Patent Application
20120166819
This invention relates to optical access networks, such as passive optical networks (PON).
Increasing demand for a range of high-bandwidth communications services is driving a need for high-capacity access networks to provide those services. Optical access networks can deliver the high bandwidths now required. An optical access network typically has apparatus called an Optical Line Terminal (OLT) at a Central Office node. The OLT serves a plurality of optical terminals, called Optical Network Units (ONU). ONUs can be deployed at subscriber premises, at kerbside cabinets, or at other remote locations, depending on the access network architecture. A Passive Optical Network is a type of optical access network with limited, or no, power requirements in the optical path between the Central Office (CO) and ONUs. There are various types of passive optical network which differ in how the resources of the fibre are shared among ONUs. In a Time Division Multiplexing Passive Optical Network (TDM-PON), the resources of the fibre are shared on a time-divided basis among ONUs. Traffic in the downstream direction is broadcast by the OLT to all ONUs, with each ONU extracting traffic destined for itself. Each ONU served by the OLT is allocated time slots in which it can transmit data to the OLT. The time slots can occur at irregular intervals and can have irregular durations. In a Wavelength Division Multiplexed Passive Optical Network (WDM-PON), each ONU is allocated a different wavelength channel, called a lambda, for communication between the OLT and that ONU.
Techniques for reducing the energy consumption of optical access networks have been proposed. In TDM-PONs, energy is consumed by transceivers to keep the link between the ONU and OLT alive, regardless of traffic. It has been proposed to power off the ONU transceiver in a TDM-PON at times of no traffic to save energy.
One proposal is that an optical network unit (ONU) can autonomously enter a low-power state during times of inactivity. This means that an ONU decides for itself, without external control, when to enter a lower power state. Another proposal is that an external entity, such as an OLT, authorises an ONU to enter a lower power state at the discretion of the ONU. When the ONU decides to sleep, it signals to the OLT so the OLT can distinguish between the ONU being asleep and the ONU being at fault. One proposal for ITU-T G.987.3 is for two non-autonomous reduced-power modes referred to as cyclic sleep and doze mode. Cyclic sleep refers to the controlled powering off of the ONU transceiver during short time intervals. Doze mode refers to the controlled powering off of the ONU transmitter, while keeping the ONU receiver powered up and active.
It is desirable to further reduce energy consumption of optical access networks.
An aspect of the present invention provides a method of power management in an optical access network. The optical access network comprises at least a first node and a second node. The method determines service information about traffic at the first node. The method controls power management of the optical access network based on the determined service information.
The “first node” can be an entity at the CO side of the access network, such as an Optical Line Terminal (OLT) and the “second node” can be an entity at the subscriber side of the access network, such as an Optical Network Unit (ONU). Alternatively, the “second node” can be an entity at the CO side of the access network, such as an Optical Line Terminal (OLT) and the “first node” can be an entity at the subscriber side of the access network, such as an Optical Network Unit (ONU).
In some embodiments of the invention, it may be possible to reduce energy consumption of the network while still providing an acceptable quality of service, as energy consumption is matched to traffic. For example, during periods of low priority traffic, such as best efforts traffic, it is possible to operate the network in a reduced power state, such as by powering down a transceiver (or part of the transceiver) at a node, or by operating the transceiver (or part of the transceiver) at a node in a cyclic sleep mode with a relatively long off period. During periods of higher priority traffic, it is possible to operate the network in a higher power state, such as by fully powering up a transceiver (or part of the transceiver) at a node, or by operating the transceiver (or part of the transceiver) at a node in a cyclic sleep mode with a relatively short off period. Increasing the length of sleep periods reduces energy consumption.
The term “state” can refer to an operating mode of an OLT or ONU, such as a mode recited in ITU-T G.987.3, or to a specific state of a state machine which describes the behaviour of an OLT or ONU.
The optical access network can be a TDM-PON, WDM-PON, point-to-point optical access network, or any other kind of optical access network.
Another aspect provides a power management control apparatus for an optical access network. The optical access network comprises at least a first node and a second node. The apparatus comprises a monitoring module arranged to determine service information about traffic at the first node. The apparatus comprises a control module arranged to control power management of the optical access network based on the determined service information.
