WO2014063014A1 - TIME DIVISION DUPLEXING FOR EPoC - Google Patents

Abstract

A method, system, and computer program for implementing an EPoC network, and especially a Time-Division Duplex (TDD) variant. Multiple Subordinate MAC & PHY-layers for coax (120, 132) or HFC segments convey downstream traffic (114) from, and/or upstream traffic (140) to, an OLT (100) or CLT (156), wherein the scheduling of said conveyance over coax is subordinate to said downstream (114') and/or upstream traffic (140').

Description

TIME DIVISION DUPLEXING FOR EPoC

RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional

Applications Nos. 61/715,381, filed October 18, 2012, and 61/715,380, filed October 18, 2012, assigned to assignee hereof the specification of which is incorporated herein by reference herein.

[0002] The present application is related to co-pending U.S. Patent

Applications, Ser. No. 13/890,1 15, filed on May 8, 2013, and co-pending international Application, Ser. No. PCT/US 13/54500, filed on August 12, 2013, assigned to the assignee hereof and expressly incorporated by reference herein.

FIELD

[0003] This disclosure is related to a communication system and more

particularly to extending Ethernet Passive Optical Networks (EPON) Protocol over Coax based access networks.

BACKGROUND INFORMATION

EPON

[0004] EPON is an IEEE 802.3 protocol specification enabling Ethernet Passive Optical Networks. Passive Optical Networks (PONs) use an Optical Distribution Network (ODN) generally using passive fiber-optic cables and passive optical splitters forming a pomt-to-multipomt topology. EPON is often deployed by Operator/Semce Providers (OSPs) as an Access Network, to provide high-speed access to the internet backbone and Business Services for medium-to-large businesses seeking strict Quality of Service (QoS) Se dee Level Agreement (SLA) contracts including low-latency, low-jitter, and guaranteed throughput. Typically there is an Optical Line Terminal (OLT) at the headend (e.g., located in an OSP's centra! office site), and there is an Optical Network Unit (ONU) at each of one or more Customer Premise Equipment (CPE) endpoint sites. The service group for an EPON OLT often comprises up to 16-32 ONUs. The headend OLT can send messages Downstream (DS) over the ODN pomt-to-muitipoint, and the ONUs at the CPE endpoints can send messages to the OLT multipoint-to-point over the ODN. The OLT produces downstream messages in the form of serial binary bitstreams that are converted to optical signals (e.g., OO On-Off-Keying pulses produced by so-called 'digital ' laser) onto a fiber-optic cable and into the ODN to reach each ONU at the CPE endpoints. The ODN generally comprises passive optical components, so substantially the same optical signals reach all the ONUs. However, due to ODN topology (e.g., lengths of fiber and location of splitters), there are generally differences in propagation times among all the branches in the ODN, often resulting in differing arrival times and differing arrival amplitudes of the optical signal among all the ONUs.

[0005] The OLT produces the downstream serial bitstream at some constant EPON data-rate, such as IGbps or 1 OGbps. If there are no messages to send downstream, then the OLT will transmit IDLE characters between data traffic Thus, EPON downstream traffic is a continuous bitstream at some constant EPON data-rate.

[0006] Upstream (US) transmissions are formed by ONUs as a serial binary bitstream, but are generally not continuous, so upstream traffic from a plurality of ONUs is coordinated by the OLT in order to ensure that non- continuous so-called burst transmissions from various ONUs do not collide (overlap in time) and that the OLT will observe an orderly sequential arrival of burst transmissions from different ONUs in a predictable order and at predictable times (within some tolerance of time-jitter). This approach is often called Time-Division Multiple Access (TDMA)

[0007] There are three versions of EPON currently specified:

IGbps svonmetric (formerly amendment 802.3ah);

l OGbps symmetric (amendment 8()2.3av~2()09); and

Asymmetric IGbps upstream, lOGbps downstream (802.3av-2009).

[0008] Upstream (US) traffic generally uses the same wavelength for both IGbps and lOGbps data-rates. Downstream (DS) traffic generally uses different optical wavelengths for IGbps and lOGbps data-rates. It can be deduced that there is interest in supporting both symmetric and asymmetric upstream/downstream data-rates .

[0009] Since EPON's upstream traffic and downstream traffic use different wavelengths, bitstreams can be transmitted over the ODN in both directions simultaneously and independently (i.e., full duplex). This particular duplexing strategy is called Wavelength Division Duplex (WDD), or more generally, Frequency Division Duplex (FDD). The OLT has exclusive use and access to the downstream wavelength(s), and the OLT can coordinate/schedule use of the upstream wavelength independently from the downstream.

[0010] OLTs use EPON's Multipoint Control Protocol (MPCP) to coordinate and schedule the TDMA upstream bursts. The MPCP protocol relies on constant Round-Trip Time (RTT) as observed and measured by the OLT. The OLT may measure a different RTT for each ONU, but that RTT must remain more or less constant (within some tolerance). MPCP messages include timestamps to facilitate OLT's measurement of RTT. Each GNU maintains its own MPCP clock by setting its clock counter value to that of the OLT's times tamp embedded in downstream MPCP messages received from the OLT. Since fibers to each ONU may have varying length, the MPCP Clocks among different ONUs are not necessarily synchronized. The RTT comprises a downstream trip plus an upstream trip, which may be different (e.g., different wavelengths may propagate at different velocities on a fiber). The OLT will observe/measure RTTs, but may also know (e.g., be configured for) or assume some fractional split (e.g., 50%: 50%) of the RTT into separate downstream and upstream link delays. 1 1] ONUs hold traffic destined for the OLT in various queues often associated with particular Semce Flows (e.g., an ordered sequence of Ethernet Frames with similar classification), and identified by Logical Link Identifiers (LLIDs) assigned by the OLT. ONUs report the status (e.g., ful lness) of their various upstream queues in the form of a MPCP REPORT message. The OLT receives such REPORTS from the ONUs, then the OLT's MAC Control Client (aka Scheduler) schedules upstream traffic from the various queues of various ONUs, then issues TDMA grants to particular ONUs in the form of MPCP GATE messages. All upstream traffic is scheduled or granted in this fashion, even REPORT messages must be granted via a GATE message in the downstream. GATE messages grant a startTime and a length. When an ONU's MPCP Clock reaches the GATE-specified startTime, the ONU transmits upstream at the constant EPON data-rate, from the GATE-specified LLID queue, and for a duration equal to the GATE-specified length. The GATE-specified grant yields an upstream transmission of some integer number of Layer 2 payload bytes (the exact number of bytes is known to both ONU transmitter and OLT receiver), which usually corresponds to some integer number of variably sized Ethernet Frames. [0012] The OLT's scheduler arranges the grants, ensuring the OLT will observe an orderly sequential arrival of burst transmissions from a plurality of ONUs, arriving in a predictable order and at predictable times (within some tolerance of time-jitter). The OLT's scheduler understands that grants will depend on the TT for each particular ONU, For example, the OLT could transmit downstream two GATE messages with identical startTime and identical short grant length, destined for two different ONUs, one with 1km effective fiber length, and the other with 20km effective fiber length;

understanding that the consequent upstream transmissions will not overlap/collide with each other, due to their differing RTTs (i.e., the upstream transmission from the more distant ONU will arrive after that from the nearby ONU).

