Patent Publication Number: US-8995280-B2

Title: System and method for an energy efficient network adapter

Description:
PRIORITY CLAIM TO PROVISIONAL APPLICATION 
     This patent application claims priority to U.S. Provisional Application No. 61/558,752 filed on Nov. 11, 2011, entitled “System and Method for an Energy Efficient Network Adaptor,” which application is hereby incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to networking systems, and more particularly to a system and method for an energy efficient network adaptor. 
     BACKGROUND 
     As networked devices have become cheaper and more capable, the market for these devices has exploded. Further, users are demanding greater speeds, better performance, and seamless operation from these devices. User demand for better QoS and high network availability coupled with device interoperability is driving the development of devices with multiple network interfaces, and standards for integrating multiple interfaces into a single home area network. Proliferation of devices and network interfaces means that power consumption of the network interface becomes an increasingly relevant concern for device owners and operators. 
     Power consumption has several negative user-visible effects, some of which include: it is a significant contributor to the long-term cost of ownership of a device; it reduces battery life and increases the cost and complexity of the power supply; and it can raise device temperature, potentially increasing design size and complexity to accommodate more powerful cooling mechanisms. Device power consumption can be reduced by reducing effective clock speed and by disabling components of the device for the period in which they are not in use. These techniques are more difficult to apply to the networking layer of a given device, as designs often assume that network requests will be unpredictable. 
     SUMMARY OF THE INVENTION 
     In accordance with an embodiment, a network device includes a network controller and at least one network interface coupled to the network controller that includes at least one media access control (MAC) device configured to be coupled to at least one physical layer interface (PHY). The network controller may be configured to determine a network path comprising the at least one network interface that has a lowest power consumption of available media types coupled to the at least one PHY. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a hybrid network system; 
         FIG. 2  illustrates a hardware block diagram of a hybrid network system; 
         FIGS. 3   a - b  illustrate implementation examples of a hybrid network system; 
         FIGS. 4   a - b  illustrate embodiment systems; 
         FIG. 5  illustrates an example Beacon period configuration for IEEE 1901; 
         FIG. 6  illustrates a conventional radio parameter negotiation process; 
         FIG. 7  illustrates an MPDU format and receive state diagram; 
         FIG. 8  illustrates a logical structure and corresponding MPDUs for a latency optimized transmission; 
         FIG. 9  illustrates a logical structure and corresponding MPDUs for an efficiency optimized transmission; 
         FIG. 10  illustrates a spectral plot showing the maximum per-frequency energy distribution of a transmission at a transmitter; 
         FIG. 11  illustrates a spectral plot showing an example energy distribution at a receiver; 
         FIG. 12  illustrates an embodiment channel estimation process with amplitude negotiation; 
         FIG. 13  illustrates a spectral plot of an adjusted transmit amplitude according to an embodiment system; 
         FIG. 14  illustrates a plot of a received frequency energy distribution with adjusted transmit amplitude according to an embodiment system; 
         FIG. 15  illustrates an example preamble waveform at the transmitter; 
         FIG. 16  illustrates a received preamble waveform using a slow gain adjustment; 
         FIG. 17  illustrates a received preamble waveform using a fast gain adjustment; 
         FIG. 18  illustrates a heat-map depicting the energy required to transmit a volume of data as a function of frame length and encoding rate; 
         FIG. 19  illustrates an embodiment convergent network; 
         FIG. 20  illustrates a network having two stations connected by two interfaces; and 
         FIG. 21  illustrates an embodiment state machine. 
     
    
    