The functionality described here can be implemented in hardware, software executed by a processing apparatus, or by a combination of hardware and software. The processing apparatus can comprise a computer, a processor, a state machine, a logic array or any other suitable processing apparatus. The processing apparatus can be a general-purpose processor which executes software to cause the general-purpose processor to perform the required tasks, or the processing apparatus can be dedicated to perform the required functions. Another aspect of the invention provides machine-readable instructions (software) which, when executed by a processor, perform any of the described methods. The machine-readable instructions may be stored on an electronic memory device, hard disk, optical disk or other machine-readable storage medium or non-transitory medium. The machine-readable instructions can be downloaded to the storage medium via a network connection or pre-installed at a time of manufacture.
Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:
In a Time Division Multiplexing Passive Optical Network (TDM-PON), the resources of the fibre 12 are shared on a time-divided basis among ONUs 10. Traffic in the downstream direction is broadcast by the OLT to all ONUs, with each ONU extracting traffic destined for itself. Each ONU served by the OLT is allocated time slots in which it can transmit data to the OLT. The time slots can occur at irregular intervals and can have regular, or irregular, durations. Typically, a scheduling function will allocate time slots to ONUs based on various criteria. In a Wavelength Division Multiplexed Passive Optical Network (WDM-PON), each ONU 10 is allocated a different wavelength channel, called a lambda, for communication between the OLT 20 and that ONU 10.
Power management functionality is provided within the optical access network. A power management control unit 60 is provided at each ONU 10. One or several power management control units 50 are provided for the OLT 20. For the OLT 20 there may be one power management control unit 50 per connected ONU 10. Power management unit 50 can form part of an OLT 20, or a power management unit 50 can be provided as a resource for a group of OLTs 20. In a further alternative, the power management unit 50 can be located in another network entity, such as a network management entity. For autonomous reduced power modes, each power management unit may operate individually. For non-autonomous reduced power modes, power management units may operate in pairs, with one unit on each side of the link which is managed. The power management control units 50, 60 implement power management functions, such as those proposed in ITU-T G.987.3 for XG-PON. Power management functions allow the ONUs 10, or parts of the ONUs (such as the transceivers 11), to reduce their energy consumption at certain times. Power management functions can allow the OLTs 20, or parts of the OLTs (such as the transceivers 21) to reduce their energy consumption at certain times. Power management control units 50, 60 may support power management functions at the same node, at the opposite node (in a pair) or both.
For a power management control unit that supports power management functions on the same node, there is a control channel to each internal node element that is controlled (e.g. transceiver). The state of a controlled node element is determined by the current state of the state machine of the power management control unit.
Regarding the power management control unit, typical forms of control include triggering a change of state in the internal state machine and/or the state machine of the opposite power management unit (in a pair). Furthermore it includes modifying internal power management settings (e.g. timer values) and/or modifying power management setting at the opposite power management unit (in a pair).
There are various scenarios that can be considered:
(i) Power management control unit 50 at an OLT 20 can issue control signals to an ONU 10 based on traffic received at the OLT 20. Control signals influence the power management at the ONU 10 such that it operates in a state matched to the traffic the OLT 20 is about to send to the ONU 10.
(ii) Power management control unit 50 at an OLT 20 can control the operating state of the OLT 20 itself based on traffic received at the OLT 20. The operating state may or may not be associated with power management functions at the OLT 20 itself.
(iii) Power management control unit 60 at an ONU 10 can control the operating state of the ONU 10 itself based on traffic received at the ONU 10. The operating state is most likely associated with power management functions on the ONU 10 itself. The ONU 10 ensures it only consumes as much energy as it needs to for the current traffic demands.
(iv) Power management control unit 60 at an ONU 10 can control the OLT 20 based on traffic received at the ONU 10. The ONU 10 ensures the OLT 20 is operating in a state matched to the traffic the ONU 10 is about to send to the OLT 20.
Each ONU 10 operates in one of a set of possible power management modes at any given time. In G.987.3, the possible modes are: Full Power; (Low Power) Doze; (Low Power) Cyclic Sleep. The modes differ in their power requirements. Each power management mode can comprise one or more power management states. A way of controlling power management is to provide a state machine 62 at each ONU 10. An ONU 10 can move between the possible states in response to stimuli, such as signalling received from the power control unit 50 at the OLT 20 or local conditions at the ONU 10, such as expiry of a timer or subscriber traffic activity. Similarly, a state machine 52 or other control logic is provided at the OLT 20 for each of the remote ONUs 10 in the PON.
Logic 53 triggers state transitions of the state machine 52 and alters power control settings 51 based on service information or service-specific traffic activity information 36. There are various events that trigger the transitions from one state to another, such as local activity triggers. ITU G.987.3 defines triggers called LDI (local doze indication), LSI (local sleep indication), LWI (local wake-up indication).
