# US 2022/0329337 A1 · Time synchronization in passive optical networks > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2022/0329337 A1 - Document ID: US20220329337A1 - Status: Published application - Kind: A1 - Application number: 17/224,532 - Filed: 2021-04-07 - Published: 2022-10-13 - Earliest claimed: 2021-04-07 - Assignees: Cisco Technology, Inc. - Applicants: Cisco Technology, Inc. - Inventors: Prashant Anand; Ashok Chandre Gowda; Ajay Sandhir - Web page: https://patentgrep.com/patent/US20220329337A1 ## CPC - 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 3/0644: {External master-clock} - H04J 3/0673: {using intermediate nodes, e.g. modification of a received timestamp before further transmission to the next packet node, e.g. including internal delay time or residence time into the packet} - 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} - H04Q 2213/1336: Synchronisation - H04Q 2213/13361: Synchronous systems - 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) - H04Q: SELECTING (switches, relays, selectors H01H; wireless communication networks H04W) ## Abstract This technology allows time synchronization in passive optical networks (“PON”). A first Ethernet device timestamps and transmits a packet to a second Ethernet device via the PON. The first Ethernet device transmits the packet to a small form-factor pluggable (“SFP”) device within the PON and connected to the first Ethernet device. The SFP device determines a transmission time to a second SFP device and modifies a correction field (“CF”) of the packet by subtracting an ingress time and the transmission time from the CF. The packet is transmitted to the second SFP device, which modifies the CF by the addition of an egress time. The modified CF value represents the real-time transmission delay incurred in the SFP devices. The packet is transmitted to a second Ethernet device to synchronize a clock using the timestamp and the CF value in accordance with the PTP/IEEE-1588 standard. ## Claims ### Claim 1 A method, comprising: communicating a packet between first and second computing devices in a network section, the network section being a separate portion of a network system; determining a residence time of the packet within the first and second computing devices in the network section, the residence time based on a first section clock associated with the first computing device in the network section and a second section clock associated with the second computing device in the network section, the first and second section clocks being disassociated from first and second system clocks that are outside of the network section; and synchronizing the first and second system clocks based on the residence time of the packet within the first and second computing devices in the network section. ### Claim 2 (depends on 1) The method of claim 1, wherein determining the residence time of the packet within the first and second computing devices in the network section comprises: by the first computing device of the network section: receiving, from a first computing device of the network system, the packet, the packet comprising one or more fields; timestamping an ingress time of the packet; determining a transmission time to the second computing device of the network section; first modifying a field of the packet using the ingress time and the transmission time; and transmitting the packet to the second computing device of the network section; by the second computing device of the network section: timestamping an egress time of the packet from the second computing device of the network section; second modifying the field of the packet using the egress time to indicate the residence time of the packet within the first and second computing devices in the network section; and transmitting the packet to a second computing device of the network system. ### Claim 3 (depends on 2) The method of claim 2, wherein the first computing device of the network section and the first computing device of the network system are a single hardware component. ### Claim 4 (depends on 2) The method of claim 2, wherein the second computing device of the network section and the second computing device of the network system are a single hardware component. ### Claim 5 (depends on 1) The method of claim 1, wherein the field of the packet is a correction field. ### Claim 6 (depends on 2) The method of claim 2, wherein the first modification of the field comprises subtracting the ingress time and the transmission time from a reference value. ### Claim 7 (depends on 6) The method of claim 6, wherein the second modification of the field comprises adding the egress time to the first modification of the correction field. ### Claim 8 (depends on 7) The method of claim 7, wherein the first computing device of the network system timestamps the packet with a sending time of the packet indicating a time that the packet is transmitted from the first computing device of the network system to a second computing device of the network system via the first computing device of the network section. ### Claim 9 (depends on 8) The method of claim 8, comprising: by the second computing device of the network system: extracting the sending time from the packet; extracting the second modification from the field of the packet; and synchronizing the second system clock which is associated with the second computing device of the network system with the first system clock which is associated with the first computing device of the network system based on the extracted sending time, the extracted second modification, and the transmission time. ### Claim 10 (depends on 1) The method of claim 1, wherein the network section is a passive optical network. ### Claim 11 (depends on 1) The method of claim 1, wherein the network system is an Internet Protocol over Ethernet over Fiber (“IPoEoF”) network system. ### Claim 12 (depends on 1) The method of claim 1, wherein the first computing device of the network section is an optical line terminal device. ### Claim 13 (depends on 2) The method of claim 2, wherein the first computing device of the network section is a small form-factor pluggable computing device connected to the first computing device of the network system. ### Claim 14 (depends on 1) The method of claim 1, wherein the second computing device of the network section is an optical network unit device. ### Claim 15 (depends on 2) The method of claim 2, wherein the second computing device of the network section is a small form-factor pluggable computing device connected to the second computing device of the network system. ### Claim 16 (depends on 2) The method of claim 2, wherein the first computing device of the network system and the second computing device of the network system are Ethernet devices. ### Claim 17 (depends on 16) The method of claim 16, wherein the Ethernet devices are routers. ### Claim 18 (depends on 1) The method of claim 1, wherein the packet is a precision time protocol (“PTP”) synchronization message in accordance with PTP/IEEE-1588 timing standard. ### Claim 19 A computer program product, comprising: a non-transitory computer-readable medium having computer-readable program instructions embodied thereon that, when executed by a computing device, cause the computing device to: communicate a packet between first and second computing devices in a network section, the network section being a separate portion of a network system; determine a residence time of the packet within the first and second computing devices in the network section, the residence time based on a first section clock associated with the first computing device in the network section and a second section clock associated with the second computing device in the network section, the first and second section clocks being disassociated from first and second system clocks that are outside of the network section; and synchronize the first and second system clocks based on the residence time of the packet within the first and second computing devices in the network section. ### Claim 20 A system, comprising: a storage device; and a processor communicatively coupled to the storage device, wherein the processor executes application code instructions that are stored in the storage device to cause the system to: communicate a packet between first and second computing devices in a network section, the network section being a separate portion of a network system; determine a residence time of the packet within the first and second computing devices in the network section, the residence time based on a first section clock associated with the first computing device in the network section and a second section clock associated with the second computing device in the network section, the first and second section clocks being disassociated from first and second system clocks that are outside of the network section; and synchronize the first and second system clocks based on the residence time of the packet within the first and second computing devices in the network section.