     Corresponding numerals and symbols in different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale. To more clearly illustrate certain embodiments, a letter indicating variations of the same structure, material, or process step may follow a figure number. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The making and using of the embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. 
     The present invention will be described with respect to embodiments in specific contexts, for example, a system and method for an energy efficient network adaptor in a hybrid network. Embodiment systems and methods, however, are not limited to hybrid networks, and can be applied to other types of networking systems. 
     In embodiments, a hybrid network approach leveraging multiple MAC/PHY stacks, such as the emerging IEEE P1905.1 standard, may reduce power consumption, by allowing communications to proceed along lower power paths when possible, and by disabling supplemental communications channels when the user does not require additional network capacity. 
     In some embodiments, power optimization is performed such that reducing device functionality is reduced in such a way that QoS is not compromised. In other words, some embodiment power optimization methods include strategically reducing certain device capabilities when these certain capabilities are not required; increasing capability only when required to do so, and only to the extent required; and, when the same function can be performed in multiple ways, choosing the most efficient method. 
     In some embodiments, power consumption optimization uses the following information: when system clients will require some function from the system; the level at which system clients require that function to be performed; the energy required to communicate those requirements and data to relevant parts of the system; and how much time and energy it takes to change the capability level of the system. Some embodiment power consumption optimization processes comprise maintaining this set of information, developing the historical knowledge that may be analyzed to detect trends and patterns as an example, and of acting on it. 
     Generally, embodiments of the present invention involve scheduling and selecting data transmission paths in hybrid systems having multiple-network interfaces. For example, an IEEE standard currently under development, “P1905.1—Standard for a Convergent Digital Home Network for Heterogeneous Technologies,” will support a converged digital home network (CDHN). Some embodiments include an abstraction layer for multi-network-interface devices operating in a home network for the purpose of providing a common data and control interface to heterogeneous network technologies including: Wi-Fi (IEEE 802.11x), Ethernet (IEEE 802.3), MoCA 1.1 and HomePlug AV 1.1. The abstraction layer common interface allows applications and upper layer protocols to be agnostic to the underlying home network technologies. 
       FIG. 1  illustrates an embodiment of the IEEE P1905.1 Draft Standard implemented as an abstraction layer. Block diagram  100  shows the abstraction layer with unified Service Access Point (SAP)  102  performing a variety of functions in blocks  104  and  106  to achieve the convergence, abstraction, and unification of previously standalone SAPs specific to each media, such as HomePlug  108 , Wi-Fi  110  and MoCA  112 . In alternative embodiments of the present invention, hybrid network structure  100  may include greater, fewer and/or different network types and functions. 
       FIG. 2  illustrates a hardware block diagram hybrid network system  200  showing Turbo Media Independent Interface (TMII)  202  coupled to hybrid network controller  204  that outputs power line communication (PLC) signal  206  at one interface and a Wi-Fi signal  208  at another interface. In one embodiment, the Wi-Fi signal  208  is produced by 802.11 adaptor  212  that is coupled to hybrid network controller  204  via PCIe interface  210 . It should be understood that the diagram of  FIG. 2  depicts just one example of a hybrid network system. Other embodiment hybrid systems may have any number of network interfaces of various network interface types. For example, this may include a standalone PLC Interface coupled to the controlled  204  via a PCIe interface coupled in the same fashion as block  212 . Alternatively, a fully integrated device may be implemented such that controller  204  also includes some or all of the functionality of adaptor  212 . 
     Hybrid networks, such as IEEE P1905.1 may be used, for example, to provide multipath data communication in which data is transmitted via multiple network connections, as is illustrated in  FIG. 3   a  showing router  220  communicating with television  222  via HomePlug network connection  224  and a Wi-Fi network connection  226 . Hybrid network systems may also be used to extend range as shown in  FIG. 3   b , in which tablet computer  230  is coupled to router  232  via a series connection of HomePlug network connection  234  and a Wi-Fi network connection  236 . In an embodiment, this series connection may be used in place of single Wi-Fi network connection  238 . It should be appreciated that the network types and device types shown in  FIGS. 1-3  are only specific representative examples of the hybrid network configurations that may be used in embodiments of the present invention. Other configurations using other different network types and connection topologies may be used. 
       FIG. 4   a  illustrates an embodiment of adapter system  300 . Data interface  302  (that may also be a SAP) is coupled to controller  304  that is further coupled to network interfaces  306 ,  308  and  310 . These network interfaces may comprise a number of different MAC and PHY blocks, or they may comprise a single MAC block and the plurality of PHY blocks coupled to the MAC block. These blocks may also be a single device which is dynamically adaptable as described in U.S. Pat. No. 7,440,443, entitled, “Coupling between power line and customer in power line communication system” and as described in U.S. Pat. No. 8,050,287, entitled, “Integrated universal network adapter,” which are hereby incorporated within in their entirety. Controller  304  inputs and outputs data to and from the data interface and determines over which of network interfaces  306 ,  308  and  310  to transmit and receive data based on power control operation and other parameters including QoS, as well as methods described herein. Data may be sent and received over the various MAC/PHY blocks simultaneously to utilize multiple media types coupled to said blocks, including such transmissions where packets are interleaved and/or repeated among multiple media types. In some embodiments, packets presented to the various MAC/PHY blocks such as blocks  108 ,  110 , and  112  illustrated in  FIG. 1  do not necessarily correspond to the packets presented at the unified SAP layer  102 , as they may undergo translation and re-packing. 
     In an embodiment, some of the MAC functions that traditionally reside in the media specific MAC are aggregated into a unified MAC engine performing said functions for multiple media types and further integrated with a CDHN type of functionality. Typically a MAC performs a lot of queuing and buffer management to deal with the QoS requirements and traffic prioritization/shaping. In some embodiments, the MAC may also perform packet retransmission and reordering. In the case of a single integrated engine performing both CDHN and multiple MAC functions, the size of the required memory may be reduced due to a reduction in the number of queues and buffers and sharing of the resources among multiple media specific interfaces. For example, in one embodiment, MAC queues may be eliminated and CDHN queues may be used for all purposes. At the same time, a single instance of a CPU may manage multiple media specific MACs, thereby providing a reduction in cost and complexity. 
     In an embodiment, the controller may also determine the state of power saving modes, such as clock frequency control, and power down states for various processing blocks and for the different MAC and PHY blocks. In some cases, the controller may also schedule intervals of time during which the network interface is not allowed to transmit or is scheduled to be powered down. The determination made by the controller may include determining which power saving strategies to use as well as issuing commands and control signals to implement these power management strategies. Moreover, the determination of power management strategies may be made in various combinations in order to meet the requirements of a particular user, or a particular type of network or network use case scenario. For example, if a content source is transmitting video and audio to a playback device, the audio content may be transmitted over a different link from the video content. Because audio and video have different bandwidth requirements, the links may be optimized further than if they were transmitted in the same stream or were different streams over the same links. 
       FIG. 4   b  illustrates adapter system  350  according to an alternative embodiment. System  350  is similar to system  300  depicted in  FIG. 4   a  with the addition of MAC processing engine  352 . In an embodiment, MAC processing engine  352  may perform queuing functions among multiple media specific MACs in the system. For example MAC processing engine  352  may aggregate queuing functions that otherwise would be residing in media specific MACs residing in MAC/PHY blocks  354 ,  356  and  358 . Advantages of such an embodiment include the ability to further reduce the size and complexity of a system implementation. 
     In an embodiment, MAC processing engine  352 , performs MAC functions that are common or similar among multiple media specific MACs in the system. As an example, it could aggregate all the queuing that otherwise would be residing in media specific MACs with the queuing necessary for the abstraction layer into a single optimized engine that further allows to reduce the size and complexity of the whole implementation. 
     The systems shown in  FIGS. 4   a - b  may be implemented on a single integrated circuit, or may be implemented using multiple integrated circuits, or other components known in the art. The controller may be implemented using a microprocessor, microcontroller, custom logic, or other circuitry known in the art. In some embodiments, operation of the controller may be software programmable, implemented in hardware with or without being configurable and/or programmable, or combination of the two. 
     In some embodiments, power may be reduced in four domains: in a single network interface in a single device; in a single network interface across all devices sharing that network; in multiple network interfaces in a single device; and in multiple network interfaces across the union of the devices that can communicate using these networks. Accordingly, in some embodiments, power may be reduced: within a single MAC/PHY implementation on a single device; within a single MAC/PHY implementation across a whole network; across multiple MAC/PHY implementations on a single device; and across multiple MAC/PHY implementations across a whole network. While embodiments are described herein with respect to IEEE 1901-2010™ standard (IEEE 1901) as an example of a network MAC/PHY, and IEEE P1905.1 (as an example of a hybrid network), embodiments are broadly applicable beyond these specifically described contexts. 
     IEEE 1901 defines a MAC/PHY for PLC, including provision for Time Division Multiple Access (TDMA) and Carrier Sense Multiple Access (CSMA) modes for medium coordination. IEEE 1901 networks include a single network management node, called the BSS Manager, which provides a stable clock reference for other devices on the network, and which coordinates the allocation of TDMA and CSMA periods for device communications. 
     TDMA regions in IEEE 1901 are managed by the BSS Manager, and communicated to network stations through the Persistent and Nonpersistent Schedule BENTRYs in network Beacons. To communicate in a TDMA region, a station must characterize the network traffic that could occur in a TDMA region in a Traffic Specification (TSPEC), and present this TSPEC to the BSS Manager in a TDMA allocation request.  FIG. 5  illustrates an example Beacon period configuration for IEEE 1901. 
     Diagram  500  illustrating a radio parameter negotiation is illustrated in  FIG. 6 . In IEEE 1901 networks, unicast communications parameters are the product of a negotiation between the source represented as Station A  502  and destination represented as Station B  504 . In the negotiation process, Station A  502  first sends a SOUND frame  506  to Station B  504 . On receiving a SOUND frame, Station B  504  collects information about receive fidelity for that frame from the PHY. This information is used to calculate the radio configuration information (or “tone-map”) that Station A  502  should use for future communications with Station B  504 . Station B  504  responds to the SOUND frame with a SOUND_ACK  508 , indicating whether or not Station A should send more SOUND frames  506  before tone-maps can be returned to Station A  502 . After enough information is collected, Station B  504  will send a CM_CHAN_EST.indication message  510  to Station A  502 . This message includes the set of tone-maps that Station A  502  should use for future transmissions to Station B  504 . 
     Though the IEEE 1901 PHY is designed to be capable of up to 4096-QAM modulation, a large percentage of the medium time will be of a form that requires much less transmitter and receiver accuracy. During such periods, the PHY clock may run at reduced rate, thereby saving power. 
