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EP-4500887-B1 - IMPROVING THE ENERGY EFFICIENCY OF OPTICAL NETWORKS

EP4500887B1EP 4500887 B1EP4500887 B1EP 4500887B1EP-4500887-B1

Inventors

  • HORSLEY, Ian

Dates

Publication Date
20260506
Application Date
20230227

Claims (14)

  1. A method (6000) of operating an optical network (5000) comprising a plurality of sets (5100) of optical network units, 'ONUs', and a commensurate plurality of exchange apparatuses (5200), the optical network being reversibly switchable between: a first configuration in which each of the sets of ONUs is optically coupled to a respective first exchange apparatus of the plurality of exchange apparatuses, such that each of the exchange apparatuses is optically coupled to only one of the sets of ONUs; and a second configuration in which one or some of the sets of ONUs, hereafter 'the second configuration transfer ONU sets', are optically uncoupled from their respective first exchange apparatuses and optically coupled to a respective second exchange apparatus of the plurality of exchange apparatuses, such that those second one or more exchange apparatuses are each optically coupled to two or more of the sets of ONUs; the method comprising: registering (s6100) each of the sets of ONUs with their respective first exchange apparatuses; registering (s6200) each of the second configuration transfer ONU sets with their respective second exchange apparatuses; and with the optical network in the first configuration, causing (s6300) optical communication between each of the sets of ONUs and their respective first exchange apparatuses; the method being characterised by then: obtaining (s6400) an indication that a period of low traffic demand on the optical network has commenced by determining, or receiving an indication, that a threshold proportion of ONUs of either i) the second configuration transfer ONU sets; or ii) the one or more sets of ONUs whose respective first exchange apparatuses act as respective second exchange apparatuses for the second configuration transfer ONU sets; are inactive, or have been inactive for a threshold inactivity duration, or have been optically decoupled from their respective first exchange apparatuses; and responsive thereto: ceasing (s6500) the optical communication between each of the second configuration transfer ONU sets and their respective first exchange apparatuses; powering down (s6600) those one or more first exchange apparatuses; switching (s6700) the optical network to the second configuration; and responsive thereto, causing (s6800) optical communication between each of the second configuration transfer ONU sets and their respective second exchange apparatuses.
  2. The method of claim 1, wherein the step of obtaining the indication that a period of low traffic demand on the optical network has commenced further comprises one or more of: a. determining, or receiving an indication, that a predetermined time window has commenced; and b. determining, or receiving an indication, that traffic on the optical network has fallen below a threshold traffic level, or has remained below a threshold traffic level for a threshold quiet duration.
  3. The method of claim 2, wherein the step of obtaining the indication that a period of low traffic demand on the optical network has commenced comprises option a., the method further comprising a step of: prior to obtaining the indication that the period of low traffic demand on the optical network has commenced, determining the predetermined time window based on historical traffic data for the optical network and/or one or more other, comparable, networks.
  4. The method of claim 3, further comprising updating the predetermined time window for future use, based on newly obtained traffic data.
  5. The method of any preceding claim, wherein the step of ceasing the optical communication precedes the step of powering down the one or more first exchange apparatuses, the method further comprising, in response to ceasing the optical communication: queuing messages received at the exchange for the second configuration transfer ONU sets until the optical network has been switched to the second configuration.
  6. The method of any preceding claim, wherein: the step of ceasing the optical communication between each of the second configuration transfer ONU sets and their respective first exchange apparatuses comprises pausing (s6520) issuance of upstream dynamic bandwidth allocation, 'DBA', grants to the second configuration transfer ONU sets; and the method further comprises: obtaining (s6540) an indication that all upstream DBA grants issued to the second configuration transfer ONU sets prior to said pausing have expired, the step of powering down the one or more first exchange apparatuses of the second configuration transfer ONU sets being responsive thereto; and in response to switching the optical network to the second configuration, resuming (s6720) issuance of upstream DBA grants to the second configuration transfer ONU sets.
  7. The method of any preceding claim, wherein the second configuration transfer ONU sets are configured to enter a popup state on detecting loss of communication from their respective first exchange apparatuses, the method further comprising: in response to obtaining the indication that the period of low traffic demand on the optical network has commenced, causing (s6530) the one or more second exchange apparatuses to commence sending respective streams of popup physical layer operations, administration and maintenance, 'PLOAM', messages; and in response to switching the optical network to the second configuration, causing (s6830) the one or more second exchange apparatuses to cease sending the stream of popup PLOAM messages.
  8. The method of any preceding claim, further comprising, subsequently: obtaining (s7400) an indication that a period of high traffic demand on the optical network has commenced; and responsive thereto: ceasing (s7500) the optical communication between each of the second configuration transfer ONU sets and their respective second exchange apparatuses; powering up (s7600) the one or more first exchange apparatuses that were powered down in response to obtaining the indication that the period of low traffic demand on the optical network had commenced; switching (s7700) the optical network back to the first configuration; and causing (s7800) optical communication between each of the second configuration transfer ONU sets and its respective first exchange apparatus to recommence.
  9. The method of claim 8, wherein the optical network is further reversibly switchable between the first configuration and a third configuration in which one or more of the plurality of sets of ONUs which are not second configuration transfer ONU sets, hereafter 'third configuration transfer ONU sets', are optically uncoupled from their respective first exchange apparatuses and optically coupled to a respective second exchange apparatus of the plurality of exchange apparatuses, such that those second one or more exchange apparatuses are each optically coupled to two or more of the sets of ONUs, the method further comprising: registering (s8200) each of the third configuration transfer ONU sets with their respective second exchange apparatuses; and subsequent to causing optical communication between each of the second configuration transfer ONU sets and its respective first exchange apparatus to recommence: obtaining (s8400) an indication that a further period of low traffic demand on the optical network has commenced; and responsive thereto: ceasing (s8500) the optical communication between each of the third configuration transfer ONU sets and their respective first exchange apparatuses; powering down (s8600) those one or more first exchange apparatuses; switching (s8700) the optical network to the third configuration; and responsive thereto, causing (s8800) optical communication between each of the third configuration transfer ONU sets and their respective second exchange apparatuses.
  10. The method of any preceding claim, wherein the network comprises a computer (17000) comprising a processor (17100) operably coupled to both a memory (17200) and an interface (17300), the interface comprising a transmitter (17320) that transmits messages, and a receiver (17310) that receives messages, to implement the steps of the method.
  11. A data processing system (17000), comprising the computer of claim 10.
  12. A computer program comprising instructions which, when the program is executed by the computer of claim 10, cause the computer to carry out the method of claim 10.
  13. A computer-readable data carrier having stored thereon the computer program of claim 12.
  14. A data carrier signal carrying the computer program of claim 12.

