Patent Publication Number: US-9906299-B2

Title: Upstream frame configuration for ethernet passive optical network protocol over coax (EPoC) networks

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 14/642,263, filed Mar. 9, 2015, which claims the benefit of U.S. Provisional Patent Application No. 61/950,054, filed Mar. 8, 2014, U.S. Provisional Patent Application No. 61/981,549, filed Apr. 18, 2014, and U.S. Provisional Patent Application No. 62/001,569, filed May 21, 2014, all of which are incorporated herein by reference in their entireties. 
     This application also claims the benefit of U.S. Provisional Patent Application No. 62/001,572, filed May 21, 2014, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This application relates generally to Ethernet, including Ethernet Passive Optical Network Over Coax (EPoC). 
     BACKGROUND 
     A Passive Optical Network (PON) includes a shared optical fiber and inexpensive optical splitters to divide the fiber into separate strands feeding individual subscribers. An Ethernet PON (EPON) is a PON based on the Ethernet standard. EPONs provide simple, easy-to-manage connectivity to Ethernet-based, IP equipment, both at customer premises and at the central office. As with other Gigabit Ethernet media, EPONs are well-suited to carry packetized traffic. An Ethernet Passive Optical Network Protocol Over Coax (EPoC) is a network that enables EPON connectivity over a coaxial network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the embodiments of the present disclosure and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the embodiments. 
         FIG. 1  illustrates an example hybrid Ethernet Passive Optical Network (EPON)-Ethernet Passive Optical Network Over Coax (EPoC) network architecture. 
         FIG. 2  illustrates another example hybrid EPON-EPoC network architecture. 
         FIG. 3  illustrates an example EPoC portion of a hybrid EPON-EPoC network according to an embodiment of the present disclosure. 
         FIG. 4  illustrates an exemplary EPoC network. 
         FIG. 5  illustrates an example of a PHY auto-negotiation and link up procedure according to an embodiment of the present disclosure. 
         FIG. 6  illustrates an example upstream frame configuration according to an embodiment of the present disclosure. 
         FIG. 7  illustrates three different types of resource blocks that span 8 OFDMA symbols in time in accordance with embodiments of the present disclosure. 
         FIG. 8  illustrate three different types of resource blocks that span 16 OFDMA symbols in time in accordance with embodiments of the present disclosure. 
         FIG. 9  illustrates an example upstream data frame that adheres to specified pilot rules in accordance with embodiments of the present disclosure. 
         FIG. 10  illustrates an example upstream data frame that adheres to specified pilot rules in accordance with embodiments of the present disclosure. 
         FIG. 11  illustrates an example computer system that can be used to implement aspects of the present disclosure. 
     
    
    
     The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the embodiments, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the disclosure. 
     References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     For purposes of this discussion, the elements in  FIGS. 1-4  shall be understood to include software, firmware, or hardware (such as one or more circuits, microchips, processors, and/or devices), or any combination thereof. In addition, it will be understood that each element in  FIGS. 1-4  can include one, or more than one, component within an actual device, and each component that forms a part of the described module can function either cooperatively or independently of any other component forming a part of the module. Conversely, multiple elements described herein can represent a single component within an actual device. Further, components within an element can be in a single device or distributed among multiple devices in a wired or wireless manner. 
     I. Example Hybrid EPON-EPoC Network Architectures 
       FIG. 1  illustrates an example hybrid Ethernet Passive Optical Network (EPON)-Ethernet Passive Optical Network Over Coax (EPoC) network architecture  100  according to an embodiment of the present disclosure. As shown in  FIG. 1 , example network architecture  100  includes an Optical Line Terminal (OLT)  102 , an optional optical passive splitter  106 , a communications node  110  including a coaxial media converter (CMC)  112 , an optional amplifier  116 , an optional coaxial splitter  118 , a coaxial network unit (CNU)  122 , and a plurality of subscriber media devices  124 . 
     OLT  102  sits at a central office (CO) of the network and is coupled to a fiber optic line  104 . OLT  102  may implement a DOCSIS (Data Over Cable Service Interface Specification) Mediation Layer (DML) which allows OLT  102  to provide DOCSIS provisioning and management of network components (e.g., CMC and Optical Network Unit (ONU)). Additionally, OLT  102  implements an EPON Media Access Control (MAC) layer (e.g., IEEE 802.3ah). 
     Optionally, optical passive splitter  106  can be used to split fiber optic line  104  into a plurality of fiber optic lines  108 . This allows multiple subscribers in different geographical areas to be served by the same OLT  102  in a point-to-multipoint topology. 
     Communications node  110  serves as a converter between the EPON side and the EPoC side of the network. Accordingly, communications node  110  is coupled from the EPON side of the network to a fiber optic line  108   a , and from the EPoC side of the network to a coaxial cable  114 . In an embodiment, communications node  110  includes a coaxial media converter (CMC)  112  that allows EPON to EPoC (and vice versa) conversion. 
     CMC  112  performs physical layer (PHY) conversion from EPON to EPoC, and vice versa. In an embodiment, CMC  112  includes a first interface (not shown in  FIG. 1 ), coupled to fiber optic line  108 , configured to receive a first optical signal from OLT  102  and generate a first bitstream having a first physical layer (PHY) encoding. In an embodiment, the first PHY encoding is EPON PHY encoding. CMC  112  also includes a PHY conversion module (not shown in  FIG. 1 ), coupled to the first interface, configured to perform PHY layer conversion of the first bitstream to generate a second bitstream having a second PHY encoding. In an embodiment the second PHY encoding is EPoC PHY encoding. Furthermore, CMC  112  includes a second interface (not shown in  FIG. 1 ), coupled to the PHY conversion module and to coaxial cable  114 , configured to generate a first radio frequency (RF) signal from the second bitstream and to transmit the first RF signal over coaxial cable  114 . 