     At times during which no station is transmitting (the medium is Idle), the PHY may only need sufficient accuracy to detect the beginning of a Priority Resolution Symbol (PRS) (during the PRS window) or a preamble. After detecting a PRS, the PHY need not receive any additional medium signals until the current PRS period ends. On the other hand, receiving payload requires increasing receiver fidelity as the Mac Protocol Data Unit (MPDU) is processed: the beginning of the preamble may be detected more simply than the preamble-to-Frame Control boundary; and it is simpler to detect the end of the preamble than to decode the frame control or payload data. In an embodiment, the simpler parts of the MPDUs may potentially be transmitted and received at a reduced sampling frequency, thereby saving power. For example, in an embodiment, initial preamble detection (and PRS detection) may run at lower sampling frequency than the preamble-boundary detection. 
       FIG. 7  illustrates MPDU format and receive state diagram  550 . The receiver starts out searching for preamble state  560  while the traffic on the wire is idle. When the receiver receives preamble  552 , the receiver transitions to search for preamble end state  562 . At the reception of Telecommunications Industry Association (TIA) Frame Control (FC)  554 , the receiver transitions to a receive TIA FC  564  state until the reception of AV FC  566 , in which case the receiver transitions to receive AC FC state. These TIA FC messages comply with the standard “TIA/TR-30.1, TIA 1113: A Medium Speed (Up to 14 mbps) Power Line Communications (PLC) Modem, May 2008” (TIA 1113), which is incorporated herein in its entirety. Once payload frames  558  are received, the receiver transitions to receive payload frame state  568 . At the conclusion of the reception of payload frames  558 , the receiver once again assumes search for preamble state  560 . 
     Reducing the sampling clock rate may have a beneficial effect on power consumption; and disabling the receive logic entirely may have an even greater positive effect. This entails identifying periods in which no valid data should be received. Such periods may be referred to as “Receiver Irrelevant Periods”, or RIPs.) Some RIPs are trivially identified (such as when the station itself is the transmitter, or during inter-MPDU intervals), some will occur due to the staged nature of the receive operation, and others are dependent on individual station properties and the region-type in the Beacon period. 
     Some RIPs include the time between detection that the MPDU data on the wire is irrelevant to the receiver, and the expiration of the receiver&#39;s virtual carrier sense timer for that MPDU. This may happen in at least two ways: early stage receive-operations for the MPDU data can fail (preventing later stage receipt—e.g. failure to detect the end of a preamble can prevent frame control receipt, and frame control decode failure can prevent payload receipt); or early stage MPDU data can indicate that the local receiver is not the intended recipient. For example, the destination terminal equipment identifier, or the short network identifier in an AV Start-of-Frame frame control may not match the local device&#39;s configuration. In either case, the frame is guaranteed not to be destined to the local device, and may be ignored in some embodiments of the present invention. 
     Other RIPs may be determined by the Beacon region allocation. In general, stations not participating in a particular global or local link are not active on the medium during the TDMA regions allocated to these links. (An exception is the BSS manager or proxy BSS manager, which needs to listen to medium activity during TDMA regions, for accounting and maintenance purposes.) Stations do not generally need to listen to the medium during Stayout or Protected regions, and only the BSS Manager will generally need to listen to the medium during Beacon Regions for foreign networks. 
     As previously described, during Stayout or Protected regions, stations neither transmit nor receive the network payload. As such, the rate of power consumption may be significantly reduced during these regions. The IEEE 1901 BSS Manager station controls the overall structure of the Beacon region.  FIG. 5  illustrates an example Beacon region configuration  400  having Stayout regions  402  and  412 , Beacon regions  404  and  414 , CSMA region  406  and TDM regions  408  and  410 . By reducing the size of CSMA region  406 , and increasing the size of a Stayout region  402  or  412  the BSS Manager may reduce power consumption across every device in the IEEE 1901 network. 
     Reducing the size of CSMA region  406  will reduce the available bandwidth for the whole network, which may reduce user-perceived network performance. In an embodiment, this concern may be partially addressed by having the BSS manager observe medium utilization during the CSMA period. When usage drops below a certain threshold for a sufficient period of time, the BSS Manager might increase the duration of Stayout region  402  or  412  and decrease the duration of CSMA region  406 . If the usage exceeds a different threshold for a sufficient period of time, the BSS manager may perform the reverse operation, making more time available for network traffic during CSMA. 
     The tone-map used for communications may have some impact on the power consumption of the transmitter. For example, high-bandwidth tone-maps may require more power per active transmission time than a low-bandwidth tone-map, due to the larger amount of data processed. High-bandwidth tone-maps may also require less active transmission time on the medium than low-bandwidth tone-maps. As placing transmit data on the medium requires more energy than polling the medium for MPDUs to receive, this implies that, at the signal-generation level, higher-bandwidth tone-maps will generally save energy over low-bandwidth tone-maps per unit transmitted data. When it is possible to choose from a set of tone-maps for transmission, embodiment power consumption may be reduced by using that tone-map that will result in: first, the lowest amount of energy being placed on the medium; and second, the lowest energy required to encode the data. In practice, this will usually mean determining which tone-maps will occupy the shortest period of time on the medium, and then choosing the lowest-bandwidth tone-map from that set. 
     In an embodiment, reducing the energy in the transmitted signal may also help in reducing power consumption in a device. While a uniform reduction in transmission amplitude likely decreases the signal-to-noise ratio (SNR) at the receiver, harming QoS, strategically reducing the transmitter amplitude in specific frequency ranges can reduce the power required to transmit an MPDU, and will not degrade—and may even improve—receiver performance in some embodiments. An embodiment transmitter may exploit this opportunity by reducing the transmit amplitude on inactive frequencies in the tone-map. This may be improved further, by modifying the tone-map negotiation process at the IEEE 1901 network level. Such a technique is described below. 
     Any IEEE 1901 Long MPDU requires communications overhead beyond what is strictly necessary for communicating payload: it includes an MPDU header; transmission of the MPDU may introduce padding into the frame stream; and a receiver will usually be expected to transmit a response MPDU. Therefore, reducing the number of MPDUs required for a given volume of payload may improve the efficiency of the IEEE 1901 network. In some cases, a station will be able to determine that data available for transmission is not immediately required by the destination. In such a case, the station may defer transmission until either the recipient requires the data, or enough data has accumulated so that the outbound transmissions would be optimally efficient. 
       FIG. 8  illustrates logical structure  600  and corresponding MPDUs  601  for a latency optimized transmission. In logical structure  600 , MSDUs  602 ,  606  and  608  are mapped into PHY blocks  612 ,  614 ,  616  and  618  along with Pad regions  604  and  610 , such that Pad region  604  extends to the end of PHY block  614 . In the resulting MPDUs PHY blocks  612  and  614  follow header  620 , and PHY blocks  616  and  618  follow header  624  separated by response block  622 . 
       FIG. 9  illustrates a logical structure  630  and corresponding MPDUs  631  for an efficiency optimized transmission. In logical structure  630 , MSDUs  602 ,  606  and  608  are mapped into PHY blocks  612 ,  614  and  616  along with Pad regions  632 , such that Pad region  632  extends to the end of PHY block  616 . In the resulting MPDUs PHY blocks  612 ,  614  and  616  follow header  634 , followed by response block  622 . 
     All TDMA regions have an expected traffic pattern (where the traffic pattern includes such aspects as expected medium usage, the two communications endpoints). Within a TDMA region, the receiving station will always know the identity of the transmitting station. As such, the receiver may improve its fidelity and decrease its activity by pre-configuring the radio to receive from this specific transmitter. For example, the signal quality from the transmitter to the receiver is not likely to change very frequently; the receiver can rely on this to pre-program the gain it expects to apply for this transmitter, prior to the transmitter sending any payload on the wire. This will simplify the dynamic receive behavior, improving performance while slightly reducing power consumption. 
     In embodiments of the present invention, various embodiment techniques may be used that may improve power consumption at the network level. In some embodiments, these improvements involve coordination between multiple devices, and enhancements may be made to the IEEE 1901 protocol to achieve these enhancements. It should be further understood that similar embodiment enhancements may also be to other systems and protocols. 
     A given IEEE 1901 station will generally use constant amplitude for all of its transmissions. This means that the transmitter will be perceived as louder or quieter to different receivers, depending on signal attenuation along the path from the transmitter. For any given receiver, the signal attenuation generally will not be uniform across all frequencies: some frequency ranges will show more attenuation than others. For example,  FIG. 10  illustrates a power spectral density plot showing the maximum per-frequency energy that can be transmitted, while  FIG. 11  illustrates a power spectral density plot showing an example energy distribution at a receiver for that transmission. In this example, all frequencies show at least 15 db of attenuation at the receiver, and there is a null around 24 MHz. 
     Receivers normalize the transmission by applying a gain to the received signal, so that the ADC from the AFE will present the maximum possible range, while avoiding clipping. This generally improves receiver accuracy, making higher-bandwidth modulations available to the transmitter. However, the gain is generally applied in a uniform manner across all frequencies. This means that receivers will usually see improved accuracy in less-attenuated frequency ranges, and less accuracy in more-attenuated frequency ranges. 
       FIG. 12  illustrates embodiment channel estimation process  700  with amplitude negotiation. Here the receiver response may be improved, and the transmitter may emit less energy on the medium, by including transmit amplitude negotiation in the channel estimation process. The receiver represented by Station B  504  detects the energy levels at different channels in SOUND frame  506 , and forwards this information to the transmitter in a new Management Message Entry (MME), which is called CHES_AMP_MAP.indication  710 . The transmitter, represented by Station A  502 , on receiving this MME, may adjust its amplitude map in such a way that the receiver observes a flatter energy distribution across frequencies by increasing the gain-adjusted usability of channels that had previously been relatively faint. A power spectral density plot of an adjusted transmit amplitude is illustrated in  FIG. 13 , and a power spectral density plot of a resulting receive frequency energy distribution with adjusted transmit amplitude is shown in  FIG. 14 . 
     This process trades off a lower SNR for an improvement in the digital output resolution of lower-energy carriers. In an embodiment, to ensure that the transmitter has enough information to make the appropriate tradeoff, the CHES_AMP_MAP.indication  710  MME may also include collected per-frequency SNR data. 
     IEEE 1901 receivers use the preamble to identify the start of modulated payload, and to determine the gain value that should be applied to the received signal after the preamble is detected. The amount of time this takes may vary, depending on the gain adjustment technique used, and on the amplitude of the signal at the receiver. In general, the larger the difference between the gain setting when the medium is idle and the target gain setting for the receive operation, the longer the time it will take for the gain to reach its target value. If the gain does not reach a target value early enough in the receive operation, data demodulation may be compromised in some cases. 
       FIG. 15  shows an example preamble waveform at the transmitter.  FIG. 16  illustrates the received preamble waveform using a slow gain adjustment at a first receiver designated as “Station A,” and  FIG. 17  illustrated the received preamble waveform using a fast gain adjustment at a second receiver designated as “Station B.” At the beginning of both  FIGS. 16 and 17 , both Stations A and B have the gain at maximum value while there is no signal on the medium. In an embodiment, this facilitates receiving the faintest possible MPDU. Station B hears the preamble much more faintly than does Station A, so it takes less time to adjust its gain to the target value. This means that the Station B may use more of the preamble than can Station A, and that some of this extra preamble data may be unnecessary for decoding the data. Had the transmitter been issuing a unicast transmission to Station B, and had it sent a shortened preamble, less energy would have been placed on the medium, and Station B would still be able to decode the transmission. In an embodiment, a receiver measures the amount of time spent adjusting its gain, and reports this time to the transmitter as part of a CM_CHAN_EST.indication. The transmitter may then use this information to shorten outbound preambles for the destination. 
     The amount of energy it takes to communicate a MPDU in an IEEE 1901 network may be expressed as follows:
 