[0013] In summary, EPO protocols were designed around assumptions based on FDD simultaneous US and DS optical fiber transmission:

a) serial bitstream emissions from Layer 2 submitted into Layer 1 of a transmitting device;

b) serial bitstream undergoing constant processing delay through Layer 1 of the transmitter (Tx);

c) serial bitstream undergoing constant propagation delay through the ODN;

d) serial bitstream undergoing constant processing delay through Layer 1 of a receiving device;

e) received serial bitstream being submitted to Layer 2 of a receiver (Rx);

f) resulting in a constant US link delay for a given serial bit, from ONU Tx Layer 2 to OLT Rx Layer 2;

g) resulting in a constant DS link delay for a given serial bit, from OLT^' Tx Layer 2 to ONU Rx Layer 2; h) US + DS link delays summing to a constant RTT, bit-for-bit, as observed/measured by the OUT.

[0014] There are other PON specifications, such as APON, BPON, and

GPON, which share many of the same characteristics as EPON so this disclosure applies to them as well.

HFC Access Networks

[0015] A publicly avail able overview of hybrid fiber and coaxial (HFC) Cable Systems (e.g., slides 5 & 6) can be found at:

http://www.ieee802.org,^/3/epoc/public/marl 2/schmitt_01_0312.pdf. HFC Cable Access Networks are typically deployed by Multiple System Operators (MSOs), which are OSPs that operate multiple HFC cable systems. They are used to provide subscribers access to a variety of services, such as pay television (TV), video on demand (VoD), voice over internet protocol (VoIP) telephony, residential cable modem internet service, and small-medium business (SMB) Business Class Internet service. These various services have been designed, and the plants engineered, to support simultaneous coexistence on the shared HFC medium. The point-to-multipoint topology deployed varies according to the si ze and footprint of the service group of CPEs, and how distant they may be from the headend (or Hub), For example, in China, the sendee group is often a multiple dwelling unit (MDU) with dense concentration of the CPEs in the semce group, and relatively short distance to the headend often located in the basement (e.g., Fiber-to-ttie- Basement (FTTB)). For example, in North America, the semce group may be larger and more dispersed (e.g., spanning suburban neighborhoods), and the headend might be remotely located (e.g., tens of miles away). [0016] CPE endpoints are connected via coax (coaxial cable), and the coax plant is driven by one or more Radio Frequency (RF) amplifiers passing a variety of modulation techniques depending on the paxticular sendee and its assigned spectral occupation in the RF band (typically within 5~1002MHz). Smaller plants can be serviced by coax alone, so the headend can interface the coax plant directly. Remote iieadends can drive the HFC via fiber, with Fiber Nodes deployed at various locations in the middle of the network to convert to/from fiber and coax. These 'analog' fiber plants in HFC networks are typically driven by 'analog' lasers, modulating the amplitude of the optical signal in direct correspondence to an RF signal waveform (i.e., amplitude modulation (AM)). Fiber Nodes perform a relatively direct media conversion:

DS: from RF -modulated optical signal on fiber to RF^' electrical signal on coax to the CPEs;

US: from RF electrical signal on coax to RF-modulated optical signal on fiber to the headend;

where imperfect Optical-to-Electrical (OE) and Electrical-to-Optical (EO) conversions, along with AM transmission over fiber, contribute impairments to the RF signal fidelity (e.g., degradation of Signal-to-Noise Ratio (SNR)).

[0017] The topology of the coax plant is a cascade of various active and

passive components, such as amplifiers, rigid trunk-line coax, feeder-line coax, multitaps, drop-line coax (to individual customer premises), and RF splitters. Cascade lengths vary from:

a) Node+G' cascades: with zero active components (e.g., no inline amplifiers) after the Fiber Node (if any), meaning the coax plant contains only passive elements (e.g., taps or splitters). Node+0 plants are quite common in China. Th ey are less common among North America MSOs, but remain a goal for the future evolution of their HFCs. b) Node+1 : with one active amplifier after the Fiber Node (if any);

c) Node+2: with two active amplifiers after the Fiber node (if any);

d) Node+N: with N amplifiers (e.g., Node+5 cascades are common among North American MSOs' HFCs).

[0018] Many HFC plants have been deployed with FDD operation within certain frequency bands, using diplex filters installed throughout the HFC infrastructure (e.g., within various RF amplifiers). This FDD infrastructure was often d eployed decad es ago, before the advent of widespread internet use, and MSOs now find their existing split locations to restrict future use cases. In particular, MSOs are studying the possibility of moving the split location to allocate additional spectrum for the upstream channel. Moving the split is an expensive and labor-intensive upgrade that may require thousands of truckrolls to deploy (and with consequent service disruptions), so MSOs tr to anticipate the evolution of future usage. Predicting the future presents its own risks if the MSO's guess is wrong, but this is the predicament that MSOs find themselves in after having FDD and HFCs already deployed.

[0019] The coax plants of HFC networks in North America are often operated as FDD within US spectral allocations (typically 5~42MHz) and DS spectral allocations (typically from 54MHz up to 750, 860 or 1.002MHz as examples), with an allowance for a so-called 'Split' or guard band (typically 42~·54ΜΗζ) where FDD diplexing filters are used to isolate the simultaneous US & DS transmissions from each other. Coax plants of HFC networks outside North America might be operated with a different FDD split location in the spectrum. An example of a FDD service is Data Over Cable System Interface Specification (DOCSIS), wherein cable modem service may occupy one or more single-carrier 'QA ' (Identify QAM) channels occupying 6MHz of spectrum in the DS band, and one or more QAM channels in the US band. DOCS IS headend equipment is known as a Cable Modem Termination System (CMTS). DOCS IS CPEs include Cable Modems, Residential Gateways and Set-Top Boxes.

[0020] As subscribers consume more and more throughput capacity in both upstream and downstream directions, MSOs have lashed more and more fiber overlaying the existing coax frastructure in order to locate additional Fiber Nodes deeper into the cascade. This has the effect of segmenting the cascade, thereby reducing the service group size such that each subscriber competes with fewer neighbors for shared coax resources, resulting in greater throughput capacity available to CPEs. DOCSIS revisions, such as version 3.1, continue to improve capacity to address the seemingly inevitable migration to 'All-IP' (Internet Protocol packetized) delivery, including video.

EPoC: EPQN Protocol over Coax

[0021 ] MSOs currently must deploy fiber to the premises to support EPQN for high-end Business Services subscribers. This often involves digging trenches or other significant cable-laying expenses, even if those customer premises are already passed by the coax plant of a SO's HFC network. The MSO may already offer Business Class Internet (DOCSIS) services over the existing HFC plant, but some subscribers will, require strict QoS performance (such as that described by the Metro Ethernet Forum specification MEF-23.1) SLAs that may require EPON to satisfy. Consequently, MSOs desire an invention that would reduce expenses by enabling deployment of EPON-class QoS to subscribers without having to deploy fiber to the premises, but instead utilizing the existing HFC plant, or the coax portion of the HFC plant. In addition, EPON OLTs are significantly less expensive than DOCSIS CMTSs, which can further reduce MSO expenses. Thus, EPoC represents a desire for MSOs to have a lower-cost option of using the existing HFC medium for EPON-like services.