     In EPoC to EPON conversion (i.e., in upstream communication), the second interface of CMC  112  is configured to receive a second RF signal from CNU  122  and generate a third bitstream therefrom having the second PHY encoding (e.g., EPoC PHY encoding). The PHY conversion module of CMC  112  is configured to perform PHY layer conversion of the third bitstream to generate a fourth bitstream having the first PHY encoding (e.g., EPON PHY encoding). Subsequently, the first interface of CMC  112  is configured to generate a second optical signal from the fourth bitstream and to transmit the second optical signal to OLT  102  over fiber optic line  108 . 
     Optionally, an amplifier  116  and a second splitter  118  can be placed in the path between communications node  110  and CNU  122 . Amplifier  116  amplifies the RF signal over coaxial cable  114  before splitting by second splitter  118 . Second splitter  118  splits coaxial cable  114  into a plurality of coaxial cables  120 , to allow service over coaxial cables of several subscribers which can be within the same or different geographic vicinities. 
     CNU  122  generally sits at the subscriber end of the network. In an embodiment, CNU  122  implements an EPON MAC layer, and thus terminates an end-to-end EPON MAC link with OLT  102 . Accordingly, CMC  112  enables end-to-end provisioning, management, and Quality of Service (QoS) functions between OLT  102  and CNU  122 . CNU  122  also provides multiple Ethernet interfaces that could range between 10 Mbps to 10 Gbps, to connect subscriber media devices  124  to the network. Additionally, CNU  122  enables gateway integration for various services, including VOIP (Voice-Over-IP), MoCA (Multimedia over Coax Alliance), HPNA (Home Phoneline Networking Alliance), Wi-Fi (Wi-Fi Alliance), etc. At the physical layer, CNU  122  may perform physical layer conversion from coaxial to another medium, while retaining the EPON MAC layer. 
     According to embodiments, EPON-EPoC conversion can occur anywhere in the path between OLT  102  and CNU  122  to provide various service configurations according to the services needed or infrastructure available to the network. For example, CMC  112 , instead of being integrated within node  110 , can be integrated within OLT  102 , within amplifier  116 , or in an Optical Network Unit (ONU) located between OLT  102  and CNU  122  (not shown in  FIG. 1 ). When CMC  112  is implemented in OLT  102  at the CO hub, OLT  102  may be more aptly referred to as a Cable Line Terminal (CLT). 
       FIG. 2  illustrates another example hybrid EPON-EPoC network architecture  200  according to an embodiment of the present disclosure. In particular, example network architecture  200  enables simultaneous FTTH (Fiber to the Home) and multi-tenant building EPoC service configurations. 
     Example network architecture  200  includes similar components as described above with reference to example network architecture  100 , including an OLT  102  located in a CO hub, a passive splitter  106 , a CMC  112 , and one or more CNUs  122 . OLT  102 , splitter  106 , CMC  112 , and CNU  122  operate in the same manner described above with reference to  FIG. 1 . 
     CMC  112  sits, for example, in the basement of a multi-tenant building  204 . As such, the EPON side of the network extends as far as possible to the subscriber, with the EPoC side of the network only providing short coaxial connections between CMC  112  and CNU units  122  located in individual apartments of multi-tenant building  204 . 
     Additionally, example network architecture  200  includes an Optical Network Unit (ONU)  206 . ONU  206  is coupled to OLT  102  through an all-fiber link, comprised of fiber lines  104  and  108   c . ONU  206  enables FTTH service to a home  202 , allowing fiber optic line  108   c  to reach the boundary of the living space of home  202  (e.g., a box on the outside wall of home  202 ). 
     Accordingly, example network architecture  200  enables an operator to service both, ONUs and CNUs using the same OLT. This includes end-to-end provisioning, management, and QoS with a single interface for both fiber and coaxial subscribers. In addition, example network architecture  200  allows for the elimination of the conventional two-tiered management architecture, which uses media cells at the end user side to manage the subscribers and an OLT to manage the media cells. 
     II. Example Coaxial EPoC Link 
       FIG. 3  illustrates an example implementation  300  of an EPoC portion of a hybrid EPON-EPoC network. Example implementation  300  may be an embodiment of the EPoC portion of example EPON-EPoC network  100 , described in  FIG. 1 , or example EPON-EPoC network  200 , described above in  FIG. 2 . As shown in  FIG. 3 , the EPoC portion includes an EPoC CMC  112  and an EPoC CNU  122 , connected via a coaxial network  304 . 
     EPoC CMC  112  includes an optical transceiver  308 , a serializer-deserializer (SERDES)  310 , an EPoC PHY  312 , including, in an embodiment, a CMC interface  314  and a modulator/demodulator  316 , a controller  318 , an analog-to-digital converter (ADC)  322 , digital-to-analog converters (DAC)  320 , and an radio frequency (RF) transceiver  326 , including RF transmit (TX) circuitry  336  and RF receive (RX) circuitry  338 . 