 E   MPDU   =E   sym   N   sym   +K   MPDU   (1)
 
where E MPDU  is the amount of energy it takes to communicate the MPDU; E sym  is the amount of energy required to communicate each data symbol; N sym  is the number of data symbols to be transmitted; and K MPDU  is some constant amount of energy for communicating the non-varying parts of the MPDU. Both E sym  and N sym  are influenced by the radio parameters used to transmit the payload. Data modulated using a low-bandwidth tone-map may be encoded and decoded with a lower PHY sampling rate, and may be reliably transmitted at lower amplitude, than can data modulated with a high-bandwidth tone-map. Assuming that the energy required to transmit a data symbol is proportional to the data encoding rate, the amount of energy it takes to transmit a data symbol may be expressed as:
 
 E   sym   =K   sym   R,   (2)
 
where R is the data encoding rate. On the other hand, data transmitted at lower data encoding rate will generally require more data symbols for transmission:
 
                     N   sym     =       ceil   ⁡     (       8   ⁢     (     L   +   8     )       R     )       .             (   3   )               
Expanding Equation (1) with the formulae for E sym  and N sym , the following formula is obtained for calculating the energy required to transmit a MPDU based on the frame length and data encoding rate:
 
     
       
         
           
             
               
                 
                   
                     E 
                     MPDU 
                   
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                         K 
                         sym 
                       
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                         R 
                         · 
                         
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                             ( 
                             
                               
                                 8 
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                                   ( 
                                   
                                     L 
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                                     8 
                                   
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                               R 
                             
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                     + 
                     
                       
                         K 
                         MPDU 
                       
                       . 
                     
                   
                 
               
               
                 
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       FIG. 18  illustrates a heat map depicting the energy required to transmit a volume of data as a function of frame length and encoding rate. As can be seen, for any given frame length, the encoding rate may have a significant effect on the amount of energy it takes to transmit a frame, particularly at high data rates. While the nature of this relationship is dependent on the formula for E sym , which will be transmitter-, receiver-, and (potentially) environment-dependent, it may be the case that, for some traffic volumes, energy may be saved by reducing the tone-map bandwidth. 
     This embodiment optimization may be supported by modifying the IEEE 1901 channel estimation process to generate and communicate a set of related tone-maps. In an embodiment, each tone-map in the set is optimized for maximum energy efficiency with a given volume of traffic—from high-volume/high-bandwidth encoding down to low-volume/low-energy. The payload receiver may take advantage of the fact that each tone-map in the set is derived from the same channel radio characteristics to efficiently encode the tone-map set for communication to the transmitter: the highest-capacity tone-map may use a current IEEE 1901 tone-map encoding mechanism, while lower-capacity tone-maps may be communicated as deltas from the next-higher capacity tone-map. When the tone-map set is synchronized between the transmitter and the receiver, the transmitter may select the optimal tone-map to use for sending payload across the medium, thereby saving power. 
     The above-described embodiment techniques may work better in TDMA regions than in CSMA regions. IEEE 1901 uses a CSMA/CA protocol to manage the shared medium, and CSMA/CA relies on all network nodes being able to detect when other nodes are communicating to avoid collisions. The above-described embodiment techniques may reduce the likelihood that uninvolved nodes will be able to reliably detect communications. In some embodiments, the above-mentioned techniques may be further refined to reduce the probability of collisions and the prospect of decreased network performance. 
     In an embodiment, the IEEE 1901 RTS/CTS protocol may be used to address this problem in CSMA regions. In one embodiment, during the RTS/CTS exchange, embodiment power reduction techniques are not employed: the RTS and CTS MPDUs are transmitted with standard transmit amplitude and with a full-length preamble. Since other stations should be able to receive the RTS and CTS MPDUs, the CSMA/CA algorithm may be much more robust in this embodiment. After a successful RTS/CTS, the payload MPDU transmission may use embodiment power reduction techniques related described above. In some embodiments, use of RTS/CTS means that there may be some additional communications overhead, increasing power consumption, increasing latency, and decreasing bandwidth. In some embodiments, a determination is made if the power savings in the payload communications will compensate for the expense of using the RTS/CTS protocol. This determination may be a part of the algorithm executed either by a single station or system wide collaboration where two or more nodes participate in the analysis. 
       FIG. 19  illustrates convergent network  800  that may be defined as a network in which each node  802  and  804  may communicate using multiple MAC/PHYs  810 ,  812  and  814  coupled to different media  820 ,  824  and  826  simultaneously. In an embodiment, each node has application layer  806  and hybrid convergence layer  808 . Each node also has a plurality of MAC/PHYs represented by IEEE 1901 interface  810  coupled to IEEE 1901 medium  820 , Wi-Fi interface  812  coupled to Wi-Fi medium  824  and MoCA interface  814  coupled to MoCA medium  826 . It should be understood that network  800  illustrated in  FIG. 19  is one example of many possible embodiment networks. Alternative embodiment networks may include, for example, greater or fewer MAC/PHY interfaces utilizing the same or different network types. 
     The P1905.1 specification allows devices to communicate along multiple underlying technologies at once. For any given P1905.1 station, it is possible that some set of its underlying network interfaces are either unconnected (i.e. no other device can be reached using that interface) or redundant (i.e. no nodes can be reached using this network interface that can&#39;t also be reached using another). Unconnected network interfaces may be disabled to reduce power consumption. Such an interface may be enabled, however, when attempting to discover other devices that might be reachable only using that interface. Discovery time will be some fraction of the device&#39;s total uptime. Redundant interfaces can potentially be disabled, but this is a delicate operation that, implemented poorly, can prevent inter-device communications. 
     Disabling a redundant interface may reduce the available communications-path redundancy in the network. Safely disabling a redundant interface involves ensuring that neighbor nodes do not disable all alternative paths to reach the local node. For example, consider the network in  FIG. 20 , which depicts two stations connected by two interfaces. Both interfaces INTERFACE 1  and INTERFACE 2  are redundant, so both stations might choose to disable either interface. In this case, if station  1  disables INTERFACE 1 , while station  2  disables INTERFACE 2 , then the stations will no longer be able to communicate in some embodiments. 
       FIG. 21  illustrates embodiment state machine  900  that implements a safe means of powering down a redundant interface. The state machine describes the enable/disable status of a network interface. Using this machine, disabling an active network interface involves sending a SAFE_POWERDOWN command to the control plane of the interface. The interface responds to this command by issuing a topology update to all remote devices in the network on alternative interfaces. If all remote devices acknowledge the topology update before a timeout expires, then it will be safe to shut down this interface. Otherwise, the operation will fail, and topology update messages are sent on all other interfaces to indicate that this network interface is still active. 
     In an embodiment, state machine  900  starts out in Idle state  902  and transitions to Active state  904  on receipt of an ACTIVATE command. At the receipt of a SAFE_POWERDOWN command, state machine  900  transitions to PowerDown_Start state  906 . If an acknowledgement is received from all remote devices, state machine  900  transitions back to Idle state  902 . Otherwise, state machine  900  re-enters Active state  904 . 
     In an embodiment, disabling a redundant interface may save energy on the device. However, some interfaces are likely to draw more power than others. Disabling these high-power interfaces will result in greater power savings. Disabling a redundant interface will also reduce a device&#39;s available communications capacity. In order to preserve QoS, such interfaces are re-enabled when more bandwidth is required for communicating to one of the stations reachable using that interface in some embodiments. 
     Streaming media applications are often characterized by communications of a large volume of media data, in which all media data is available for download immediately (limited by the bandwidth available between the media host and the rendering device), but where rendering occurs over time. In such applications, it will often be the case that a significant volume of data is available for rendering, well ahead of the time at which that data will be rendered. The large period of time between when the data enters the network and when the application requires it creates an opportunity to optimize network power consumption by manipulating transmission timing, and the transmission path. Optimizing the transmission path may use network-level information, and will be described below. 
     Depending on the environmental circumstances, it can take more or less energy to transmit the same volume of data across a network link. For example, if a user runs a microwave, this may interfere with Wi-Fi traffic, such that any attempt to communicate during this interval will require significantly more power to be successful. If a user runs a vacuum cleaner, this may interfere with IEEE 1901 traffic, meaning that communications will consume significantly more power for the same volume of data. A P1905.1 device may detect when there is a sudden decrease in communications efficiency, for example, by measuring the transmission success rate as determined by MAC-level acknowledgements. (As the success rate declines, so does communications efficiency). A P1905.1 device may avoid transmissions while the medium is uncharacteristically inefficient, or until the user application requires the data. By using embodiment methods to avoid communications while communications operations are relatively inefficient, overall energy efficiency may be improved. 
     Convergent networks are characterized by the existence of multiple media connecting network stations (see  FIG. 19 ). This implies that there will usually be multiple available communication paths between any two stations in the convergent network, and each such path will have an independent power consumption profile. Choosing the most power-efficient path requires information about the power efficiency of the paths under consideration. 
     The power consumed for communications depends on several factors, including: the power required keeping a network interface active; the power required to place a signal on the medium; and medium link quality. Each of these factors is itself a function of the underlying network interface technology, and of the physical network topology. As the IEEE P1905.1 network topology concept incorporates both the network interfaces available to a single device, as well as the available device-to-device links along those interfaces, the IEEE P1905.1 topology table is a natural place to store these power consumption data. To facilitate this, the IEEE P1905.1 topology query messages may be expanded, in an embodiment, to include information such as: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Expanded IEEE P1905.1 topology query messages 
               