[0022] MSOs also desire that EPoC devices be manageable in some similar way as they manage EPON (e.g., DPoE DOCSIS Provisioning of EPON specification from CableLabs). Consequently, there is a desire to maintain most/all of EPON's layers and sublayers above Layer 1 PHYsical layer. Most particularly, the IEEE EPoC effort seeks to preserve unchanged EPON 's Ethernet Medium Access Control (MAC) Sublayer within Layer 2, and to make only 'minimal augmentation' of other sublayers in Layer 2 (e.g., in the MPCP sublayer) and higher layers (such as Operations, Administration, and Management (OAM)), by confining most of the new RF coax protocols to a Layer 1 PHY specification. MSOs believe that end-to-end management of EPoC devices will be easier to accomplish if a single EPON MAC domain can span from OLT to EPoC CPEs. Consequently, there is a desire to make operation of EPoC CPEs transparent to the OLT. Since EPON protocols were designed around an FDD medium, and because North American MSOs have already deployed FDD HFCs, EPoC intends to support FDD over coax,

EPoC Architecture

[0023] EPoC CPEs, which connect directly to the coax plant 20, are called coax networking units (CNUs) 10, and are desired to resemble ONUs 12 at Layer 2 and above, as illustrated in Figs. 1 and 2. An un- augmented or minimally augmented EPON OLT 14 connects to fiber plant 1 at the headend. In one embodiment, an optical-coax unit (OCU) 18, aka FCU fiber- coax unit can be located somewhere in the middle that performs bidirectional conversions from EPON's 'digital' fiber 16 to RF coax 20. OCU 18 and its conversions are desired to be transparent to OLT 14 so that the OLT can remain un-augmented or minimally augmented. In the presently claimed invention, an OCU may filter-out DS payloads (based on LLID or some other criteria) that are not intended for CNUs residing on the coax that the OCU sendees. In other words, the digital fiber may cany payloads intended for ONUs, or intended for CNUs belonging to some other OCU, and it is desirable for OCUs to filter-out these payloads out before relaying DS traffic onto the RF coax in order to avoid unnecessary traffic from consuming coax resources.

SUMMARY

[0024] The presently claimed invention provides solutions to the problems raised above. EPoC specifically contemplates a new Coax Line Terminal (CLT) 22 device that would resemble an OUT, but instead interface via RF signals, either to the 'analog' fiber 24 at the headend of an HFC, or directly to the headend of an all-coax plant, as shown in Figs. 3 and 4.

[0025] Preserving the EPON MAC sublayer at both endpoints implies PHY- layer processing and transport of the serial bitstream with constant RTT, corresponding to the sum of the downstream and upstream link delays:

in the downstream, measured from emission by the CLT/OLT MAC sublayer, to submission to the EPON MAC sublayer in the C U; and,

in the upstream: measured from emission by the EPON MAC sublayer in the CNU, to submission to the CLT/OLT MAC¹ sublayer.

[0026] In EPoC, there may be alternative ways of measuring DS and US (and hence RTT) delays, such as measuring the difference in arrival times of Ethernet frames, instead of the usual bit-for-bit delay of the serial bitstream .

[0027] An FDD mode of operation for EPoC seems certain. In the FDD mode of operation, downstream traffic gets converted relatively directly by the OCU from WDD/FDD over digital fiber into FDD over RF coax. Such relatively direct conversion by the OCU is also known as Media Conversion (aka PFFY- level Repeater), since there is little complication beyond straightforward conversion from fiber medium to coax medium. Similarly, upstream burst traffic from CNUs gets converted by the OCU from FDD on coax to

WDD/FDD on digital fiber. In the FDD mode of operation, the OCU performs media conversions for both downstream and upstream traffic simultaneously, by using to two different RF channels over coax. Such PHY- layer Media Conversion can be accomplished with constant processing delay to satisfy EPON protocols' reliance on constant RTT.

[0028] However, many MSOs desire an additional TDD mode of operation for EPoC. Such a TDD mode seems quite challenging to specify because the EPON protocols that MSOs wish to preserve were specifically designed only for FDD's simultaneously available full-duplex US & DS channels. EPON protocols were not designed for alternative duplexing strategies, such as Time- Division Duplex (TDD), where a single wavelength or RF spectral channel- width would be used, altemating-in-time between upstream and downstream (half duplex). TDD's single half-duplex channel alternates between US and DS traffic, which implies the DS link would be unavailable during US traffic, resulting in fluctuating delays for DS traffic while waiting for the DS phase of the TDD Cycle and vice versa, resulting in fluctuating delays for US traffic while waiting for the US phase of the TDD Cycle. Further complicating the challenge of TDD operation are EPON constraints outlined above such as maintaining constant RTT, and the desire to preserve unchanged the MAC sublayer.

[0029] Despite these severe challenges, MSOs nevertheless wish to consider such a mode due to TDD's increased flexibility (compared to FDD) for adapting to the evolution of future US and DS traffic patterns. One benefit of TDD is that the symmetry or asymmetry of the US and DS capacities is a relatively simple (and possibly realtime) adjustment of the duty-cycle phasing of the TDD Cycle. Use of TDD in the Access Network would have enabled a more flexible way for MSOs to easily, quickly, and inexpensively adjust the relative throughput capacity of the upstream and downstream directions within a single spectral allocation, whereas FDD requires paired spectral allocations established by inflexible diplex filters distributed throughout the coax cascade. For a given total aggregate spectral allocation, TDD's single spectral allocation could be made as wide as the sum of FDD's paired allocations, enabling TDD's burst datarate capability in either direction being

approximately double that of FDD in either direction (for symmetric US and DS FDD allocations). Use of TDD in the A ccess Network would have enabled fewer or no splits in some coax plants.

[0030] The following presents a simplified summary of one or more

embodiments in order to provide a basic understanding of some aspects of such embodiments. This summary is not an extensive overview of the one or more embodiments, and is intended to neither identify key or critical elements of the embodiments nor delineate the scope of such embodiments. Its sol e purpose is to present some concepts of the described embodiments in a simplified form as a prelude to the more detailed description that is presented later.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The disclosed method and apparatus, in accordance with one or more various embodiments, is described with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict examples of some embodiments of the disclosed method and apparatus. These drawings are provided to facilitate the reader's understanding of the disclosed method and apparatus. They should not be considered to limit the breadth, scope, or applicability of the claimed invention. It should be noted that for clarity and case of illustration these drawings are not necessarily made to scale.

[0032] Fig. 1 is an illustration of an OLT to ONU fiber connection and an OCU conversion from a fiber to a coax for CNUs.

[0033] Fig. 2 illustrates the OCU conversion of Fig, 1.

[0034] Fig. 3 illustrates a new CLT that resembles the combination of an OLT plus an OCU that interfaces to an analog fiber.

[0035] Fig. 4 illustrates a CLT that connects directly to a coax.

[0036] Figs. 5 A and 513 illustrate an embodiment including Subordinate MAC and PHY layers for the coax segments,

[0037] Fig. 6 illustrates the communication and scheduling between the OLT and the OCUs and CNUs of the embodiments of Figs. 5 A and 5B.

[0038] Fig. 7 illustrates a preferred embodiment wherein the single TDD Cycle of additional upstream latency for a subordinate request/grant cycle is no longer suffered.

[0039] Fig. 8 depicts an embodiment of proportional mapping applied to downstream traffic over FDD coax.