     Optical transceiver  308  may include a digital optical receiver configured to receive an optical signal over a fiber optic cable  302  coupled to CMC  112  and to produce an electrical data signal therefrom. Fiber optic cable  302  may be part of an EPON network that connects CMC  112  to an OLT, such as OLT  102 . Optical transceiver  308  may also include a digital optical laser to produce an optical signal from an electrical data signal and to transmit the optical signal over fiber optic cable  302 . 
     SERDES  310  performs parallel-to-serial and serial-to-parallel conversion of data between optical transceiver  308  and EPoC PHY  312 . Electrical data received from optical transceiver  308  is converted front serial to parallel for further processing by EPoC PHY  312 . Likewise, electrical data front EPoC PHY  312  is converted from parallel to serial for transmission by optical transceiver  308 . 
     EPoC PHY  312 , optionally with other modules of CMC  112 , forms a two-way PHY conversion module. In the downstream direction (i.e., traffic to be transmitted to EPoC CNU  122 ), EPoC PHY  312  performs PHY level conversion from EPON PHY to coaxial PHY and spectrum shaping of downstream traffic. For example, CMC interface  314  may perform line encoding functions, Forward Error Correction (FEC) functions, and framing functions to convert EPON PHY frames into EPoC PHY frames for downstream transmissions to CNU  122 . Modulator/demodulator  316  may modulate the data received from SERDES  310  using either a single carrier or multicarrier modulation technique (e.g., orthogonal frequency division multiplexing (OFDM), orthogonal frequency division multiple access (OFDMA), sub-band division multiplexing, etc.). When using a multicarrier technique modulator/demodulator  316  can perform multicarrier functions, including determining sub-carriers for downstream transmission, determining the width and frequencies of the sub-carriers, selecting the modulation order for downstream transmission, and dividing downstream traffic into multiple streams each for transmission onto a respective sub-carrier of the sub-carriers. In the upstream direction (i.e., traffic received from EPoC CNU  112 ), EPoC PHY  312  performs traffic assembly and PHY level conversion from coaxial PHY to EPON PHY. For example, modulator/demodulator  316  may assemble streams received over multiple sub-carriers to generate a single stream. Then, CMC interface  314  may perform line encoding functions, FEC functions, and framing functions to convert EPoC PHY frames into EPON PHY frames. 
     Controller  318  provides configuration, management, and control of EPoC PHY  312 , including CMC interface  314  and modulator/demodulator  316 . In addition, controller  318  registers CMC  112  with the OLT servicing CMC  112 . In an embodiment, controller  318  is an ONU chip, which includes an EPON MAC. 
     DAC  320  and ADC  322  sit in the data path between EPoC PHY  312  and RF transceiver  326 , and provide digital-to-analog and analog-to-digital data conversion, respectively, between EPoC PHY  312  and RF transceiver  326 . 
     RF transceiver  326  allows CMC  112  to transmit/receive RF signals over coaxial network  304 . In other embodiments, RF transceiver  326  may be external to CMC  112 . RF TX circuitry  336  includes RF transmitter and associated circuitry (e.g., mixers, frequency synthesizer, voltage controlled oscillator (VCO), phase locked loop (PLL), power amplifier (PA), analog filters, matching networks, etc.). RF RX circuitry  338  includes RF receiver and associated circuitry (e.g., mixers, frequency synthesizer, VCO, PLL, low-noise amplifier (LNA), analog filters, etc.). 
     EPoC CNU  122  includes RF transceiver  326 , including RF TX circuitry  336  and RF RX circuitry  338 , DAC  320 , ADC  322 , an EPoC PHY  328 , including modulator/demodulator  316  and a CNU interface  330 , an EPoC MAC  332 , and a PHY  334 . 
     RF transceiver  326 , DAC  320 , ADC  322 , and modulator/demodulator  316  may be as described above with respect to EPoC CMC  112 . Accordingly, their operation in processing downstream traffic (i.e., traffic received from CMC  112 ) and upstream traffic (i.e., traffic to be transmitted to CMC  112 ), which should be apparent to a person of skill in the art based on the teachings herein, is omitted. 
     CNU interface  330  provides an interface between modulator/demodulator  316  and EPON MAC  332 . As such, CNU Interface  330  may perform coaxial PHY level decoding functions, including line decoding and FEC decoding, and framing functions to generate EPoC PHY frames for upstream transmission. EPON MAC  332  implements an EPON MAC layer, including the ability to receive and process EPON Operation, Administration and Maintenance (OAM) messages, which may be sent by an OLT and forwarded by CMC  112  to CNU  122 . In addition, EPON MAC  332  interfaces with a PHY  334 , which may implement an Ethernet PHY layer. PHY  334  enables physical transmission over a user-network interface (UNI)  306  (e.g., Ethernet cable) to a connected user-equipment. 
     It should be noted that, in an alternate network configuration, CMC  112  can be implemented within an OLT at the CO hub, such as within OLT  102  shown in  FIG. 1 . In such an instance, it will be apparent to one of ordinary skill in the art that the implementation of CMC  312 , shown in  FIG. 3 , can be modified to accommodate such a change. As noted above, when CMC  112  is implemented in an OLT, the OLT may be more aptly referred to as a Cable Line Terminal (CLT). 
     III. EPoC PHY Auto-Negotiation and Link Up 
     The EPON standard defines an ONU registration procedure for pure EPON networks. This, procedure is a MAC-level only procedure and thus is not sufficient to enable proper operation of an EPoC network because the physical layer is not addressed. Specifically, the coaxial portion of an EPoC network requires an auto-negotiation to determine the coaxial link spectrum, link bandwidth, and power level, and to establish precise timing between the CMC (or CLT) and the CNU. For example, in an EPON network, a link is designed to work at 1 Gbps or 10 Gbps. In an EPoC network, the coaxial link will likely be limited to a lower bandwidth, which needs to be discovered before the link can be used. In addition, this auto-negotiation, should be compatible with the EPON standard, which governs MAC-level interaction. 
