Title: Cable tester
Abstract: A physical layer device communicates with a second physical layer device over a cable. The physical layer device includes a cable tester that identifies when the second physical layer device is disconnected from the cable. The cable tester includes a test initiating circuit that initiates a cable test when a link is lost, a test module that transmits test pulses on the pairs of the cable, measures reflection amplitudes, calculates cable lengths, and determines whether the pairs have said open status based on said measured amplitude and said calculated cable length, and a reporting circuit that generates a disconnect signal when at least one of the pairs has an open status.
Patent Number: 7,002,353 Issued on 02/21/2006 to Lo, et al.
| Inventors:
|
Lo; William (Cupertino, CA);
Guo; Yiqing (Cupertino, CA);
Tsui; Tak (Sunnyvale, CA);
Leung; Tsin-Ho (San Jose, CA);
He; Runsheng (Sunnyvale, CA);
Janofsky; Eric (Sunnyvale, CA)
|
| Assignee:
|
Marvell International, Ltd. (Hamilton, BM)
|
| Appl. No.:
|
400864 |
| Filed:
|
March 27, 2003 |
| Current U.S. Class: |
324/534; 324/533; 324/543 |
| Current Intern'l Class: |
G01R 31/11 (20060101) |
| Field of Search: |
324/534,539,533,543
|
References Cited [Referenced By]
U.S. Patent Documents
| 5461318 | Oct., 1995 | Borchert et al.
| |
| 6138080 | Oct., 2000 | Richardson.
| |
| 6198727 | Mar., 2001 | Wakeley et al.
| |
| 6377640 | Apr., 2002 | Trans.
| |
| 6434716 | Aug., 2002 | Johnson et al.
| |
| 6448899 | Sep., 2002 | Thompson.
| |
| 6522152 | Feb., 2003 | Tonti et al.
| |
| 6694017 | Feb., 2004 | Takada.
| |
| 6728216 | Apr., 2004 | Sterner.
| |
| 2002/0124110 | Sep., 2002 | Tanaka.
| |
| Foreign Patent Documents |
| WO 01/1186/1 | Feb., 2001 | WO.
| |
| WO 01/1186/1 | Feb., 2001 | WO.
| |
| WO 01/1186/1 | Feb., 2001 | WO.
| |
Other References
Intel, "LXT9784 Octal 10/100 Transceiver Hardware Integrity Function Overview",
Jan. 2001, pp. 1-14.
MP0042="Movable Tap Finite Impulse Response Filter", U.S. Appl. No. 09/678,728,
filed Oct. 4, 2000.
MP0042PR="Finite Impulse Response Filter" U.S. Appl. No. 60/217,418, filed Jul.
11, 2000.
MP0113="Method and Apparatus for Detecting and Supplying Power by a First Network
Device to a Second Network Device", U.S. Appl. No. 10/098,865, filed Mar. 15, 2002.
U.S. Appl. No. 09/991,043, filed Nov. 21, 2001, William Lo.
U.S. Appl. No. 09/991,03, filed Nov. 2001, William Lo.
IEEE std. 802.3 IEEE Standard for Information technology—Telecommunications
and information exchange between systems—Local and metropolitan area networks—Specific
requirements; Part 3: Carrier sense multiple access with collison detection (CSMA/DC)
access method and physical layer specifications, 2002, pp. 1-173.
|
Primary Examiner: Nguyen; Vincent Q.
Assistant Examiner: Dole; Timothy J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent application Ser. No.
10/331,221, filed Dec. 30, 2002, which is a continuation-in-part of U.S. patent
application Ser. No. 10/165,467, filed Jun. 7, 2002 now U.S. Pat. No. 6,825,672.
The disclosures of the above applications are incorporated herein by reference
in their entirety.
Claims
What is claimed is:
1. A physical layer device that communicates with a second physical layer device
over a cable, said physical layer device comprising:
a cable tester that identifies when the second physical layer device is disconnected
from the cable, wherein said cable tester includes:
a test initiating circuit that communicates with said cable tester and that initiates
a cable test when a link is lost;
a test module that transmits test pulses on pairs of the cable, measures reflection
amplitudes, calculates cable lengths, and determines whether the pairs have said
open status based on said measured amplitude and said calculated cable length within
a predetermined time after said link is lost; and
a reporting circuit that communicates with said test module and that generates
a disconnect signal when at least one of the pairs has an open status.
2. The physical layer device of claim 1 further comprising an indicator for displaying
at least one of said cable status, said open status, said disconnect signal, said
calculated cable length and said measured reflection amplitude.
3. The physical layer device of claim 1 wherein said physical layer device is
implemented in a network device.
4. The physical layer device of claim 1 wherein said cable tester is integrated
with said physical layer device in a single integrated circuit.
5. The physical layer device of claim 1 wherein said reporting circuit generates
said disconnect signal when all of the pairs have said open status.
6. The physical layer device of claim 1 wherein said physical layer device is
implemented in an Ethernet device that is 802.3ab compliant.
7. The physical layer device of claim 1 wherein said test module senses activity
on a first pair of said cable and enables testing if activity is not detected for
a first period and enables testing of said first pair if, during said first period,
activity is detected on said first pair and is subsequently not detected on said
first pair for a second period after said activity is detected.
8. The physical layer device of claim 1 further comprising a lookup table that
includes a plurality of sets of reflection amplitudes as a function of cable length,
wherein said test module communicates with said lookup table and determines said
status based on said measured amplitude and said calculated cable length, wherein
said sets of reflection amplitudes define a plurality of windows including a first
window that is defined by first and second thresholds, wherein said first threshold
is based on a first set of reflection amplitudes that are measured as a function
of cable length when a test cable type is an open circuit, and wherein said second
threshold is based on a second set of reflection amplitudes that are measured as
a function of cable length when said test cable type is terminated using a first
impedance having a first impedance value.
