and screen-shots

d. Documenting test results in a report

For 1000BASE-T testing, the DUT needs to be set to specific test modes and the signal needs to be probed at specific test points on the test fixture. Any human error can lead to incorrect results if there is no mechanism to check the validity of the signal.

Performing the tests using TekExpress Ethernet Compliance Test Software

The TekExpress Ethernet automation software walks you through the test process from setup to execution to reporting. Figure 14 indicates the DUT panel of TekExpress Ethernet software with data rate selection.

Figure 14: TekExpress Ethernet DUT panel with data rate selection.

TekExpress Ethernet enables testing per the standard, including scaling of the mask to 0.95 and 1.05. The user interface follows a logical test workflow yet allows flexibility in setting up tests. Figure 15 shows the test selection panel. Users can select the entire range of tests by clicking on the “Select All” button and run the tests at a press of a button.

Figure 15: Test selection panel. ‘Select All’ option optimizes the testing workflow with minimal connection changes.

TekExpress Ethernet enables testing per the standard, including scaling of the mask to 0.95 and 1.05. The user interface follows a logical test workflow yet allows flexibility in setting up tests. Figure 15 shows the test selection panel. Users can select the entire range of tests by clicking on the “Select All” button and run the tests at a press of a button.

Pressing the Start button initiates the test process. After performing all the tests, the application presents the report in an .MHT format as shown in Figure 16. The report includes:

Setup details

Test summary table

Detailed test results with specification limits, margins, pass/fail status

Waveform plot images

Reports can also be generated in comma-separated-variable (CSV) or PDF format by choosing the report file type in the reports panel. This is useful when testing multiple ports or performing statistical analysis and summarizing the results. The .csv format allows easy documentation in popular tools like Microsoft Excel and helps to parse and customize the test reports in company-specific report formats.

TekExpress Ethernet compliance test software cuts validation cycles from hours to minutes.

Figure 16: TekExpress Ethernet sample test report.

To verify repeatability and to help characterize performance, new multi-run functions facilitate repeated testing and a flexible limits editor lets you test to design margins beyond the specification limits. Figure 17 and Figure 18 highlight these capabilities.

Figure 17. TekExpress Ethernet multi-run feature runs a test, or group of tests for the number of times you specify, and generates a single test report for all of the runs.

Figure 18. TekExpress Ethernet limits editor lets you define your own limits outside the 1000BASE-T specification.

Summary

Engineers designing or validating the Ethernet physical layer on their products need to perform a wide range of tests, quickly, reliably and efficiently.

The number of tests coupled with multi-level signals present several challenges for the test engineer. Tight margins require careful measurements and a thorough understanding of error contributors.

TekExpress Ethernet test automation software delivers significant efficiency improvements by performing a wide range of tests quickly and reliably. And innovative oscilloscope-based return loss measurements helps reduce equipment requirements while performing tests at 85, 100 and 115 Ω impedances per the standard.

Find more valuable resources at TEK.COM

Copyright © Tektronix. All rights reserved. Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supersedes that in all previously published material. Specification and price change privileges reserved. TEKTRONIX and TEK are registered trademarks of Tektronix, Inc. All other trade names referenced are the service marks, trademarks or registered trademarks of their respective companies.

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Performing a loopback test on an Ethernet interface

[x]Configuring common Ethernet interface settings > Performing a loopback test on an Ethernet interface  NextPerforming a loopback test on an Ethernet interfaceIf an Ethernet interface does not work correctly, you can perform a loopback test on it to identify the problem. An Ethernet interface in a loopback test does not forward data traffic.Loopback tests include the following types:Internal loopback test—Tests all on-chip functions related to Ethernet interfaces.External loopback test—Tests the hardware of Ethernet interfaces. To perform an external loopback test on an Ethernet interface, connect a loopback plug to the Ethernet interface. The device sends test packets out of the interface, which are expected to loop over the plug and back to the interface. If the interface fails to receive any test packets, the hardware of the interface is faulty.Configuration restrictions and guidelinesWhen you perform a loopback test on an Ethernet interface, follow these restrictions and guidelines:On an administratively shut down interface (displayed as in ADM or Administratively DOWN state), you cannot perform an internal or external loopback test.The speed, duplex, mdix-mode, and shutdown commands are not available during a loopback test.During a loopback test, the Ethernet interface operates in full duplex mode. When a loopback test is complete, the port returns to its duplex setting.Configuration procedureTo perform a loopback test on an Ethernet interface:StepCommandRemarks1. Enter system view.system-viewN/A2. Enter Ethernet interface view.interface interface-type interface-numberN/A3. Perform a loopback test.loopback { external | internal }By default, no loopback test is performed.The external keyword is not supported in the current version, and it is reserved for future support.prev up nextConfiguring physical state change suppression on an Ethernet interface home Configuring generic flow control on an Ethernet interface© Copyright 2014 Hewlett-Packard Development Company, L.

Configuring loopback testing on an Ethernet interface

[x]Configuring basic settings of an Ethernet interface > Configuring loopback testing on an Ethernet interface  NextConfiguring loopback testing on an Ethernet interfaceYou can perform loopback testing on an Ethernet interface to check whether the interface functions properly. Note that the Ethernet interface cannot forward data packets during the testing. Loopback testing falls into the following two categories:Internal loopback testing, which tests all on-chip functions related to Ethernet interfaces. As shown in Figure 2, internal loopback testing is performed on Port 1. During the internal loopback testing, the port sends out a certain number of test packets, which are looped back to the port over the self-loop created on the switching chip.Figure 2: Internal loopback testingExternal loopback testing, which tests the hardware of Ethernet interfaces. As shown in Figure 3, external loopback testing is performed on Port 1. To perform external loopback testing on an Ethernet interface, insert a loopback plug into the port. During the external loopback testing, the port sends out a certain number of test packets, which are looped over the plug and back to the interface. If the interface fails to receive any test packet, the hardware of the interface is faulty. Figure 3: External loopback testingFollow these steps to enable Ethernet interface loopback testing:To do…Use the command…RemarksEnter system viewsystem-view—Enter Ethernet interface viewinterface interface-type interface-number—Perform loopback testingloopback { external | internal }OptionalDisabled by default.NOTE:On an interface administratively shut down (in the state ADM DOWN), you can perform neither internal nor external loopback testing.The speed, duplex, mdi, and shutdown commands are unavailable on an interface with loopback testing enabled.During loopback testing, an Ethernet interface works in full duplex mode. When you disable loopback testing, the duplex configuration of the interface is restored.Loopback testing is a one-time operation, and is not recorded in the configuration file.prev up nextConfiguring link down suppression on an Ethernet interface home Configuring a port group© Copyright 2015 Hewlett Packard Enterprise Development

