Granted Patent B2

US 7,929,576 · App. 11/478,492 · Granted Apr 19, 2011

Abstract

Claims (87)

1. A method for accommodating different clock frequencies in an Ethernet passive optical network (EPON), the EPON including an optical line terminal (OLT) and one or more one or more optical network units (ONU's), the method comprising:

receiving, by an ONU from among the ONU's, a signal from the OLT;

deriving, by the ONU, an OLT clock from the signal;

maintaining, by the ONU, a local clock to simulate the OLT clock;

comparing, by the ONU, the local clock and the OLT clock; and

requesting, by the ONU, an upstream transmission window based on the comparison, the upstream transmission window being configured to accommodate an upstream data burst transmitted based on the local clock.

2. The method of claim 1 , further comprising:

determining a duration of the upstream transmission window based on a size of the upstream data burst and the local clock;

determining a size of the upstream transmission window in terms of an amount of data that is to be transmitted based on the OLT clock during the duration of the upstream transmission window; and

wherein requesting the upstream transmission window comprises:

communicating the size of the upstream transmission window in terms of the amount of data that is to be transmitted based on the OLT clock.

3. A system for accommodating different clock frequencies in an Ethernet passive optical network (EPON), the EPON including an optical line terminal (OLT) and one or more one or more optical network units (ONU's), the system comprising:

an OLT-clock derivation module configured:

(i) to receive a signal,

(ii) to derive an OLT clock from the signal, and

(iii) to maintain a local clock to simulate an OLT clock;

a comparison module configured to compare the local clock and the OLT clock; and

a request module configured to request an upstream transmission window based on the comparison, the upstream transmission window being configured to accommodate an upstream data burst transmitted based on the local clock.

4. The system of claim 3 , further comprising:

a determination module configured to:

(i) determine a duration of the upstream transmission window based on a size of the upstream data burst and the local clock; and

(ii) to determine a size of the upstream transmission window in terms of an amount of data that is to be transmitted based on the OLT clock during the duration of the upstream transmission window; and

wherein the requesting module is configured to communicate the size of the upstream transmission window in terms of the amount of data that is to be transmitted based on the OLT clock.

5. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for accommodating different clock frequencies in an Ethernet passive optical network (EPON), the EPON including an optical line terminal (OLT) and one or more one or more optical network units (ONU's), the method comprising:

receiving a signal;

deriving an OLT clock from the signal;

maintaining a local clock to simulate the OLT clock;

comparing the local clock and the OLT clock; and

requesting an upstream transmission window based on the comparison, the upstream transmission window being configured to accommodate an upstream data burst transmitted based on the local clock.

6. The non-transitory computer-readable storage medium of claim 5 , wherein the method further comprises:

determining a duration of the upstream transmission window based on a size of the upstream data burst and the local clock;

determining a size of the upstream transmission window in terms of an amount of data that is to be transmitted based on the OLT clock during the duration of the upstream transmission window; and

wherein requesting the upstream transmission window comprises:

communicating the size of the upstream transmission window in terms of the amount of data that is to be transmitted based on the OLT clock.

7. A method for accommodating different clock frequencies in an Ethernet passive optical network (EPON), the EPON including an optical line terminal (OLT) and one or more optical network units (ONU's), comprising:

receiving, by an ONU from among the ONU's, a signal from the OLT;

deriving, by the ONU, an OLT clock from the signal;

maintaining, by the ONU, a local clock to simulate the OLT clock;

receiving, by the ONU, an assignment for an upstream transmission window for transmission of an upstream data burst to the OLT based on the local clock;

determining, by the ONU, a size of the upstream transmission window in terms of an amount of data that is to be transmitted based on the OLT clock;

adjusting, by the ONU, a number of bits of the upstream data burst without affecting a payload data carried in the upstream data burst by inserting or removing unused bits in corresponding inter-packet gaps between packets contained in the upstream data burst, thereby allowing the upstream data burst to fit properly within the upstream transmission window and compensating for frequency differences between the local clock and the OLT clock, wherein a number of bits inserted or removed is determined by the difference between the size of the upstream transmission window and a size of upstream data burst; and

transmitting the upstream data burst based on the local clock in the upstream transmission window.

8. The method of claim 7 , wherein the adjusting the number of bits of the upstream data burst comprises:

inserting one or more of the unused bits into the upstream data burst without affecting the payload data when a transmission time of the upstream data burst based on the local clock is shorter than a transmission time based on the OLT clock by a pre-determined threshold.

9. The method of claim 8 , wherein the pre-determined threshold corresponds to a transmission time of a character based on the local clock or the OLT clock; and

wherein inserting the one or more of the unused bits into the upstream data burst comprises:

inserting an idle character into the corresponding inter-packet gaps between the packets contained in the upstream data burst.