            
           
           
               
               
               
            
               
                 Category 
                 Data 
                 Interpretation 
               
               
                   
               
               
                 Network 
                 Startup 
                 Power required to bring the network interface 
               
               
                 Interface 
                 Cost 
                 from a powered-off state to a powered-on state. 
               
               
                 Network 
                 Shutdown 
                 Power required to bring the network interface 
               
               
                 Interface 
                 Cost 
                 from a powered-on state to a powered-off state. 
               
               
                 Network 
                 Running 
                 Power required to keep the network interface 
               
               
                 Interface 
                 Cost 
                 available to send and receive traffic. 
               
               
                 Network 
                 Transmit 
                 Power required to send a unit of data to this 
               
               
                 Interface and 
                 Cost 
                 destination across this network interface. 
               
               
                 Destination 
               
               
                 Network 
                 Data Rate 
                 The data rate this station would achieve 
               
               
                 Interface and 
                   
                 sending data directly to this destination 
               
               
                 Destination 
                   
                 across this network interface. 
               
               
                   
               
            
           
         
       
     
     If any of this power-consumption information changes (e.g. due to a new interference source making transmissions to a destination more expensive), this may be considered a change in network topology, and may be communicated using the P1905.1 topology update mechanism in some embodiments. 
     In an embodiment, if the network topology table has been augmented with power consumption information, then this information may be used to determine the most power-efficient path to use for data communications. In this case, a weighted routing algorithm, such as Dijkstra&#39;s algorithm, may be used to traverse the topology table to find the most power-efficient path from the data ingress station to the data egress station that can support the required traffic load. Dijkstra&#39;s algorithm is described in E W Dijkstra, “A Note on Two Problems in Connexion with Graphs,” Numerische Mathematik, Vol. 1, pp. 269-271, 1959, which is incorporated herein by reference in its entirety. 
     In an embodiment, if the resulting path consists of a single hop, then the traffic may be directly sent to the destination. On the other hand, if the path consists of multiple hops, there are at least two available routing strategies: the origin may configure each station along the path with a routing rule, directing each node to forward data from this data stream along the subsequent edge in the communications path; or the origin may forward the data stream to the next station in the path, and the next station can use its topology table to determine the station it should forward the packet to along the same path. In some embodiments, the second mechanism may be more robust if there is a sudden change in network topology. This, however, may lead to routing loops if the local topology tables are not synchronized between the different nodes in the path. 
     Another embodiment approach to conserving power is to attack the problem from the other direction: instead of considering how to reduce power consumption while leaving other aspects of network performance unchanged, one may take power consumption as the constraint, and consider how to achieve maximum network performance while not allowing power consumption to exceed a user-specified envelope. In this case, embodiment techniques described herein may be applied with some modification, and may result in increasing available communications capacity without increasing power consumption. 
     In an embodiment, power is reduced by using two user-specified parameters: maximum power consumption, and time interval. Available power is reduced as it is needed for communications, and increased as time passes. If available power gets too low, communications techniques can become more conservative. In this way, communications will be possible, but performance will degrade as power consumption approaches the user-defined limit. 
     In a networking context, the term “Quality of Service” (QoS) is intended to capture all user-visible aspects of network performance. Commercial attempts to improve QoS have a strong tendency to focus on those aspects of QoS where users are the least satisfied—i.e. where the market demand is strongest. As networking technology becomes less expensive and more capable, many new types of networked applications may become economically viable. For some of these applications, high power consumption may significantly degrade the user experience, as when a smartphone&#39;s battery is drained too quickly, or when a tablet device or laptop becomes hot to the touch. Power consumption is becoming an increasingly relevant aspect of QoS in fast-growing market segments. 
     In some embodiments, applying any given technique individually may lead to some improved efficiency. In some cases, greater efficiency may be gained by applying multiple embodiment techniques at once. For example, automatically setting the receive gain during TDMA intervals will enable the transmitter to communicate using much shorter preambles than would be possible if the receiver had to spend time adjusting the gain—combining the TDMA fixed gain with the ability to shorten the transmitted preamble may yield better efficiency than would applying each technique in isolation. 
     In an embodiment CDHN, common setup procedures may be used for adding devices to a network, establishing secure links, implementing QoS, and managing the network. When a link goes down temporarily or is congested, an alternative route may be available to maintain data transmission. Furthermore, throughput may be aggregated and/or maximized via the multiple interfaces of a CDHN. These multiple interfaces may even allow for multiple simultaneous streams. With applications such as interactive TV, even a single person may be watching multiple streams simultaneously. 
     CDHNs such as IEEE P1905.1 may also support traffic load balancing in which, for example, intelligently distributed multiple video streams are intelligently distributed over different paths to limit congestion on any single media and maintain reliability. Quality of service (QoS) may also be supported via prioritization over multiple technologies. IEEE P1905.1 may also allow devices to be configured in the same manner, for example, with a simple button push. An IEEE P1905.1 hybrid network may also support advanced diagnostics in which the overall network monitors itself. Moreover, an IEEE P1905.1 hybrid network may also support mobility via wireless connectivity (mobile handsets, and tablets) and universal connectivity. For example, CDHN/IEEE P1905.1 may support a hybrid network in which one may connect to the hybrid network from every room in the house without having to be aware of which part of the network and what media their device is currently interfacing. 
     At the same time, the proliferation of User Generated Content (UGC), the shift to Over The Top (OTT) delivery, and the explosive growth in the number of nomadic and stationary content rendering points, has dramatically increased the importance of the networking layer to device function: users demand reliable, QoS-aware networking platforms. There are at least two complementary approaches to meeting this market need: one can work to improve the performance of a given network interface, such as a MAC/PHY; and one can attempt to leverage multiple types of media for link-level communications, as in IEEE P1905.1 hybrid networks. 
     Higher performance within a single network MAC/PHY may lead to increased power consumption. For example, communicating across a wider frequency band may need more signal energy on the medium; more advanced FEC techniques may need more complicated circuitry to implement the more complicated algorithms; and MIMO techniques may need multiple instances of certain parts of the PHY layer to run in parallel for a given transceiver operation. Each of these techniques may increase the power consumption of the system. 
     In an embodiment, metrics, such as energy and traffic metrics are used to determine lower energy ways to communicate from one device to at least one other device over at least one media type. Embodiments may apply intelligent means to proactively and dynamically adjust the parameters of the devices and selected communications networks in order to minimize the amount of energy used to communicate. In some embodiments, energy is reduced while the user&#39;s expected quality of service is maintained. 
     In one embodiment, for example, in a simple network, embodiments systems and method use information, for example, about the devices ability to manage power, the ability to reduce the transmission power to the minimum level necessary for a particular application, and knowledge about which protocols to use (e.g. with or without security, or retries). 
     In a multi-protocol and hybrid media network embodiment, embodiment power reduction techniques offers greater benefits because the network nodes may have the option of using multiple paths or multiple-contemporaneous paths to get the data delivered from one node to at least another node. 
     Embodiment systems may involve a single MAC/PHY implementation on a single device, a single MAC/PHY implementation on multiple devices across a whole network, a single device across multiple MAC/PHY interfaces coupled to different media types, and/or multiple devices across multiple MAC/PHY interfaces coupled to different media types across a whole network. 
     In an embodiment integrated network adapter, a best path though the network is dynamically selected based on the lowest power consumption of the available media types that can support the traffic. The determination of power consumption may include the dynamic reduction of a PHY output power based on a receiver&#39;s channel conditions based on quality parameters including AGC (Automatic Gain Control), SNR, and QoS (tolerance to losing packets). 