9. The physical layer device of claim 1 wherein said test module transmits said
test pulse, measures offset, subtracts said offset from said reflection amplitude,
and detects peaks, and wherein if a second peak is not detected after a first peak
and said reflection amplitude of said first peak is greater than a first threshold,
said test module transmits a second test pulse having a second amplitude that is
less than a first amplitude of said first test pulse.
10. The physical layer device of claim 1 further comprising a converter that
measures said reflection amplitude, wherein said test module measures offset at
said converter, subtracts said offset from said reflection amplitude, and zeroes
said reflection amplitude below a floor.
11. A physical layer device that communicates with a second physical layer device
over a cable including pairs, said physical layer device comprising:
cable testing means for identifying when the second physical layer device is
disconnected from the cable, wherein said cable testing means includes:
test initiating means that communicates with said cable testing means for initiating
a cable test when a link is lost;
test means for transmitting test pulses on pairs of the cable, for measuring
reflection amplitudes, for calculating cable lengths, and for determining whether
the pairs have said open status based on said measured amplitude and said calculated
cable length within a predetermined time after said link is lost; and
reporting means that communicates with said test means for generating a disconnect
signal when at least one of the pairs has said open status.
12. The physical layer device of claim 11 further comprising indicating means
for displaying at least one of said cable status, said open status, said disconnect
signal, said calculated cable length and said measured reflection amplitude.
13. The physical layer device of claim 11 wherein said physical layer device
is implemented in a network device.
14. The physical layer device of claim 11 wherein said cable testing means is
integrated with said physical layer device in a single integrated circuit.
15. The physical layer device of claim 11 wherein said reporting means generates
said disconnect signal when all of the pairs have said open status.
16. The physical layer device of claim 11 wherein said physical layer device
is implemented in an Ethernet device that is 802.3ab compliant.
17. The physical layer device of claim 11 wherein said test means senses activity
on a first pair of said cable and enables testing if activity is not detected for
a first period and enables testing of said first pair if, during said first period,
activity is detected on said first pair and is subsequently not detected on said
first pair for a second period after said activity is detected.
18. The physical layer device of claim 11 further comprising lookup means for
storing a plurality of sets of reflection amplitudes as a function of cable length,
wherein said test means determines said status using said lookup means, said measured
reflection amplitude and said calculated cable length, wherein said sets of reflection
amplitudes define a plurality of windows including a first window that is defined
by first and second thresholds, wherein said first threshold is based on a first
set of reflection amplitudes that are measured as a function of cable length when
a test cable type is an open circuit, and wherein said second threshold is based
on a second set of reflection amplitudes that are measured as a function of cable
length when said test cable type is terminated using a first impedance having a
first impedance value.
19. The physical layer device of claim 11 wherein said test means transmits said
test pulse, measures offset, subtracts said offset from said reflection amplitude,
and detects peaks, and wherein if a second peak is not detected after a first peak
and said reflection amplitude of said first peak is greater than a first threshold,
said test means transmits a second test pulse having a second amplitude that is
less than a first amplitude of said first test pulse.
20. The physical layer device of claim 11 further comprising converting means
for measuring said reflection amplitude, wherein said test means measures offset
at said converting means, subtracts said offset from said reflection amplitude,
and zeroes said reflection amplitude below a floor.
21. A method for operating a physical layer device, comprising:
initiating a cable test within a predetermined period after a link is lost;
transmitting test pulses on pairs of the cable;
measuring reflection amplitudes;
calculating cable lengths;
determining whether the pairs have an open status based on said measured amplitude
and said calculated cable length; and
generating a disconnect signal when one at least one of the pairs has said open status.
22. The method of claim 21 further comprising displaying at least one of said
cable status, said open status, said disconnect signal, said calculated cable length
and said measured reflection amplitude.
23. The method of claim 21 further comprising generating said disconnect signal
when all of the pairs have said open status.
24. The method of claim 21 further comprising:
sensing activity on a first pair of said cable and enables testing if activity
is not detected for a first period; and
enables testing of said first pair if, during said first period, activity is
detected on said first pair and is subsequently not detected on said first pair
for a second period after said activity is detected.
25. The method of claim 21 further comprising:
storing a plurality of sets of reflection amplitudes as a function of cable length; and
determining said status based on said measured amplitude and said calculated
cable length,
wherein said sets of reflection amplitudes define a plurality of windows including
a first window that is defined by first and second thresholds, wherein said first
threshold is based on a first set of reflection amplitudes that are measured as
a function of cable length when a test cable type is an open circuit, and wherein
said second threshold is based on a second set of reflection amplitudes that are
measured as a function of cable length when said test cable type is terminated
using a first impedance having a first impedance value.
26. The method of claim 21 further comprising:
transmitting said test pulse;
measuring offset;
subtracting said offset from said reflection amplitude;
detecting peaks; and
transmitting a second test pulse having a second amplitude that is less than
a first amplitude of said first test pulse if a second peak is not detected after
a first peak and said reflection amplitude of said first peak is greater than a
first threshold.
27. The method of claim 21 further comprising:
measuring said reflection amplitude;
measuring offset;
subtracting said offset from said reflection amplitude; and
cancelling said reflection amplitude below a floor.
Description
FIELD OF THE INVENTION
The present invention relates to electronic diagnostic systems, and more particularly
to testing equipment for cable used in a network.
BACKGROUND OF THE INVENTION
One goal of a network manager is to control total cost of ownership of the network.
Cabling problems can cause a significant amount of network downtime and can require
troubleshooting resources, which increase the total cost of ownership. Providing
tools that help solve cabling problems more quickly will increase network uptime
and reduce the total cost ownership.
