Abstract:
A system for serving an individual node in a shared communication network having a MAC layer and a PHY layer, the system being operative to interface between the MAC layer and the PHY layer. The system may include a first physical channel transferring at least one packet between the layers, a second physical channel transferring at least one burst parameter between the layers, and a third physical channel transferring at least one timing signal, for a burst characterized by the at least one burst parameter and comprising the at least one packet, between the layers.

Description:
CROSS-REFERENCE TO OTHER APPLICATIONS 
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 11/924,457, filed Oct. 25, 2007, entitled “MAC TO PHY INTERFACE APPARATUS AND METHODS FOR TRANSMISSION OF PACKETS THROUGH A COMMUNICATIONS NETWORK.” U.S. patent application Ser. No. 11/924,457 is a nonprovisional of the following U.S. Provisional Applications, all of which are hereby incorporated by reference herein in their entireties: U.S. Provisional Application No. 60/866,532, entitled, “A METHOD FOR PACKET AGGREGATION IN A COORDINATED HOME NETWORK”, filed on Nov. 20, 2006, U.S. Provisional Application No 60/866,527, entitled, “RETRANSMISSION IN COORDINATED HOME NETWORK” filed on Nov. 20, 2006, U.S. Provisional Application No. 60/866,519, entitled, “IQ IMBALANCE CORRECTION USING 2-TONE SIGNAL IN MULTI-CARRIER RECEIVERS”, filed on Nov. 20, 2006, U.S. Provisional Application No. 60/907,111, “SYSTEM AND METHOD FOR AGGREGATION OF PACKETS FOR TRANSMISSION THROUGH A COMMUNICATIONS NETWORK” filed on Mar. 21, 2007, U.S. Provisional Application No. 60/907,126, entitled, “MAC TO PHY INTERFACE APPARATUS AND METHODS FOR TRANSMISSION OF PACKETS THROUGH A COMMUNICATIONS NETWORK”, filed on Mar. 22, 2007, U.S. Provisional Application No. 60/907,819, entitled “SYSTEMS AND METHODS FOR RETRANSMITTING PACKETS OVER A NETWORK OF COMMUNICATION CHANNELS”, filed on Apr. 18, 2007, and U.S. Provisional Application No. 60/940,998, entitled “MoCA AGGREGATION”, filed on May 31, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to information networks and specifically to transmitting information such as media information over communication lines such as coax, thereby to form a communications network. 
       BACKGROUND 
       [0003]    Many structures, including homes, have networks based on coaxial cable (“coax”). 
         [0004]    The Multimedia over Coax Alliance (“MoCA™”), provides at its website (www.mocalliance.org) an example of a specification (viz., that available under the trademark MoCA 1.0, which is hereby incorporated herein by reference in its entirety) for networking of digital video and entertainment information through coaxial cable. The specification has been distributed to an open membership. 
         [0005]    Technologies available under the trademark MoCA, other specifications and related technologies (“the existing technologies”) tap into the vast amounts of unused bandwidth available on the coax. For example, coax has been installed in more than 70% of homes in the United States. Some homes have existing coax in one or more primary entertainment consumption locations such as family rooms, media rooms and master bedrooms. MoCA™ technology allows homeowners to utilize installed coax as a networking system and to deliver entertainment and information programming with high quality of service (“QoS”). 
         [0006]    The existing technologies provide high speed (270 mbps), high QoS, and the innate security of a shielded, wired connection combined with state of the art packet-level encryption. Coax is designed for carrying high bandwidth video. Today, it is regularly used to securely deliver millions of dollars of pay per view and premium video content on a daily basis. Networks based on the existing technologies can be used as a backbone for multiple wireless access points to extend the reach of wireless service in the structure. 
         [0007]    Existing technologies provide a consistent, high throughput, high quality connection through the existing coaxial cables to the places where the video devices currently reside in the home without affecting other service signals that may be present on the cable. The existing technologies provide a link for digital entertainment, and may act in concert with other wired and wireless networks to extend entertainment throughout the structure. 