[0040] Fig. 9 illustrates an example embodiment enabling reduction of time- iitter. [0041] Figs. 10A and 10B depict an embodiment of proportional mapping for TDD downstream.

[0042] Fig. 11 depicts proportional mapping for upstream traffic via FDD coax.

[0043] Figs. 12A and 12B depict an embodiment teaching proportional

mapping for upstream TDD traffic.

[0044] Fig. 13 shows the preferred embodiment of discovery of TDD CNUs, and the new TDD CNU Discovery Window.

[0045] The figures are not intended to be exhaustive or to limit the claimed invention to the precise form disclosed. It should be understood that the disclosed method and apparatus can be practiced with modification and alteration, and that the invention should be limited only by the claims and the equivalents thereof.

DETAI LED DESCRIPTION

[0046] Most state-of-the-art PHY-layers have no need, and make no attempt, to establish a constant DS delay time, constant US delay time, or constant RTT. These characteristics are largely unique to EPON networks. Current state of the art methods for guaranteeing these characteristics in EPON involve each PHY-layer establishing a constant delay time. Consequently, the EPON RTT includes a sequence of additive delay times, each of which may be different, but each held constant, summing to some constant RTT. Applying these same methods to EPoC would be appropriate for a FDD mode of operation, where the US delay would include:

a) fixed delay through the CNU PHY onto coax;

b) a fixed propagation delay over coax; and c) followed by another fixed delay through the CLT PHY.

[0047] Correspondingly, the DS delay would comprise:

a) fixed delay through the CLT PHY onto coax;

b) a fixed propagation delay over coax; and

c) followed by another fixed delay through the CNU PHY.

[0048] These fixed delay times for US and DS would sum to produce a fixed RTT, as required for EPoC.

[0049] However, these same methods would be problematic for a TDD mode of operation in EPoC that satisfies MSOs' desire to re-use existing EPON OLTs with little or no augmentation. In this case, an EPON OLT would be largely unaware of the coax segments, or that the coax is operated as TDD, having new PHY-iayers for EPoC hiding the complexity of TDD and its delays from the OLT, yet maintaining some constant RTT for each CNU. Each CNU can have a different RTT, but each of those RTTs must remain constant. TDD operation generally involves having some traffic suffer a wait until an appropriate phase of the TDD Cycl e is available for transmission. Since traffic ingress generally arrives or otherwise become available asynchronously, at any time, its delay suffered waiting for a TDD Cycle phase is not constant, but variable. Such variable delays are the antithesis of EPON, and the current state of the art for EPoC, where a transmitting PHY establishes a fixed delay onto coax and a separate fixed delay is established by a receiving PHY.

[0050] The DS and US channels each are comprised of several links and

paths. For example, the DS channel may comprise all or some of: the OLT's Tx PHY, the digital fiber ODN, the OCU's fiber Rx PHY (similar to an ONU's Rx PHY), the OCU's coax Tx PHY, the coax cable plant, and the CNU's coax Rx PHY. Conversely, the US channel may comprise the corresponding path links but in reverse direction: CNU's coax Tx PHY, the coax cable plant, the OCU's coax Rx PHY, the OCU's fiber Tx PHY (similar to an ONU's Tx PHY), the digital fiber ODN, and the OLT's Rx PHY. For EPoC configurations using a CLT (instead of an OLT and one or more OCUs) the DS channel may comprise: the CLT's coax Tx PHY, the coax cable plant, and the CNU's coax Rx PHY, as well as the converse US channel comprising: the CNU's coax Tx PHY, the coax cable plant, and the CLT's coax Rx PHY,

Subordinate MAC and PHY layers

[0051 ] Figs. 5 A and 5B shows an embodiment wherein a minimally

augmented EPON OLT 100 schedules and transmits downstream traffic 102 over fiber 104 to an OCLI 106, and OLT 100 also schedules and receives upstream traffic 108 via fiber 110 from (M l 106. OCU's EPON PHYs 112 receive OLT's downstream traffic via fiber 104, and transmit upstream traffic to OLT via fiber 110. Fiber 104 and fiber 110 may in fact be different wavelengths on the same fiber optic cable. Downstream serial bitstream 114" ingressing from OCU's EPON PHY 112 is timestamped 116 before being temporarily stored in a Downstream Ingress Buffer 118. Subordinate MAC 120 observes the fullness of Downstream i ngress Buffer 118, then schedules and transmits via coax PHY 150 over coax 122 that traffic. The downstream traffic propagates over the coax plant to one or more CNUs 124. The CNU PHY 146 and MAC 132 receive the downstream traffic and temporarily store it in a Downstream Egress Buffer (DEB) 128. Downstream serial bitstream ί 14" is reconstructed by metering traffic out of Downstream Egress Buffer 128 according to the downstream timestamps and DS Knob 130, which controls the overall downstream delay through the EPoC PHY for CLT 158 and EPoC PHY for CNU 126. Downstream serial bitstream 114" in the CNU is metered to a minimally augmented EPON ONU M AC 134 for relay to its output interfaces 136 (e.g., Ethernet links to subscribers). Upstream traffic from subscriber premises is queued in the minimally augmented EPON ONU MAC 134. The upstream serial bitstream 140' in CNU 124 from queues 138 is upstream timestamped 142 before being temporari ly stored in Upstream Ingress Buffer 144 in CNU 124. Subordinate MAC in the CNU 132 receives scheduling grants from Subordinate MAC¹ in the OCU 120 by which

Subordinate PHY in the CNU 146 can transmit upstream traffic from upstream ingress buffer 144, propagating over coax 122, to the Subordinate PHY 150 in the OCU 120. Subordinate MAC in the OCU 120 temporarily stores upstream traffic 140" in Upstream Egress Buffer 152. Upstream serial bitstream 140'^'" is reconstructed by metering traffic out of Upstream Egress Buffer 152 according to the upstream timestamps and US Knob 154, which controls the overall upstream delay through the EPoC PHY for CNU 126 and EPoC PHY for CLT 158. Upstream serial bitstream MO"' in OCU 106 is transmitted over fiber 110 to the minimally augmented OLT 100 via EPON PHYs 112.

[0052] Still referring to Figs. 5A and 5B, an alternative embodiment

comprises an optional CLT 156 at the headend, which substantially resembles the combination of an OLT plus an OCU, although in a CLT embodiment the fiber segment is not necessarily required because the OLT and OCU may be more directly connected in close proximity to each other.

[0053] As shown in Fig.5, EPoC PHY for CNU 126 comprises a Subordinate MAC and PHY for the CPE ends of the coax plant 132. The minimally augmented OLT 100 and minimally augmented EPON ONU MAC 134 may- remain substantially unaware of the Subordinate MAC and PHY layers over coax 120 and 132. In other words. Subordinate MAC and PHYs over coax 120 and 132 are substantially transparent to minimally augmented OLT 100 and EPON ONU MAC 134. Similarly, OCU 106 and EPoC PH ^{^} for CLT 158, and EPoC PHY for CNU 126, and their Subordinate MAC and PHY over coax 120 and 132, are also substantially transparent to the minimally augmented OLT 100 and EPON GNU MAC 134.