     In the following, a PHY auto-negotiation and link up procedure for an exemplary EPoC network  400  illustrated in  FIG. 4  is described. The PHY auto-negotiation and link up procedure is preferably compliant with the EPON standard and is performed between a CMC (or CLT) EPoC PHY  402  and CNU EPoC PHYs  404  over (at least) a shared coaxial medium  406 . The PHY auto-negotiation and link up procedure can be further used to enable periodic maintenance of the links between the CMC (or CLT) EPoC PHY  402  and the CNU EPoC PHYs  404 . CMC EPoC PHY  402  can be implemented in a CMC similar to CMC  112 , and one or more of CNU EPoC PHYs  404  can be implemented in CNUs similar to CNU  122  described above with reference to  FIG. 3 . 
     Referring now to  FIG. 5 , an example of the PHY auto-negotiation and link up procedure  500  is illustrated. As shown in  FIG. 5 , the procedure  500  begins at step  502 , which includes the CMC (or CLT) EPoC PHY  402  periodically broadcasting a link information (info) broadcast message over the coaxial medium  406  to the CNU EPoC PHYs  404 . As mentioned above, data is generally transmitted over an EPoC network, using a multi-carrier or multi-channel transmission technique, such as orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA). The CMC (or CLT) EPoC PHY  402  is configured to broadcast the link info message over one or more carriers or channels, collectively referred to as the downstream PHY link channel, of the EPoC transmission spectrum. This downstream PHY link channel is dedicated to carrying PHY auto-negotiation and link information (and no MAC-level data) to limit interference with the MAC-level operation of the network. 
     The link info broadcast message can include several pieces of link information. For example, the link info broadcast message can provide link information regarding the modulation mode used and the duplexing mode used (e.g. time division duplexing or frequency division duplexing). If the modulation used is multicarrier modulation, the link information can further include the configuration of sub-carriers in the EPoC spectrum used to carry MAC-level data and control messages in the upstream and/or downstream direction. This configuration information can include all (or some) of the information required for the CNU PHY to be able to receive MAC-level data and control messages. For example, the configuration information can include the location in the EPoC spectrum of active downstream and upstream sub-carriers, the total number of sub-carriers, which sub-carriers carry data and/or pilots, and the sub-carriers respective modulation orders, as well as the location of any inactive sub-carriers in the EPoC spectrum. The link info broadcast message can further provide possible PHY configurations and capabilities, including an interleaver depth and a forward error correction type and size. In addition, when the downstream PHY link channel is used to convey timing information, it can carry time stamp information. In addition, the downstream PHY link channel can be used to carry power management messages. In this case, the downstream PHY link channel can carry information on wake-up times and modes, or moving into standby or sleeping mode, for each of the CNUs using unicast or broadcast messages. In addition, where OFDM is used to encode data transmitted in either the downstream or upstream direction, the configuration information can include, in addition, to the parameters already mentioned, the number of sub-carriers per OFDM symbol, the center frequency of the sub-carriers that make up OFDM symbols, and the size of any cyclic prefix added to OFDM symbols. 
     In step  506 , unlinked ones of the CNU EPoC PHYs  404  are configured to “hunt” in the EPoC spectrum to locate the downstream PHY link channel and receive the link info broadcast message transmitted by the CMC (or CLT) EPoC PHY  402 . The unlinked ones of the CNU EPoC PHYs  404  can “hunt” in the EPoC spectrum, for example, by looking for a predetermined preamble or bit pattern transmitted by the CMC (or CLT) EPoC PHY  402  at various frequencies to identify the downstream PHY link channel. 
     After unlinked ones of the CNU EPoC PHYs  404  locate the downstream PHY link channel and receive/decode the link info broadcast message from the CMC (or CLT) EPoC PHY  402 , the unlinked ones of the CNU EPoC PHYs  404  can respond to the link info broadcast message using, for example, an echo protocol to perform auto negotiation and link up. An echo protocol can be used to provide a mechanism to share access to the coaxial medium  406  in the upstream direction between the unlinked ones of the CNU EPoC PHYs  404 . For example, in the event that two or more unlinked ones of the CNU EPoC PHYs  404  attempt to respond to the link info broadcast message at the same time, the unlinked ones of the CNU EPoC PHYs  404  can implement random back off times to resolve the contention. 
     At step  506 , an unlinked one of the CNU EPoC PHYs  404  will respond to the link info broadcast message by transmitting a reply message (e.g., an “echo” or copy of the link info broadcast message) upstream to the CMC (or CLT) EPoC PHY  402 . The reply message can include a preamble to allow the CMC (or CLT) EPoC PHY  402  to determine initial range timing and transmit power of the unlinked one of the CNU EPoC PHYs  404  and an address of the unlinked one of the CNU EPoC PHYs  404 . The address of the unlinked one of the CNU EPoC PHYs  404  can be the Ethernet MAC address of its associated CNU (or at least a portion of the Ethernet MAC address) or some other configurable address, for example. The reply message is sent during an upstream PHY discovery window, which is described further below in regard to the upstream frame configuration shown in  FIG. 6 . 