Performing a loopback test on an Ethernet interface

[x]Configuring common Ethernet interface settings > Performing a loopback test on an Ethernet interface  NextPerforming a loopback test on an Ethernet interfaceIf an Ethernet interface does not work correctly, you can perform a loopback test on it to identify the problem. An Ethernet interface in a loopback test does not forward data traffic.Loopback tests include the following types:Internal loopback test—Tests all on-chip functions related to Ethernet interfaces.External loopback test—Tests the hardware of Ethernet interfaces. To perform an external loopback test on an Ethernet interface, connect a loopback plug to the Ethernet interface. The device sends test packets out of the interface, which are expected to loop over the plug and back to the interface. If the interface fails to receive any test packets, the hardware of the interface is faulty.Configuration restrictions and guidelinesWhen you perform a loopback test on an Ethernet interface, follow these restrictions and guidelines:On an administratively shut down interface (displayed as in ADM or Administratively DOWN state), you cannot perform an internal or external loopback test.The speed, duplex, mdix-mode, and shutdown commands are not available during a loopback test.During a loopback test, the Ethernet interface operates in full duplex mode. When a loopback test is complete, the port returns to its duplex setting.Configuration procedureTo perform a loopback test on an Ethernet interface:StepCommandRemarks1. Enter system view.system-viewN/A2. Enter Ethernet interface view.interface interface-type interface-numberN/A3. Perform a loopback test.loopback { external | internal }By default, no loopback test is performed.The external keyword is not supported in the current version, and it is reserved for future support.prev up nextConfiguring physical state change suppression on an Ethernet interface home Configuring generic flow control on an Ethernet interface© Copyright 2014 Hewlett-Packard Development Company, L.

Configuring loopback testing on an Ethernet interface

[x]Configuring basic settings of an Ethernet interface > Configuring loopback testing on an Ethernet interface  NextConfiguring loopback testing on an Ethernet interfaceYou can perform loopback testing on an Ethernet interface to check whether the interface functions properly. Note that the Ethernet interface cannot forward data packets during the testing. Loopback testing falls into the following two categories:Internal loopback testing, which tests all on-chip functions related to Ethernet interfaces. As shown in Figure 2, internal loopback testing is performed on Port 1. During the internal loopback testing, the port sends out a certain number of test packets, which are looped back to the port over the self-loop created on the switching chip.Figure 2: Internal loopback testingExternal loopback testing, which tests the hardware of Ethernet interfaces. As shown in Figure 3, external loopback testing is performed on Port 1. To perform external loopback testing on an Ethernet interface, insert a loopback plug into the port. During the external loopback testing, the port sends out a certain number of test packets, which are looped over the plug and back to the interface. If the interface fails to receive any test packet, the hardware of the interface is faulty. Figure 3: External loopback testingFollow these steps to enable Ethernet interface loopback testing:To do…Use the command…RemarksEnter system viewsystem-view—Enter Ethernet interface viewinterface interface-type interface-number—Perform loopback testingloopback { external | internal }OptionalDisabled by default.NOTE:On an interface administratively shut down (in the state ADM DOWN), you can perform neither internal nor external loopback testing.The speed, duplex, mdi, and shutdown commands are unavailable on an interface with loopback testing enabled.During loopback testing, an Ethernet interface works in full duplex mode. When you disable loopback testing, the duplex configuration of the interface is restored.Loopback testing is a one-time operation, and is not recorded in the configuration file.prev up nextConfiguring link down suppression on an Ethernet interface home Configuring a port group© Copyright 2015 Hewlett Packard Enterprise Development

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks

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 ON THIS PAGEChecklist for Using Loopback Testing for Fast Ethernet and

Gigabit Ethernet InterfacesDiagnose a Suspected Hardware Problem with a Fast Ethernet

or Gigabit Ethernet InterfaceCreate a LoopbackVerify That the Fast Ethernet or Gigabit Ethernet Interface

Is UpConfigure a Static Address Resolution Protocol Table EntryClear Fast Ethernet or Gigabit Ethernet Interface StatisticsPing the Fast Ethernet or Gigabit Ethernet InterfaceCheck for Fast Ethernet or Gigabit Ethernet Interface Error

StatisticsDiagnose a Suspected Circuit Problem 

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet

Interfaces

Checklist for Using Loopback Testing for Fast Ethernet and

Gigabit Ethernet Interfaces

Purpose

Action

PurposeTo use loopback testing to isolate Fast Ethernet and

Gigabit Ethernet interface problems.

ActionTable 1 provides links and

commands for using loopback testing for Fast Ethernet and Gigabit

Ethernet interfaces.

Table 1: Checklist

for Using Loopback Testing for Fast Ethernet and Gigabit Ethernet

InterfacesTasks

Command or Action

Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface

Create a Loopback

Create a Physical Loopback for a Fiber-Optic Interface

Connect the transmit port to the receive port.

Create a Loopback Plug for an RJ-45 Ethernet Interface

Cross pin 1 (TX+) and pin 3 (RX+) together, and pin 2

(TX-) and pin 6 (RX-) together.

Configure a Local Loopback

[edit interfaces

interface-name (fastether-options | gigether-options)]

set loopback

show

commit

Verify That the Fast Ethernet or Gigabit Ethernet

Interface Is Up

show interfaces (fe-fpc/pic/port | ge-fpc/pic/port)

Configure a Static Address Resolution Protocol Table

Entry

show interfaces ge-fpc/pic/port [edit interfaces

interface-name unit logical-unit-number family inet address

address]

set arp ip-address mac mac-address show

commit

run show

arp no-resolve

Clear Fast Ethernet or Gigabit Ethernet Interface

Statistics

clear interfaces statistics fe-fpc/pic/port | ge-fpc/pic/port

Ping the Fast Ethernet or Gigabit Ethernet Interface

ping remote-IP-address bypass-routing

interface (fe-fpc/pic/port |

ge-fpc/pic/port

count 100 rapid

Check for Fast Ethernet or Gigabit Ethernet Interface

Error Statistics

show interfaces (fe-fpc/pic/port | ge-fpc/pic/port ) extensive

Diagnose

a Suspected Circuit Problem

Perform Steps 2 through 8 from Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface.

Diagnose a Suspected Hardware Problem with a Fast Ethernet

or Gigabit Ethernet Interface

Problem

Solution

ProblemDescriptionWhen you suspect a hardware problem, take

the following steps to help verify if there is a problem.

SolutionTo diagnose a suspected hardware problem

with the Ethernet interface, follow these steps:

Create a Loopback

Verify That the Fast Ethernet or Gigabit Ethernet

Interface Is Up

Configure a Static Address Resolution Protocol Table

Entry

Clear Fast Ethernet or Gigabit Ethernet Interface

Statistics

Check for Fast Ethernet or Gigabit Ethernet Interface

Error Statistics

Create a Loopback

You can create a physical loopback or configure a local

loopback to help diagnose a suspected hardware problem. Creating a

physical loopback is recommended because it allows you to test and

verify the transmit and receive ports. If a field engineer is not

available to create the physical loopback, you can configure a local

loopback for the interface. The local loopback creates a loopback

internally in the Physical Interface Card (PIC).

Create a Physical Loopback for a Fiber-Optic Interface

Create a Loopback Plug for an RJ-45 Ethernet Interface

Configure a Local Loopback

Create a Physical Loopback for a Fiber-Optic Interface

Action

To create a physical loopback at the port, connect the transmit

port to the receive port using a known good fiber cable.