     In an embodiment, unused media interfaces, functions or components are turned off or put into a power save mode to a reduction power when not selected for communications. An embodiment power save mode may include reduction in the frequency of CPU clocks, logic block clocks, and/or system clocks. In some embodiments, CPU power intensive functions such as compression are disabled or not used to save power when a traffic controller determines they are not necessary to meet the traffic requirements and channel conditions. Using lower orders of modulation also allows for the use of lower clock rates. 
     In an embodiment, different devices in the network that support the traffic requirements are selected based on each device&#39;s network power rating metric. This power rating metric may be assigned as a single or plurality of metrics and stored digitally in the device, and may be measured by a power measuring device that reports results to the device or is otherwise accessible by the network to make its metrics available to a hybrid network controller. In some embodiments, power is reduced by scheduling traffic in time or in packet sequence. Bursting, buffering, signal level, modulation methods and density, FEC techniques, and media access mechanisms may be selected to adjust power. Information based on queue statistics, traffic type, QoS requirements, application information, channel history, etc. may be used to determine selected network parameters that affect power consumption. In one embodiment, data is routed per data stream or per packet in response to the traffic type, channel conditions, network congestion. In another embodiment, the network protocol may increase or decrease the CSMA contention windows or Stayout region, (allocated time slots) to further reduce the energy required to use the network. Using such a method, the network controller may effectively reduce power consumption across every device in the network. 
     In an embodiment, multiple networks may be linked though a plurality of CDHN devices, where CDHN devices may perform either a simple packet forwarding or more sophisticated functions such as IP routing or even multi-protocol translation. Each link may be a “hop”, wherein each device sends the source CDHN controller, the relevant power consumption data and the source CDHN controller (or another device/node tasked with such a decision making) decides which path and power management methods are appropriate to use, and routes traffic accordingly. Multiple networks may be linked though a plurality of CDHN devices, each link being a “hop”, wherein each device can share relevant power consumption data (metrics) with devices on either side so it can decide, itself, which path and power management means are appropriate to use the minimum energy. In some embodiments, systems and methods described in U.S. Patent Publication No. 2005/0043858 entitled, “Atomic Self-Healing Architecture,” which publication is incorporated herein by reference in its entirety, may be applied. 
     In an embodiment centralized approach, the controller is most likely to be associated with the CCo-like function in IEEE 1901. In this case, information related to the overall system bandwidth requirements is available to the controller to make such decisions. An embodiment decentralized approach would fit the networks if a central coordinating function does not exist or is not desirable. In this case, a networking node may monitor the network loading level and make decisions related to the transmit power reduction for a specific link based on the historical (recent or analyzed over extended periods of time) network loading, the trend of the network loading (increase or decrease in loading), and the loading of the local TX queues. In an embodiment, the algorithm provides for the constant network loading monitoring so in the case of the increased congestion the TX power may be raised to increase the link performance. In an embodiment, power consumption analysis is to be associated with the traffic type and either a node or the whole system can “learn” how to associate power consumption patterns with certain traffic types (VoIP, Video Streaming, bursty downloads, etc.) and apply power management schemas either stored in the memory of a device or a system, or develop the best suitable power management schema learning the traffic pattern and apply such schema next time when the same type of traffic is detected. Such a learning mechanism may also include the ability to improve itself with each operation cycle. For example, in one embodiment a hybrid network controller may associate power consumption patterns with traffic types, and apply a power management schema to the associated traffic type. The hybrid network controller may associate power consumption patterns by logging monitored traffic types and measured power consumption data corresponding to the monitored traffic types. 
     In an embodiment, network behavior is used as an input to a power and system management controller. By introducing power consumption metrics to a path selection algorithm, power consumption of the hybrid network may be reduced. This type of power consumption optimization by selecting various data paths, and by selecting various power down and power savings options, can be applied to a number of different types of networks. 
     For example, embodiments of the present invention may be applied toward a network based on a single media type and a hybrid network that is based on two or more media types. One example of a single media type network is an IEEE 1901 power line network, while an example of a multiple media network, is a network that includes IEEE 1901, IEEE 802.11x, and/or other network types as discussed above. In some embodiments, power consumption is predicted on a device level. This prediction may be based on the content of data queues, QoS parameters and network behavior. In some embodiments, historical metrics, for example, network usage statistics, may be used to determine and predict power consumption, and help determine appropriate path selection algorithms and power-down parameters. On the device level, historical information about how the device itself is used may also be considered. 
     With respect to single media type (single path) network, such as an IEEE 1901 network, device and system power consumption may be optimized by changing data scheduling, bursting buffering and other types of network behaviors. With respect to multipath hybrid networks, data path selection and device power parameters may be performed on both the device level, as stated above, and by changing data scheduling, bursting buffering and other types of network behaviors as in the case of the single path network. 
     Power consumption may be optimized for a particular datalink and/or application. This optimization may be based on a QoS driven slot assignment or bandwidth reservation, using heartbeat techniques, or other methods. In some embodiments, these methods allow traffic to be scheduled so the times when the relevant interfaces and components need to be active are predictable. Heartbeat techniques may also be used to indicate which the parts of a system have gone to sleep or are not available. In one embodiment, for example, in the case of a multi-hop data connection, power per hop is also included as an input in the embodiment power optimization algorithms. Embodiment power optimizations algorithms may also determine how much power is reduced if different orders of modulation are used. Peripherals may also be disabled. For example, if an embodiment power optimization algorithm determines that one technology end point/network interface is sufficient to deliver a requisite amount of data at a requisite QoS, other interfaces and/or peripherals may be shut down and/or disabled in order to allow the hybrid network to operate at a lower power. In an embodiment, an interface between a physical layer and media access layer embodiment and a system to which they are attached allows the system to receive from PHY/MAC the information related to the “power cost” of the transmission and such other parameters as an example required time to “wake up” or transition from “STAND BY” to “IDLE” or “ACTIVE” states. This same interface may further allow for the system to configure power management option and/or patterns. 
     In one example of a preferred embodiment a system may be composed in such way that each media specific PHY/MAC is capable of providing a centralized controller with the information that contains power cost per unit of information transmitted and received, time required for the specific PHY/MAC to transition from “IDLE” to “ACTIVE” and furthermore from “Receive” to “Transmit” and vice versa. At the same time the centralized controller may be also responsible for the scheduling of the traffic. In this case the system may also select a mode of operation where a transmission of a video stream is done via Media A, while the receive operation associated with infrequent status updated information from the receiving node is done over Media B, additionally the PHY/MAC associated with Media B is transitioning from “IDLE” to “Receive” and back to “IDLE” based on the scheduled operation. 
     In some embodiments, the power consumption of the various components of the hybrid network system may be determined in the laboratory environment and power profiles are assigned based on the measured performance. In some embodiments, each network device may even assign themselves power metrics. When measuring the power in the lab, a live measurement may be performed near power distribution, in order to determine system level power consumption. In one embodiment, the power consumed by the system as measured at the energy supply is measured and compared with the energy consumption measured by the interfaces so that an accurate metric of system energy consumption required for each network is assessed. In some embodiments, queue, content, scheduling, types, volume, etc. are used to control power consumption. Combinations of power saving methods may also be used. 
     In an embodiment, depending on different amount of power used by hardware or the CPU, it may be determined whether to use burst operation (perform all the processes at once), continual operation (perform process but share time with other CPU or hardware processes), or whether to use functions that consume lots of CPU cycles such as compression. 
     In some embodiments of the present invention, transmit power may be based on the throughput requirements and available SNR. For example, if the link offers a high SNR that affords a very high throughput, but the only traffic that needs to be transmitted on this link is a relatively low bitrate audio, then shorter preambles and/or lower transmit power may be used in order to reduce power consumption while providing the required throughput. Feedback mechanisms may also be used. Furthermore, transmit power may be reduced based on QoS requirements and overall network loading to avoid artificially created network congestion as an example. 