Referring now to FIG. 1, conventional cable testers 10 are frequently
used to isolate cabling problems. The cable testers 10 are coupled by a
connector 12 (such as an RJ-45 or other connector) to a cable 14.
A connector 15 connects the cable to a load 16. Conventional cable
testers typically require the load 16 to be a remote node terminator or
a loop back module. Conventional cable tests may generate inaccurate results when
the cable is terminated by an active link partner that is generating link pulses
during a test. The cable tester 10 performs cable analysis and is able to
detect a short, an open, a crossed pair, or a reversed pair. The cable tester 10
can also determine a cable length to a short or open.
A short condition occurs when two or more lines are short-circuited together.
An
open condition occurs when there is a lack of continuity between ends at both ends
of a cable. A crossed pair occurs when a pair communicates with different pins
at each end. For example, a first pair communicates with pins 1 and 2
at one end and pins 3 and 6 at the other end. A reversed pair occurs
when two ends in a pair are connected to opposite pins at each end of the cable.
For example, a line on pin 1 communicates with pin 2 at the other
end. A line on pin 2 communicates with pin 1 at the other end.
The cable tester 10 employs time domain reflection (TDR), which is based
on transmission line theory, to troubleshoot cable faults. The cable tester 10
transmits a pulse 17 on the cable 14 and measures an elapsed time
until a reflection 18 is received. Using the elapsed time and a cable propagation
constant, a cable distance can be estimated and a fault can be identified. Two
waves propagate through the cable 14. A forward wave propagates from a transmitter
in the cable tester 10 towards the load 16 or fault. A return wave
propagates from the load 16 or fault to the cable tester 10.
A perfectly terminated line has no attenuation and an impedance that is matched
to a source impedance. The load is equal to the line impedance. The return wave
is zero for a perfectly terminated line because the load receives all of the forward
wave energy. For open circuits, the return wave has an amplitude that is approximately
equal to the forward wave. For short circuits, the return wave has a negative amplitude
is also approximately equal to the forward wave.
In transmission line theory, a reflection coefficient is defined as:
##EQU1##
Where Z
L is the load impedance and Z
O is the cable impedance.
The return loss in (dB) is defined as:
##EQU2##
Return loss performance is determined by the transmitter return loss, the
cable characteristic impedance and return loss, and the receiver return loss. IEEE
section 802.3, which is hereby incorporated by reference, specifies receiver and
transmitter minimum return loss for various frequencies. Additional factors that
may affect the accuracy of the return loss measurement include connectors and patch
panels. Cable impedance can also vary, for example CAT5 UTP cable impedance can
vary ±15 Ohms.
Consumers can now purchase lower cost switches, routers, network devices
and network appliances that include physical layer devices with ports that are
connected to cable. When connecting these network devices to cable, the same types
of cabling problems that are described above may occur. In these lower cost applications,
the consumer typically does not have a cable tester or want to purchase one. Therefore,
it is difficult to identify and diagnose cable problems without simply swapping
the questionable cable with a purportedly operating cable. If the purportedly operating
cable does not actually work, the consumer may incorrectly conclude that the network
device is not operating and/or experience further downtime until the cable problem
is identified.
SUMMARY OF THE INVENTION
A physical layer device according to the present invention communicates with a
second physical layer device over a cable. The physical layer device includes a
cable tester that identifies when the second physical layer device is disconnected
from the cable. The cable tester includes a test initiating circuit that initiates
a cable test when a link is lost. A test module transmits test pulses on the pairs
of the cable, measures reflection amplitudes and calculates cable lengths. The
test module determines whether the pairs have an open status based on the measured
amplitude and the calculated cable length. A reporting circuit generates a disconnect
signal when at least one of the pairs has the open status.
In other features, an indicator displays the cable status, the open status, the
disconnect signal, the calculated cable length and/or the measured reflection amplitude.
The physical layer device is implemented in a network device. The cable tester
is integrated with the physical layer device in a single integrated circuit. The
reporting circuit generates the disconnect signal when all of the pairs have the
open status. The physical layer device is implemented in an Ethernet device that
is 802.3ab compliant.
A physical layer device according to the present invention communicates over a
cable. The physical layer device includes a cable tester that tests the cable and
determines a cable status including an open status, a short status, and a normal
status. A pretest module senses activity on the cable and selectively enables testing
based on said sensed activity. A test module is enabled by the pretest module,
transmits a test pulse on the cable, measures a reflection amplitude and calculates
a cable length. The test module determines the cable status based on the measured
amplitude and the calculated cable length. The cable tester repeats the test N
times and performs a calculation on at least one of the cable status, the measured
amplitude and the calculated cable length.
In other features, the calculation includes at least one of a mathematical function
and a Boolean function. The mathematical function is an averaging function. A comparing
circuit compares the calculation to a predetermined threshold to determine the
cable status. An indicator displays the cable status, the calculation, the calculated
cable length and/or the measured reflection amplitude. The comparing circuit compares
at least one of an average amplitude and an average calculated length to at least
one of first and second predetermined thresholds to determine the cable status.
A physical layer device according to the present invention includes a first port,
a second port, and a cable that has one end that communicates with the first port
and an opposite end that communicates with the second port. The physical layer
device includes a cable tester that communicates with the first and second ports
and that tests the cable to determine a cable status, which includes an open status,
a short status, and a normal status. A pretest module senses activity on the cable
and selectively enables testing based on said sensed activity. A test module is
enabled by the pretest module, transmits a test pulse on the cable, measures a
reflection amplitude and calculates a cable length. The test module determines
the cable status based on the measured amplitude and the calculated cable length.