Note: Make sure you use single-mode fiber for a

single-mode port and multimode fiber for a multimode port.

Meaning

When you create and then test a physical loopback, you are testing

the transmit and receive ports of the PIC. This action is recommended

if a field engineer is available to create the physical loop as it

provides a more complete test of the PIC.

See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces

Create a Loopback Plug for an RJ-45 Ethernet Interface

Action

To create a loopback plug, cross pin 1 (TX+) and pin 3 (RX+) together, and cross pin

2 (TX-) and pin 6 (RX-) together. You need the following equipment to create the

loopback:

A 6-inch long CAT5 cable

An RJ-45 connector

A crimping tool

Figure 1 illustrates how to create a loopback plug for an RJ-45 Ethernet

interface.

Figure 1: RJ-45 Ethernet Loopback Plug

Meaning

When you create and then test a physical loopback, you are testing the RJ-45

interface of the PIC. This action is recommended if a field engineer is available to

create the physical loop as it provides a more complete test of the PIC.

See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces

Configure a Local Loopback

Action

To configure a local loopback without physically connecting

the transmit port to the receive port, follow these steps:

In configuration mode, go to the following hierarchy level:

Configure the local loopback:

Verify the configuration:

For example:

Commit the change:

For example:

When you create a local loopback, you create an internal loop

on the interface being tested. A local loopback loops the traffic

internally on that PIC. A local loopback tests the interconnection

of the PIC but does not test the transmit and receive ports. On an

Ethernet interface, you cannot create a remote loopback, therefore

there is no option to use a local or remote statement.

Simply including the loopback statement at the [edit

interfaces interface-name (fastether-options

| gigether-options] hierarchy level, places the interface into

local loopback mode.

Note: Remember to delete the loopback statement

after completing the test.

See AlsoCreate a Loopback

See AlsoVerify That the Fast Ethernet or Gigabit Ethernet Interface Is Up

Configure a Static Address Resolution Protocol Table Entry

Clear Fast Ethernet or Gigabit Ethernet Interface Statistics

Ping the Fast Ethernet or Gigabit Ethernet Interface

Check for Fast Ethernet or Gigabit Ethernet Interface Error Statistics

Verify That the Fast Ethernet or Gigabit Ethernet Interface

Is Up

Purpose

Action

Meaning

PurposeDisplay the status of the Fast Ethernet or Gigabit

Ethernet interface to provide the information you need to determine whether the physical link is up

or down.

ActionTo verify that the status of the Fast Ethernet or Gigabit

Ethernet interface is up, use the following Junos OS command-line

interface (CLI) operational mode command:

Sample Output

Meaning

The sample output shows that the link is up and there are no

alarms in this loopback configuration. When an internal loopback is

configured, the physical loopback should come up without an alarm.

Sample Output

When you see that the physical link is down, there may be a

problem with the port. The following output is an example of the show

interfaces fe-fpc/pic/port command when the physical link is down:

MeaningThe sample output shows that the physical link is down

and there are active alarms and defects.

Table 2 presents problem

situations and actions for a physical link that is down.

Table 2: Problems

and Solutions for a Physical Link That Is Down Problem

Action

Cable mismatch

Verify that the fiber connection is correct.

Damaged

and/or dirty cable

Verify that the fiber can successfully loop a known good

port of the same type.

Too much or too little optical

attenuation

Verify that the attenuation is correct per the PIC optical

specifications.

The transmit port is not transmitting within the dBm

optical range per the specifications

Verify that the Tx power of the optics is within range

of the PIC optical specification.

Mismatch between the cable type and the port

Verify that a single-mode fiber cable is connected to

a single-mode interface and that a multimode fiber cable is connected

to a multimode interface. (This problem does not always cause the

physical link to go down; errors and dropped packets are sometimes

the result.)

Configure a Static Address Resolution Protocol Table Entry

Purpose

Configure a static Address Resolution Protocol (ARP) entry to

allow a packet to be sent out of a looped Ethernet interface.

Note: Remove the static ARP entry at the end of

the loop test after you have completed the tests and monitored interface

traffic.

Action

To configure a static ARP table entry for a Gigabit Ethernet

interface, follow these steps. You can follow the same procedure to

configure a static ARP entry for a Fast Ethernet interface.

Find the Media Access Control (MAC) address for the Gigabit

Ethernet interface:

user@host> show interfaces ge-fpc/pic/port

In configuration mode, go to the following hierarchy level:

Configure the static ARP entry:

Commit the configuration:

Verify that the static ARP entry is installed:

Meaning

The sample output is for Step 1 through Step 6 and shows that

a static ARP entry was configured on Gigabit Ethernet interface ge-4/0/6.

Clear Fast Ethernet or Gigabit Ethernet Interface Statistics

Purpose

You can reset the Fast Ethernet and Gigabit Ethernet interface

statistics. Resetting the statistics provides a clean start so that

previous input/output errors and packet statistics do not interfere

with the current diagnostics.

Action

To clear all statistics for the interface, use the following

Junos OS CLI operational mode command:

Sample Output

Meaning

This command clears the interface statistics counters

for the Gigabit Ethernet interface only.

Ping the Fast Ethernet or Gigabit Ethernet Interface

Purpose

Action

Meaning

PurposeUse the ping command to verify the loopback connection.

ActionTo send ping packets from the Ethernet interface, use

the following Junos OS CLI operational mode command:

Sample Output

MeaningThe sample output shows that the time to live (TTL)

expired, indicating that the link is receiving the frames from the

ping test. The MAC address used is the same as the physical address

of the port being tested because this allows the port to accept the

frames from the ping test. As the packet is looped over the link,

you expect to receive a TLL exceeded message for each ping sent. These

messages are generated because the ping packets are repeatedly looped

between the router and the physical loopback. When the packet is sent

to the other end of the link, which does not exist, the loopback returns

the packet back to the same interface, where it is again subjected

to the Packet Forwarding Engine fabric for routing. After the route

lookup, the TTL is decremented, and the packet is again sent out of

the looped interface. This process repeats until the packed is either

lost, or the TLL expires with subsequent TTL expired message displayed.

Should any errors occur, the packet is discarded and a time-out error

is displayed, rather than the expected TTL expired message. Note that

the default TTL for ICMP echo packets in Junos OS is 64. This means

a given test packet must be successfully sent and received 63 times

before a TTL expired message can be generated. You can alter the TTL

value to adjust the tolerance for loss, for example, a value of 255

is the most demanding test because now the packet must be sent and

received error free 254 times.

Check for Fast Ethernet or Gigabit Ethernet Interface Error

Statistics

Purpose

Action

Meaning

PurposePersistent interface error statistics indicate that

you need to open a case with the Juniper Networks Technical Assistance

Center (JTAC).

ActionTo check the local interface for error statistics, use

the following Junos OS CLI operational mode command:

Sample Output

MeaningCheck for any error statistics. There should not be

any input or output errors. If there are any persistent input or output

errors, open a case with the Juniper Networks Technical Assistance

Center (JTAC) at support@juniper.net, or at 1-888-314-JTAC

(within the United States) or 1-408-745-9500 (from outside the United

States).

