TESTING AN UPSTREAM PATH OF A CABLE NETWORK

• US 20130003565A1
• Filed: 06/30/2011
• Published: 01/03/2013
• Est. Priority Date: 06/30/2011
• Status: Active Grant

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Acterna LLC (Lumentum Holdings Inc.)
• Inventors: Gotwals, Michael D., Jones, David W.
• Granted Patent: US 9,450,686 B2
• Time in Patent Office: Days
• US Class Current: 370/248
• CPC Class Codes: H04B 17/00 Monitoring; Testing of line transmission systems H04B3/46; arrangements for monitoring or testing transmission systems employing electromagnetic waves other than radio waves H04B10/07
• CPC Class Codes: H04B 17/309 Measuring or estimating channel quality parameters
• CPC Class Codes: H04L 1/24 Testing correct operation
• CPC Class Codes: H04L 2101/622 Layer-2 addresses, e.g. medium access control [MAC] addresses
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/366 Arrangements for compensating undesirable properties of the transmission path between the modulator and the demodulator
• CPC Class Codes: H04L 43/026 using flow identification
• CPC Class Codes: H04L 43/028 by filtering
• CPC Class Codes: H04L 43/045 for graphical visualisation of monitoring data
• CPC Class Codes: H04L 43/50 Testing arrangements

Abstract

An apparatus and method for testing an upstream path of a cable network are disclosed. The upstream path is tested by capturing and analyzing upstream data packets generated by a specific terminal device. A test instrument is connected at a node of the cable network. The test instrument establishes a communication session with the headend, informing the headend of an identifier of the device that will generate the test upstream data packet. The test upstream data packet is captured and analyzed at the headend, so that the results of the analysis can be communicated back to the test instrument. To speed up the packet capturing and filtering process, the upstream data packets can be pre-filtered based on packet duration and/or arrival time.

Claims

1. A method of testing an upstream path of a cable network including a headend and a node connected to the headend, the method comprising:

(a) sending from a test instrument operably connected to the node a request to the headend to demodulate and obtain signal quality information of an upstream data packet generated by a first terminal device connected to the cable network;

(b) receiving the test request at the headend;

(c) receiving and demodulating at the headend the upstream data packet generated by the first terminal device;

(d) obtaining, at the headend, at least one pre-equalization coefficient used by the first terminal device to generate the upstream data packet;

(e) obtaining, at the headend, the signal quality information of the upstream data packet demodulated in step (c), wherein the signal quality information is corrected for pre-equalization using the at least one pre-equalization coefficient obtained in step (d).

2. The method of claim 1, further comprising:

(f) communicating the signal QAM quality information obtained in step (e) to the test instrument; and

(g) displaying the obtained signal quality information on a display of the test instrument.

3. The method of claim 1, wherein the first terminal device is identified by a MAC address.

4. The method of claim 1, wherein in step (d), the at least one pre-equalization coefficient is obtained from a terminal devices database including records of terminal devices connected to the cable network.

5. The method of claim 1, wherein in step (a), the first terminal device is the test instrument, the method further comprising

(h) generating the upstream data packet by the test instrument.

6. The method of claim 5, wherein in step (d), the at least one pre-equalization coefficient is communicated by the test instrument to the headend.

7. The method of claim 6, wherein the upstream data packet generated in step (h) includes the at least one pre-equalization coefficient digitally encoded therein, wherein step (d) is performed after step (c).

8. The method of claim 1, wherein the signal quality information includes at least one of MER, in-band frequency response, in-band group delay, micro-reflections, impulse noise, number of captured symbols in the upstream data packet, number of erroneously detected symbols in the upstream data packet, a constellation map, and RF power level.

9. A method of testing an upstream path of a cable network including a headend and a node connected to the headend, the method comprising:

(a) sending from a test instrument operably connected to the node a request to the headend to demodulate and obtain signal quality information of an upstream data packet generated by a first terminal device connected to the cable network;

(b) receiving the test request at the headend;

(c) receiving and demodulating at the headend the upstream data packet generated by the first terminal device;

(d) obtaining, at the headend, the signal quality information of the upstream data packet demodulated in step (c),

wherein the upstream data packet has a target packet length; and

wherein step (c) includes pre-filtering upstream data packets based on packet length, so that only upstream data packets having the target packet length are selected for demodulation.