A frequency synthesizer communicates with the cable and selectively outputs a plurality
of signals at a plurality of frequencies on the cable. An insertion loss calculator
receives the signals and estimates insertion loss.
In other features, a comparing circuit compares the estimated insertion loss
to
a predetermined threshold. An indicator displays at least one of the status, the
estimated insertion loss, the calculated cable length and the measured reflection amplitude.
A physical layer device according to the present invention includes a cable tester
that tests a cable and that determines a cable status, which includes an open status,
a short status and a normal status. A pretest module senses activity on pairs of
the cable and selectively enables testing based on said sensed activity. A test
module is enabled by the pretest module, transmits test pulses on the pairs of
the cable, measures a reflection amplitude and calculates a cable length. The test
module determines the cable status based on the measured amplitude and the calculated
cable length. A polarity detector communicates with the cable tester and detects
a polarity of at least one of the pairs.
Further areas of applicability of the present invention will become apparent
from the detailed description provided hereinafter. It should be understood that
the detailed description and specific examples, while indicating the preferred
embodiment of the invention, are intended for purposes of illustration only and
are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description
and the accompanying drawings, wherein:
FIG. 1 is a functional block diagram of a cable tester according to the prior art;
FIG. 2 is a functional block diagram of a cable tester according to the present invention;
FIG. 3 is a state diagram of a pretest state machine;
FIG. 4 is a state diagram of a first test state machine for a cable tester for
a media that transmits and receives on the same wire;
FIG. 5 is a state diagram of a second test state machine for a cable tester
for a media that does not transmit and receive on the same wire;
FIG. 6 is a waveform diagram illustrating a time-based receiver floor;
FIG. 7 is an exemplary cable reflection amplitude vs. cable length relationship
for a first type of cable;
FIG. 8 is a functional block diagram of an exemplary network device that includes
one or more physical layer devices and that includes a hardware or software based
cable testing switch for initiating cable testing;
FIG. 9 is a flowchart illustrating steps for performing a cable test for the
exemplary network device in FIG. 8;
FIG. 10A is a functional block diagram of an exemplary power over Ethernet (POE) device;
FIG. 10B is a flowchart illustrating steps for performing a cable test for the
exemplary network device in FIG. 8 when POE devices are possibly connected at remote
cable ends;
FIG. 11 is a functional block diagram of an exemplary network device that includes
one or more physical layer devices and that initiates cable testing at power on;
FIG. 12 is a flowchart illustrating steps for performing a cable test for the
exemplary network device in FIG. 11;
FIG. 13 is a flowchart illustrating steps for performing a cable test for the
exemplary network device in FIG. 11 when POE devices are possibly connected at
remote cable ends;
FIGS. 14A-14E illustrate exemplary LEDs during testing cable testing;
FIG. 15 illustrates the exemplary LEDs showing the results of cable testing; and
FIG. 16 illustrates exemplary LEDs of a network device that includes more than
one LED per port.
FIG. 17 illustrates steps performed by a cable test module to test for shorts
between pairs of the same cable;
FIG. 18 illustrates cable powerdown and powerup steps that are performed when
a short is detected in FIG. 17;
FIG. 19 illustrates steps of a cable test method employing A out of B pass/fail criteria;
FIG. 20 illustrates steps of a cable test method that performs calculations
on the results of repeated cable tests on the same cable;
FIG. 21 illustrates a state machine with timer that can be disabled when link
partners are not present;
FIG. 22 is a functional block diagram of an echo and crosstalk distance estimator;
FIG. 23 is a waveform of an exemplary transmitted signal on a pair with echo
signal components;
FIG. 24 is a waveform of an exemplary signal on another pair with crosstalk
signal components;
FIG. 25 is a functional block diagram of a cable test module that displays skew,
polarity and crossover status data;
FIG. 26 illustrates steps performed by a cable test module to estimate an insertion loss;
FIG. 27 illustrates steps performed by a cable test module to estimate a return loss;
FIG. 28A illustrates steps for calibrating cable length as a function of digital gain;
FIG. 28B is a waveform illustrating cable length as a function of digital gain;
FIG. 29 illustrates steps performed by a cable length estimator;
FIG. 30A illustrates steps for calibrating impedance as a function of reflection amplitude;
FIG. 30B is a waveform illustrating impedance as a function of reflection amplitude;
FIG. 31 illustrates steps performed by a cable impedance estimator;
FIG. 32A is a functional block diagram of a cable test module that triggers
an autonegotiation downshift based on a detected open or
FIG. 32B illustrates steps performed by the cable test module in FIG. 32A;
FIG. 33 is a functional block diagram of cable test module that estimates skew
between pairs;
FIG. 34 illustrates steps that are performed by the cable test module to estimate skew;
FIGS. 35 and 36 is a functional block diagram of a cable test module in a multiple
port network device with an integrated frequency synthesizer and an insertion loss estimator;
FIG. 37A is a functional block diagram of a cable disconnect detector using
the cable test module; and
FIG. 37B illustrates steps that are performed by the cable disconnect detector
in FIG. 37A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiment(s) is merely exemplary
in nature and is in no way intended to limit the invention, its application, or
uses. For purposes of clarity, the same reference numbers will be used in the drawings
to identify the same elements.
Referring now to FIG. 2, a cable tester
20 according to the present
invention is shown. The cable tester
20 is capable of testing 10/100BaseT
cable, 1000BaseT cable, and/or other cable media. For example, 10/100BaseT includes
two pairs of twisted pair wires and 1000BaseT cable includes four pairs of twisted
pair wires. A transmitter
28 and a receiver
30 are coupled to the
I/O interface
26. A test module
32 includes state machines for testing
a media
34 such as cable. The test module
32 can be implemented in
combinatorial logic, using discrete circuits, and/or using a processor and memory
that executes testing software.