Diagnose a Suspected Circuit Problem

Purpose

Action

PurposeWhen you suspect a circuit problem, it is important

to work with the transport-layer engineer to resolve the problem.

The transport-layer engineer may create a loop to the router from

various points in the network. You can then perform tests to verify

the connection from the router to that loopback in the network.

ActionAfter the transport-layer engineer has created the loop

to the router from the network, you must verify the connection from

the router to the loopback in the network. Follow Step 2 through Step

8 in Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface. Keep in mind that

any problems encountered in the test indicate a problem with the connection

from the router to the loopback in the network.

By performing tests to loopbacks at various points in the network,

you can isolate the source of the problem.

Configuring loopback testing on an Ethernet interface

[x]Performing general configurations > Configuring loopback testing on an Ethernet interface  NextConfiguring loopback testing on an Ethernet interfaceIf an Ethernet interface does not work normally, you can enable loopback testing on it to identify the problem. An Ethernet interface in a loopback test does not forward data traffic.Loopback testing has the following types:Internal loopback testing—Tests all on-chip functions related to Ethernet interfaces.External loopback testing—Tests hardware of Ethernet interfaces. To perform external loopback testing on an Ethernet interface, connect a loopback plug to the Ethernet interface. The device sends test packets out of the interface, which are expected to loop over the plug and back to the interface. If the interface fails to receive any test packets, the hardware of the interface is faulty.Configuration restrictions and guidelines On an interface administratively shut down, you cannot perform internal or external loopback testing.The speed, duplex, mdi, and shutdown commands are not available during loopback testing.During loopback testing, the Ethernet interface operates in full duplex mode. When you disable loopback testing, the port returns to its duplex setting.Loopback testing is a one-time operation, and is not recorded in the configuration file.Configuration procedureTo enable loopback testing on an Ethernet interface:StepCommandRemarks1. Enter system view.system-viewN/A2. Enter Ethernet interface view.interface interface-type interface-numberN/A3. Enable loopback testing.loopback { external | internal }By default, loopback testing is disabled.prev up nextConfiguring physical state change suppression on an Ethernet interface home Configuring the link mode of an Ethernet interface © Copyright 2016 Hewlett Packard Enterprise Development

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks

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 ON THIS PAGEChecklist for Using Loopback Testing for Fast Ethernet and

Gigabit Ethernet InterfacesDiagnose a Suspected Hardware Problem with a Fast Ethernet

or Gigabit Ethernet InterfaceCreate a LoopbackVerify That the Fast Ethernet or Gigabit Ethernet Interface

Is UpConfigure a Static Address Resolution Protocol Table EntryClear Fast Ethernet or Gigabit Ethernet Interface StatisticsPing the Fast Ethernet or Gigabit Ethernet InterfaceCheck for Fast Ethernet or Gigabit Ethernet Interface Error

StatisticsDiagnose a Suspected Circuit Problem 

Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet

Interfaces

Checklist for Using Loopback Testing for Fast Ethernet and

Gigabit Ethernet Interfaces

Purpose

Action

PurposeTo use loopback testing to isolate Fast Ethernet and

Gigabit Ethernet interface problems.

ActionTable 1 provides links and

commands for using loopback testing for Fast Ethernet and Gigabit

Ethernet interfaces.

Table 1: Checklist

for Using Loopback Testing for Fast Ethernet and Gigabit Ethernet

InterfacesTasks

Command or Action

Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface

Create a Loopback

Create a Physical Loopback for a Fiber-Optic Interface

Connect the transmit port to the receive port.

Create a Loopback Plug for an RJ-45 Ethernet Interface

Cross pin 1 (TX+) and pin 3 (RX+) together, and pin 2

(TX-) and pin 6 (RX-) together.

Configure a Local Loopback

[edit interfaces

interface-name (fastether-options | gigether-options)]

set loopback

show

commit

Verify That the Fast Ethernet or Gigabit Ethernet

Interface Is Up

show interfaces (fe-fpc/pic/port | ge-fpc/pic/port)

Configure a Static Address Resolution Protocol Table

Entry

show interfaces ge-fpc/pic/port [edit interfaces

interface-name unit logical-unit-number family inet address

address]

set arp ip-address mac mac-address show

commit

run show

arp no-resolve

Clear Fast Ethernet or Gigabit Ethernet Interface

Statistics

clear interfaces statistics fe-fpc/pic/port | ge-fpc/pic/port

Ping the Fast Ethernet or Gigabit Ethernet Interface

ping remote-IP-address bypass-routing

interface (fe-fpc/pic/port |

ge-fpc/pic/port

count 100 rapid

Check for Fast Ethernet or Gigabit Ethernet Interface

Error Statistics

show interfaces (fe-fpc/pic/port | ge-fpc/pic/port ) extensive

Diagnose

a Suspected Circuit Problem

Perform Steps 2 through 8 from Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface.

Diagnose a Suspected Hardware Problem with a Fast Ethernet

or Gigabit Ethernet Interface

Problem

Solution

ProblemDescriptionWhen you suspect a hardware problem, take

the following steps to help verify if there is a problem.

SolutionTo diagnose a suspected hardware problem

with the Ethernet interface, follow these steps:

Create a Loopback

Verify That the Fast Ethernet or Gigabit Ethernet

Interface Is Up

Configure a Static Address Resolution Protocol Table

Entry

Clear Fast Ethernet or Gigabit Ethernet Interface

Statistics

Check for Fast Ethernet or Gigabit Ethernet Interface

Error Statistics

Create a Loopback

You can create a physical loopback or configure a local

loopback to help diagnose a suspected hardware problem. Creating a

physical loopback is recommended because it allows you to test and

verify the transmit and receive ports. If a field engineer is not

available to create the physical loopback, you can configure a local

loopback for the interface. The local loopback creates a loopback

internally in the Physical Interface Card (PIC).

Create a Physical Loopback for a Fiber-Optic Interface

Create a Loopback Plug for an RJ-45 Ethernet Interface

Configure a Local Loopback

Create a Physical Loopback for a Fiber-Optic Interface

Action

To create a physical loopback at the port, connect the transmit

port to the receive port using a known good fiber cable.

Note: Make sure you use single-mode fiber for a

single-mode port and multimode fiber for a multimode port.

Meaning

When you create and then test a physical loopback, you are testing

the transmit and receive ports of the PIC. This action is recommended

if a field engineer is available to create the physical loop as it

provides a more complete test of the PIC.

See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces

Create a Loopback Plug for an RJ-45 Ethernet Interface

Action

To create a loopback plug, cross pin 1 (TX+) and pin 3 (RX+) together, and cross pin

2 (TX-) and pin 6 (RX-) together. You need the following equipment to create the

loopback:

A 6-inch long CAT5 cable

An RJ-45 connector

A crimping tool

Figure 1 illustrates how to create a loopback plug for an RJ-45 Ethernet

interface.

Figure 1: RJ-45 Ethernet Loopback Plug

Meaning

When you create and then test a physical loopback, you are testing the RJ-45

interface of the PIC. This action is recommended if a field engineer is available to

create the physical loop as it provides a more complete test of the PIC.