[0054] Variable downstream delays 160 are suffered through the Subordinate MAC & PHY in the OCU 120 and/or EPoC PHY for CLT 158, for example due to dwell time in Downstream Ingress Buffer 118 while waiting for the downstream phase of the TDD Cycle and waiting for the Subordmate MAC to schedule downstream traffic over coax, or due to block processing the in Subordinate PHY layers over coax. The actual propagation of downstream traffic over coax comprises a constant delay. Consequently, in order to establis a constant coax downstream delay 162, EPoC PHY for CNU 126 and its Subordinate MAC & PHY 132 must implement downstream delays, which are complementary 164 to variable downstream delays 160. DS Knob 130 controls the establishment of complementary downstream delays 164, and hence controls constant coax downstream delay 162. Whenever there is no downstream traffic being metered from Downstream Egress Buffer 128, IDLE characters 166 may be multiplexed into downstream serial bitstream 114" to EPON ONU MAC¹ 134.

[0055] Again, referring to Figs. 5 A and 5B, variable upstream delays 168 are suffered through the Subordmate MAC & PHY in the CNU 132 and/or the EPoC PHY for CNU 126, for example due to dwell time in the Upstream Ingress Buffer 144 while waiting for the upstream phase of the TDD Cycle and waiting for the Subordmate MACs 120 and 132 to schedule upstream traffic over coax, or due to block processing in the Subordinate PHY layers over coax. The actual propagation of upstream traffic over coax comprises a constant delay 176. Consequently, in order to establish a constant coax upstream delay 174, the EPoC PHY for CLT 158 and its Subordinate MAC & PHY 120 must implement upstream delays, which are complementary to the variable upstream delays 168. US Knob 154 controls the establishment of complementary upstream delays 172, and hence controls constant coax upstream delay 174.

[0056] In one embodiment, DS Knob control 130 establishes an overall

downstream delay, and/or the US Knob control 154 establishes an overall upstream delay. For example, timestamped downstream traffic 116 carries some header or other indication of the timestamped time of arrival at

Downstream Ingress Buffer 118, and DS Knob control 130 establishes the overall delay to emission from Downstream Egress Buffer 128 (e.g., constant delay from serial bit entering the EPoC PHY for CLT 158, to the same serial bit emitted from EPoC PHY for CNU 126, including the downstream propagation delay on coax 170). Similarly, in another embodiment, for example, timestamped upstream traffic 142 carries some header or other indication of the timestamped time of arrival at the Upstream Ingress Buffer 144, and the US Knob control 154 establishes the overall delay to emission from the Upstream Egress Buffer 152 (e.g., constant delay from serial bit entering the EPoC PHY for CNU 126, to the same serial bit emitted from EPoC PHY for CLT 158, including the upstream propagation delay on coax 176).

[0057] In another embodiment, DS Knob control 130 establishes a delay for the sum of both EPoC PHY for CLT 158 plus EPoC PHY for CNU 126, but NOT including the downstream propagation delay on coax 170. For example, timestamped downstream traffic 116 carries some header or other indication of the Lateness (e.g., variable delays 160) suffered in the EPoC PHY for CLT 158. As another example, timestamped downstream traffic 116 carries some header or other indication of the Complementary Delays 164 to be established by the EPoC PHY^" for CNU 126 (i.e., to complement variable delays 160 suffered in the EPoC PHY for CLT 158). Similarly, for the upstream, the US Knob control 154 establishes a delay for the sum of both EPoC PHY for CNU 126 plus EPoC PHY for CLT 158, but NOT including the upstream

propagation delay on coax 176. For example, timestamped upstream traffic 142 carries some header or other indication of the Lateness (e.g., variable delays 168) suffered in the EPoC PHY for CNU 126. As another example, timestamped upstream traffic 142 carries some header or other indication of Complementary Delays 172 to be established by the EPoC PHY for CLT 158 (i.e., to complement variable delays 1 8 suffered in the EPoC PHY for CNU 126).

[0058] Still referring to Figs. 5 A and 5B, the optical propagation over fiber, if present, comprises a constant fiber downstream delay 178, and a constant fiber upstream delay 180. Consequently, OLT 100 observes a constant RTT 182, comprising constant fiber downstream delay 178, plus constant coax downstream delay 162, plus constant coax upstream delay 174, plus constant fiber upstream delay 180. RTT 182 observed and measured by OLT 100 may be different for each CNU 124 (e.g., depending on the length of coax over which traffic must be conveyed, and depending on the design &

implementation of the Subordinate MAC & PHYs), or the RTT observed and measured by OLT 100 might be the same for each CNU 124 (e.g., depending on the design & implementation of the Subordinate MAC & PHYs).

[0059] As shown in Figs. 5 A and 5B, PLL 184 depicted in OCU 106 or EPoC PHY for CLT 158 comprises establishment of the proper timing of the upstream serial bitstream 140^m for OLT 100, for example being synchronized to the same bitrate as downstream serial bitstream 114' from OLT 100, or being synchronized to 1/10* the bitrate in cases such as asymmetric IGbps upstream, lOGbps downstream (802.3av~2009). An alternative embodiment establishes an MPCP clock in OCU 106 or EPoC PHY for CLT 158 for substantially the same purpose. Whenever there is no upstream traffic being metered from Upstream Egress Buffer 152, IDLE characters 188 may be multiplexed, into upstream serial bitstream 140"' to OLT 100.

[0060] Still referring to Figs. 5A and 5B, Subordinate MAC & PHY-layers for coax 120 and 132 optionally maintain their own Coax Time Clock (CTC) 1 0 and 192, shared between the MAC & PHY on the OCU/CLT headend side of the coax plant, and the coax MAC¹ & PHY layers in the CNUs on the CPE ends of the coax plant. When such a CTC 190 and 192 of sufficient quality is available, it can be used in the tirnestamping and egress metering of the downstream and upstream serial bitstreams. Alternative embodiments use MPCP or XTAL clocks 186 for substantially the same purpose. For example, the clock 186 used for metering downstream serial bitstream out of

Downstream Egress Buffer 128 can be MPCP, XTAL, CTC or other suitable clock.