The test module
32 includes a pretest state machine or module
50.
The test module
32 also includes a first test state machine or module
52
and/or a second test state machine
54. One or more lookup tables
56
containing cable empirical data are also provided as will be described below. The
cable tester
20 may also include a display
58 for presenting fault
status, cable length and/or reflection amplitude data. The display
58 can
be a graphical user interface (GUI), a light emitting diode (LED) and/or any other
type of display. A cancellation circuit
59 cancels the test pulse when testing
on media that transmits and receives on the same wire such as 1000BaseT. The cancellation
circuit
59 is not used when testing media that transmits and receives on
different wires such as in 10/100BaseT. The cancellation circuit
59 can
be a hybrid circuit.
Referring now to FIG. 3, the pretest state machine
50 is illustrated
in further detail. On reset, the pretest state machine
50 moves to a wait
enable state
100. Pair is set equal to zero and testover is set equal to
one. When a test enabled signal is received, the pretest state machine
50
transitions to a wait powerdown state
102. A powerdown timer is incremented
and testover is set equal to zero. The powerdown timer should have a period that
is sufficient to bring a link down. When the powerdown timer exceeds a first period
P
1, the pretest state machine
50 transitions to a first timer start
state
104.
A first timer is set equal to zero and a blind timer is incremented. The blind
timer waits for a blind timer period to allow a sufficient amount of time for transitions
between pairs. Typically several clock cycles are sufficient. When wire_activity
is high, the pretest state machine
50 transitions to a signal find state
106 and resets a second timer. Wire_activity is present when a signal on
the wire varies above a predetermined threshold.
When wire_activity is low in the signal find state
106, the pretest state
machine
50 transitions back to the signal find state
106 and resets
the second timer. If the second timer is greater than a second period P
2,
the pretest state machine
50 transitions to a test state
110. Tdrwrstart
is set equal to one. If a test pass signal is received, the pretest state machine
50 transitions to a test over state
114. Pair is incremented, tdrwrstart
is set equal to zero, and the register is recorded.
If pair is less than 4 for 1000BaseT operation or 2 for 10/100BaseT operation,
the pretest state machine
50 transitions from the test over state
114
to the first timer start state
104. If pair is equal to 4 for 1000BaseT
operation or 2 for 10/100BaseT operation, the pretest state machine
50 transitions
from the test over state
114 to the wait enable state
100.
In the first timer start state
104, the pretest state machine
50
transitions to the test state
110 if the first timer is greater than a third
period P
3. In the signal find state
106, the pretest state machine
50 transitions to the test over state
114 if the first timer is greater
than the third period P
3.
In a preferred embodiment, the first period P
1 is preferably 1.5 s, the
second period P
2 is equal to 5 ms, and the third period is equal to 625
ms. Skilled artisans will appreciate that the first, second and third periods P
1,
P
2 and P
3, respectively, may be varied. The P
3 is preferably
selected based on a worst case spacing of link pulses and a longest duration between
MDI/MDIX crossover. P
2 is preferably selected to allow testing between fast
link pulses (FLP). FLP bursts have a length of 2 ms and a spacing of 16 ms. By
setting P
2=5 ms, the delay is a total of 7 ms, which is approximately half
way between FLPs. P
1 may be longer than 1.5 seconds if required to bring
the link down.
Referring now to FIG. 4, the first test state machine
52 for media
that transmits and receives on the same wire is shown. The cancellation circuit
59 cancels the transmit test pulse. On reset, the first test state machine
52 transitions to a wait start state
150. Peak is set equal to zero
and cutoff is set equal to peak/2. When tdrwr_start_r rising edge is received from
the pretest state machine
50, the first test state machine
52 transitions
to a detect offset state
154. tdr_sel_pulse is set equal to 1 to generate
a pulse and start a timer. The pulse is preferably a 128 ns pulse having a 2V amplitude.
After an offset is subtracted from tdr_in, the first test state machine
52
transitions to a detect peak state
158. Peak stores the current value of
tdr_in. If tdr_in is less than or equal to peak/2, the first test state machine
52 transitions to a detect cutoff state
162 where distance is set
equal to a counter. If tdr_in is greater than peak, the first test state machine
52 transitions to state
158 and peak is replaced by a new tdr_in.
If a timer is greater than a fifth period P
5, the first test state machine
52 transitions to a test over state
166 where peak/distance is calculated,
tdr_pass is set equal to 1, and tdr_sel_pulse is set equal to 0.
While in the detect cutoff state
162, the first test state machine
52
transitions to the detect peak state
158 if tdr_in>peak. While in the
detect peak state
158, the first state machine
52 transitions to
the test over state
166 if the timer is greater than the fifth period P
5.
In a preferred embodiment, P
5 is equal to 5/s.
Referring now to FIG. 5, the second test state machine
54 is shown
in further detail. On reset, the second test state machine
54 transitions
to a wait start state
200. Peak is set equal to zero, cutoff is set equal
to peak/2, and distance is set equal to 0. When tdrwr_start_r rising edge is received
from the pretest state machine
50, the second test state machine
54
transitions to a detect offset state
204 where tdr_in =filtered magnitude
and tdr_sel_pulse is set equal to 1 and tdr_sign is set to 1 if ADC input is greater
than or equal to offset, 0 otherwise. The second test state machine
54 transitions
to a first detect peak state
208 where peak1 is set equal to maximum of
tdr_in and pulse_mid is set equal to tdr_in after 17 clock cycles.