         [0008]    The existing technologies work with access technologies such as asymmetric digital subscriber lines (“ADSL”), very high speed digital subscriber lines (“VDSL”), and Fiber to the Home (“FTTH”), which provide signals that typically enter the structure on a twisted pair or on an optical fiber, operating in a frequency band from a few hundred kilohertz to 8.5 MHz for ADSL and 12 MHZ for VDSL. As services reach such a structure via any type of digital subscriber line (“xDSL”) or FTTH, they may be routed via the existing technologies and the coax to the video devices. Cable functionalities, such as video, voice and Internet access, may be provided to the structure, via coax, by cable operators, and use coax running within the structure to reach individual cable service consuming devices in the structure. Typically, functionalities of the existing technologies run along with cable functionalities, but on different frequencies. 
         [0009]    The coax infrastructure inside the structure typically includes coax, splitters and outlets. Splitters typically have one input and two or more outputs and are designed to transmit signals in the forward direction (input to output), in the backward direction (output to input), and to isolate outputs from different splitters, thus preventing signals from flowing from one coax outlet to another. Isolation is useful in order to a) reduce interference from other devices and b) maximize power transfer from Point Of Entry (“POE”) to outlets for best TV reception. 
         [0010]    Elements of the existing technologies, such as that available under the trademark MoCA, are specifically designed to propagate backward through splitters (“insertion”) and from output to output (“isolation”). One outlet in a structure can be reached from another by a single “isolation jump” and a number of “insertion jumps.” Typically isolation jumps have an attenuation of 5 to 40 dB and each insertion jump attenuates approximately 3 dB. MoCA™ technology has a dynamic range in excess of 55 dB while supporting 200 Mbps throughput. Therefore MoCA™ technology can work effectively through a significant number of splitters. 
         [0011]    Managed network schemes, such as MoCA™ technology, are specifically designed to support streaming video without packet loss providing very high video quality between outlets. 
         [0012]    Because digital cable programming is delivered to a structure with a threshold Packet Error Rate (“PER”) below 1 per million, programming transmitted from outlet to outlet within the structure should have a similar or better error rate so as to provide similar viewability. It would therefore be desirable to provide systems and methods for communicating information over the coax in structure networks. 
       SUMMARY 
       [0013]    There is thus provided, in accordance with the principles of the invention, a system servicing an individual node in a shared communication network having a MAC layer and a PHY layer, the system being operative to interface between the MAC layer and the PHY layer, the system comprising a first physical channel transferring at least one packet between the layers, a second physical channel transferring at least one burst parameter between the layers, and a third physical channel transferring at least one timing signal, for a burst characterized by the at least one burst parameter and comprising the at least one packet, between the layers. 
         [0014]    Further in accordance with a preferred embodiment of the present invention, the timing signal comprises an indication, provided by the MAC layer to the PHY layer, of a time at which to transmit at least one burst. 
         [0015]    Still further in accordance with a preferred embodiment of the present invention, the timing signal comprises an indication, provided by the MAC layer to the PHY layer, of a time at which to receive at least one burst. 
         [0016]    Additionally in accordance with a preferred embodiment of the present invention, the at least one burst parameter is transferred before the burst, from the MAC layer to the PHY layer. 
         [0017]    Further in accordance with a preferred embodiment of the present invention, at least one burst parameter comprises at least one status parameter of the burst transferred after the burst, from the PHY layer to the MAC layer. 
         [0018]    Additionally, in accordance with a preferred embodiment of the present invention, at least one burst parameter comprises at least one reception configuration attribute of the burst. 
         [0019]    Further in accordance with a preferred embodiment of the present invention, at least one burst parameter comprises at least one transmission configuration attribute of the burst. 
         [0020]    Still further in accordance with a preferred embodiment of the present invention, the second physical channel is operative to transfer, from the PHY layer to the MAC layer, an indication of the PHY layer&#39;s extent of interest in different types of status parameters. 
         [0021]    Additionally in accordance with a preferred embodiment of the present invention, the second physical channel comprises a multi-standard pre-processor operative to pre-process, for transfer from layer to layer, at least one burst parameter formatted in accordance with any of a plurality of access mode-defining standards. 