10. The method of claim 9, wherein the target packet length is selected by

(e) obtaining a probability distribution of upstream packet lengths in the cable network;

and

(f) selecting a packet length having a probability of no more than 25% of a maximum probability of the probability distribution as the target packet length.

11. The method of claim 9, wherein in step (a), the first terminal device is the test instrument, the method further comprising

(g) generating, at a regular time intervals, the upstream data packets of the target packet length by the test instrument;

and

(h) pre-filtering, at the headend, upstream data packets based on arrival time of upstream data packets of the target packet length, thereby identifying the upstream data packets generated at the regular time intervals by the test instrument.

12. An apparatus for testing an upstream path of a cable network including a headend and a node connected to the headend, the apparatus comprising:

a test instrument for operably coupling to the node, wherein the test instrument is configured for sending a request to the headend to demodulate and obtain signal quality information of an upstream data packet generated by a first terminal device connected to the cable network, and

a test module disposed at the headend, the test module including;

a communication circuit for receiving the test request and the upstream data packet;

a demodulator coupled to the communication circuit, for demodulating the upstream data packet generated by the first terminal device; and

a processor coupled to the demodulator and the communication circuit, for obtaining the signal quality information of the demodulated upstream data packet, wherein the signal quality information is corrected for pre-equalization using at least one pre-equalization coefficient used by the first terminal device to generate the upstream data packet.

13. The apparatus of claim 12, wherein the test module is coupled to a database of terminal devices for obtaining the at least one pre-equalization coefficient used by the first terminal device to generate the upstream data packet.

14. The apparatus of claim 12, wherein the communication circuit is configured for communicating the obtained signal quality information back to the test instrument, and wherein the test instrument has a display for displaying the obtained signal quality information.

15. The apparatus of claim 14, wherein the test instrument comprises a packet generator for generating the upstream data packet, a pre-equalization circuit coupled to the packet generator, for pre-equalizing the upstream data packet, and a communication unit coupled to the pre-equalization circuit, for communicating the at least one pre-equalization coefficient to the test module.

16. The apparatus of claim 12, wherein the test instrument is programmed to communicate with the test module via a dedicated DOCSIS connection.

17. An apparatus for testing an upstream path of a cable network including a headend and a node connected to the headend, the apparatus comprising:

a test instrument for operably coupling to the node, wherein the test instrument is configured for sending a request to the headend to demodulate and obtain signal quality information of an upstream data packet generated by a first terminal device connected to the cable network, and

a test module disposed at the headend, the test module including;

a communication circuit for receiving the test request and the upstream data packet;

a demodulator coupled to the communication circuit, for demodulating the upstream data packet generated by the first terminal device; and

a processor coupled to the demodulator and the communication circuit, for obtaining the signal quality information of the demodulated upstream data packet,

wherein the test instrument is configured to generate upstream data packets of a fixed length; and

wherein the test module is configured to pre-filter upstream data packets based on packet length.

18. The apparatus of claim 17,

wherein the test instrument is configured for generating, at regular time intervals, upstream data packets of a target packet length;

and

wherein the test module is configured for pre-filtering upstream data packets based on arrival time of the upstream data packets of the target packet length, thereby identifying the upstream data packets generated by the test instrument at the regular time intervals.

19. The apparatus of claim 17, wherein the test instrument comprises a packet generator for generating the upstream data packet.

20. A cable network comprising the test apparatus of claim 17, the headend, the node connected to the headend, and a plurality of terminal devices connected to the node, the plurality of terminal devices including the first terminal device,

wherein the first terminal device is configured for generation of an upstream test data packet of a first length selectable by the test module;

wherein the test module is configured to send, upon receiving a command form the test instrument, a request to the first terminal device to generate the upstream test data packet of the first length; and

wherein the test module is configured to pre-filter upstream data packets based on packet length, for identifying the upstream test data packet of the first length.