# US 9,432,144 B2 · Precision time transfer systems and methods in optical networks

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- Number: US 9,432,144 B2
- Document ID: US9432144B2
- Status: Granted
- Kind: B2
- Application number: 14/485,117
- Filed: 2014-09-12
- Published: 2016-03-17
- Granted: 2016-08-30
- Earliest claimed: 2014-09-12
- Assignees: Ciena Corporation
- Applicants: Sebastien Gareau; Daniel Perras
- Inventors: Sebastien Gareau; Daniel Perras
- Web page: https://patentgrep.com/patent/US9432144B2

## CPC

- H04L 1/0045: {Arrangements at the receiver end}
- H04B 10/27: Arrangements for networking
- H04B 10/60: Receivers
- H04J 3/065: {using timestamps}
- H04J 3/0667: {Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864)}
- H04J 3/1652: {Optical Transport Network [OTN]}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04B: TRANSMISSION
- 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

A precision time transfer method, in a first node that communicates with a second node, to determine a difference in time between the first node and the second node, the precision time transfer method includes receiving a departure time, TD-A, from the second node, wherein the departure time is determined by the second node based on detecting a timing marker in a Forward Error Correction (FEC) frame or logical layer; determining an arrival time, TA-B, based on detecting the timing marker in the FEC frame; and determining a time difference based on the departure time and the arrival time wherein the timing marker is detected at a last point in a transmitter of the second node and at a first point in a receiver of the first node, during FEC processing.

## Claims

### Claim 1

A precision time transfer method, in a first node that communicates with a second node, to determine a difference in time between the first node and the second node, the precision time transfer method comprising:
receiving a departure time, TD-A, from the second node, wherein the departure time, TD-A, is determined by the second node based on detecting a timing marker included in a Forward Error Correction (FEC) frame or layer;
determining an arrival time, TA-B, based on detecting the timing marker in the FEC frame or layer; and
determining a time difference based on the departure time and the arrival time;
wherein the timing marker is detected subsequent to FEC encoding in a transmitter of the second node and prior to FEC decoding in a receiver of the first node.

### Claim 2 (depends on 1)

The precision time transfer method of claim 1, wherein the receiving is performed by a protocol layer separate from the FEC frame or layer.

### Claim 3 (depends on 1)

The precision time transfer method of claim 1, further comprising:
transmitting a FEC frame to the second node and determining a departure time, TD-B, responsive to detecting a timing marker in the FEC frame; and
receiving an arrival time, TA-A, from the second node, wherein the arrival time, TA-A, is determined by the second node based on detecting the timing marker in the FEC frame.

### Claim 4 (depends on 3)

The precision time transfer method of claim 3, further comprising:
determining a delay between the first node and the second node as:
Round_Trip
⁢
_Delay
=
[
(
T
A
-
B
-
T
D
-
A
)
+
(
T
A_A
-
T
D
-
B
)
]
Delay
=
Round_Trip
⁢
_Delay
2
.

### Claim 5 (depends on 1)

The precision time transfer method of claim 1, wherein the FEC frame utilizes Soft Decision FEC.

### Claim 6 (depends on 1)

The precision time transfer method of claim 1, wherein the FEC encoding is in a FEC encoder engine in the transmitter and the FEC decoding is in a FEC decoder engine in the receiver.

### Claim 7 (depends on 1)

The precision time transfer method of claim 1, wherein the timing marker is detected subsequent to FEC encoding and line adaptation and the timing marker is detected prior to FEC decoding and line adaptation thereby eliminating timing uncertainty based thereon.

### Claim 8 (depends on 1)

The precision time transfer method of claim 1, wherein the first node and the second node communicate via Optical Transport Network.

### Claim 9 (depends on 1)

The precision time transfer method of claim 1, wherein the time difference is independent from an amount of time spent processing in the FEC layer.

### Claim 10 (depends on 1)

The precision time transfer method of claim 1, wherein the timing marker is present in the FEC frame or layer at a given interval.