         [0022]    According to some communication standards, transmission of information between the PHY layers of various nodes in a network, which may include, say, up to dozens of nodes, is multi-tone. Some of these standards include, for each individual node N 1  in the network, and for each node with which the individual node N wishes to interact (receive (“RX” from or transmit (“TX”) to) Tx and Rx bit loading tables. Node N i &#39;s TX bit loading table for a particular node N n  defines for each of a plurality of tones such as 256 or 512 tones, the number of bits to be loaded on that tone when transmitting to node N. Node N i &#39;s RX bit loading table for a particular node N n  defines for each of a plurality of tones such as 256 or 512 tones, the number of bits loaded on that tone when receiving from node N. The key accessing these tables is present in the MAC layer. 
         [0023]    Further in accordance with a preferred embodiment of the present invention, the system also comprises at least one bit-loading table stored externally to the PHY layer. 
         [0024]    Still further in accordance with a preferred embodiment of the present invention, the second physical channel is operative to transfer an individual bit-loading table, characterizing a pair of nodes including a Tx node and an Rx node, to a PHY layer of at least one of the Tx node and the Rx node when the nodes are preparing to communicate with one another. 
         [0025]    Further in accordance with a preferred embodiment of the present invention, the second physical channel is operative to transfer at least one item of information regarding a burst, other than contents of packets included in the burst and other than an indication of a time at which to transmit the burst. 
         [0026]    Still further in accordance with a preferred embodiment of the present invention, the timing signal comprises an alert, provided by the PHY layer to the MAC layer, that a burst has been received. 
         [0027]    Further in accordance with a preferred embodiment of the present invention, the system also comprises at least one gain-per-tone table stored externally to the PHY layer. 
         [0028]    According to some communication standards, transmission of information between the PHY layers of various nodes in a network, which may include, say, up to dozens of nodes, is multi-tone. Some of these standards include, for each individual node N in the network, a gain-per-tone table defining the transmission power for each of a plurality of tones such as 256 or 512 tones when node N transmits to other nodes. The key accessing these tables is present in the MAC layer. 
         [0029]    Further in accordance with a preferred embodiment of the present invention, the second physical channel is operative to transfer an individual gain-per-tone table, characterizing an individual Tx node, to the PHY layer of the Tx node. 
         [0030]    Still further in accordance with a preferred embodiment of the present invention, at least one status parameter transferred after the burst may include at least one of the following: SNR information characterizing the burst; and channel response information characterizing the burst. 
         [0031]    Further in accordance with a preferred embodiment of the present invention, the second physical channel transfers information characterizing a configuration of an individual burst while at least one packets of a burst previous to the individual burst are still traversing the first physical channel, thereby to shorten an inter-frame gap defined between the individual burst and the previous burst. 
         [0032]    Also provided, in accordance with the principles of the invention, is a method for operating an individual node in a shared communication network having a MAC layer and a PHY layer, the method being operative to interface between the MAC layer and the PHY layer, the method comprising transferring at least one packet between the layers over a first physical channel, transferring at least one burst parameter between the layers over a second physical channel; and transferring at least one timing signal, for a burst characterized by the at least one burst parameter and comprising the at least one packet, between the layers over a third physical channel. 
