# US 2013/0156423 A1 · Method and apparatus for laser overlap detection

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- Number: US 2013/0156423 A1
- Document ID: US20130156423A1
- Status: Published application
- Kind: A1
- Application number: 13/327,418
- Filed: 2011-12-15
- Published: 2013-06-20
- Earliest claimed: 2011-12-15
- Assignees: Cortina Systems, Inc.
- Inventors: Dongsheng ZHANG; Eugene W. LEE; Wei YAO
- Web page: https://patentgrep.com/patent/US20130156423A1

## CPC

- H04B 10/272: Star-type networks {or tree-type networks}
- H04Q 11/0067: {Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring}
- H04J 2203/006: Fault tolerance and recovery
- H04Q 2011/0083: {Testing; Monitoring}
- H04B: TRANSMISSION
- H04Q: SELECTING (switches, relays, selectors H01H; wireless communication networks H04W)
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)

## Abstract

There are disclosed systems and methods for detecting whether an Optical Network Unit (ONU) in a network may be causing a communications interference due to laser overlap. In one embodiment, an Optical Line Terminal (OLT) selects a pair of ONUs suspected of possibly causing laser overlap. The OLT then grants a first window to a first ONU for transmitting a first message, and grants to another ONU different from the pair of ONUs a second window for transmitting a second message. If the first message is not received by the OLT, then the OLT indicates that the first ONU may be causing laser overlap. In another embodiment, the OLT grants to an ONU a window for transmitting a message to the OLT. If the message is not received by the OLT when expected, then the OLT indicates that the ONU may be causing laser overlap. Other embodiments are disclosed.

## Claims

### Claim 1

A method in an Optical Line Terminal (OLT), the method comprising:
in respect of a pair of Optical Network Units (ONUs) comprising a first ONU and a second ONU, performing at least one of (a) and (b);
wherein (a) comprises:
granting to the first ONU a first time window for transmitting a first message from the first ONU to the OLT, and granting to another ONU different from both the first ONU and the second ONU a second time window for transmitting a second message from the another ONU to the OLT, the second time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the first time window for the purpose of enabling communications interference detection;
if the first message is not received by the OLT, then indicating that the first ONU may be causing communications interference;
and wherein (b) comprises:
granting to another ONU different from both the first ONU and the second ONU a third time window for transmitting a third message from the another ONU to the OLT, and granting to the second ONU a fourth time window for transmitting a fourth message from the second ONU to the OLT, the fourth time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the third time window for the purpose of enabling communications interference detection;
if the third message is not received by the OLT, then indicating that the second ONU may be causing communications interference.

### Claim 2 (depends on 1)

The method of claim 1 wherein:
when performing (a), the second time window is scheduled, from the perspective of the OLT, to begin adjacent to or partially overlapping the first time window and later than the scheduled transmission of the first message;
when performing (b), the fourth time window is scheduled, from the perspective of the OLT, to begin adjacent to or partially overlapping the third time window and later than the scheduled transmission of the third message.

### Claim 3 (depends on 2)

The method of claim 2 wherein:
when performing (a), the second time window is scheduled, from the perspective of the OLT, to begin immediately after the scheduled transmission of the first message;
when performing (b), the fourth time window is scheduled, from the perspective of the OLT, to begin immediately after the scheduled transmission of the third message.

### Claim 4 (depends on 1)

The method of claim 1 further comprising:
when performing (a), if the first message is received by the OLT, then indicating that the second ONU may be causing communications interference;
when performing (b), if the third message is received by the OLT, then indicating that the first ONU may be causing communications interference.

### Claim 5 (depends on 1)

The method of claim 1 wherein at least one of the pair of ONUs is either suspected of causing laser overlap, known to be causing laser overlap, or is assumed to be causing laser overlap.

### Claim 6 (depends on 1)

The method of claim 1 wherein the another ONU that is different from both the first ONU and the second ONU is either not suspected of causing laser overlap, known not to cause laser overlap, or is assumed not to cause laser overlap.

### Claim 7 (depends on 1)

The method of claim 1 wherein at least one of: (i) the first message and the second message are both REPORT messages; and (ii) the third message and the fourth message are both REPORT messages.

### Claim 8 (depends on 2)

The method of claim 2 wherein:
(i) when performing (a), the first time window includes a laser turn-on segment, a data transmission segment, and a laser turn-off segment, and the second time window is scheduled, from the perspective of the OLT, to begin during the first time window, but no earlier than the start of the laser turn-off segment;
(ii) when performing (b), the third time window includes another laser turn-on segment, another data transmission segment, and another laser turn-off segment, and the fourth time window is scheduled, from the perspective of the OLT, to begin during the third time window, but no earlier than the start of the another laser turn-off segment.