[0061 ] Still referring to Fig.5, GATE Decrypt block 194 depicted adjacent to Subordinate MAC in the OCU 120 or EPoC PHY for CLT 158 allows the Subordinate MAC to optionally access, decrypt if necessary, and process the OLT's GATE grants, even if they were encrypted by OLT 100. OLT 100 may apply encryption which is common to its various GATE messages, or OLT 100 may apply encryption which is specific (e.g., per LLID) to some GATE messages, or OLT 100 may not apply encryption to some G ATE messages. If G ATE messages are encrypted (e.g., per LLID), and the Subordinate MAC & PHY in the OCU 120 or EPoC PHY for CLT 158 does not otherwise have access to the cryptographic key information needed to decrypt those GATE messages, then the Subordinate MAC & PHY 120 obtains the cryptographic key information from the intended CNU(s), from the OLT, or from the CLT, e.g., through some Authenticated Key Exchange (AKE), as is known to someone skilled in the art. In a preferred embodiment, the Subordinate MAC 120 obtains the cryptographic key information (e.g., per LLID) via AKE with its Subordinate MAC & PHY(s) in those intended CNU(s) 132. In any case, the Subordinate MAC 120 optionally has access to the content of OLT's GATE grants intended for its CNUs, which enables the Subordinate MAC on the OCU/CLT side to predict upstream traffic 140^f from CNUs even before it arrives in Upstream Ingress Buffers 144 of the CNUs, The prediction includes not only the amount of upstream traffic 140' to expect from each CNU, but also when to expect it. This optional access to GATE messages provides the benefit of the Subordinate MAC pre-scheduling upstream traffic to reduce upstream latency. The alternative embodiment would instead wait (i.e., incurring additional latency) for upstream traffic 140' to fill the CNUs' Upstream Ingress Buffers 144 before the Subordinate MAC responds by scheduling that upstream traffic over the coax PHY. 2] The presently described embodiment enables the Subordinate MAC & PHY to re-schedule downstream and upstream traffic over coax, and in a manner specific to the Subordinate MA ' & PHY link over coax but in subordinate accordance with the OLT's own expectations for: a) timely delivery of O LT's downstream traffic 114 to minimally augmented EPON ONU MACs 134 in each CNU; and, b) timely reception at OLT of GATE- specified upstream traffic 140 from minimally augmented EPON ONU M ACs 134 in each CNU. A specific benefit of this embodiment allows the traffic to be conveyed in a manner that is specifically optimized for transmission over coax, while remaining substantially transparent to OLT 100 and EPON ONU MAC 134, thereby NOT being burdened by the EPON's restrictive timing constraints (e.g., GATE-specified TDMA grants). Such optimizations for coax can include TDD or FDD. single carrier or multi-carrier, OFDM.

OFDMA, LDPC block-coding, frequency-domain interleaving, time-domain interleaving, aggregated scheduling (e.g., MAP messages), traffic aggregation, RF or baseband modulation, and the like. While the Subordinate MAC & PHY is free to use such coax-optimizations, it remains constrained primarily by the requirement that its scheduling be subordinate to that of the OLT's. in other words, the presently described embodiments teach that the Subordinate MAC & PHY must convey over coax the OLT's downstream traffic before that traffic is due to be metered out of Downstream Egress Buffer 128, and it must convey over coax EPO ONU MACs' 134 upstream traffic 140 ' and 140" before it is due to be metered out of Upstream Egress Buffer 152 as serial bitstream 140'" towards OLT 100. The Subordinate MAC & PHY may schedule more traffic than the OLT, or at least as much traffic as the OLT itself has scheduled, but if it schedules less traffic than the OLT, then the effect on the EPON network is equivalent to the disturbance of dropped traffic, or some error in traffic.

[0063] The presently described embodiments teach how the Subordinate MAC & PHY can be largely decoupled from that of the OLT and EPON ONU MAC. This benefit is so profound that someone skilled in the art will recognize that the described embodiments can be applied to adapt most any coax MAC & PHY^" solution to become a Subordinate MAC & PHY. The incorporate provisional application describes how MoCA can be used, or how a variant called MoCA Access (aka c.LINK Access) can be used, but a variety of other coax MAC & PHYs can also be adapted, such as DOCSIS, LiNoC, or possibly yet to be specified IEEE 802.3bn. Regardless of these various embodiments, this disclosure teaches that they remain subordinate to the OLT's downstream and upstream traffic schedules.

[0064] The presently described embodiments teach that the Subordinate MAC & PHY re-schedule traffic over coax. The OLT's downstream traffic can be reordered or aggregated or otherwise processed in some optimal way for efficient downstream conveyance over coax. Similarly, the upstream traffic can be reordered or aggregated or otherwise processed in some optimal way for efficient upstream conveyance over coax. Re-scheduling traffic over the coax link is beneficial not just for optimal conveyance, but also because EPON's GATE messages, as issued by the OLT, are substantially

inappropriate for scheduling allocation of resources of the Subordinate MAC & PHY or the coax plant. Consequently, some transposition or rescheduling is needed (or at least beneficial). Even if traffic is transmitted out-of-order over coax, the Egress Buffers will restore the proper order, as expected by EPON MACs, according to the complementary delays (e.g., derived from

timestamping information) , 5] Fig. 6 depicts an embodiment wherein: a) an OCU 106 relays the OLT's 100 GATE 200 messages to the intended CNU(s) 124 during a

Downstream Phase (DS) of the TDD Cycle 202; b) CNU(s) 124 respond to the Subordinate MAC in OCU 106 or EPoC PHY for CLT during a subsequent Upstream Phase (US) 204 of the TDD Cycle wi th Requests 206 for upstream transmit opportunities on coax (e.g., REPORT messages, or a RR Reservation Requests in MoCA, or Traffic Flags as described in METHOD AND

APPARATUS FOR IMPLEMENTING TRAFFIC FLAGS FOR LARGE SERVICE GROUPS, for which a U.S. provisional patent application was filed on March 21, 2012, under Serial No. 61/613,964, and a PCT patent application was filed on March 21 , 2013, under Serial No. PCT/U82Q 13/033329, incorporated herein by reference ; c) the Subordinate MAC in OCU 106 or EPoC PHY for CLT (e.g., a MoCA NC Network Coordinator) processes Request messages 206, thereby producing a schedule for a subsequent Upstream Phase 212 of the TDD Cycle on coax; d) the Subordinate MAC in the OCU 106 or EPoC PHY for CLT distributes its schedule for coax to CNU(s) 124 during a subsequent Downstream Phase (DS) 2Θ8 of the TDD Cycle in the form of Grants 210 (e.g., coax-specific GATE messages, or MA P Media Access Plan messages in MoCA); e) CNU(s) 124 receive coax Grants 210 and respond by transmitting their upstream traffic or payloads 214 over coax during a subsequent Upstream Phase (US ) 212 of the TDD Cycle according to schedule of Grants 210; f) OCU 106 relays upstream traffic 214 from CNU(s) 124 to OLT 100 in accordance with the presently described embodiments. Fig. 6 also depicts a single TDD Cycle of latency 216, comprising US phase 204, and DS phase 208, that is suffered while the Subordinate MAC & PHY conducts the US Request and DS Grant cycle to schedule upstream traffic from the CNU(s). This embodiment is beneficial when the Subordinate MAC in the OCU (or in EPoC PHY for CLT) does NOT have direct access to the content of GATE messages intended for CNUs under its control. 6] Fig. 7 depicts a preferred embodiment wherein the single TDD Cycle of additional upstream latency for a subordinate request/grant cycle is no longer suffered. This embodiment is beneficial when the Subordinate MAC in OCU 106 (or in EPoC PHY for CLT) has access to the content of GATE messages 218 intended for CNUs 124 under its control. Such access to content of GATE messages 218 is available when the GATEs are not encrypted, or if the Subordinate MAC in OCU 106 (or in the EPoC PHY for C LT) is somehow informed of the cryptographic key information from intended CNU(s) 124, or from the CLT, through some private messaging (e.g., ARE). In this embodiment, the Subordinate M AC in OCU 106 (or in the EPoC PHY for CLT), having access to GATE-specified foreknowledge of upstream traffic 140^? from queues 138 that the OLT or CLT has scheduled (and hence which upstream traffic will according!)' soon ingress into CNUs' Upstream Ingress Buffers (UIB)), is enabled to schedule coax grants 22Θ corresponding to conveyance of that upstream traffic 226 over coax, without suffering (e.g., a full TDD Cycle of) additional upstream latency for a subordinate request/grant cycle (see further explanation below). Please note that OCU's 106 direct transposition of GATEs 218 into GRANTS 220 of coax resources (e.g., MoCA M AP) eliminates the need for a full. TDD Cycle of additional upstream latency for a subordinate request/grant cycle. [0067] A specific benefit of the presently described embodiments enable the coax scheduler in the Subordmate MAC in OCU 106 (or in the EPoC PHY for CLT) to determine which particular GATE messages 218 from OLT 100 or CLT will produce upstream traffic payloads 226 from CNUs 124 that need to be subordinately scheduled in which particular TDD Cycles, such as during US phase 222. This benefit is important since OLT^' 100 or CLT^' can opt to send GATE messages 218 significantly in advance of the traffic startTime they schedule. For example, the scheduler's MAP message would reschedule on coax only upstream traffic whose GATEs yield upstream traffic 226 in the CNUs' Upstream Ingress Buffers ready for conveyance over coax during US phase 222. This association of particular GATEs 218 with particular TDD Cycles are complicated by the differences in MPCP clock counters among all the CNUs 124 under control of an OCU 106 (or EPoC PHY in CLT). An embodiment enables this association, wherein the CNUs 124 each inform the Subordinate MAC scheduler in OCU 106 (or EPoC PHY in CLT) of how to compensate for their individual clock differences (e.g., informing the difference between each CNU's MPCP Clock count, and the CTC Coax Time Clock count in that same CNU's Subordinate MAC & PHY).

[0068] A benefit of the presently described embodiment is enabling an OCU to identify that downstream traffic destined for the CNUs 124 under its own control, and discriminate other downstream traffic from OLT 100 destined for ONUs on the ODN, or destined for CNUs under control of some other QCLT on OLT's EPON network. Consequently, this enables the OCU's Subordinate MAC to reschedule and convey only that downstream traffic (e.g., via LLIDs) destined for its own CNUs 124. This benefit reduces the amount of downstream traffic requiring conveyance over the Subordinate MAC & PHY's coax link, thereby preserving limited coax resources, e.g., enabling smaller spectral allocations on coax, and/or enabling improved throughput, latency and QoS. In another embodiment, OLT 100 applies traffic shaping of either downstream and/or upstream traffic for substantially the same purposes (e.g., to avoid congesting the coax link or overflowing the Ingress Buffers). 9] Those skilled in the art will recognize that the presently described embodiment enables the Subordinate MAC to use any of a wide variety of mechanisms to re-schedule OLT's downstream traffic and upstream traffic over coax. For example: MAP messages (e.g., once per TDD Cycle, near the end of each downstream phase) from the coax scheduler in Subordinate MAC in the OCU/CLT that aggregate the coax grants for distribution to the

Subordinate MACs in the CNUs. For example: Individual coax grants per CNU, or per LLID, can be transposed and unicast to each CNU. The coax grants instruct CNUs how & when to transmit their upstream traffic over coax. In another embodiment, the Subordinate MAC in the OCU or EPoC PHY for CLT creates GATE messages intended specifically for the Subordinate MAC(s) in the CNU(s) that are created to substantially correspond with OLT's GATE messages sent to EPON ONU MAC in the same CNU(s) (e.g., the coax-specific GATE messages could schedule on coax the same upstream traffic that the OLT's corresponding GATE messages scheduled for the EPON ONU MAC(s)). Optionally, the grams or other scheduling messages may also inform the Subordinate MACs in the CNUs about how and when to expect their downstream traffic. Still other mechanisms are enabled, such as contention-based access systems that do not rely upon strict schedules, rather the Subordinate MAC & PHYs contend for transmission opportunities over coax, optionally with packet headers that identify the traffic (e.g., source address, destination address, LLID, and the like). Even hybrid mechanisms are possible, that combine characteristics from strict scheduling and strict contention. [0070] The presently described embodiments allow the Subordinate MAC to prepare a schedule for upstream and downstream transmissions over coax that is specific to, and/or optimized for, the coax link between the Subordinate MAC & PHYs of the OCU/CLT and CNU. Preparation of such schedules requires a significant amount of processing, and hence processing time, in some implementations, it is desirable or necessary to convey any such scheduling information in a timely manner, in order to give the Subordinate MAC & PHYs enough time to prepare in advance for its transmissions and receptions. One benefit of the presently described embodiments is the ability to prepare and deliver processed scheduling information substantially coincidently, or even before, the OLT's own GATE messages. The disclosed embodiments enable this via the DS Knob control that establishes the downstream delays. The Subordinate MAC in the OCU/CLT has optional access to the GATE message, and it can perform the processing and prepare the processed scheduling information and convey it over coax to the

Subordinate MAC in the CNU coincidently with, or before, the corresponding GATE messages in the OLT's downstream are metered out of the

Downstream Egress Buffer to the EPON ONU MAC in the CNU. If the DS Knob control is increased, then the sojourn time in the Downstream Egress Buffer will be increased, thereby allowing more processing time for the Subordinate MAC in the OCU/CLT to prepare the schedule and convey it to the Subordinate MAC in the CNU coincidently with, or even before, the EPON ONU M AC in the CNU receives the OLT's GATE messages upon which the processed schedule is based.

[0071] An alternative embodiment enables the additional processing time for the Subordinate MAC¹ in the OCU or EPoC PHY for CLT to prepare coax scheduling information: The OLT could be minimally augmented to transmit its GATE messages downstream sooner than otherwise required by EPON. For example, the OLT could transmit its GATE messages a few hundred microseconds earlier than the startTime, thereby allowing the Subordinate MAC in the OCU or EPoC PHY for CLT sufficient time to process the GATEs into some coax-specific schedule. 2] Formation of, and admission into, EPoC networks is rather

problematic. The EPON layers have their own admission procedures, such as Discovery GATE messages, and diseoveryWindow, but those procedures rely on constant RTT. The rub is that a CNU that is newly connected to the coax, or an existing CNU that is switched-on and booting-up, does NOT know the coax link parameters, particularly those that affect its RTT. The presently described embodiments establish a constant RTT through an inventive interplay of e.g., variable delays on the transmitting side of a coax link, followed by complementary delays on the receiving side, DS and US Knob control settings, etc., but these coax link parameters are unknown to a new CNU or may have been reconfigured while a CNU was powered-off. In a preferred embodiment, the formation and admission procedures are implemented in a layered approach: a CNU that is switched-on would_search, discover, form or join a coax network with an OCU or EPOC' PHY for CLT^', then receive or negotiate coax link parameters (e.g., LIS Knob or DS Knob control settings) to form or join a Subordinate M AC & PHY^' network, thereby establishing a constant RTT rangeable by an OLT or CLT during admission or other MPCP protocols. Consequently, a constant RTT is thereby established through the Subordinate M AC & PHY layers, finally enabling the CNU to announce or admit itself to the EPON or EPoC network by responding to Discovery GATE or other messages from the OLT or CLT with a rangeable RTT. The procedures for formation and admission to the Subordinate MAC & PHY are specific to the design and implemen tation of the Subordinate M AC & PHYs. For example, MoCA and c.Link coax networks have elaborate admission procedures, including channel -search, beacon discovery, channel- probing, negotiation of coax PHY link parameters (e.g., bitloading, Tx launch power, etc...) as well as MAC link parameters (e.g., CTC clock

synchronization, MAP or TDD Cycle timing, etc...), e.g., to adapt to the channel condi tions of the coax plant. After admission to the Subordinate MAC & PHY network, and after the DS Knob and US Knob control settings have been established, then the CNU's EPO ONU MAC can respond to the OLT's Discovery GATE messages, and the OLT can observe and measure a constant RTT for the new CNU, thereby joining the OLT's EPON network or CLT's EPoC network.