10. The method of claim 7 , wherein the adjusting the number of bits of the upstream data burst comprises:

removing the one or more of the unused bits from the upstream data burst without affecting the payload data when a transmission time of the upstream data burst based on the local clock is longer than a transmission time based on the OLT clock by a pre-determined threshold.

11. The method of claim 10 , wherein the pre-determined threshold corresponds to a transmission time of a character based on the local clock or the OLT clock; and

wherein removing the one or more of the unused bits from the upstream data burst comprises:

removing an idle character into the corresponding inter-packet gaps between the packets contained in the upstream data burst.

12. A system for accommodating different clock frequencies in an Ethernet passive optical network (EPON), the EPON including an optical line terminal (OLT) and one or more optical network units (ONU's), comprising:

an OLT-clock derivation module configured:

(i) to receive a signal,

(ii) to derive an OLT clock from the signal, and

(iii) to maintain a local clock to simulate an OLT clock;

a receiving module configured to receive an assignment for an upstream transmission window for transmission of an upstream data burst based on the local clock;

a determination module configured to determine a size of the upstream transmission window in terms of an amount of data that is to be transmitted based on the OLT clock;

an adjustment module configured to adjust a number of bits of the upstream data burst without affecting a payload data carried in the upstream data burst by inserting or removing unused bits in corresponding inter-packet gaps between packets contained in the upstream data burst, thereby allowing the upstream data burst to fit properly within the upstream transmission window and compensating for frequency differences between the local clock and the OLT clock, wherein a number of bits inserted or removed is determined by the difference between the size of the upstream transmission window and a size of upstream data burst; and

a transmission module configured to transmit the upstream data burst based on the local clock during the upstream transmission window.

13. The system of claim 12 , wherein the adjustment module comprises:

an insertion module configured to insert one or more unused bits into the upstream data burst without affecting the payload data when a transmission time of the upstream data burst based on the local clock is shorter than a transmission time based on the OLT clock by a pre-determined threshold.

14. The system of claim 13 , wherein the pre-determined threshold corresponds to a transmission time of a character based on the local clock or the OLT clock; and

wherein the insertion module is configured to insert an idle character into the corresponding inter-packet gaps between the packets contained in the upstream data burst.

15. The system of claim 12 , wherein the adjustment module comprises:

a removal module configured to remove one or more unused bits from the upstream data burst without affecting the payload data when a transmission time of the upstream data burst based on the local clock is longer than a transmission time based on the OLT clock by a pre-determined threshold.

16. The system of claim 15 , wherein the pre-determined threshold corresponds to a transmission time of a character based on the local clock or the OLT clock; and

wherein the removal module is configured to remove an idle character into the corresponding inter-packet gaps between the packets contained in the upstream data burst.

17. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for accommodating different clock frequencies in an Ethernet passive optical network (EPON), the EPON including an optical line terminal (OLT) and one or more optical network units (ONU's), the method comprising:

receiving a signal;

deriving an OLT clock from the signal;

maintaining a local clock to simulate the OLT clock;

receiving an assignment for an upstream transmission window for transmission of an upstream data burst to the OLT based on the local clock;

determining a size of the upstream transmission window in terms of amount of data that is to be transmitted based on the OLT clock;

adjusting a number of bits of the upstream data burst without affecting a payload data carried in the upstream data burst by inserting or removing unused bits in corresponding inter-packet gaps between packets contained in the upstream data burst, thereby allowing the upstream data burst to fit properly within the upstream transmission window and compensating for frequency differences between the local clock and the OLT clock, wherein a number of bits inserted or removed is determined by the difference between the size of the upstream transmission window and a size of upstream data burst; and

transmitting the upstream data burst based on the local clock in the upstream transmission window.

18. The non-transitory computer-readable storage medium of claim 17 , wherein adjusting the number of bits of the upstream data burst comprises:

inserting one or more of the unused bits into the upstream data burst without affecting the payload data when a transmission time of the upstream data burst based on the local clock is shorter than a transmission time based on the OLT clock by a pre-determined threshold.

19. The non-transitory computer-readable storage medium of claim 18 , wherein the pre-determined threshold corresponds to a transmission time of a character based on the local clock or the OLT clock; and

wherein inserting the one or more of the unused bits into the upstream data burst comprises:

inserting an idle character into the corresponding inter-packet gaps between the packets contained in the upstream data burst.

20. The non-transitory computer-readable storage medium of claim 17 , wherein adjusting the number of bits of the upstream data burst comprises:

removing the one or more of the unused bits from the upstream data burst without affecting the payload data when a transmission time of the upstream data burst based on the local clock is longer than a transmission time based on the OLT clock by a pre-determined threshold.

21. The non-transitory computer-readable storage medium of claim 20 , wherein the pre-determined threshold corresponds to a transmission time of a character based on the local clock or the OLT clock; and

wherein removing the one or more of the unused bits from the upstream data burst comprises:

removing an idle character into the corresponding inter-packet gaps between the packets contained in the upstream data burst.

Assignments (11)