     At step  508 , the CMC (or CLT) EPoC PHY  402  receives and processes the reply message from the unlinked one of the CNU EPoC PHYs  404  and, using the address provided in the received message, sends a link configuration unicast message back to the unlinked one of the CNU EPoC PHYs  404 . The link configuration unicast message can include additional configuration settings to adjust, for example, the transmit power and a transmit delay of the unlinked one of the CNU EPoC PHYs  404 . 
     More specifically, for the transmit delay, the CMC (or CLT) EPoC PHY  402  can monitor the time it takes from the last link info broadcast message it sends to the time it takes to receive the reply message from the unlinked one of the CNU EPoC PHYs  404  and, based on this time, determine an adjustment to the transmit delay in the unlinked one of the CNU EPoC PHYs  404 . The adjustment can be determined to align upstream symbol transmissions from the unlinked one of the CNU EPoC PHYs  404  with the upstream, symbol transmissions of the other CNU EPoC PHYs  404  operating on the network. This adjustment value can be provided as a configuration setting in the link configuration unicast message sent by the CMC (or CLT) EPoC PHY  402  over the downstream PHY link channel at step  508 . 
     Similarly, for the transmit power setting, the CMC (or CLT) EPoC PHY  402  can monitor the power level of the reply message received from the unlinked one of the CNU EPoC PHYs  404  and, based on this power level, determine an adjustment to the transmit power in the unlinked one of the CNU EPoC PHYs  404  to further optimize the data rate and/or hit-error rate of the shared upstream channel. Again, this adjustment value can be provided as a configuration setting in the link configuration unicast message sent by the CMC (or CLT) EPoC PHY  402  ever the downstream PHY link channel at step  508 . 
     At step  510 , the unlinked one of the CNU EPoC PHYs  404  receives and decodes the link configuration, unicast message and makes adjustments to, for example, its transmit power level and transmit delay based on the values in the decoded message. In addition, the unlinked one of the CNU EPoC PHYs  404  is configured to respond by transmitting a reply message (e.g., an “echo” or copy of the link configuration unicast message or another appropriate response) upstream to the CMC (or CLT) EPoC PHY  402 . The reply message includes status information of the unlinked one of the CNU EPoC PHYs  404 . This status information can include, for example, an error indicator or an indication of the power level of the messages the unlinked one of the CNU EPoC PHYs  404  is receiving from the CMC (or CLT) EPoC PHY  402 . The reply message sent at step  510  can be sent over an upstream PHY link channel. 
     At step  512 , the CMC (or CLT) EPoC PHY  402  receives and processes the reply message and status information sent by the unlinked one of the CNU EPoC PHYs  404  and responds by transmitting another link configuration unicast message over the DS PHY link channel. This link configuration unicast message can inform the unlinked one of the CNU EPoC PHYs  404  to transition to a linked state. For example, if the power level and symbol timing of the reply message to the link configuration unicast message the CMC (or CLT) EPoC PHY  402  receives at step  512  from the unlinked one of the CNU EPoC PHYs  404  are acceptable, the CNU EPoC PHYs  404  can send the link configuration unicast message over the DS PHY link channel to inform the unlinked one of the CNU EPoC PHYs  404  to transition to a linked state. Otherwise, if the power level and symbol timing are not acceptable, CMC (or CLT) EPoC PHY  402  can go back, to step  508  and send another link configuration unicast message to the unlinked one of the CNU EPoC PHYs  404  to adjust the transmit power and/or the transmit delay of the unlinked one of the CNU EPoC PHYs  404 . 
     Assuming that the CMC (or CLT) EPoC PHY  402  sent a link configuration unicast message to the unlinked one of the CNU EPoC PHYs  404  to inform it to transition to a linked state at step  512 , at step  514  the unlinked one of the CNU EPoC PHYs  404  can respond to this message by transmitting a reply message (e.g., an “echo” or copy of the link configuration unicast message it just received) upstream to the CMC (or CLT) EPoC PHY  402 . The reply message includes status information indicating that the unlinked one of the CNU EPoC PHYs  404  is now linked and ready to transmit and receive EPON MAC-level messages. The reply message can be sent upstream over the upstream PHY link channel, which is described further below in regard to the upstream frame configuration shown in  FIG. 6 . 
     It should be noted that after (or even before) a CNU EPoC PHY has been linked, a CMC (or CLT) EPoC PHY can continue to transmit link configuration unicast messages to the linked CNU EPoC PHY (and in response receive a reply message from the linked CNU EPoC PHY) to determine if any further or additional adjustments need to be made to the configuration settings of the linked CNU EPoC PHY. For example, after having been linked (or even before), adjustments can be made to the transmit power and/or transmit delay of the CNU EPoC PHY. Other adjustments can be made to coefficients of a pre-equalizer at the CNU EPoC PHY used to pre-equalize upstream transmissions before the transmissions are sent to the CMC (or CLT) EPoC PHY. 
     IV. EPoC Network Upstream Frame Configuration 
     Upstream transmissions from the CNU EPoC PHYs  404  to the CMC (or CLT) EPoC PHY  402 , including the reply messages described above in regard to  FIG. 5  and MAC-level data, are organized into upstream frames that cyclically repeat. The exact configuration of these frames is determined in part by the link information included in the link info broadcast message received by the CNU EPoC PHYs  404  from the CMC (or CLT) EPoC PHY  402  at step  506  as described above in regard to  FIG. 5 . 