### Claim 9 (depends on 1)

The method of claim 1 wherein:
(i) when performing (a), the first message is not considered to be received by the OLT if it is not received within an expected window of arrival determined by the OLT;
(ii) when performing (b), the third message is not considered to be received by the OLT if it is not received within another expected window of arrival determined by the OLT.

### Claim 10 (depends on 1)

The method of claim 1 further comprising the OLT either:
causing deregistration of an ONU suspected of causing communications interference; or
performing at least one of: (i) reducing a duration of a transmission window granted to the ONU suspected of causing communications interference; (ii) increasing a duration of time between an end of an earlier and adjacent transmission window granted to another ONU and a start of a transmission window granted to the ONU suspected of causing communications interference; and (iii) increasing a duration of time between an end of a transmission window granted to the ONU suspected of causing communications interference and a start of a later and adjacent transmission window granted to another ONU.

### Claim 11 (depends on 1)

The method of claim 1 wherein:
(i) when performing (a), the first message is transmitted immediately before the first ONU turns off its laser;
(ii) when performing (b), the third message is transmitted immediately before the another ONU turns off its laser.

### Claim 12 (depends on 1)

The method of claim 1 wherein:
when performing (a), said indicating that the first ONU may be causing communications interference comprises indicating that the first ONU may be causing laser overlap;
when performing (b), said indicating that the second ONU may be causing communications interference comprises indicating that the second ONU may be causing laser overlap.

### Claim 13

A method in an Optical Line Terminal (OLT), the method comprising:
(a) granting to an Optical Network Unit (ONU) a time window for transmitting a message from the ONU to the OLT;
(b) if the message is not received by the OLT during an expected window of arrival, then indicating that the ONU may be causing communications interference.

### Claim 14 (depends on 13)

The method of claim 13 further comprising performing at least one of:
if the message is received by the OLT later than the expected window of arrival, then indicating that the ONU may be causing communications interference by turning on its laser too late; and
if the message is received by the OLT earlier than the expected window of arrival, then indicating that the ONU may be causing communications interference by turning on its laser too early.

### Claim 15 (depends on 13)

The method of claim 13 further comprising computing the expected window of arrival by computing a start time of the expected window as an expected arrival time of a beginning of the message minus a margin, and computing an end time of the expected window as the expected arrival time of an end of the message plus another margin.

### Claim 16 (depends on 15)

The method of claim 15 wherein the margin and the another margin have the same value.

### Claim 17 (depends on 16)

The method of claim 16 further comprising computing the expected arrival time using a round trip time (RTT) for the ONU and a scheduled start time of transmission of the message.

### Claim 18 (depends on 13)

The method of claim 13 wherein said indicating that the ONU may be causing communications interference comprises indicating that the ONU may be causing laser overlap.

### Claim 19 (depends on 13)

The method of claim 13 further comprising selecting a pair of optical network units (ONUs) comprising (i) a first ONU for which the OLT had previously granted a first time window for transmitting one or more messages from the first ONU to the OLT, and (ii) a second ONU for which the OLT had previously granted a second time window for transmitting one or more messages from the second ONU to the OLT, the second time window scheduled, from the perspective of the OLT, adjacent to the first time window and later than the first time window;
setting one of the first ONU and the second ONU as the ONU;
wherein at least one of the pair of ONUs is either suspected of causing laser overlap, assumed to be causing laser overlap, or known to cause laser overlap.

### Claim 20

A system comprising:
a computer having a graphical display for representing at least a portion of a network, the network including an Optical Line Terminal (OLT), a pair of Optical Network Units (ONUs) comprising a first ONU and a second ONU, and another ONU different from both the first ONU and the second ONU;
a communication interface for communicatively connecting the computer to the OLT, thereby allowing the computer to instruct the OLT to perform at least one of (a) and (b);
wherein (a) comprises: granting to the first ONU a first time window for transmitting a first message from the first ONU to the OLT, and granting to the another ONU a second time window for transmitting a second message from the another ONU to the OLT, the second time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the first time window for the purpose of enabling communications interference detection; and
wherein (b) comprises: granting to the another ONU a third time window for transmitting a third message from the another ONU to the OLT, and granting to the second ONU a fourth time window for transmitting a fourth message from the second ONU to the OLT, the fourth time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the third time window for the purpose of enabling communications interference detection;
the graphical display further for displaying (i) that the first ONU is causing communications interference if (a) is performed and the first message is not received by the OLT, and (ii) that the second ONU is causing communications interference if (b) is performed and the third message is not received by the OLT.

