Method and apparatus for upstream burst transmission synchronization in cable modems

• US 6,553,040 B2
• Filed: 07/19/2001
• Issued: 04/22/2003
• Est. Priority Date: 10/09/1999
• Status: Expired due to Fees

• Current Assignee: Entropic Communications Incorporated (Maxlinear Incorporated)
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Mehta, Manoj, Brooks, John Milford, Bernath, Brett Alan, Goldenberg, Yoav Pesach
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): Phan, M.
• Application Number:
  US09/908,759
• Publication Number:
  US 20010043622A1
• Time in Patent Office: 642 Days
• Field of Search: 370/342, 370/503, 370/509, 370/508, 370/510, 370/512, 370/335, 370/314, 370/449, 370/461, 348/10-13, 348/521, 348/536, 348/537, 375/219, 375/376, 375/375
• US Class Current: 370/509
• CPC Class Codes: H04N 21/2389 Multiplex stream processing, e.g. multiplex stream encrypting
• CPC Class Codes: H04N 21/4385 Multiplex stream processing, e.g. multiplex stream decrypting
• CPC Class Codes: H04N 21/8547 involving timestamps for synchronizing content

Abstract

A system for synchronizing the upstream burst transmission in a cable system to a time specified by the cable head end is disclosed. The system includes a free running counter within a cable modem (CM) or network interface unit (NIU), along with logic to capture the value of this free running counter at the time a frame of MPEG-2 SYNC data arrives, to create a time tag stored in memory. A computer within the cable modem or network interface unit has access to the time tags in memory and the contents of a time synchronization message from the head end, also stored in memory. The computer contains a program to calculate the value of the local counter that corresponds to a time to transmit commanded by the cable system head end. The system includes logic within the CM or NIU to initiate an upstream burst transmission when the value of the local counter becomes equal to a calculated value, thus causing the cable modem to initiate its upstream burst transmission precisely at the time commanded by the head end.

Claims

1. A network interface apparatus for providing data transmissions to a network controller that are synchronized with transmissions from other network interface apparatuses to the network controller, the apparatus comprising:

a clock from which the network interface unit obtains a local time;

a message receiver for receiving messages from the network controller;

a time tag generator for recording local times of arrival of synchronizing messages at the interface unit, the synchronizing messages containing synchronizing information comprising an offset from the beginning of a received frame marker and a number of a transmit slot relative to the offset in which to transmit;

a phase lock loop for accepting time tag information and synchronizing information corresponding to synchronizing messages and generating corresponding local transmit time information therefrom; and

a transmission unit for generating data transmissions from the network interface unit to the network control unit in accordance with said local transmit time information.

2. An apparatus as claimed in claim 1 wherein the network interface unit operates according to a DVB protocol.

3. An apparatus as claimed in claim 1 wherein the phase lock loop is a software phase lock loop.

4. An apparatus as claimed in claim 1 wherein the phase lock loop accepts a center frequency for biasing the phase lock loop towards an operating frequency.

5. An apparatus as claimed in claim 1 wherein the phase lock loop accepts a decimation period and samples synchronizing information in accordance with the decimation period.

6. An apparatus as claimed in claim 5 wherein the decimation period corresponds to the arrival of synchronizing messages.

7. An apparatus as claimed in claim 1, wherein the phase lock loop further accepts phase adjustment information from ranging phase adjustment messages and generates local transmit time information from time tag information and synchronizing information and said phase adjustment information.

8. An apparatus as claimed in claim 7, wherein said phase adjustment information comprises a measure of a fixed transmission delay between the network interface apparatus and the network controller.

9. An apparatus as claimed in claim 1, wherein said offset comprises a number of received symbols.

10. A method in a network interface unit for synchronizing data transmissions from multiple network interface units to a network controller, the method comprising:

receiving synchronizing information from the network controller comprising an offset from the beginning of a received frame marker and a number of a transmit slot relative to the offset in which to transmit;

receiving phase adjustment information from a ranging phase adjustment message;

recording a local time of arrival of the synchronizing information at the interface unit;

determining local transmit time information for transmission to the network controller in accordance with said offset, said transmit slot number, said local time of arrival and said phase adjustment information; and

transmitting data to the network controller in accordance with said local transmit time information.

11. A method as claimed in claim 10 wherein receiving synchronizing information from the network controller comprises:

receiving a synchronizing message from the network controller;

placing the synchronizing message into memory; and

extracting an offset and a number of a transmit slot relative to the offset from the synchronizing message.

12. A method as claimed in claim 10, wherein said phase adjustment information comprises a measure of a fixed transmission delay between the network interface apparatus and the network controller.

13. A method as claimed in claim 10, wherein said offset comprises a number of received symbols.

14. A network interface apparatus for providing data transmissions to a network controller that are synchronized with transmissions from other network interface apparatuses to the network controller, the apparatus comprising:

at least one processor; and

computer readable media coupled to the at least one processor and containing programming instructions for performing processing comprising;

receiving synchronizing information from the network controller comprising an offset from the beginning of a received frame marker and a number of a transmit slot relative to the offset in which to transmit;

receiving phase adjustment information from a ranging phase adjustment message;

recording a local time of arrival of the synchronizing information at the interface unit;

determining local transmit time information for transmission to the network controller in accordance with said offset, said transmit slot number, said local time of arrival and said phase adjustment information; and

transmitting data to the network controller in accordance with said local transmit time information.

15. A network interface apparatus as claimed in claim 14, wherein receiving synchronizing information from the network controller comprises:

receiving a synchronizing message from the network controller;

placing the synchronizing message into memory; and

extracting an offset and a number of a transmit slot relative to the offset from the synchronizing message.

16. A network interface apparatus as claimed in claim 14, wherein said phase adjustment information comprises a measure of a fixed transmission delay between the network interface apparatus and the network controller.

17. A network interface apparatus as claimed in claim 15, wherein said offset comprises a number of received symbols.