Energy efficiency has become a mainstream requirement for all consumer products and specifically set-top boxes (STBs) and networking equipment. US federal and state governments as well as some European governments have started initiatives to regulate the maximum allowed annual energy consumption of STBs and networking equipment (see Appendix). Given the expected power consumption of STBs and other network devices with MoCA, a practical way to limit the annual energy consumption is to minimize power consumption during times when these devices do not need to be fully functional.
In support of the effort to reduce annual energy consumption the Multimedia over Coax Alliance (MoCA) included in its second generation of the specification, MoCA 2.0, requirements for supporting multiple power states, allowing a MoCA device, under the control of its host processor, to move into and out of low power states in coordination with the other devices in the network. By doing so, MoCA 2.0 reduces the annual energy consumption of the MoCA based home network as well as enables significantly lower energy consumption of all devices - such as gateways, media servers, IP-STBs, and MoCA Wi-Fi extenders - connected on that network.
This paper describes the low power features supported by the MoCA 2.0 specifications and their impact on the energy consumption of both the MoCA devices and the rest of the system.
MoCA Features Supporting Power Savings
MoCA 1.x (MoCA 1.0 and MoCA 1.1) specifications do not have any requirements in support of MoCA Nodes* operating in different power states. As a result, all potential power savings mechanisms for MoCA 1.x Nodes are implemented by either removing the Node completely from the MoCA network (e.g. shutting the Node down) for maximum savings, or keeping the Node fully operational meeting all the MoCA protocol and performance requirements and resulting in no power savings.
With a trend towards green implementations and greater interest in ENERG Y STAR certification, MoCA 2.0 has defined multiple power states. These power states enable a MoCA 2.0 Node to provide different levels of functionality at different levels of power consumption. MoCA 2.0 supports the following power states (see Table 1)
Table 1: MoCA 2.0 Low Power States
- Active (M0): This is the normal state of operation of the Node. In this state the Node is fully powered and is required to support the full functionality and performance of the MoCA 2.0 spec.
- Idle (M1): A reduced activity state allowing the Node to consume lower power. In this state the Node receives broadcast and unicast transmissions from other Nodes, and participates in Link Maintenance Operations (LMO s) and other network features, but does not transmit data packets to other Nodes in the MoCA network. In this state the Node can be triggered from the MoCA interface to move to the Active state via a Wake on MoCA (WoM) Message.
- Standby (M2): A minimal activity state allowing the Node to consume even lower power (relative to the Idle state). In this state the Node can receive broadcast packets which are relayed to it by the Network Coordinator (NC ), but doesn’t receive any packets directly from other Nodes nor does it transmit any packets to other Nodes in the MoCA network. In this state, the Node can be triggered to Wake on MoCA (WoM). Since a Node in this state doesn’t participate in any of the regular network activities, to be considered part of the network the Node is required to send heartbeat messages to the NC in a specified time interval. The Node in this power state forwards all broadcast packets received from the NC to its Power Management Subsystem (PMS). The content of these packets may trigger the PMS to instruct the Node to move to the Active state.
- Sleep (M3): An inactive state allowing the Node to reduce its power consumption to the lowest level possible other than a complete power shutdown. In this state the Node is essentially disconnected from the network while it is still able to return to the Active state. In this state the Node does not pass any data traffic and cannot be triggered to Wake on MoCA (WoM). To be considered part of the network the Node in this state is required to send heartbeat messages to the NC in a specified time interval.
*MoCA NODE: Throughout this paper, we refer to any device with MoCA functionality as a “Node”