       FIG. 6  illustrates an exemplary configuration of an upstream frame  600  used in an EPoC network. Upstream frame  600  includes two types of sub-frames: a probe frame that spans P OFDMA symbols in time followed by Nf data frames that each span M OFDM A symbols in time, where P, Nf and M are integers. The spectrum of upstream frame  600  spans Ns OFDMA subcarriers where, in one embodiment, Ns is equal to the number of subcarriers in a single upstream OFDMA symbol. In one embodiment, the value of Ns is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . Further details on the specific structure of the Nf data frames and the probe frame are described further below in turn. 
     In one embodiment, the Nf data frames have a fixed length in terms of OFDMA symbols of 256 and each of the Nf data frames has either M=8 or M=16 OFDMA symbols. Assuming each of the Nf data frames has M=8 OFDMA symbols, the number of data frames in upstream frame  600  is given by Nf=256/8 or 32. If, on the other hand, each of the Nf data frames has M=16 OFDMA symbols, the number of data frames in upstream frame  600  is given by Nf=256/16 or 16. In one embodiment, either the number of data frames Nf (i.e., either 32 or 16) or the number of OFDMA symbols M in each data frame (i.e., either 8 or 16) is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . In other embodiments, the Nf data frames can have a different fixed length in terms of OFDMA symbols other than 256 and/or the Nf data frames can have a different number M of OFDMA symbols other than 8 or 16. 
     As further shown in  FIG. 6 , each data frame is further broken down into a column of resource blocks, where each resource block spans the M OFDMA symbols in time but only a single OFDMA subcarrier in spectrum. In one embodiment, the number of OFDMA symbols M in each resource block is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . 
     Resource blocks can carry MAC-level data or data associated with the upstream PHY link channel. The upstream PHY link channel can be used by the CNU EPoC PHYs  404  to transmit reply messages upstream to the CMC (or CLT) EPoC PHY  402 . For example, the upstream PHY link channel can be used by the CNU EPoC PHYs  404  to transmit the reply messages at steps  510  and  512  in  FIG. 5  described above. In one embodiment, the upstream PHY link channel occupies 8 adjacent resource blocks from each of the Nf data frames and does not extend into the probe frame. In another embodiment, the specific number and/or location of the resource blocks that the upstream PHY link channel occupies within the Nf data frames is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . 
     All remaining resource blocks from the Nf data frames not assigned to or occupied by the upstream PHY link channel can be used by the CNU EPoC PHYs  404  to transmit MAC-level data upstream to the CMC (or CLT) EPoC PHY  402 . In one embodiment, the CMC (or CLT) EPoC PHY  402  can assign each resource block within a data frame not assigned to or occupied by the upstream PHY link channel to any one of the CNU EPoC PHYs  404  to transmit MAC-level data upstream. In addition, the CMC (or CLT) EPoC PHY  402  can assign, on a per resource block basis, a constellation size for the symbols to be transmitted over the associated subcarrier of the resource block. The constellation size determines the number of bits (or bit-loading) carried by the symbols transmitted over a sub-carrier. For example, a QAM symbol with a 64 point constellation can carry 6-bits of information. In one embodiment, the constellation size assignments is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . 
     Referring now to the probe frame, in one embodiment the probe frame has a fixed length in terms of OFDMA symbols of 6. The probe frame can include one or more of a PHY discovery window, a fine ranging window, and a probe region. 
     The PHY discovery window was mentioned above in regard to  FIG. 5 . In particular, the PHY discovery window is a portion of the probe frame during which unlinked ones of the CNU EPoC PHYs  404  can send a reply message upstream to the CMC (or CLT) EPoC PHY  402  to allow the CMC (or CLT) EPoC PHY  402  determine initial range timing and transmit power of the unlinked ones of the CNU EPoC PHYs  404  and an address of the unlinked ones of the CNU EPoC PHYs  404 . The reply message can specifically include a preamble to allow the CMC (or CLT) EPoC PHY  402  to determine initial range timing and transmit power of the unlinked ones of the CNU EPoC PHYs  404 . The CNU EPoC PHYs  404  can subsequently adjust the transmit power and transmit delay of the unlinked one of the CNU EPoC PHYs  404  based on the determined initial range timing and transmit power. In one embodiment, the specific region of the probe frame that the upstream PHY discovery window occupies is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . 
     After the CMC (or CLT) EPoC PHY  402  performs initial ranging and determines the address of one of the CNU EPoC PHYs  404 , the CMC (or CLT) EPoC PHY  402  can direct the one of the CNU EPoC PHYs  404  to transmit upstream during a fine ranging window to permit the CMC (or CLT) EPoC PHY  402  to determine fine adjustments of the transmit delay and/or transmit power of the one of the CNU EPoC PHYs  404 . In one embodiment, the specific region of the probe frame that the fine ranging window occupies is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . The CMC (or CLT) EPoC PHY  402  can assign a particular one of the CNU EPoC PHYs  404  to transmit upstream during a fine ranging window using a unicast message to the particular one of the CNU EPoC PHYs  404 . 
     The probe region of a probe frame is used by the CNU EPoC PHYs  404  to transmit known pilot patterns upstream to the CMC (or CLT) EPoC PHY  402 . The CMC (or CLT) EPoC PHY  402  can use a received pilot pattern to determine a response of the upstream channel between the one of the CNU EPoC PHYs  404  that transmitted the known pilot pattern and the CMC (or CLT) EPoC PHY  402 . The channel estimate can then be used by the CMC (or CLT) EPoC PHY  402  to determine or adjust pre-equalization coefficients of a pre-equalizer at the one of the CNU EPoC PHYs  404  to better match the channel response characteristics. In one embodiment, the specific region of the probe frame that the probe region occupies is provided to the CNU EPoC PHYs  404  via the link information in the link info broadcast message as described above in regard to step  506  in  FIG. 5 . The CMC (or CLT) EPoC PHY  402  can assign a particular one of the CNU EPoC PHYs  404  to transmit upstream during at least a part of the probe region using a unicast message to the particular one of the CNU EPoC PHYs  404 . 
     The known pilots in the probe symbols (i.e., the symbols of the probe frame) can also be used to range CNUs in time offset and transmission power, for the fine ranging of new CNUs and for periodic maintenance of existing CNUs. 
     V. EPoC Network Upstream Pilot Provisioning 
     As described above in regard to  FIG. 6 , data frames within an upstream frame are made up of a column of resource blocks. Each resource block within a data frame can span 8 or 16 OFDMA symbols in time and a single OFDMA subcarrier in spectrum. 
     Beyond the basic size and positioning of resource blocks within a data frame, resource blocks can also take on different, predetermined types that, in general, determine a number and configuration, of pilots included in a resource block. For example, and in one embodiment, resource blocks can be assigned to one of three different, types: type-0, type-1, and type-2. 
     A type-0 resource block includes zero pilot symbols. Thus, all of the symbols in a type-0 resource block can be used to carry data, such as MAC level data, for example. 
     A type-1 resource block includes two normal pilot symbols on the first and third symbols of the resource block. All other remaining symbols of a type-1 resource block can be used to carry data, such as MAC level data, for example. A normal pilot, in contrast to a low density pilot, is a known symbol with a low-order constellation (e.g., BPSK). A low density pilot is a symbol that carriers data but with a smaller number of bits than the other symbols of the resource block used to carry data. For example, and in one embodiment, a low density pilot has four fewer hits than the other symbols of the resource block used to carry data. 
     Finally, a type-2 resource block includes two normal pilots and two low density pilots. The two normal pilots are on the first and third symbols of the resource block. The two low density pilots are on the last and third to last symbols of the resource block. All other remaining symbols of a type-2 resource block can be used to carry data, such as MAC level data, for example. 
       FIG. 7  illustrates the three different types of resource blocks  702 ,  704 , and  706  for a resource block that spans 8 OFDMA symbols in time in accordance with embodiments of the present disclosure. Each square in a resource blocks  702 ,  704 , and  706  represents a sub-carrier at a specific symbol time. Normal pilots are denoted by “P”, and low density pilots are denoted by “LD”. All other empty squares in resource blocks  702 ,  704 , and  706  can be used to carry data. 
     As can be seen from  FIG. 7 , the type-0 resource block  702  includes zero pilot symbols. Thus, all of the symbols in the type-0 resource block  702  can be used to carry data, such as MAC level data, for example. The type-1 resource block  704  includes two pilot symbols on the first and third symbols of the resource block. All other remaining symbols of the type-1 resource block  704  can be used to carry data, such as MAC level data, for example. The type-2 resource block  706  includes two pilots and two low density pilots. The two pilots are on the first and third symbols of the resource block  706 . The two low density pilots are on the last and third to last symbols of the resource block  706 . All other remaining symbols of the type-2 resource block  706  can be used to carry data, such as MAC level data, for example. 
       FIG. 8  illustrates the three different types of resource blocks  802 ,  804 , and  806  for a resource block that spans 16 OFDMA symbols in time in accordance with embodiments of the present disclosure. Each square in a resource blocks  802 ,  804 , and  806  represents a sub-carrier at a specific symbol time. Normal pilots are denoted by “P”, and low density pilots are denoted by “LD”. All other empty squares in resource blocks  802 ,  804 , and  806  can be used to carry data. 
     As can be seen from  FIG. 8 , the type-0 resource block  802  includes zero pilot symbols. Thus, all of the symbols in the type-0 resource block  802  can be used to carry data, such as MAC level data, for example. The type-1 resource block  804  includes two pilot symbols on the first and third symbols of the resource block. All other remaining symbols of the type-1 resource block  804  can be used to carry data, such as MAC level data, for example. The type-2 resource block  806  includes two pilots and two low density pilots. The two pilots are on the first and third symbols of the resource block  806 . The two low density pilots are on the last and third to last symbols of the resource block  806 . All other remaining symbols of the type-2 resource block  806  can be used to carry data, such as MAC level data, for example. 
     The pilots transmitted upstream in resource blocks can be used by a CMC (or CLT) for acquiring the frequency of carriers transmitted upstream from a CNU and/or for estimating the upstream channel between the CMC (or CLT) and CNU. To be able to effectively perform frequency acquisition and/or channel estimation (or even some other function), resource block types can be positioned within upstream data frames in accordance with particular pilot rules. In one embodiment, the pilot rules include using type-2 resource blocks on the boundaries of upstream data frames, the edges of an area of excluded sub-carriers, and the first and last resource block in an upstream transmission burst. 
       FIG. 9  illustrates an example upstream data frame  900  that adheres to these pilot rules in accordance with embodiments of the present disclosure. In particular, at the two upstream frame boundaries  902  and  904  of upstream data frame  900 , a type-2 resource block is used. In addition, at the edges  906  and  908  of an area of excluded sub-carriers  910 , a type-2 resource block is used. 
     In the remaining resource blocks of upstream data frame  900 , an example pilot pattern is used. In particular, type-1 and type-2 resource blocks are alternately used every 4 th  resource block in upstream data frame  900  with type-0 resource blocks used in between. The pilot pattern specifically begins at the bottom of upstream data frame  900  with a type-2 resource block, and does not interfere with the adherence of any of the pilot rules detailed above. 