See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces

Configure a Local Loopback

Action

To configure a local loopback without physically connecting

the transmit port to the receive port, follow these steps:

In configuration mode, go to the following hierarchy level:

Configure the local loopback:

Verify the configuration:

For example:

Commit the change:

For example:

When you create a local loopback, you create an internal loop

on the interface being tested. A local loopback loops the traffic

internally on that PIC. A local loopback tests the interconnection

of the PIC but does not test the transmit and receive ports. On an

Ethernet interface, you cannot create a remote loopback, therefore

there is no option to use a local or remote statement.

Simply including the loopback statement at the [edit

interfaces interface-name (fastether-options

| gigether-options] hierarchy level, places the interface into

local loopback mode.

Note: Remember to delete the loopback statement

after completing the test.

See AlsoCreate a Loopback

See AlsoVerify That the Fast Ethernet or Gigabit Ethernet Interface Is Up

Configure a Static Address Resolution Protocol Table Entry

Clear Fast Ethernet or Gigabit Ethernet Interface Statistics

Ping the Fast Ethernet or Gigabit Ethernet Interface

Check for Fast Ethernet or Gigabit Ethernet Interface Error Statistics

Verify That the Fast Ethernet or Gigabit Ethernet Interface

Is Up

Purpose

Action

Meaning

PurposeDisplay the status of the Fast Ethernet or Gigabit

Ethernet interface to provide the information you need to determine whether the physical link is up

or down.

ActionTo verify that the status of the Fast Ethernet or Gigabit

Ethernet interface is up, use the following Junos OS command-line

interface (CLI) operational mode command:

Sample Output

Meaning

The sample output shows that the link is up and there are no

alarms in this loopback configuration. When an internal loopback is

configured, the physical loopback should come up without an alarm.

Sample Output

When you see that the physical link is down, there may be a

problem with the port. The following output is an example of the show

interfaces fe-fpc/pic/port command when the physical link is down:

MeaningThe sample output shows that the physical link is down

and there are active alarms and defects.

Table 2 presents problem

situations and actions for a physical link that is down.

Table 2: Problems

and Solutions for a Physical Link That Is Down Problem

Action

Cable mismatch

Verify that the fiber connection is correct.

Damaged

and/or dirty cable

Verify that the fiber can successfully loop a known good

port of the same type.

Too much or too little optical

attenuation

Verify that the attenuation is correct per the PIC optical

specifications.

The transmit port is not transmitting within the dBm

optical range per the specifications

Verify that the Tx power of the optics is within range

of the PIC optical specification.

Mismatch between the cable type and the port

Verify that a single-mode fiber cable is connected to

a single-mode interface and that a multimode fiber cable is connected

to a multimode interface. (This problem does not always cause the

physical link to go down; errors and dropped packets are sometimes

the result.)

Configure a Static Address Resolution Protocol Table Entry

Purpose

Configure a static Address Resolution Protocol (ARP) entry to

allow a packet to be sent out of a looped Ethernet interface.

Note: Remove the static ARP entry at the end of

the loop test after you have completed the tests and monitored interface

traffic.

Action

To configure a static ARP table entry for a Gigabit Ethernet

interface, follow these steps. You can follow the same procedure to

configure a static ARP entry for a Fast Ethernet interface.

Find the Media Access Control (MAC) address for the Gigabit

Ethernet interface:

user@host> show interfaces ge-fpc/pic/port

In configuration mode, go to the following hierarchy level:

Configure the static ARP entry:

Commit the configuration:

Verify that the static ARP entry is installed:

Meaning

The sample output is for Step 1 through Step 6 and shows that

a static ARP entry was configured on Gigabit Ethernet interface ge-4/0/6.

Clear Fast Ethernet or Gigabit Ethernet Interface Statistics

Purpose

You can reset the Fast Ethernet and Gigabit Ethernet interface

statistics. Resetting the statistics provides a clean start so that

previous input/output errors and packet statistics do not interfere

with the current diagnostics.

Action

To clear all statistics for the interface, use the following

Junos OS CLI operational mode command:

Sample Output

Meaning

This command clears the interface statistics counters

for the Gigabit Ethernet interface only.

Ping the Fast Ethernet or Gigabit Ethernet Interface

Purpose

Action

Meaning

PurposeUse the ping command to verify the loopback connection.

ActionTo send ping packets from the Ethernet interface, use

the following Junos OS CLI operational mode command:

Sample Output

MeaningThe sample output shows that the time to live (TTL)

expired, indicating that the link is receiving the frames from the

ping test. The MAC address used is the same as the physical address

of the port being tested because this allows the port to accept the

frames from the ping test. As the packet is looped over the link,

you expect to receive a TLL exceeded message for each ping sent. These

messages are generated because the ping packets are repeatedly looped

between the router and the physical loopback. When the packet is sent

to the other end of the link, which does not exist, the loopback returns

the packet back to the same interface, where it is again subjected

to the Packet Forwarding Engine fabric for routing. After the route

lookup, the TTL is decremented, and the packet is again sent out of

the looped interface. This process repeats until the packed is either

lost, or the TLL expires with subsequent TTL expired message displayed.

Should any errors occur, the packet is discarded and a time-out error

is displayed, rather than the expected TTL expired message. Note that

the default TTL for ICMP echo packets in Junos OS is 64. This means

a given test packet must be successfully sent and received 63 times

before a TTL expired message can be generated. You can alter the TTL

value to adjust the tolerance for loss, for example, a value of 255

is the most demanding test because now the packet must be sent and

received error free 254 times.

Check for Fast Ethernet or Gigabit Ethernet Interface Error

Statistics

Purpose

Action

Meaning

PurposePersistent interface error statistics indicate that

you need to open a case with the Juniper Networks Technical Assistance

Center (JTAC).

ActionTo check the local interface for error statistics, use

the following Junos OS CLI operational mode command:

Sample Output

MeaningCheck for any error statistics. There should not be

any input or output errors. If there are any persistent input or output

errors, open a case with the Juniper Networks Technical Assistance

Center (JTAC) at support@juniper.net, or at 1-888-314-JTAC

(within the United States) or 1-408-745-9500 (from outside the United

States).

Diagnose a Suspected Circuit Problem

Purpose

Action

PurposeWhen you suspect a circuit problem, it is important

to work with the transport-layer engineer to resolve the problem.

The transport-layer engineer may create a loop to the router from

various points in the network. You can then perform tests to verify

the connection from the router to that loopback in the network.

ActionAfter the transport-layer engineer has created the loop

to the router from the network, you must verify the connection from

the router to the loopback in the network. Follow Step 2 through Step

8 in Diagnose a Suspected Hardware Problem with a Fast

Ethernet or Gigabit Ethernet Interface. Keep in mind that

any problems encountered in the test indicate a problem with the connection

from the router to the loopback in the network.

By performing tests to loopbacks at various points in the network,

you can isolate the source of the problem.

10/100/1000 Interface Testing with the PhyView Analyzer

10/100/1000 Interface Testing with the PhyView Analyzer

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为基于 RFC 2544 的基准测试|配置以太网环路瞻博网络

为基于 RFC 2544 的基准测试|配置以太网环路瞻博网络

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为基于 RFC 2544 的基准测试配置以太网环路

以太网环路是一项可用于验证连接以及识别或隔离网络故障的功能。

在 ACX 系列路由器上，在出口用户到网络接口 （UNI） 方向上支持以太网环路，以实现系列 bridge 配置。在 ACX 系列路由器中，以太网环路配置在逻辑接口上。以太网环路功能可用于性能测量，其中数据包被循环回测量设备，以测试各种服务。

图 1：在以太网环路模式下

测试端到端服务

图 1 显示了一个方案，其中 UNI-B 接口在出口方向的以太网环路模式下配置。在 ACX 系列路由器的网络到网络接口 （NNI） 上收到的数据包将转发到 UNI-B 接口，并在交换源和目标 MAC 地址后环路回 UNI-B 接口。这是测试端到端服务的用例。

您可以使用以下可选参数来识别以太网环路的出口流量：

源 MAC 地址

目标 MAC 地址

源 IPv4 地址

目标 IPv4 地址

Vlan

VLAN.1p 优先级

EtherType

测试更新器持续时间

在执行 RFC2544 基准测试时，通过在层次结构级别包含 Ethernet-loopback CLI 语句，将以太网环路配置为逻辑接口上的 [edit services rpm rfc2544-benchmarking] 测试模式。

如果在逻辑接口上配置以太网环路而不配置任何可选参数，则同一桥接域中的任何未知单播流量也会被环路回传，在执行测试时不会转发到其他逻辑接口。

在执行 RFC2544 基准测试时，如果未配置 测试周期 参数，则以太网环路将继续执行，直到测试完成或终止。

注意：

执行 RFC2544 基准测试时，可以在发起器、反射器或环路模式下配置测试。您不能将这些测试模式组合在一起执行 RFC2544 基准测试。

以下是以太网环路配置示例：

相关文档

基于 RFC 2544 的 ACX 路由器基准测试概述

基于 RFC 2544 的第 2 层和第 3 层基准测试概述

配置基于 RFC 2544 的基准测试

基于 RFC 2544 的基准测试状态

示例：为第 3 层 IPv4 服务配置基于 RFC 2544 的基准测试

示例：为以太网伪线的 NNI 方向配置基于 RFC 2544 的基准测试

示例：为以太网伪线的 UNI 方向配置基于 RFC 2544 的基准测试

Configuring Interface Diagnostics Tools to Test the Physical Layer Connections | Junos OS | Juniper Networks

Configuring Interface Diagnostics Tools to Test the Physical Layer Connections | Junos OS | Juniper Networks

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 ON THIS PAGEConfiguring Loopback TestingConfiguring BERT TestingStarting and Stopping a BERT Test 

Configuring Interface Diagnostics Tools to Test the Physical

Layer Connections

Configuring Loopback Testing

Loopback testing allows you to verify the connectivity of a

circuit. You can configure any of the following interfaces to execute

a loopback test: aggregated Ethernet, Fast Ethernet, Gigabit Ethernet,

E1, E3, NxDS0, serial, SONET/SDH, T1, and T3.

The physical path of a network data circuit usually consists

of segments interconnected by devices that repeat and regenerate the

transmission signal. The transmit path on one device connects to the

receive path on the next device. If a circuit fault occurs in the

form of a line break or a signal corruption, you can isolate the problem

by using a loopback test. Loopback tests allow you to isolate segments

of the circuit and test them separately.

To do this, configure a line loopback on

one of the routers. Instead of transmitting the signal toward the

far-end device, the line loopback sends the signal back to the originating

router. If the originating router receives back its own Data Link

Layer packets, you have verified that the problem is beyond the originating

router. Next, configure a line loopback farther away from the local

router. If this originating router does not receive its own Data Link

Layer packets, you can assume that the problem is on one of the segments

between the local router and the remote router’s interface card.

In this case, the next troubleshooting step is to configure a line

loopback closer to the local router to find the source of the problem.

The following types of loopback testing are supported

by Junos OS:

DCE local—Loops packets back on the local data circuit-terminating

equipment (DCE).

DCE remote—Loops packets back on the remote DCE.

Local—Useful for troubleshooting physical PIC errors.

Configuring local loopback on an interface allows transmission of

packets to the channel service unit (CSU) and then to the circuit

toward the far-end device. The interface receives its own transmission,

which includes data and timing information, on the local router's

PIC. The data received from the CSU is ignored. To test a local loopback,

issue the show interfaces interface-name command. If PPP keepalives transmitted on the interface are

received by the PIC, the Device Flags field contains the

output Loop-Detected.

Payload—Useful for troubleshooting the physical

circuit problems between the local router and the remote router. A

payload loopback loops data only (without clocking information) on

the remote router’s PIC. With payload loopback, overhead is

recalculated.

Remote—Useful for troubleshooting the physical circuit

problems between the local router and the remote router. A remote

loopback loops packets, including both data and timing information,

back on the remote router’s interface card. A router at one

end of the circuit initiates a remote loopback toward its remote partner.

When you configure a remote loopback, the packets received from the

physical circuit and CSU are received by the interface. Those packets

are then retransmitted by the PIC back toward the CSU and the circuit.

This loopback tests all the intermediate transmission segments.

Table 1 shows the

loopback modes supported on the various interface types.

Table 1: Loopback

Modes by Interface TypeInterface

Loopback Modes

Usage Guidelines

Aggregated Ethernet, Fast Ethernet, Gigabit Ethernet

Local

Configuring Ethernet Loopback

Capability

Circuit Emulation E1

Local and remote

Configuring E1 Loopback Capability

Circuit Emulation T1

Local and remote

Configuring T1 Loopback Capability

E1 and E3

Local and remote

Configuring E1 Loopback Capability and Configuring E3 Loopback Capability

NxDS0

Payload

Configuring

NxDS0 IQ and IQE Interfaces, Configuring T1 and NxDS0 Interfaces, Configuring Channelized OC12/STM4

IQ and IQE Interfaces (SONET Mode), Configuring Fractional E1 IQ

and IQE Interfaces, and Configuring Channelized T3 IQ Interfaces

Serial (V.35 and X.21)

Local and remote

Configuring Serial Loopback Capability

Serial (EIA-530)

DCE local, DCE remote, local, and remote

Configuring Serial Loopback Capability

SONET/SDH

Local and remote

Configuring SONET/SDH Loopback

Capability to Identify a Problem as Internal or External

T1 and T3

Local, payload, and remote

Configuring T1 Loopback Capability and Configuring T3 Loopback Capability

See also Configuring the T1 Remote

Loopback Response

To configure loopback testing, include the loopback statement:

You can include this statement at the following hierarchy

levels:

[edit interfaces interface-name aggregated-ether-options]

[edit interfaces interface-name ds0-options]

[edit interfaces interface-name e1-options]

[edit interfaces interface-name e3-options]

[edit interfaces interface-name fastether-options]

[edit interfaces interface-name gigether-options]

[edit interfaces interface-name serial-options]

[edit interfaces interface-name sonet-options]

[edit interfaces interface-name t1-options]

[edit interfaces interface-name t3-options]

Configuring BERT Testing

To configure BERT:

Configure the duration of the test.