     In one embodiment, a channel estimation process may be extended to include a function that negotiates not only the source (transmitter) transmit power, but also the receiver&#39;s transmit and response power level if the protocol requires the receiver to provide acknowledgments or any other type of response to the transmitter. For example, a transmitted power field may be added to a channel estimation request. In the intermediate channel estimation responses, the receiver may indicate how the transmitter should modify the transmit power level. For example, the receiver may request a particular increase in transmit power. In some embodiments it is ensured that the receiver can hear the transmitter channel estimation request. In some embodiments, ready to send/clear to send (RTS/CTS) frame controls may be used at maximum transmit power during negotiation. Such an embodiment example may be used to determine back-channel signal amplitude for responses. In some embodiments, the controller or receiving devices extrapolates tone maps that would be optimized for maximum energy efficiency for a given volume of traffic, for example from high traffic volume/high bandwidth to low traffic volume/low bandwidth. Using sets of maps for specific levels of performance reduces the energy required to transmit multiple dynamic tone maps. 
     In an embodiment, an optimum transmitter power is computed based on the channel estimation responses without burdening the receiver with the need to provide additional information. This technique may be applied, for example, in cases where an embodiment system is operating on a network that is comprised in part of older devices not equipped with this functionality. 
     In some embodiments, power optimization may be performed on the aggregate signal level or on each carrier (in the multi-carrier or OFDM system) individually. In the case of the per-carrier adjustment, well performing carriers may be used while shutting down carriers with poor performance. It is likely that carriers exhibiting low performance would be associated with the lower impedance of the network as seen by transmitter. This may help with the additional reduction of power while improving the linearity of the transmit path drivers/amplifiers. In some embodiments, systems and method described in U.S. Patent Publication No. 2003/0071721 entitled, “Adaptive Radiated Emission Control,” which publication is incorporated herein by reference in its entirety, may be applied. 
     In one embodiment, the transmitting node may be the same method to perform the channel estimation, but after the computation of the tone map was accomplished at the full TX power, a new request is generated after the TX power is adjusted by the TX node to maintain enough SNR (overall or per carrier) to provide sufficient throughput. 
     In one embodiment, early preamble symbols may be detected at a divided clock rate in order to save power. In some embodiments, these preamble symbols may not need phase measurements or precise demarcation. 
     In an embodiment, the network device or interface may use energy from a more energy efficient source. For example, AC power may be taken from a PLC network interface connected to AC mains or a DC circuit. Ethernet networks may be carrying DC power over Ethernet and be more efficient or convenient for devices to use, especially if power to a device is cut off. 
     In some embodiments, the power may be accumulated from received transmissions. For example, some of the transmit energy may be harvested from the received signal for use in subsequent transmissions, or from a power supply at the lower current. Furthermore, a software level understanding of the network state may be used to enable or disable portions of the network hardware. One embodiment approach is harvesting the energy from the receive signal to perform “wake on LAN” functions at significantly reduced power consumption while other components of the system including the AC/DC or DC/DC power supplies are either in standby or power down mode. 
     In some embodiments, the frequency ranges used for transmissions may be managed with respect to transmissions different destinations based on parameters such as the SNR. For example, communications may be performed using fewer IEEE 1901-based carriers. Alternatively, the number of transmit carriers may be reduced in other systems in order to save power. In some embodiments, transmissions may be looped back to the source, thereby allowing the source to measure the energy it&#39;s actually outputting on different portions of the transmit spectrum. In some embodiments, this loop back transmission scheme is performed using an attenuator. The information obtained from loopback transmissions may be given to data recipients, such that actual signal degradation along different frequencies may be measured rather than inferring the level of signal degradation based on an assumption of a perfect transmitter. In one embodiment the system or a node may learn how to transmit in fewer carriers that are grouped in a contiguous frequency band and reduce clocking speed requirements for the transmitting and receiving nodes operating in this mode. 
     In some embodiments, aspect oriented programming (AOP) may be used in the software code that controls the hybrid network adapter in order to centralize power management decisions while making sure that there is no interference with the composition of the rest of the system. In an embodiment, using a message passing software architecture, power management code may be allowed to intercept messages between different components of the system. The power management code then maintains an internal model of how the system will behave. This internal model may be used to enable, disable, and adjust voltages, clocks, and other parameters of different hardware components according to whether the hardware components are required according to the particular power consumption state of the system and/or operational decisions made by such management code. In some embodiments, the hybrid adapter has the ability to learn the network topology along its associated power consumption. 
     In some embodiments, a determination is made on whether to use per flow or per packet routing. For example, in a network with plenty of bandwidth available, per packet routing may be selected when congestion is encountered. In some embodiments, per flow routing may be less computationally intensive then per packet routing. In some embodiments, throttle clocks may be used to minimize power consumption. 
     In some embodiments, power may be controlled by enabling or disabling particular underlying interfaces within the network adapter system, depending on bandwidth requirements and device coverage. For example, if there are only two devices that may connect over a particular network, for example a Wi-Fi device or a MoCA device, the lowest power connection for the communications may be the only one used until it can no longer meet its bandwidth requirements. 
     In one embodiment, a hybrid network may have a device for discovering how much marginal power would be dissipated by establishing a traffic pattern along a network path, and by transmitting a given traffic pattern along the path. For example, the power dissipated by establishing the traffic pattern would be the power dissipated by the power takes to enable particular network interfaces. In one example, a path proceeds from an IEEE 1901 device interface (STA1), to an IEEE 1901 interface in a second device (STA2), to an Ethernet device in the second device (STA2 ETH), to an Ethernet interface in a third device (STA ETH) to the third device (STA3). This particular path or setup sequence may be represented as: STA1 IEEE 1901→STA2 IEEE 1901→STA2 ETH→STA3 Eth→STA3. It should be understood that this particular path is just one specific embodiment example of a particular path, as other embodiment paths using other combinations of devices and interface types may be implemented. In some embodiments, clock scaling may be managed based on knowledge related to traffic requirements and bandwidth reservation and scheduling. In some embodiments, the power dissipated by the setup sequence may be determined using various combinations of paths and patterns, measuring the power consumption changed by the network, and reporting this power consumption change back to the controller. 
     In accordance with an embodiment, a network device includes a first data interface, a hybrid network controller coupled to the first data interface, and a plurality of network interfaces coupled to the hybrid network controller. The plurality of network interfaces include at least one media access control (MAC) device configured to be coupled to a plurality of physical layer interfaces (PHYs). The hybrid network controller is configured to determine a network path comprising at least one of the plurality of network interfaces that has a lowest power consumption of available media types coupled to the plurality of PHYs, and determine over which of the plurality of network interfaces the first data interface sends data to and receives data from, based on the determined network path. The network path may be dynamically determined during operation of the hybrid network controller, and/or the network path may be dynamically determined on a per packet basis or on a per packet segment basis. 
     In an embodiment, an interface between a physical layer and a media access layer is configured to receive a power cost metric of a transmission from the MAC device or from one of the plurality of PHYs. The hybrid network controller may be further configured to reduce an output power of at least one PHY based on channel conditions seen by at least one of the plurality of network interfaces. The controller may reduce an output power of the at least one PHY by reducing a number of transmitted carriers grouped in a contiguous frequency band in a reduced carrier mode and/or by reducing clocking speed requirements for transmitting and receiving node when operating in the reduced carrier mode. 
     The hybrid network controller may be further configured to determine a lowest power consumption of available media types based on parameters including automatic gain control (AGC) setting, signal to noise ratio (SNR) of the available media types, and quality of service (QoS) parameters of transmitted data. In some cases, the QoS parameters comprise a priority parameter. The hybrid network controller may also be further configured to reduce an output power of a network interface of the plurality of network interfaces by powering down the network interface or placing the network interface in a power saving mode when the network interface is not selected for communication. In some embodiments, the hybrid network controller is configured to place the network interface in the power saving mode by reducing a frequency of a CPU clock or a system clock. 
     The hybrid network controller may be configured to reduce a power of the PHY or the MAC by disabling data compression and encryption when a traffic controller determines that data compression and encryption are not necessary based on traffic requirements channel conditions. In some embodiments, the hybrid network controller may include the traffic controller. 