Power management control unit 50 comprises a store 51 of power control settings. These are parameters for the logic 53 and operation of the state machine 52. A list of parameters in ITU G.987.3 is provided in Table 3. Values of these parameters can be changed and optimised depending on traffic monitoring.
A monitoring unit 35 monitors traffic 22 arriving at the OLT 20. The monitoring unit monitors traffic activity which can be measured, for example, by packet inter-arrival time or buffer state information. It also determines service information 36 for the monitored traffic or traffic activity of traffic categorized depending on service information. The term “service information” 36 can comprise at least one of the following:
service type of the received traffic;
traffic class of the received traffic; and/or
quality of service requirements of the received traffic.
Traffic activity information and service information 36 is applied to the power management control unit 50. This enables the generation of control signals to the power control state machine 52 which are class/service dependent. The monitored class/service information 36 can also be used for updating power management settings 51, such as timer settings which control transition between states of the state machine 52.
Consider a system where power management (of sleep parameters) is dependent on monitoring of different traffic classes (with different QoS requirements). In BroadBand Forum (BBF) architecture standards there are typically a minimum number of traffic classes that should be supported. These have different priority levels and are scheduled differently in the network.
Classification of traffic can be performed in various ways. Packets/frames carrying traffic can include a header which carries priority or QoS information. For example, some Ethernet formats add a Tag with Priority bits. The header is inspected and traffic is classified based on the header contents. Other ways of classifying traffic include: classifying by user port; classifying by VLAN Identifier (VID) of an Ethernet frame; deep packet inspection. Advantageously, the classification relates to QoS-requirements, such as traffic with different latency requirements.
Monitoring 35, 65 can monitor the queue sizes of different logical queues at the OLT 20 or ONU 10. It could also monitor arrival or inter-arrival time of packets for each class/service.
The format of the input 36, 66 to the power management control unit could, for example, be a simple indication of active services that the power saving mechanism should take into account. Implementation of the control logic within the power management control unit can be vendor-specific. There is a wide range of algorithm possibilities. If the monitoring information is inter-arrival time between packets, the criteria could be one or several thresholds for the average inter-arrival time (or some other function of the inter-arrival time) at which control signals or setting updates are generated. If the monitoring information is buffer state information, the criteria could consist in one or several thresholds related to buffer size. Power control settings such as timer values for e.g. the sleep period can be determined by a function of the monitored information (e.g. the packet inter-arrival time). As described above, the criteria can be made service specific.
At a particular point in time, traffic between a pair of nodes (OLT, ONU) may comprise multiple different services, such as telephony traffic and best efforts data traffic. Power management control units 50, 60 can adapt power management operation to the most demanding of the currently active services by using power control settings for this service. Hence, service aware power management is used to implement optimal power management settings with respect to type of active traffic, with power control settings defined for each traffic “type”. The traffic types can be ranked with respect to requirements. In some embodiments, the power control settings can be determined based on a combination of service/traffic type and other properties of the monitored information, such as packet inter arrival time.
At times of idleness, system messages between network nodes prevent optimal power management by triggering wake-up. Some of these messages could be considered unnecessary for a node in certain low power states. Messages could include e.g. Address Resolution Protocol (ARP) messages, Internet Group Management Protocol (IGMP) multicast messages, etc. In service aware power management these messages can be buffered so as not to interrupt low power operation. It is also possible to discard messages which are deemed “unimportant” to a node in a low power state. This can be called “service aware dropping”. This avoids extensive buffering at a sending node. This process depends on the destination node, power state information (for the sending node or the destination node) and service information.
An XG-PON is an example TDM-PON architecture to which the service-aware power management can be applied. The following power management control messages are used in an XG-PON: OLT-LWI or !OLT-LWI; Local Wake-up Indication (LWI), Local Sleep Indication (LSI); Local Doze Indication (LDI). With the service/traffic type information available by means of the invention, the criteria for issuing, for example, an LWI, LSI or LDI could be made service/traffic type dependent. For high priority services an LWI could be issued at the arrival of a single packet associated with the service. For low priority services the LWI could be issued first when the amount of traffic associated with that service surpasses a certain threshold. Within the XG-PON framework there is limited bandwidth availability also during the cyclic sleep/doze periods that could be used for low bandwidth traffic with low QoS requirements. Also, the duration of sleep/doze periods can be controlled dynamically by means of monitoring service information as well as transition between doze mode and sleep mode.
Modifications and other embodiments of the disclosed invention will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
The following table gives a summary of the power management states at an ONU in G.987.3:
The following table gives a summary of the power management states at an OLT in G.987.3:
