MoCA 2.0 features (cont.)
MoCA 2.0 defines an interface between the Node and the PMS and specifies the rules for transitioning the Node from the Active state to any of the other power states and from the other power states back to the Active state. The interface between the Node and the PMS support the following transactions:
- A Node indicating to the PMS the current Power state capabilities of the Node. These capabilities could change over time, for example, when the network changes from pure MoCA 2.0 mode to Mixed Mode* due to the introduction of 1.x Nodes to the network.
- The PMS requesting the Node to transition into a power state M0 – M3, and allowing the Node to acknowledge when the transition is completed or to refuse the request if the Node is requested to transition to a power state which is not currently supported.
- A Node in the Idle (M1) or Standby (M2) state signaling the PMS that it has received a broadcast packet.
- A Node in the Idle state (M1) signaling the PMS that it has received a unicast packet, which is available for retrieval.
- A Node in the Standby state (M2) signaling the PMS that it received a WoM request due to a unicast packet destined to the Node which is pending at another Node.
- A Node in the Idle (M1) or Standby (M2) state signaling the PMS that it is being instructed by the NC to transition to the Active state (M0).
In general MoCA 2.0 gives the PMS full control over when and to which power state the Node will transition. The only case when the Node transitions to a power state without direct instruction from the PMS is when it needs to move immediately to the Active state to support the functionality of the network. This can occur when a 1.x Node starts admission to the network while the Node is in the Idle state.
All power state transitions must go through the Active state (i.e. no transition is allowed directly between the low power states) and involve a request-grant protocol between the Node requesting to transition to a new power state and the NC which must grant every transition before it can actually happen. The NC will always grant the request unless it interferes with the operation of the network. For example, if it is in the middle of admitting a Node to the network, or in some cases when the Node is the backup NC.
If all other Nodes in the network have transitioned away from the Active state, the NC is allowed to move to the Idle state (M1). The NC is not allowed to move to the Standby (M2) or Sleep (M3) states. This guarantees that:
- The NC is ready to respond to Nodes requesting to Wake-Up, and
- Supports admissions of new Nodes to the network.
The time it takes for a Node to Wake-Up from Standby (M2) or Sleep (M3) states is less than 2 sec while waking up from the Idle (M1) state is immediate.
In a home network comprised of a media server and multiple thin Clients, all connected through the MoCA network; the different Nodes may use different power states to save energy. Figure 1 shows two examples of devices transitioning to different power states.
Figure 1: MoCA 2.0 Low Power States
A thin client which doesn’t record any broadcast service can go into a lower power state based solely on user input. As an example when the user turns off the TV and pushes the STBY button of the thin client, the Node in the thin client can move to the Sleep state (M3). To move to the Sleep state the Node requests and gets a grant from the NC for the move and then can lower its power consumption and be in the Sleep state. This Node needs only to Wake-Up when the user starts watching TV again.
When that happens the PMS in the thin client will instruct the MoCA Node to Wake- Up and the Node will rejoin the MoCA network and resume full operation. Figure 1 shows an example of an IP-STB going in and out of Sleep state following a user pushing the STBY and ON buttons of the remote control respectfully.
The media server on the other hand may receive a request at any time from any of the client Nodes in the MoCA network to start forwarding a recorded movie. To be able to send such a request to the media server through the MoCA network while the media server is in a low power state, the Node in the thin client has to Wake- Up the media server. This can only be done if the Node in the media server limits its low power states to either Idle (M1) or Standby (M2). These are the only power states supporting WoM.
As shown in Figure 1, when the media server is in Standby state (M2), as soon as the thin client (the MoCA Wi-Fi Extender) gets a request to start watching a movie it sends a request to the NC to Wake-Up the media server and the NC sends a WoM message to the Node in the media server. At that point the Node in the media server rejoins the network and the media server returns to full operation in order to send the recorded movie to the client Node. The decision of the media server on whether to use Idle or Standby is a trade-off between the requirements of power savings and quickness of waking up the Node from the low power state.
*MIXED MODE: Mixed Mode refers to a network in which the NC is a MoCA 2.0 Node, but there is at least one MoCA 1.x Node in the network.