     In an embodiment, the hybrid network controller determines the network path based on a power rating metric of the network device. The power rating metric of the network device may be digitally stored on the device as a single power rating metric or as a plurality of power rating metrics. The network device may further include a power measuring sub-system configured to measure the power rating metric and report the power rating metric to hybrid network controller. The power measuring device may be further configured to make the power rating metric available to a traffic controller and to a network coupled to the network device. 
     In an embodiment, the hybrid network controller is further configured to reduce power consumption of the network device by scheduling traffic in time on in a packet sequence using bursting, buffering, modulation complexity, preamble methods, or using information based on queue statistics, traffic type, application information or channel history. The hybrid network controller may be further configured to route data per data stream or per packet in response to a traffic type, channel conditions, and a measure of traffic congestion. 
     In an embodiment, the hybrid network controller is further configured to associate power consumption patterns with traffic types. For example, the hybrid network controller may be further configured to apply a power management schema to the associated traffic type. The hybrid network controller may further associate power consumption patterns by logging monitored traffic types and measured power consumption data corresponding to the monitored traffic types. 
     In accordance with a further embodiment, a network device includes a network controller and at least one network interface coupled to the network controller that includes at least one media access control (MAC) device configured to be coupled to at least one physical layer interface (PHY). The network controller may be configured to determine a network path comprising the at least one network interface that has a lowest power consumption of available media types coupled to the at least one PHY. In some embodiments, the network controller may be a hybrid network controller. 
     In some embodiments, the network controller is further configured to determine the network path by receiving power consumption data from further network devices, selecting a plurality of the further network devices based on the received power consumption data, and routing data on the selected plurality of further network devices. The network controller may be further configured to determine a data path of the selected plurality of further network devices, and determine path and power management methods for at least one of the selected plurality of further network devices. 
     In some embodiments, the network controller is further configured to transmit power consumption data to a first further network device, receive a data path assignment from the further network device based on the transmitted power consumption data, and relay data from the further network device to a second further network device based on the path assignment. The network controller may also be configured to receive a requested path and power management method from the first further network device, and relay the data from the further network device to the second further network device based further on the received path and power management method. 
     In some embodiments, the network controller is configured to determine a power management method, and relay the data from the further network device to the second further network device based further on the determined path and power management method. 
     In accordance with a further embodiment, method of operating a network device includes determining a network path comprising at least one of a plurality of network interfaces that has a lowest power consumption of available media types, and determining over which of the plurality of network interfaces the first data interface sends data to and receives data from, based on the determined network path. Determining the network path may be dynamically performed during operation of the network device. 
     In some embodiments, the method also includes reducing an output power of at least one physical layer interface (PHY) based on channel conditions seen by at least one of the plurality of network interfaces. The method may also include determining a lowest power consumption of available media types based on parameters including automatic gain control (AGC) setting, signal to noise ratio (SNR) of the available media types, and quality of service (QoS) parameters of the available media types. 
     In an embodiment, the method further includes reducing an output power of a network interface of the plurality of network interfaces, reducing comprising by powering down the network interface or placing the network interface in a power saving mode when the network interface is not selected for communication. Placing the network interface in the power saving mode may include reducing a frequency of a CPU clock or a system clock. 
     In an embodiment, the method further includes determining that data compression and encryption are not necessary based on traffic requirements channel conditions, and reducing a power consumed by the network device by disabling data compression based on determining that data compression and encryption are not necessary. The method may further include determining that data compression and encryption may be relaxed based on traffic requirements channel conditions, and reducing a power consumed by the network device by reducing a complexity of forward error correction (FEC) disabling data compression based on determining that data compression and encryption may be relaxed. 
     In an embodiment, the method may further include determining a power rating metric of the network device, wherein determining the network path is performed based on the determined power rating metric. Determining the power rating metric may include performing a power measurement, and the power metric rating may be defined as a power consumed per unit of transmitted or received information. The method may further include reporting the power rating metric to a further network device coupled to the network device. 
     In an embodiment, the method further includes reducing power consumption of the network device by scheduling traffic in time on in a packet sequence, using bursting, buffering, modulation complexity, preamble methods, or using information based on queue statistics, traffic type, application information or channel history. The method may also include routing data per data stream or per packet in response to a traffic type, channel conditions, and a measure of traffic congestion. 
     In accordance with a further embodiment, a network device includes a hybrid network controller, and a plurality of network interfaces coupled to the hybrid network controller. Each of the plurality of network interfaces may be configured to be coupled to a corresponding physical layer interface (PHY). The network device also includes a processing engine configured to perform MAC functions common to the plurality of network interfaces. The hybrid network controller may be further configured to determine a network path comprising at least one network interface that has a lowest power consumption of available media types coupled to the plurality of PHYs. In some embodiments, the MAC functions comprise queuing functions for the plurality of network interfaces. 
     In accordance with a further embodiment, a network device includes a plurality of network interfaces coupled to a hybrid network controller. Each of the plurality of network interfaces may be configured to be coupled to a corresponding physical media via a corresponding physical layer interface (PHY). The network device also includes a processing engine configured to perform MAC functions common to the plurality of network interfaces and a hybrid network controller function. The hybrid network controller may be configured to determine a network path that includes at least one network interface of the plurality of network interfaces having parameters that decrease power consumption. In some embodiments, the hybrid network controller is further configured to determine a network path that meets a Quality of Service (QoS) requirement. In some embodiments, the hybrid network controller is configured to determine a network path comprising at least one network interface of the plurality of network interfaces having the parameters that best meet Quality of Service and power consumption requirements. As with other embodiments, MAC functions may include queuing functions for the plurality of network interfaces and a network convergence layer. 
     Advantages of embodiment systems include the ability to reduce energy, cost of ownership and improve the system design by using embodiment systems, methods and combinations of systems and method described herein to optimize energy consumption. 
     Another advantage of embodiment systems includes the ability to improve power efficiency while maintaining traditional QoS metrics. Further advantages include, the ability to reduce the range in which it is practical to eavesdrop on a communications link, the ability to decrease interference between radio networks; and the ability to decrease the demand placed on the power distribution infrastructure. 
     The following U.S. Patent Application Publications and U.S. Patents are incorporated herein by reference in their entirety: U.S. Patent Publication No. 2003/0071721, entitled “Adaptive radiated emission control;” U.S. Patent Publication No. 2005/0043858, entitled “Atomic self-healing architecture;” U.S. Patent Publication No. 2008/0205534, entitled “Method and system of channel analysis and carrier selection in OFDM and multi-carrier systems;” U.S. Pat. No. 6,891,796, entitled, “Transmitting data in a power line network using link quality assessment;” U.S. Pat. No. 6,917,888, entitled, “Method and system for power line network fault detection and quality monitoring;” U.S. Pat. No. 7,106,177, entitled, “Method and system for modifying modulation of power line communications signals for maximizing data throughput rate;” U.S. Pat. No. 7,193,506, entitled, “Method and system for maximizing data throughput rate in a power line communications system by modifying payload symbol length;” U.S. Pat. No. 7,245,625, entitled, “Network-to-network adaptor for power line communications;” and U.S. Pat. No. 7,286,812, entitled, “Coupling between power line and customer in power line communication system.” Systems and methods described in the above mentioned U.S. Patents and U.S. Patent Applications can be applied to embodiments described herein. 
     The following standards document is incorporated by reference herein in its entirety: IEEE Std 1901-2010™—IEEE Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications, New York, N.Y.: IEEE. 
     It will also be readily understood by those skilled in the art that materials and methods may be varied while remaining within the scope of the present invention. It is also appreciated that the present invention provides many applicable inventive concepts other than the specific contexts used to illustrate embodiments. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.