         [0033]    Further in accordance with a preferred embodiment of the present invention, the burst, to be transmitted from the individual node to another node. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The above and other features of the present invention, its nature and various advantages will be more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, and in which: 
           [0035]      FIG. 1  is a simplified functional block diagram of a MAC-PHY interface, constructed and operative in accordance with principles of the invention, in a single device configuration; 
           [0036]      FIG. 2A-2B , taken together, form a table describing the signals of  FIG. 1  from the PHY&#39;s point of view in accordance with principles of the invention; 
           [0037]      FIG. 3  is a MAC to PHY Timing Diagram describing preferred timing from the MAC of  FIG. 1  to the PHY of  FIG. 1  in accordance with principles of the invention; 
           [0038]      FIG. 4  is a diagram of several operation states for the PHY of  FIG. 1  in accordance with principles of the invention; 
           [0039]      FIG. 5  is a table of parameters for the PHY layer of  FIG. 1  in accordance with principles of the invention; 
           [0040]      FIG. 6  is a diagram showing a preferred structure for data passing between the MAC and PHY over the MAC Protocol Data (“MPD”) interface in  FIG. 1 ; 
           [0041]      FIG. 7  is a diagram of a burst initialization parameters structure in accordance with principles of the invention; 
           [0042]      FIG. 8  is a preferred timing diagram for a preferred mode of operation for the interface apparatus of  FIG. 1 ; 
           [0043]      FIG. 9  is a timing diagram for a burst initialization in accordance with principles of the invention; 
           [0044]      FIG. 10  is a diagram of receive (“RX”) burst result timing in accordance with principles of the invention; 
           [0045]      FIG. 11  is a diagram of RX result budget time in accordance with principles of the invention; 
           [0046]      FIG. 12  is a timing diagram of a burst initialization interrupting an RX burst result, in a system constructed and operative in accordance with principles of the invention; 
           [0047]      FIGS. 13-16  are tables and timing diagrams which together illustrate features of exemplary embodiments of a portion of the interface of  FIG. 1  in accordance with principles of the invention; 
           [0048]      FIGS. 17-20  are timing diagrams which together illustrate one implementation of a portion of the interface of  FIG. 1  in accordance with principles of the invention; and 
           [0049]      FIG. 21  shows a schematic diagram of an illustrative single or multi-chip device that may be used in connection with the interface of  FIG. 1  in accordance with principles of the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0050]      FIG. 1  shows illustrative MAC-PHY interface  1 , constructed and operative in accordance with principles of the invention, in a single device configuration. Interface  1  may be a MoCA™ technology MAC-PHY Interface (“MPI”), which is typically built in a modular way to support communication between PHY layer  10  and MAC layer  20 , which are in communication with different devices. 
         [0051]    Interface  1  includes MAC Protocol Data (“MPD”) interface  110 , which may include 8-bit data bus  112 , management interface  120 , which may include 4-bit data bus  122 , control interface  130  and configuration interface  140 . Interface  110  may be used to transfer data from and to MAC  20 . Management interface  120  may be used to transmit burst initial parameters and to receive RX burst result parameters. Control interface  130  may be used for PHY operations and for burst arrival time. Interface  140  may be used to configure PHY layer  10 . 
         [0052]      FIGS. 2A-2B , taken together, form a table showing attributes of illustrative signals that may be communicated by interface  1  (see  FIG. 1 ) from the point of view of PHY layer  10  (i.e., signals designated as input (“I”) are sourced in MAC layer  20  and are inputs with respect to PHY layer  10 . 
         [0053]    A CPU in communication with MAC layer  20  may use interface  1  to accesses PHY layer  10  through MAC layer  20  (see  FIG. 1 ). The CPU may do so via a serial interface for configuration, initialization and debug. A configuration port may use the PHY_CLK  134  (see  FIG. 1 ) signal as a serial clock. A protocol is typically defined in connection with the serial interface to allow read and write access. 
         [0054]    Management interface  120  is a channel through which MAC layer  20  may configure PHY layer  10 , typically with MoCA™ burst parameters, and receive from PHY layer  10  burst results and status. 
         [0055]      FIG. 3  shows a MAC to PHY Timing Diagram showing timing from MAC layer  20  to PHY layer  10 . MNG_DIR signal  124  may be used to set the direction of data transfer. 
         [0056]    MPD interface  110  may be used to transfer RX/TX data. 
         [0057]      FIG. 4  shows several operation states, such as Reset, Standby and Active in which PHY layer  10  may operate. In Reset, PHY layer  10  and MAC layer  20  typically drive their signals to inactive values. The Reset signal is not part of the MAC-PHY interface apparatus shown and described herein. Standby is the state of the PHY layer  10  when PHY layer  10  is not active in either RX or TX. In Standby, PHY layer  10  reduces power consumption by turning unnecessary functions off However, the parameters registers are typically left active for read and write. PHY layer  10  enters the Active state upon PHY_STRT  132  (see  FIG. 1 ) assertion and remains in that state until the burst process ends. In Active, paths MPD_TX  116  and/or MPD RX  118  (see interface  110  in  FIG. 1 ) may be active. Both MPD_TX  116  and MPD_RX  118  could be active if and when TX follows RX and RX is still not finished when TX starts. In Active, the only active path is on. The other path should be off. 