### Claim 11 (depends on 1)

The precision time transfer method of claim 1, wherein the timing marker, in the FEC frame or layer, is one of a toggling signal, a fixed pattern, one or more overhead bits, a delimiter, and a line encoding signal.

### Claim 12

A node that communicates with a second node, and the node is configured to determine a difference in time from the second node, the node comprising:
one or more line ports communicatively coupled to the second node; and
a controller communicatively coupled to the one or more line ports, wherein the controller is configured to
receive a departure time, TD-A, from the second node, wherein the departure time, TD-A, is determined by the second node based on detecting a timing marker included in a Forward Error Correction (FEC) frame,
determine an arrival time, TA-B, based on detecting the timing marker in the FEC frame, and
determine a time difference based on the departure time and the arrival time,
wherein the timing marker is detected subsequent to FEC encoding in a transmitter of the second node and prior to FEC decoding in a receiver of a line port.

### Claim 13 (depends on 12)

The node of claim 12, wherein the controller is communicatively coupled to the second node via a protocol layer separate from the FEC frame, to receive the departure time, TD-A.

### Claim 14 (depends on 12)

The node of claim 12, wherein the controller is further configured to:
determine a departure time, TD-B, responsive to detecting the timing marker in a FEC frame transmitted to the second node; and
receive an arrival time, TA-A, from the second node, wherein the arrival time, TA-A, is determined by the second node based on detecting the timing marker in the FEC frame.

### Claim 15 (depends on 12)

The node of claim 12, wherein the controller is further configured to:
determine a delay to the second node as:
Round_Trip
⁢
_Delay
=
[
(
T
A
-
B
-
T
D
-
A
)
+
(
T
A_A
-
T
D
-
B
)
]
Delay
=
Round_Trip
⁢
_Delay
2
.

### Claim 16 (depends on 12)

The node of claim 12, wherein the FEC encoding is in a FEC encoder engine in the transmitter and the FEC decoding is in a FEC decoder engine in the receiver.

### Claim 17 (depends on 12)

The node of claim 12, wherein the timing marker is detected subsequent to FEC encoding and line adaptation and the timing marker is detected is prior to FEC decoding and line adaptation thereby eliminating timing uncertainty based thereon.

### Claim 18 (depends on 12)

The node of claim 12, wherein the timing marker is present in the FEC frame or logical layer at a given interval.

### Claim 19 (depends on 12)

The node of claim 12, wherein the timing marker, in the FEC frame, is one of a toggling signal, a fixed pattern, one or more overhead bits, a delimiter, and a line encoding signal.

### Claim 20

An optical modem, configured to determine precise time information regardless of timing uncertainties due to Forward Error Correction (FEC) processing and adaptation therein, the optical modem comprising:
a FEC encoder configured to encode FEC;
a transmitter configured to optically transmit the FEC encoded signal;
a receiver configured to receive an optical signal; and
a FEC decoder configured to decode FEC on the received optical signal;
wherein the encoded signal and the received optical signal have one or more timing markers included therewith in the FEC encoded signal that are detected by circuitry in the FEC encoder subsequent to FEC encoding or by circuitry in the FEC decoder prior to FEC decoding, and wherein, responsive to detecting the one or more timing markers, the FEC encoder and the FEC decoder are configured to cause a timing determination.

### Claim 21 (depends on 20)

The optical modem of claim 20, wherein the timing marker is detected subsequent to FEC encoding and line adaptation and the timing marker is detected is prior to FEC decoding and line adaptation thereby eliminating timing uncertainty based thereon.

### Claim 22 (depends on 20)

The optical modem of claim 20, wherein the timing determination is based on one of i) an arrival time from the FEC decoder and a departure time from a second FEC encoder associated with a second optical modem and ii) a departure time from the FEC encoder and an arrival time from a second FEC decoder associated with the second optical modem.

### Claim 23 (depends on 20)

The optical modem of claim 20, wherein the one or more timing markers, in the FEC encoded signal, are one of a toggling signal, a fixed pattern, one or more overhead bits, a delimiter, and a line encoding signal.