### Claim 21

An Optical Line Terminal (OLT) comprising:
an optical transceiver for communicating with (i) a pair of Optical Network Units (ONUs) comprising a first ONU and a second ONU, (ii) and another ONU different from both the first ONU and the second ONU;
a grant scheduler for granting time windows for transmitting messages to the OLT; and
a communications interference detector for controlling the OLT to perform at least one of (a) and (b);
wherein (a) comprises:
the grant scheduler granting to the first ONU a first time window for transmitting a first message from the first ONU to the OLT, and the grant scheduler granting to the another ONU a second time window for transmitting a second message from the another ONU to the OLT, the second time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the first time window for the purpose of enabling communications interference detection;
if the first message is not received by the OLT, then indicating that the first ONU may be causing communications interference;
and wherein (b) comprises:
the grant scheduler granting to the another ONU a third time window for transmitting a third message from the another ONU to the OLT, and the grant scheduler granting to the second ONU a fourth time window for transmitting a fourth message from the second ONU to the OLT, the fourth time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the third time window for the purpose of enabling communications interference detection;
if the third message is not received by the OLT, then indicating that the second ONU may be causing communications interference.

### Claim 22 (depends on 21)

The OLT of claim 21 wherein at least one of the pair of ONUs is either suspected of causing laser overlap, known to be causing laser overlap, or is assumed to be causing laser overlap.

### Claim 23 (depends on 21)

The OLT of claim 21 wherein the another ONU is either not suspected of causing laser overlap, known not to cause laser overlap, or is assumed not to cause laser overlap.

### Claim 24 (depends on 21)

The OLT of claim 21 wherein:
when performing (a), the second time window is scheduled, from the perspective of the OLT, to begin adjacent to or partially overlapping the first time window and later than the scheduled transmission of the first message;
when performing (b), the fourth time window is scheduled, from the perspective of the OLT, to begin adjacent to or partially overlapping the third time window and later than the scheduled transmission of the third message.

### Claim 25 (depends on 21)

The OLT of claim 21 wherein:
when performing (a), said indicating that the first ONU may be causing communications interference comprises indicating that the first ONU may be causing laser overlap;
when performing (b), said indicating that the second ONU may be causing communications interference comprises indicating that the second ONU may be causing laser overlap.

### Claim 26

An Optical Line Terminal (OLT) comprising:
an optical transceiver for communicating with an Optical Network Unit (ONU);
a grant scheduler for granting time windows to the ONU for transmitting messages to the OLT; and
a communications interference detector for:
(a) controlling the grant scheduler to grant to the ONU a time window for transmitting a message from the ONU to the OLT;
(b) if the message is not received by the OLT during an expected window of arrival, then indicating that the ONU may be causing communications interference.

### Claim 27 (depends on 26)

The OLT of claim 26, wherein the communications interference detector is further for computing the expected window of arrival by computing a start time of the expected window as an expected arrival time of the message minus a margin, and computing an end time of the expected window as the expected arrival time of the message plus another margin.

### Claim 28 (depends on 27)

The OLT of claim 27, wherein the communications interference detector is further for computing the expected arrival time using a round trip time (RTT) for the ONU and a scheduled start time of the time window.

### Claim 29

A computer readable medium having stored thereon computer readable instructions for execution in one or more processing devices in an Optical Line Terminal (OLT); the computer readable instructions comprising:
code for performing at least one of (a) and (b) in respect of a pair of Optical Network Units (ONUs) comprising a first ONU and a second ONU;
wherein (a) comprises:
granting to the first ONU a first time window for transmitting a first message from the first ONU to the OLT, and granting to another ONU different from both the first ONU and the second ONU a second time window for transmitting a second message from the another ONU to the OLT, the second time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the first time window for the purpose of enabling communications interference detection;
if the first message is not received by the OLT, then indicating that the first ONU may be causing communications interference;
and wherein (b) comprises:
granting to another ONU different from both the first ONU and the second ONU a third time window for transmitting a third message from the another ONU to the OLT, and granting to the second ONU a fourth time window for transmitting a fourth message from the second ONU to the OLT, the fourth time window scheduled, from the perspective of the OLT, to begin at a select time later than the beginning of the third time window for the purpose of enabling communications interference detection;
if the third message is not received by the OLT, then indicating that the second ONU may be causing communications interference.

### Claim 30

A computer readable medium having stored thereon computer readable instructions for execution in one or more processing devices in an Optical Line Terminal (OLT); the computer readable instructions comprising:
code for granting to an Optical Network Unit (ONU) a time window for transmitting a message from the ONU to the OLT; and
code for indicating that the ONU may be causing communications interference if the message is not received by the OLT during an expected window of arrival.