         [0058]      FIG. 5  shows illustrative parameters, which may include both capability and dynamic parameters, of PHY layer  10  (see  FIG. 1 ). The parameters may be based on a vendor specific implementation. PHY layer  10  dynamic parameters are preferably separate from burst parameters and configuration parameters. The burst parameters may be changed in connection with every burst and the configuration parameters may be changed during the operation of interface  1  (see  FIG. 1 ) and may affect the operation of PHY layer  10 . Burst parameters may be accessed via management interface  120  and configuration parameters via the configuration interface  140 . 
         [0059]      FIG. 6  shows that data passing between MAC layer  20  and PHY layer  10  over MPD interface  140  may comprise illustrative MAC frame  200 , which may include CRCs  210  and  214  for header  218  and payload  222 , respectively. Forward error correction (“FEC”) padding  230  is typically added by PHY layer  10 . In MoCA™ RX (PHY to MAC), typically, a FEC pad such as  230  is transferred over an MPD interface such as  140  and a MAC layer such as  20  de-pads the FEC pad. 
         [0060]      FIG. 7  shows an illustrative format for passing data over management interface  120  (see  FIG. 1 ). The format typically includes a variable parameters list. Different parameters are typically initiated according to TX, RX and the burst type. The data may start with a 32-bit section length and a list of parameters, e.g. as shown in  FIG. 7 . 
         [0061]      FIG. 8  shows an illustrative mode of operation for interface  1  (see  FIG. 1 ). Before each RX or TX burst, MAC layer  20  typically sends to PHY layer  10 , via MNG DATA bus  122 , parameters that are to be used by PHY layer  10  for transmitting or receiving. After the RX burst, PHY layer  10  typically sends to MAC layer  20  RX burst parameters that typically include receive burst status, RX learning parameters and, in the probe, the probe result. 
         [0062]      FIG. 9  shows an illustrative burst initialization (“burst init”). PHY STRT  132  is typically asserted at Burst Delay time before the first symbol of the preamble present at the coax. A first part of the Burst Delay time may be used by MAC layer  20  to send burst init parameters. A second part of the Burst Delay Time may be used for PHY layer  10  delay from the burst init end to the first symbol of the preamble being present at the coax. In the RX burst, PHY layer  10  typically starts acquisition at the end of the Burst Delay. Upon PHY STRT  132  assertion, PHY layer  10  may start reading burst parameters from MAC layer  20  even while RX results are being sent. Burst init time typically allows 400 bytes of burst parameters to be sent to PHY layer  10  before the burst. The PHY layer  10  start delay may be 5 microseconds (“uS” or “μS”) so as to provide increased pre-burst preparation time. 
         [0063]      FIG. 10  shows that PHY layer  10  may begin sending RX burst results after an RX process delay end time. RX Process Delay time is typically measured from the end of the last symbol on the coax to the maximum delay to process the RX burst.  FIG. 11  shows that the maximum time for sending RX result parameters may be 33.8 μS (845B).  FIG. 12  shows that RX burst results may be interrupted by burst init. 
         [0064]      FIGS. 13-16  show illustrative features of an illustrative data interface such as MPD interface  110  (see  FIG. 1 ). 
         [0065]    The MPD interface  110  of  FIG. 1  typically comprises a data bus such as MPD DATA bus  112 , a data enable signal such as MPD_DATA_EN signal  114 , and TX/RX signals such as MPD_TX signal  116  and MPD_RX signal  118 . Signals  116  and  118  typically define the direction of data bus  112  and typically are not active together. MPD RX signal  118  typically finishes transferring to MAC layer  20  before MPD_TX  116  is sent. The tail of MPD_RX signal  118  may be transmitted over the MPD_DATA  112  during the preamble of the next TX burst start transmit. 