     The example pilot pattern shown in upstream frame  900  is shown for exemplary purposes only. Other pilot patterns can be used in an upstream frame, such as upstream frame  900 , as would be appreciated by one of ordinary skill in the art. To further be able to effectively perform frequency acquisition and/or channel estimation (or some other function), the CMC (or CLT) can configure the particular pilot pattern used in an upstream data frame, such as upstream data frame  900 . For example, the CMC (or CLT) can configure the particular pilot pattern such that a type-1 resource block is to be used every x resource blocks of the plurality of resource blocks in the upstream data frame and a type-2 resource block is to be used every y resource blocks of the plurality of resource blocks in the upstream data frame, where x and y are integers. In one embodiment, CNU interface  330  in  FIG. 3  is used to construct upstream data frame  900 . 
       FIG. 10  illustrates another example upstream data frame  1000  that adheres to the above described pilot rules in accordance with embodiments of the present disclosure. In particular, at the two upstream frame boundaries  1002  and  1004  of upstream data frame  1000  and the edges  1006  and  1008  of an area of excluded sub-carriers  1010 , a type-2 resource block is used. In addition, a type-2 resource block is used on the first and last resource block in the upstream transmission burst  1012 , which is delineated by a dark rectangle. Upstream transmission burst  1012  represents a portion of upstream data frame reserved by a CMC (or CLT) for upstream transmissions from a particular CNU. 
     In the remaining resource blocks of upstream data frame  1000 , the same example pilot pattern in upstream frame  900  in  FIG. 9  is used. Again, it should be noted that the example pilot pattern shown in upstream frame  1000  is shown for exemplary purposes only. Other pilot patterns can be used in an upstream frame, such as upstream frame  1000 , as would be appreciated by one of ordinary skill in the art. In one embodiment, CNU interface  330  in  FIG. 3  is used to construct upstream data frame  1000 . 
     VI. Example Computer System Environment 
     It will be apparent to persons skilled in the relevant art(s) that various elements and features of the present disclosure, as described herein, can be implemented in hardware using analog and/or digital circuits, in software, through the execution of instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software. 
     The following description of a general purpose computer system is provided for the sake of completeness. Embodiments of the present disclosure can be implemented in hardware, or as a combination of software and hardware. Consequently, embodiments of the disclosure may be implemented in the environment of a computer system or other processing system. An example of such a computer system  1100  is shown in  FIG. 11 . Elements depicted in  FIGS. 1-4  may execute on one or more computer systems  100 . Furthermore, each of the steps of the processes depicted in  FIG. 5  can be implemented on one or more computer systems  1100 . 
     Computer system  1100  includes one or more processors, such as processor  1104 . Processor  1104  can be a special purpose or a general purpose digital signal processor. Processor  1104  is connected to a communication infrastructure  1102  (for example, a bus or network). Various software implementations are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the disclosure using other computer systems and/or computer architectures. 
     Computer system  1100  also includes a main memory  1106 , preferably random access memory (RAM), and may also include a secondary memory  1108 . Secondary memory  1108  may include, for example, a hard disk drive  1110  and/or a removable storage drive  1112 , representing a floppy disk drive, a magnetic tape drive, an optical disk drive, or the like. Removable storage drive  1112  reads from and/or writes to a removable storage unit  1116  in a well-known manner. Removable storage unit  1116  represents a floppy disk, magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive  1112 . As will be appreciated by persons skilled in the relevant art(s), removable storage unit  1116  includes a computer usable storage medium having stored therein computer software and/or data. 
     In alternative implementations, secondary memory  1108  may include other similar means for allowing computer programs or other instructions to be loaded into computer system  1100 . Such means may include, for example, a removable storage unit  1118  and an interface  1114 . Examples of such means may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, a thumb drive and USB port, and other removable storage units  1118  and interfaces  1114  which allow software and data to be transferred from removable storage unit  1118  to computer system  1100 . 
     Computer system  1100  may also include a communications interface  1120 . Communications interface  1120  allows software and data to be transferred between computer system  1100  and external devices. Examples of communications interface  1120  may include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via communications interface  1120  are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface  1120 . These signals are provided to communications interface  1120  via a communications path  1122 . Communications path  1122  carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels. 
     As used herein, the terms “computer program medium” and “computer readable medium” are used to generally refer to tangible storage media such as removable storage units  1116  and  1118  or a hard disk installed in hard disk drive  1110 . These computer program products are means for providing software to computer system  1100 . 
     Computer programs (also called computer control logic) are stored in main memory  1106  and/or secondary memory  1108 . Computer programs may also be received via communications interface  1120 . Such computer programs, when executed, enable the computer system  1100  to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor  1104  to implement the processes of the present disclosure, such as any of the methods described herein. Accordingly, such computer programs represent controllers of the computer system  1100 . Where the disclosure is implemented using software, the software may be stored in a computer program product and loaded into computer system  1100  using removable storage drive  1112 , interface  1114 , or communications interface  1120 . 
     In another embodiment, features of the disclosure are implemented primarily in hardware using, for example, hardware components such as application-specific integrated circuits (ASICs) and gate arrays. Implementation of a hardware state machine so as to perform the functions described herein will also be apparent to persons skilled in the relevant art(s). 
     VII. Conclusion 
     Embodiments have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein, for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. 
     The foregoing description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.