Testing an upstream path of a cable network
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.
1. A system for testing an upstream path of a cable network, the system comprising a terminal device connected to a node associated with the upstream path of the cable network, the terminal device comprising:
a packet generator to generate test data packets of a target packet length;
a pre-equalization circuit coupled to the packet generator to pre-equalize the test data packets using pre-equalization coefficients;
a communication circuit to:
transmit a test request message to a headend of the cable network to obtain pre-equalized signal quality information of the upstream path of the cable network,
transmit the pre-equalization coefficients and the test data packets at a regular time interval to the headend of the cable network, and
receive the pre-equalized signal quality information from the headend, wherein the pre-equalized signal quality information includes a frequency response based on the test data packets; and
a display to display the pre-equalized signal quality information.
2. The system of claim 1 , wherein the target packet length is generated according to:
a probability distribution of upstream packet lengths in the cable network, wherein the target packet length has a probability of no more than 25% of a maximum probability of the probability distribution of upstream packet lengths.
3. The system of claim 1 , further comprising:
test logic disposed at the headend, the test logic including:
a second communication circuit for receiving the test data packets via the upstream path of the cable network;
a packet duration filter to identify the test data packets arriving at the regular time interval and having the target packet length; and
a processor to:
determine the pre-equalized signal quality information for the upstream path of the cable network, wherein the pre-equalized signal quality information includes a measured in-band frequency response; and
correct the measured in-band frequency response to account for pre-equalization of the test data packets.
4. The system of claim 1 , wherein the test request message includes a terminal device identifier.
5. The system of claim 1 , wherein the terminal device communicates with the headend via a dedicated Data Over Cable Service Interface Specification (DOCSIS) connection.
6. The system of claim 1 , further comprising an interoperations server in communication with the headend, the interoperations server providing a list of currently active nodes of the cable network.
7. An apparatus for testing an upstream path of a cable network, the apparatus comprising:
a packet generator to generate, at a regular time interval, an upstream data packet of a packet length no more than a predetermined value based on a probability distribution of upstream packet lengths in the cable network;
a pre-equalization circuit coupled to the packet generator to pre-equalize the upstream data packet using pre-equalization coefficients;
a communication circuit to:
transmit a test request message to a headend of the cable network, the test request message including an identifier of a connected device;
transmit the pre-equalization coefficients and the pre-equalized upstream data packet to the headend; and
receive, from the headend, pre-equalized signal quality information of the upstream path of the cable network based on the pre-equalized upstream data packet; and
a display to display the pre-equalized signal quality information.
8. The apparatus of claim 7 , wherein the packet length has a probability of no more than 25% of a maximum probability of the probability distribution.
9. The apparatus of claim 7 , wherein the communication circuit is to form a line of communication with the headend, wherein the line of communication is formed using a DOCSIS bidirectional communications channel.
10. The apparatus of claim 9 , in communication with an interoperations server to provide a list of currently active nodes of the cable network, a user of the apparatus to select a node from the list.
11. A method of testing an upstream path of a cable network, the method comprising:
generating, by a packet generator at a regular time interval, a test packet, the test packet having a packet length no more than a predetermined value based on a probability distribution of upstream packet lengths in the cable network;
pre-equalizing, by a pre-equalization circuit coupled to the packet generator, the test packet using pre-equalization coefficients;
communicating, by a communication circuit, the pre-equalization coefficients and the test packet to a headend of the cable network via the upstream path of the cable network; and
receiving pre-equalized signal quality information from the headend based on the test packet.
12. The method of claim 11 , wherein the packet length has a probability of no more than 25% of a maximum probability of the probability distribution.
13. The method of claim 11 , wherein communicating of the pre-equalization coefficients and the test packet to a headend of the cable network includes, establishing a DOCSIS bidirectional communications channel with an interoperations server and receiving a list of currently active nodes of the cable network.