If tdr_in is less than peak1/2 or tdr_sign is set equal to 0, the second test
state machine
54 transitions to a second detect peak state
212 and
sets peak2 equal to maximum of tdr_in. If tdr_in is less than peak2/2, the second
test state machine
54 transitions to a detect cutoff state
216. Distance
is set equal to a counter. If a fourth timer is greater than a fourth period P
4,
the second test state machine
54 transitions to a test over state
220.
Peak/distance is calculated, tdr_pass is set equal to 1, and tdr_sel_pulse is set
equal to 0.
In the detect cutoff state
216, if tdr_in is greater than peak2, the second
test state machine
54 transitions to the second peak detect state
212.
In the second detect peak state
212, if the fourth timer is greater than
P
4, peak2 is equal to 0 and pulse_mid is greater than a threshold, the second
test state machine
54 transitions to a second test state
224. In
the second test state
224, tdr_sel_half_pulse is set equal to 1 to send
a half pulse and the fourth timer is restarted and incremented and second_peak
is set to a maximum of tdr_in. The second test state machine
54 transitions
from the second test state
224 to the test over state
220 if the
fourth timer is greater than P
4 or tdr_in is less than second_peak/2.
In the first detect peak state
208, if the fourth timer is greater than
P
4, the second test state machine
54 transitions to the test over
state
220. In the second detect peak state
212, if the fourth timer
is greater than P
4, peak2 =0, and pulse_mid is less than or equal to a second
threshold, the second test state machine
54 transitions to the test over
state
220.
The link is brought down and the pretest state machine
50 waits until
the line is quiet. For each pair, the cable tester
20 generates a TDR pulse
and measures the reflection. In 10/100BaseT media, after the test is enabled, the
pretest state machine
50 waits until the line is quiet. A pulse is generated
and the reflection is measured. The status receiver and transmitter pairs are determined
sequentially. For the first pair, the receiver is preferably in MDIX mode and the
transmitter is preferably in MDI mode. For the second pair, the receiver is preferably
in MDI mode and transmitter is preferably in MDIX mode.
The pretest state machine
50 ensures that the line is quiet before the
pulse is transmitted. After the test is enabled, the pretest state machine
50
waits P
1 (such as 1.5 seconds or longer) to make sure that the link is brought
down. The pretest state machine
50 determines whether there is activity
on a first pair (MDI+/-[0] for 1000BaseT network devices and TX for 10/100BaseT products).
In a preferred embodiment, activity is found when activity minus systemic offset
such as a noise floor that is calculated in states
154 and
204 is
greater than a predetermined threshold. If there is no activity for P
3 (such
as 625 ms), the pretest state machine
50 proceeds to the test state and
sends a pulse on the selected pair. If there is activity on the pair and the line
is quiet for 5 ms afterwards, the pretest state machine proceeds to the test state.
The test fail state is reached and a test failure declared if the line has not
been quiet for more than P
2 (such as 5 ms) during P
3 (such as 625
ms). If a test failure is declared on the first pair or the TDR test is completed
for the pair, the same procedure is conducted on MDI+/-[1], MDI+/-[2], MDI+/-[3]
sequentially for 100BaseT devices and the RX pair for 10/100BaseT devices.
In 1000BaseT devices, the original 128 ns test pulse is cancelled by the cancellation
circuit
59. The pulse received at the ADC output is the reflection. The
test pulse preferably has 2V swing. Before testing, the offset on the line is measured
and is subtracted from the received ADC value.
Referring now to FIG. 6, the cancellation circuit
59, which can
be an analog hybrid circuit, does not perfectly cancel the test pulse. To prevent
false reflection identification, a 250 mv floor within 32 clock cycles (125 Mhz
clock) and a 62.5 mv floor after 32 clock cycles are used to allow a residual of
cancellation of the test pulse and noise to be filtered. The peak value on the
line is detected for 5 μs. The amplitude of reflection is the maximum magnitude
that is detected. The amplitude is adjusted according to the sign of the reflection.
The distance to the reflection is located at 50% of the peak.
The cable status is determined by comparing the amplitude and the calculated
cable length to the lookup table
56 for the type of cable being tested.
The measured reflection amplitude falls into a window. There are two adjustable
thresholds for open circuit and short circuit cable. The open threshold is preferably
based on experimental data, which can be produced by refection amplitudes for CAT3
and CAT5 cable that is terminated with a first impedance value such as 333 Ohms.
The default short circuit threshold is based on experimental data of refection
amplitudes for CAT3 and CAT5 cable that is terminated with a second impedance value
such as a 33 Ohms. As can be appreciated, the lookup table
56 may contain
data for other cable types. Other impedance values may be used to generate the thresholds.
If measured amplitude falls between open and short circuit thresholds, the cable
status is declared normal. If the amplitude is above the open threshold, the cable
status is declared an open circuit. If the amplitude is below a short circuit threshold,
the cable status is declared a short circuit. The cable status, reflection amplitude
and cable distance are stored and/or displayed.
In the second test state machine, the original test pulse is not cancelled. Both
the original pulse and the reflection are monitored. When an open circuit is located
near the cable tester, the two pulses may be overlapping, which may cause saturation
in the ADC. The test state machine preferably sends out a 128 ns pulse that has
a 1V swing. The offset on the line is measured and subtracted from the received
ADC value. A 250 mv floor is used within 32 clock cycles (125 Mhz clock) and a
62.5 mv floor is used after 32 clock cycles so that the residual of cancellation
and noise can be filtered. Signals below the floor are considered to be 0. The
peak value on the line is detected for 5 μs. As can be appreciated, the test
pulse can have longer or shorter durations and amplitudes.