You can configure the BERT period to last from 1 through

239 seconds on some PICs and from 1 through 240 seconds

on other PICs. By default, the BERT period is 10 seconds.

Configure the error rate to monitor when the inbound pattern

is received.

rate is the bit error rate. This can be

an integer from 0 through 7, which corresponds to a bit error rate

from 10–0 (1 error per bit) to 10–7 (1 error per 10 million bits).

Configure the bit pattern to send on the transmit path.

algorithm is the pattern to send in the

bit stream. For a list of supported algorithms, enter a ? after the bert-algorithm statement; for example:

For specific hierarchy information, see the individual interface

types.

Note: The four-port E1 PIC supports only the following algorithms:

When you issue the help command from the CLI, all

BERT algorithm options are displayed, regardless of the PIC type,

and no commit check is available. Unsupported patterns for a PIC type

can be viewed in system log messages.

Note: The 12-port T1/E1 Circuit Emulation (CE) PIC supports

only the following algorithms:

When you issue the help command from the CLI, all

BERT algorithm options are displayed, regardless of the PIC type,

and no commit check is available. Unsupported patterns for a PIC type

can be viewed in system log messages.

Note: The IQE PICs support only the following algorithms:

When you issue the help command from the CLI, all

BERT algorithm options are displayed, regardless of the PIC type,

and no commit check is available. Unsupported patterns for a PIC type

can be viewed in system log messages.

Note: BERT is supported on the PDH interfaces of the Channelized

SONET/SDH OC3/STM1 (Multi-Rate) MIC with SFP and the DS3/E3 MIC. The

following BERT algorithms are supported:

Table 2 shows the

BERT capabilities for various interface types.

Table 2: BERT Capabilities

by Interface TypeInterface

T1 BERT

T3 BERT

Comments

12-port T1/E1 Circuit Emulation

Yes (ports 0–11)

—

Limited algorithms

4-port Channelized OC3/STM1 Circuit Emulation

Yes (port 0–3)

—

Limited algorithms

E1 or T1

Yes (port 0–3)

Yes (port 0–3)

Single port at a time

Limited algorithms

E3 or T3

Yes (port 0–3)

Yes (port 0–3)

Single port at a time

Channelized OC12

—

Yes (channel 0–11)

Single channel at a time

Limited algorithms

No bit count

Channelized STM1

Yes (channel 0–62)

—

Multiple channels

Only one algorithm

No error insert

No bit count

Channelized T3 and Multichannel T3

Yes (channel 0–27)

Yes (port 0–3 on channel 0)

Multiple ports and channels

Limited algorithms for T1

No error insert for T1

No bit count for T1

These limitations do not apply to channelized IQ interfaces.

For information about BERT capabilities on channelized IQ interfaces,

see Channelized IQ and IQE Interfaces

Properties.

Starting and Stopping a BERT Test

Before you can start the BERT test, you must disable the interface.

To do this, include the disable statement at the [edit

interfaces interface-name] hierarchy level:

After you configure the BERT properties and commit the configuration,

begin the test by issuing the test interface interface-name interface-type-bert-start operational

mode command:

The test runs for the duration you specify with the bert-period statement. If you want to terminate the test sooner, issue the test interface interface-name interface-type-bert-stop command:

For example:

To view the results of the BERT test, issue the show interfaces

extensive | find BERT command:

For more information about running and evaluating the results

of the BERT procedure, see the CLI Explorer.

Note: To exchange BERT patterns between a local router and a

remote router, include the loopback remote statement in

the interface configuration at the remote end of the link. From the

local router, issue the test interface command.

Related Documentationshow interfaces diagnostics

optics (Gigabit Ethernet, 10-Gigabit Ethernet, 40-Gigabit Ethernet,

100-Gigabit Ethernet, and Virtual Chassis Port)

A Brief Introduction to Ethernet | GraniteRiverLabs

A Brief Introduction to Ethernet | GraniteRiverLabs

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By GRL Team

on

February 25, 2021

Ethernet

A Brief Introduction to Ethernet

Granite River Labs (GRL)By Raymond Huang – Test Engineer, GRL (Taipei)

Ethernet is one of the most commonly-used technologies in local area networks (LANs) and the network architectures. It is based on the specifications established by the Institute of Electrical and Electronics Engineers (IEEE) and included in the IEEE 802.3 standard. This article is intended to provide an introduction to Ethernet (10M/100M/1000M) and the relevant tests based on the standard.

 Ethernet is primarily designed to transmit information through multiple nodes on a network via cable, fiber channel and other media. Each Node has a specific address number. The global 48-bit MAC address (Media Access Control Address) is used to ensure identification among the Nodes and avoid transmission errors.

To understand Ethernet, it is helpful to be familiar with two technical terms:

Network topology

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

Network topology

Network topology can take a variety of forms, among which Star Topology and Bus Topology are the most common.

In Star Topology, a host controls the workstations around it and creates a star structure (as shown in Figure 1), with point-to-point on-line through media, such as Twisted Pair cable or Optical Fiber, which is convenient for routing and network maintenance. The quality and stability of the host are important.

Figure 1: Star Topology

Bus Topology does not use a specific host as its core. Instead, this is shared by using twisted pair, coaxial cable and a Hub (see Figure 2). Routing is convenient and requires no specific settings when adding or removing a device. Its main disadvantage is that a problem occurring in any part of the transmission trunk will paralyze the whole network.

Figure 2: Bus Topology

CSMA/CD

CSMA/CD mainly operates in the bus structure. All the hosts (or workstations) that want to transmit data are required to broadcast data to the transmission media, while all workstations should be capable of receiving data broadcast on the network.

Ideally, only one source transmits information at a time. Before transmitting data, the host (or workstation) must confirm whether there is a signal being transmitted on the network. Data can be transmitted if no other signal source is transmitting, or if the rest of the workstations on the network are idle. Otherwise, the host must wait and keep detecting. If two hosts (or workstations) transmit signals at the same time, collisions between the signals will occur on the network (as shown in Figure 3), resulting in a message error that cannot be interpreted by the receiver.

When a collision occurs, the rest of units must stop transmitting signals. The transmitter sends out a jamming signal and informs the other workstations that a collision has occurred, and transmission of the signal should be stopped. The transmission terminal will wait for a Random Time before retransmitting.

Figure 3

10Base-T：(IEEE 802.3 Clause 1 through Clause 20)

10 stands for 10 Mbps; Base, for Baseband; T, for Twisted Pair, and 10Base-T, for Cat-3 UTP.

10Base-T is Manchester Encoded. It defines 0 and 1 by the transmission state of the original signal. The minimum bandwidth required on twisted pair is 20M. It retains the original characteristics of CSMA/CD, but follows a tree topology (hybrid star and bus) in terms of network structure (See Figure 4).

Figure 4: Common Hub

The device in the bus shown in Figure 4 is the common Hub. A disconnection between workstations and the Hub does not affect the transmission or reception of messages by the unit.