         [0066]    A medium data gap (“MDG”) is defined herein as the time, as measured at the coax, between the end of an RX last symbol and a first symbol of the TX payload. During the gap, all RX data is typically transferred to MAC layer  20  and enough data is read for transmission after the preamble ends. In some embodiments, the MDG may be 21.52 us in 50 MHz bandwidth, but any suitable MDG may be used. In some embodiments, the MDG may be 14.66 in turbo mode (100 MHz), but any suitable MDG may be used. The MDG typically comprises the minimum inter-frame gap (“IFG”) of 7.8 us (10 us-2.2 us) and minimum preamble time. In some embodiments, at 50 MHz bandwidth, the minimum preamble time (the minimal-size preamble, “P4,” size with the minimum allowed cyclic prefix, “CP,” size of 10 samples) may be 13.72 us, but any suitable minimum preamble time may be used. In some embodiments, in turbo mode the time may be 6.86 us, but any suitable minimum preamble time may be used. 
         [0067]    A medium symbol gap (“MSG”) is defined as the time, as measured at the coax, between the end of an RX last symbol and a first symbol from a device (e.g., a consumer electronics (“CE”) device). During the gap, a FFT machine typically finishes processing the last RX symbol, an IFFT typically finishes the CE symbol processing and the first CE sample is typically present on the medium at the end of the preamble. In some embodiments, at 50 MHz bandwidth, the MSG may be 9.08 us, but any suitable MSG may be used. In some embodiments, in turbo mode (100 MHz), the MSG may be 8.44, but any suitable MSG may be used. The MSG typically comprises the minimum IFG of 7.8 us (10 us-2.2 us) and a short preamble time. In some embodiments, at, 50 MHz bandwidth, the short preamble time may be 1.28 us (L2), but any short preamble time may be used. In some embodiments, in turbo mode the time may be 0.64 us, but any short preamble time may be used. 
         [0068]    IFG (see  FIGS. 11 and 12 ) is the gap time on MPD DATA bus  112  between two bursts of data transferring on the MPD_DATA bus  112 . IFG is typically the MAC time for internal delay. The time is typically 0.5 us (25 cycles of PHY_CLK). 
         [0069]    PHY layer  10  timing is now described. There are typically two time-critical paths between the RX burst to the TX burst in the PHY:
       Path A: FFT to IFFT. The time between the FFT end processing the last symbol of the RX burst to starting IFFT for the first symbol (CE) of the TX burst; and   Path B: RX data to TX data. The time between the last byte of the RX burst passing over interface  1  (see  FIG. 1 ) to the first byte of the TX burst start transmitted over interface  1 .
 
For Path A, time from the RX path through the FFT in addition to time from the IFFT to the TX path are typically accumulated. For Path B, all RX and TX path time in addition to the MPD_IFG are typically accumulated.
       
 
         [0072]      FIGS. 13 and 14  show examples of the RX path delay and TX path delay, respectively. 
         [0073]    Referring again to the two data bursts that transfer on MPD_DATA bus  112 , and as shown in  FIG. 15 , MPD_TX signal  116  is typically asserted by PHY layer  10  when the first data byte of TX burst TX(1) has been transferred over MPD_DATA bus  112  until the last byte of the burst.  FIG. 16  shows that MPD RX signal  118  is typically asserted from the start of the first data symbol (e.g., an Adaptive Constellation Multitone (“ACMT”) symbol) received on the coax medium and until the transmission of the last byte of the RX burst on the MPD_DATA bus  112 . MAC layer  20  typically detects the assertion of MPD_RX signal  118  and latches a Network Timer (“NT”) for an Arrival Time Stamp (“ATS”). The ATS is typically used for comparing with a Transmit Start Time for synchronization of the NT to a Network Controller NT. MPD RX signal  118  is typically de-asserted when the acquisition is finished and the two CE symbols have arrived within a tolerance defined by a predetermined number of samples. The time between the start preamble presented on the medium to the assertion of MPD RX signal  118  typically depends on the preamble type and the CP. 