Description

Field The present disclosure relates to improving the energy efficiency of optical networks. More specifically, aspects relate to optical networks, methods of operating such optical networks, data processing systems configured to perform such methods, computer programs comprising instructions which, when the program is executed by a computer, cause the computer to carry out such methods, computer-readable data carriers having stored such computer programs thereon and data carrier signals carrying such computer programs. Background WO 2021/103344 A1, CN 106 160 918 A, Jingjing Zhang et al: "Designing energy-efficient optical line terminal for TDM passive optical networks", Sarnoff Symposium, 2011 34th IEEE, and Pulak Chowdhury et al: "Building a Green Wireless-Optical Broadband Access Network (WOBAN)", Journal of Lightwave Technology, IEEE, USA, vol. 27, no. 16 all disclose background art. Passive optical networks (PONs), otherwise known as the 'last mile' between internet service providers (ISPs) and subscribers, communicate data between exchanges (otherwise known as the service provider's central office (CO) or point of presence (PoP)) and end users over optical fibres. The term 'downstream' will be used herein to refer to the direction from the exchange to a subscriber device, and 'upstream' from the subscriber device to the exchange. Each PON comprises an optical line terminal (OLT) at the exchange and one or more optical network units (ONUs) or optical network terminals (ONTs) at customer premises. The International Telecommunication Union (ITU) defines an ONT as a special case of an ONU; an ONT being an optical terminal that serves a single subscriber, while an ONU is an optical terminal that serves one or more subscribers, for example in a residential or office block. The generic term ONU will be used in this document. Generally, a single optical fibre couples the OLT to a passive optical splitter, which has multiple output fibres. Each ONU is coupled to the splitter by one of those output fibres. Data can be transmitted bidirectionally over the PON by using one wavelength of light for downstream transmissions from the OLT, via the splitter, to the ONUs and another wavelength of light for upstream transmissions from the ONUs, via the splitter, to the OLT. When discussing inputs and outputs to splitters in this document, these terms are to be understood as referring to light traversing the splitter in the downstream direction. Accordingly, upstream light traversing a splitter enters the splitter through one of its 'outputs' and exits the splitter through one of its 'inputs'. Figure 1 illustrates the abovementioned features in an example optical network 1000. An exchange 1100 houses several OLTs 1110, 1120, 1130. Each of those OLTs is the upstream-most point of one or more PONs, but only one PON is shown, extending via a 'feeder' or 'spine' fibre 1210 from the OLT 1110 to a 2 x 32 splitter 1310. (2 x 32 is currently the most commonly used splitter in the UK, though PON technologies can also support 64- and 128-way splits. Higher split ratios reduce reach since downstream optical power is split between the splitter outputs.) The splitter 1310 has 32 outputs including output fibres 1410 and 1411 which are in use. Output fibre 1410 is routed to an office block 1510 which has an ONU 1511 coupled to the output fibre 1410. The office block 1510 houses three subscriber business premises 1512, 1513 and 1514, each of which is served by the ONU 1511 via either an optical or electrical connection (not shown). The output fibre 1411 is routed to a house 1520 where it is coupled to an ONU 1521. Figure 2 illustrates an example chassis based OLT 2110, which could for example correspond to the OLT 1110 of Figure 1. The OLT 2110 comprises a management card 2112, an ethernet card 2114 used for backhaul or point-to-point (PTP) services and a plurality of line cards 2116, 2118 etc. Each line card 2116, 2118 comprises one or more medium access control (MAC) chips (not shown). A first line card 2116 comprises a plurality of small form factor pluggable transceivers (SFPs) 2117a, 2117b etc. which comprise PON optics. Similarly, a second line card 2118 comprises a plurality of SFPs 2119a, 2119b etc. which comprise PON optics. One SFP typically provides one PON's connection to the OLT, though multi-transceiver SFP+s capable of connecting multiple PONs are available. Each PON is supported by a MAC chip, though not necessarily in a one-to-one relationship (i.e. a single MAC chip can support multiple PONs). Leaf/spine-based OLTs are sometimes deployed as an alternative to chassis-based OLTs. In leaf/spine-based OLTs leaf switches perform a similar role to the line cards of chassis-based OLTs. Both will be referred to herein generically as 'OLT subunits'. The way in which PONs use a wavelength or power splitter in the distribution network to allow multiple premises to be served by one spine fibre (1210 in the example of Figure 1) and