The first peak that is observed should be the test pulse. The amplitude of reflection
is the maximum magnitude detected after the test pulse is detected. The distance
of reflection is at 50% cutoff of the peak. If another pulse is not detected after
the test pulse and the magnitude of the test pulse when the counter
17 reaches
a preset threshold, is greater than a preset threshold, the cable tester decides
whether there is an open cable that is located relatively close or a perfectly
terminated cable by sending a second test pulse that has one-half of the magnitude
of the first test pulse.
If the maximum magnitude on the line is greater than ¾ of the original pulse,
there is an open circuit that is located relatively close. Otherwise, if the first
peak is detected after a predetermined number of clock cycles, the cable tester
20 declares an open circuit. If the first peak is within after the predetermined
number of clock cycles, the cable tester
20 declares a perfectly terminated
cable. In one exemplary embodiment, the predetermined number of clock cycles is 33.
The cable status is determined by comparing the amplitude and distance of reflection
to the lookup table
56 based on the type of cable being tested. There are
two adjustable thresholds for open and short circuit cable. The default open threshold
is from the experimental data of refection amplitudes for CAT3 and CAT5 cable terminated
with a first impedance value such as 333 Ohms. The default short circuit threshold
is from the experimental data of refection amplitude of CAT3 and CAT5 cable that
is terminated with a second impedance value such as 33 Ohms. Other impedance values
may be employed for generating thresholds.
If the measured amplitude falls between open and short circuit thresholds, the
cable status is declared normal. If the amplitude is above the open circuit threshold,
the cable status is declared an open circuit. If the amplitude is below a short
circuit threshold, the cable status is declared a short circuit. The cable status,
reflection amplitude and cable length are stored and/or displayed.
Referring now to FIG. 8, the cable tester can be implemented in an exemplary
network device
300 that includes a physical layer device
308 and
a cable tester or cable test module (CTM)
312, as described above. The network
device
300 can be a switch
304 that includes an n port physical layer
device
308 and a cable test module (CTM)
312. While the switch
304
is shown, any other network device
300 that contains a physical layer device,
a port and the CTM can be used. For example, the network device
300 may
be a network appliance, a computer, a switch, a router, a fax machine, a telephone,
a laptop, etc.
Cables
314-
1,
314-
2, . . . , and
314-n
can be connected to the switch
304 using connectors
318-
1,
318-
2, . . . , and
318-n, such as RJ-45 connectors or any
other suitable connector type. The switch
304 can be connected to other
network devices such as, but not limited to, computers, laptops, printers, fax
machines, telephones and any other network device or network appliance.
In the embodiment shown in FIG. 8, the network device
300 includes a software
or hardware based switch
324 that is used to trigger the cable test during
operation. The network device
300 also includes one or more light emitting
diodes (LEDs)
326-
1,
326-
2, . . . , and
326-n.
If a single LED per port is used, the LEDs
326 are fully burdened during
normal use. For example, the LEDs
326 are used to display the presence or
absence of a link, link speed, link activity and other information during normal
(non-cable-testing) use. While LEDs are shown, any other audio and/or visual indicator
can be used. For example, audible tones from a speaker or other audio device can
be used to indicate cable status. If the network device includes illuminated switches,
the illumination of the switches can be flashed, brightened, dimmed or otherwise
used to indicate cable status. Still other indicators include incandescent lights.
Referring now to FIG. 9, steps for operating the network device
300
are shown generally at
330. Control begins with step
332. In step
334, control determines whether the test switch
324 has been pushed.
If the test switch has not been pushed, control loops back to step
334.
Otherwise, control continues with step
336 where control sets the port equal
to 1.
Control determines whether the link associated with a current port is up
in step
338. If not, control performs the cable test on the designated port
in step
340. Control continues from step
340 or step
338 (if
true) with step
342 where control determines whether all ports have been
tested. For example, the cable may include four ports that are associated with
four pairs of twisted wire, although additional or fewer ports and pairs can be
used. If not, control continues with step
344, increments the port, and
continues with step
338. If all ports are tested as determined in step
342,
control displays the results for the tested port(s) in step
346 using the
LEDs and control ends in step
348. If the network device
300 has
only one port, steps
336,
342 and
344 can be skipped. As can
be appreciated by skilled artisans, the cable test can be executed sequentially
for each port as set forth above or simultaneously for all ports. For simultaneous
operation, additional cable test modules or portions thereof may need to be duplicated.
Referring now to FIGS. 10A and 10B, additional steps are performed when
the network device may be connected to power over Ethernet (POE) devices or data
terminal equipment (DTE), which will be collectively referred to herein as POEs.
Examples of POEs include computers (notebooks, servers and laptops), equipment
such as smart videocassette recorders, IP telephones, fax machines, modems, televisions,
stereos, hand-held devices, or any other network device requiring power to be supplied
over the cable. These devices typically include a filter or other circuit that
is connected across center taps of transformers at the POE end of the cable. If
not accommodated by the cable test module, the filters or other circuits that are
used by the POEs may cause the cable test to generate inaccurate results.
Referring now to FIG. 10A, an exemplary network device
350 provides
cable power to an exemplary cable-powered POE
351. The network device
350
includes a controller
352 that communicates with a signal generator
353,
a detector
354 and a selector switch
355. The signal generator
353
communicates with a transmitter
356 having an output that communicates with
a secondary of a transformer
357. The detector
354 communicates with
a receiver
359 having an input that communicates with a secondary of a transformer
360. The selector switch
355 selectively connects center taps of
primaries of the transformers
357 and
360 to a power source
361.
Pair A of a cable
362 communicates with a primary of a transformer
363.
A secondary of the transformer
363 communicates with a selector switch
364,
which selects either a receiver
365 or a filter
366. Pair B of the
cable
362 communicates with a primary of a transformer
367. A secondary
of the transformer
367 communicates with the selector switch
364,
which selects either the transmitter
368 or the filter
366.