         [0074]      FIGS. 17-20  show features of an illustrative embodiment of configuration interface  140  (see  FIG. 1 ).  FIG. 17  illustrates a serial read operation in which MAC layer  20  drives the first part of the transaction, which includes a PHY register address. PHY layer  10  drives the second part of the transaction, which includes requested data. Whether MAC layer  20  or PHY layer  10  drives management interface  120 , every bit driven on CNFG_SERIAL_DATA line  142  is always synchronized with PHY_CLK  134  (see  FIG. 1 ). MAC layer  20  may drive a “1” as the first bit on CNFG_SERIAL_DATA line  142 . The second bit is a “1”, which indicates a read operation. MAC layer  20  may drive the next 16 bits, which store the PHY register address. After the 16-bit address, MAC layer  20  typically drives a ‘0’ bit to place the CNFG_SERIAL_DATA line  142  in a known state. 
         [0075]    PHY layer  10  may drive from 0 to 32 ‘0’ bits on CNFG SERIAL DATA line  142  beginning on the second PHY_CLK  134  after MAC layer  20  stops driving interface  1  (see  FIG. 1 ). PHY layer  10  may drive a ‘1’ bit to indicate start of data followed by 32 data bits. The transaction is typically completed by driving a terminating ‘0’ bit to place CNFG_SERIAL_DATA line  142  in a known state before releasing the line to be driven by MAC layer  20 . 
         [0076]      FIG. 18  shows typical timing for the fastest PHY layer  10  response to a read operation. An implementer may use internal or external pull-down resistors to set the CNFG SERIAL DATA line  142  to  0  when MAC layer  20  is no longer driving the signal. CNFG SERIAL DATA pin  142  typically continues to be controlled by MAC layer  20 . 
         [0077]      FIG. 19  shows an illustrative serial write operation. For a serial write operation, MAC layer  20  typically drives the entire transaction. Each bit that MAC layer  20  drives on the CNFG_SERIAL_DATA line  142  is typically synchronized with PHY CLK signal  134 . MAC layer  20  typically drives a “1” as the first bit on CNFG_SERIAL_DATA line  142 . The second bit is a “0”, which indicates a write operation. The next 16 bits are typically the PHY layer  10  address location. The next 32 bits are typically the data to be written to the addressed PHY layer  10  register. At the end of 32-bits of data, MAC layer  20  typically drives a terminating “0.” Once the transaction is complete MAC layer  20  typically stops driving management interface  120 . An implementer can use, e.g., internal or external pull-down resistors to set the CNFG_SERIAL_DATA line  142  to  0  when MAC layer  20  is no longer driving the signal. CNFG SERIAL DATA line  142  typically continues to be controlled by MAC layer  20 . 
         [0078]      FIG. 20  shows the fastest timing for a read operation followed immediately by a write operation. 
         [0079]      FIG. 21  shows a single or multi-chip module  2102  according to the invention, which can be one or more integrated circuits, in an illustrative data processing system  2100  according to the invention. Data processing system  2100  may include one or more of the following components: I/O circuitry  2104 , peripheral devices  2106 , processor  2108  and memory  2110 . These components may be coupled together by a system bus or other interconnections  2112  and are disposed on a circuit board  2120  in an end-user system  2130  that may be in communication with a coax medium via an interface such as interface  1  (see  FIG. 1 ). 
         [0080]    For the sake of clarity, the foregoing description, including specific examples of parameter values provided, is sometimes specific to certain protocols such as those identified with the name MoCA™ and/or Ethernet protocols. However, this is not intended to be limiting and the invention may be suitably generalized to other protocols and/or other packet protocols. The use of terms that may be specific to a particular protocol such as that identified by the name MoCA™ or Ethernet to describe a particular feature or embodiment is not intended to limit the scope of that feature or embodiment to that protocol specifically; instead the terms are used generally and are each intended to include parallel and similar terms defined under other protocols. 
         [0081]    It is appreciated that software components of the present invention including programs and data may, if desired, be implemented in ROM (read only memory) form, including CD-ROMs, EPROMs and EEPROMs, or may be stored in any other suitable computer-readable medium such as but not limited to disks of various kinds, cards of various kinds and RAMs. Components described herein as software may, alternatively, be implemented wholly or partly in hardware, if desired, using conventional techniques. 
         [0082]    Features of the present invention which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, features of the invention which are described for brevity in the context of a single embodiment may be provided separately or in any suitable subcombination.