The Hub offers the advantages of both topologies in terms of routing and network maintenance.

The CSMA/CD properties of 10MBASE-T can be tested with the equivalent TPM (Twisted Pair Model). The quality of the signal is tested first. The test condition is when the Link Pulse and the signal of transmission returns to "Idle" after the transmitter and the receiver are connected. The impedance value of DUT should be confirmed to ensure that it matches the specification, because this could impact the return loss result (see detailed test items in Table 1).

Table 1

100Base-TX：(IEEE 802.3 Clause 21 through Clause 33)

In 100Base-TX, data is transmitted at 100 Mbps, and X indicates that its Spec meets the X3T9.5 standard proposed by the American National Standards Institute (ANSI). 100BASE-TX uses two pairs of twisted pair cables – one for sending signals and the other for receiving signals. High bandwidth Cat-5 UTP is usually chosen to transmit high frequency signals and ensure signal quality,

The communication protocol is also CSMA/CD. It differs from 10Base-T in its encoding and Auto negotiation function. Unlike 100Base-TX, it adopts 4B/5B and NRZI (Non-Return Zero Inverted code) instead of Manchester Encoding. Then, it is encoded with Multi-Level Transmission-3 (MLT-3) and transmitted as shown in Figure 5. Therefore, the required bandwidth of the cable is 31.25 MHz (100 × 5/4 × 1/2 × 1/2 = 31.25 MHz). Major tests tend to focus on the signal integrity of MLT-3.

Figure 5

100Base-TX with Auto-negotiation is imported for downward compatibility with 10Base-T. It judges the capabilities supported by the receiver through Auto negotiation – such as transmission rate, the number of signal channels, transmission mode (full-duplex or half-duplex) – and then completes the transmission conditions after the transmitter is connected to the receiver.

Since the peak of Differential signal is significant to MLT-3 encoding, specifications have been formulated for the peak voltage (+Vout, -Vout) and Overshoot of both positive and negative voltages. Symmetry is also required for testing to avoid too large a gap between negative and positive voltages. In addition to voltage, the time offset is also specified, as shown in Figure 6. A large time offset will lead to signal distortion, resulting in a misjudgment of the signal as 0 or 1 by the receiver (see the detailed test items in Table 2).

Figure 6

Table 2

1000Base-T：(IEEE 802.3z, IEEE 802.3ab)

The 1000Base-T Gigabit Ethernet (GBE) communication protocol also follows the CSMA/CD mode, with a Cat-5 UTP cable comprising four pairs of twisted pair wires used for signal transmission, and PAM-5(Pulse Amplitude Modulation 5) for encoding (see Figure 7).

Figure 7

Four pairs of twisted pair wires can simultaneously transmit or receive signals, each at a frequency of 250 MHz. However, as two bits are expressed as one potential in PAM-5 encoding, the frequency of each pair may ultimately be measured as 125MHz. 1000Base-T is backward compatible with 100/10Base-T and has the same Auto negotiation function as 100Base-TX, so it can be downgraded to 100Base-TX if necessary. The Pam-5 code used by 1000Base-T also has Pulse-Shaping, which means that after the data is encoded, the five potentials are shown similarly to the continuous signals. This can reduce the high frequency noise and low frequency component, and ultimately strengthen the relative signal-to-noise ratio of the output.

The test items for 1000Base-T are shown in Table 3. Different test conditions have been defined for each item according to the specification:

Table 3

Test Mode 1

Pattern Test Mode 1 is used to confirm the five accurate positions of PAM-5, to ensure that data transmission is error-free. It also confirms that the potential at points such as A, B, C and D does not shift too much, and that G relative to F, and J relative to H has not decayed too far. There is also a Template specification for this waveform to test signal waveform integrity to ensure signal quality.

Figure 8

Test Mode 2 & 3:

Pattern Test Modes 2 & 3 are shown as periodic 125 MHz signals in Figure 9. These test modes confirm the amount of jitter in Auto negotiation through the Pattern in master and slave Mode to avoid Auto negotiation failure, by verifying whether the jitter of the signal complies with the specification.

Figure 9

Test Mode 4

In Pattern Test Mode 4, the transmitter sends signals generated when passing through the scrambler generator polynomial. This is an 11-bit signal with iterative properties, as shown in Figure 10. A schematic of its iterative concept is shown in Figure 1. Bits followed by the 11th bit are output after performing an exclusive or logic operation (e.g. AND, OR, XOR). For detailed algebraic operations, please refer to IEEE 802.3ab.

Iterative test signals can be used to verify whether the level of electric potential distortion is within IEEE specifications and check whether the Common Mode caused by each Pair meets the specifications.

Figure 10

Figure 11

Granite River Labs (GRL) has found that with the increasing use of cloud computing by enterprises, the demand for servers has increased in recent years. Network interfaces are more widely used for a variety of reasons, and transmission speeds are improving, which also means that quality and testing requirements are increasingly important.

References

IEEE Standard for Ethernet (IEEE Std 802.3™-2018)

Keysight N5392A/N5392B Ethernet Compliance Test Application MOI

https://linksprinterblog.wordpress.com/2014/05/14/there-is-more-to-life-than-increasing-its-speed/

Wiki MLT-3 encoding

AuthorRaymond Huang – Test Engineer, GRL (Taipei)

A graduate of National Taiwan University with a master’s degree in Chemical Engineering, Raymond Huang has over two years test experience and is familiar with the DisplayPort DisplayHDR and Ethernet test specifications.

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Published by GRL Team

February 25, 2021

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Configuring loopback testing on an Ethernet interface

[x]Performing general configurations > Configuring loopback testing on an Ethernet interface  NextConfiguring loopback testing on an Ethernet interfaceIf an Ethernet interface does not work normally, you can enable loopback testing on it to identify the problem. An Ethernet interface in a loopback test does not forward data traffic.Loopback testing has the following types:Internal loopback testing—Tests all on-chip functions related to Ethernet interfaces.External loopback testing—Tests hardware of Ethernet interfaces. To perform external loopback testing on an Ethernet interface, connect a loopback plug to the Ethernet interface. The device sends test packets out of the interface, which are expected to loop over the plug and back to the interface. If the interface fails to receive any test packets, the hardware of the interface is faulty.Configuration restrictions and guidelines On an interface administratively shut down, you cannot perform internal or external loopback testing.The speed, duplex, mdi, and shutdown commands are not available during loopback testing.During loopback testing, the Ethernet interface operates in full duplex mode. When you disable loopback testing, the port returns to its duplex setting.Loopback testing is a one-time operation, and is not recorded in the configuration file.Configuration procedureTo enable loopback testing on an Ethernet interface:StepCommandRemarks1. Enter system view.system-viewN/A2. Enter Ethernet interface view.interface interface-type interface-numberN/A3. Enable loopback testing.loopback { external | internal }By default, loopback testing is disabled.prev up nextConfiguring physical state change suppression on an Ethernet interface home Configuring the link mode of an Ethernet interface © Copyright 2016 Hewlett Packard Enterprise Development