A load
371 and a controller
372 are connected across center taps
of the primaries of the transformers
363 and
367. The load
371
includes, for example, the load of the receiver
365, the transmitter
368
and other circuits in the cable-powered POE device
351. The controller
372
controls the position of the selector switch
364. In a de-energized state
or when power is not supplied over data the cable
362, the selector switch
364 connects the secondaries of the transformer
363 and
367
to the filter
366. Typically the filter
366 is a low-pass filter.
The controller
372 detects when the network device
350 supplies
power to the cable
362. Since the load
371 is in parallel with the
controller
372, power is also supplied to the load
371 at the same
time as power is supplied to the controller
372. When power is supplied
to the controller
372, the selector
364 is controlled to connect
the secondary of the transformer
363 to the receiver
365 and the
secondary of transformer
367 to the transmitter
368. At substantially
the same time, power is supplied to the receiver
365, the transmitter
368
and the other circuits of cable-powered POE device
351. At this point, the
cable-powered POE device
351 can begin autonegotiating with the network
device
350.
The cutoff frequency of the low-pass filter
366 filters out fast link
pulses (FLPs). Without the filter
366, when the POE
351 communicates
with a non-POE enabled network device, the FLPs generated by the non-POE network
device could be sent back to the non-POE network device. The non-POE network device
may receive the FLPs that it sent and attempt to establish a link with itself or
cause other problems. The filter
366 will also adversely impact the cable
test. Thus, the network device
350 transmits test signals having pulse widths
greater than FLPs, which will pass through the low-pass filter
352. Once
the selector switch closes, the network device
350 performs cable testing.
For additional details concerning these and other POE devices, see "Method and
Apparatus for Detecting and Supplying Power by a First Network Device to a Second
Network Device", U.S. patent application Ser. No. 10/098,865, filed Mar. 15, 2002,
and "System and Method for Detecting A Device Requiring Power", WO 01/11861, filed
Aug. 11, 2000, which are both incorporated by reference in their entirety.
Referring now to FIG. 10B, steps for performing the cable test when the
network device may be connected to POE devices are shown generally at
380.
Common steps from FIG. 9 have been identified using the same reference number.
If the link is not up in step
338, control continues with step
382
where control determines whether the filter
366 is detected. Is false, control
continues with step
340 as described above. If the filter
366 is
detected, control powers up the POE device in step
384. In step
386,
control determines whether the selector switch
355 is on. If not, control
loops back to step
386. Otherwise, control continues with step
340
as described above.
Referring now to FIG. 11, a network device
400 includes a physical
layer device
408 and a cable tester
412, as described above. For
example, the network device
400 can be a switch
404 that includes
an n port physical layer device
408 and a cable test module (CTM)
412.
However, any other network device that contains a physical layer device can be
used. Cables
314-
1,
314-
2, . . . , and
314-n
can be connected to the switch
404 using connectors
318-
1,
318-
2, . . . , and
318-n, such as RJ-45 connectors or any
other suitable connector type. The switch
404 can be connected to other
network devices such as, but not limited to, computers, laptops, printers, fax
machines, telephones and any other network device or POE. In the embodiment shown
in FIG. 11, the network device
400 initiates the cable test when powered
on by a power supply
416. The cable test can be initiated manually and/or
automatically on power up. The network device
400 also includes one or more
LEDs
326-
1,
326-
2, . . . , and
326-n.
Referring now to FIG. 12, steps for operating the network device
400
are shown generally at
430. Control begins with step
432. In step
434, control determines whether power is on. When power is on, control sets
a port equal to 1 in step
436. In step
438, control performs the
cable test as described above. In step
440, control determines whether all
of the ports have been tested. If not, control increments the port and returns
to step
438. If the network device has only one port, the steps
436,
440 and
442 may be skipped. Otherwise, control displays the results
in step
444 and control ends in step
446. As can be appreciated by
skilled artisans, the cable test can be executed sequentially for each port as
set forth above or simultaneously for all ports.
Referring now to FIG. 13, additional steps are performed when the network
device may be connected to power over Ethernet (POE) devices as shown generally
at
460. Common steps from FIG. 12 have been designated using the same reference
number. In step
470, control determines whether the filter
466 is
detected. If false, control continues with step
438 as described above.
If a filter is detected, control powers up the POE device in step
474. In
step
478, control determines whether the switch is on. If not, control loops
back to step
478. Otherwise, control continues with step
438 as described above.
Referring now to FIGS. 14A-14E, control successively tests each port. Each
port may be associated with one or more LEDs. During normal operation, the LEDs
are used to indicate the presence or absence of a link, link activity, link speed
or any other information. These same LEDs are also used to indicate testing in
progress and the results of the cable test. As can be appreciated, other than the
addition of the cable test module, no other hardware needs to be added.
When testing, the CTM may optionally turn on, turn off, or blink one or more
of the LEDs to designate that a cable test is occurring on the associated port.
Each of the ports are tested one or more times sequentially, randomly or in any
order. When the tests are complete, the network device indicates the results using
the LEDs, for example as shown in FIG. 15. For example, turning on the LED associated
with a port indicates that a good cable communicates with the port. Turning the
LED off indicates an open circuit. Blinking the LED indicates a short. As can be
appreciated, the on, off and blinking states or speed and LED color can be assigned
in a different manner to cable states of good, open, and short. The LEDs can be
monochrome or color. Color LEDs can be used to indicate additional information
such as the relative location of the failure (such as near, intermediate, far or
other distance ranges), the identification of the signal pair with the fault, whether
the fault relates to impedance mismatch, and/or the magnitude of the measured impedance
(such as low, medium, high, open). By using existing, fully burdened LEDs to