[0073] After admission to the Subordinate MAC & PHY network, and after admission to the OLT's EPON network or CLT's EPoC network, then the Subordinate MAC & PHY network optionally conducts ongoing maintenance of PHY^" link parameters and MAC link parameters (e.g., including LLID assignments per CNU, and associated decryption key information, if any), adapting to channel and traffic conditions as they might evolve over time, while still remaining substantially transparent to the EPON network layers. Maintenance of parameters generally means exchanging updated values of those parameters.

Proportional Mapping

[0074] Some of the benefits of the presently described embodiments are that they enable the Subordinate MAC layer to be relatively thin, i.e., not necessarily comprising a fully-featured layer 2 implementation. The

Subordinate MAC layer may implement relatively few features, e.g., the minimum necessary to accomplish the subordinate conveyance over coax, the advantage being simplified implementations avoiding complexities, which can add latency, overhead, cost, and the like. In one embodiment, Medium Access Control for coax is scheduled by the Subordinate MAC layer in the OCU or EPoC PHY for CLT. In another embodiment, Medium Access Control for upstream traffic over coax can be distributed among CNUs by processing the GATE grants from the OLT. As explained above, these GATE grants are intended for QNUs, not CNUs, so they are generally not appropriate for medium access control on coax without some processing. The Subordinate MACs in the CNUs process their GATE-specified startTimes into grants that are appropriate for the coax links. In one embodiment, the processed grant for coax is calculated as a proportional mapping, where an adjusted start time is calcul ated from the position of the GATE-specified startTime relati ve to the preceding TDD Cycle phasing. For example, a GATE with startTime at the beginning of the preceding TDD Cycle is remapped to a new position at the beginning of the downstream phase. Similarly, a GATE with startTime at the end of the preceding TDD Cycle is remapped to a new position at the end of the downstream phase, and a GATE with startTime in the middle of the preceding TDD Cycle is remapped to a new position in the middle of the downstream phase. 5] Fig. 8 depicts an embodiment of proportional mapping applied to downstream traffic over FDD coax 122. Downstream traffic in the form of a serial bitstream payloads 306, 308 and 310 (optionally over fiber) from the OLT 100 or CLT is received by the OCU or EPoC PHY for CLT, where consecutive Fiber Time Periods 304 are identified for conveyance in corresponding Coax Frame Periods 122 comprising one or more OFDM or OFDMA symbols. The temporal location of individual traffic payloads 306, 308, 310 within the consecutive Fiber Time Periods 304 determines

(comprising proportional mapping) which subcarriers are occupied by the corresponding payloads 306', 308^f, 310' within the OFDM: or OFDMA symbols in the corresponding Coax Frame Periods 122. The proportional mapping occurs after some OCU or EPoC PHY for CLT processing period 314 (e.g., for serial-to-OFDMA block processing or deserialization). The OCU or EPoC PHY for CLT launches the OFDMA symbols downstream over coax to one or more CNU(s). After downstream propagation over coax, each CNU receives the OFDMA transmission and performs some processing 316 to reconstruct (e.g., OFDMA-to-serial block processing or re-serialization) the serial bitstream payloads 306^?f, 308^?f and 310^?f during the corresponding consecutive time intervals 318 for timely delivery to the EPON QNU MACs in the intended destination CNUs 326, This reserialization or reconstruction 318 comprises an inverse process to that of OCU 314: the temporal location of the reserialized downstream traffic payloads 306", 308" and 310" within the corresponding consecutive time intervals 318 is determined (comprising proportional mapping) according to which particular subcarriers were occupied by the corresponding traffic payloads 306^f, 308' and 310' on coax. Transmissions on coax are preceded by an optional Preamble, such as is well- known in MoCA, for purposes such as burst-detection, and frequency-offset estimation, and payload identification (e.g., LLID). Alternative embodiments could comprise payload headers and/or Pilot subcarriers for substantially the same purposes. Transmissions on coax may be separated by an optional IFG (inter-frame gap) period, such as is well-known in MoCA, for purposes such as avoiding overlapping or colliding transmissions, or for allowing time periods for transceivers to change state, 6] Proportional mapping may introduce some time-jitter into the traffic timing. The following expression describes the jitter associated with proportional mapping into individual subcarriers:

lime-Jitter ~ (Fiber Time Period)÷(# usable subcarrier starting positions per Coax Frame Period)

In a specific example of EPoC-over-MoC A, using a Fiber Time Period comprising, for example, 10 MoCA symbols (5.12μ,8 each) per corresponding Coax Frame period, and having 490 usable subcarrier starting positions per Coax Frame Period, this above expression yields a time-jitter - 104 nanoseconds. Note that this level of jitter for this example of EPoC-over- MoCA is within the tolerance of EPON which specifies up to 8^xTime_Quanta (16 nanoseconds each) or 128 nanoseconds.

[0077] Fig. 9 illustrates example embodiments enabling reduction of time- jitter. In one embodiment, the Fiber Time Period 304 corresponding to Coax Frame Period 122 can be made shorter (e.g., by dividing the serial bitstream into smaller consecutive time periods); and in another embodiment, the time- jitter is reduced by increasing the number of usable subcarrier positions per Coax Fame Period 122. There are two such embodiments to the later: 1) increase the number of usable subcarriers per symbol that comprise the start and stop of coax payloads 306% 308', 310' (such as increasing the DFT block size); or, 2) increase the number of usable positions within each Coax Frame Period 122 that comprise the start and stop of coax payloads 306', 308 ' and 310'. For example, the usable position comprises not only a subcarrier number, but a combination of {subcarrier number, and symbol #} pair. In this embodiment, the mapping location for the start and end of particular traffics from the serial bitstream, is NOT constrained to a subcarrier at the start of a Coax Frame Period, but can be mapped more finely, e.g., to a particular subcarrier at a particular symbol position 320 within the Coax Frame Period 122. Transmissions on coax are preceded by an optional Preamble, such as is well-known in MoCA, for purposes such as burst-detection, and frequency- offset estimation, and payioad identification (e.g., LLID). Alternative embodiments could comprise payioad headers and/or Pilot subcarriers for substantial])' the same purposes. Transmissions on coax may be separated by an optional IFG (inter-frame gap) period, such as is well-known in MoCA, for purposes such as avoiding overlapping or colliding transmissions, or for allowing time periods for transceivers to change state.

[0078] Figs. 10A and 10 B depict an embodiment of proportional mapping for TDD downstream. This embodiment comprises the steps of Fig. 8, but further comprises the step of buffering the downstream traffic 322 in the OC U or EPoC PHY for CLT, sufficient to hold the traffic for at least the duration of an upstream phase of a TDD Cycle. This results in additional processing time in the OCU or EPoC PHY for CLT (e.g., waiting for an upstream phase to finish), comprising variable delays. After these delays, the OCU or EPoC PHY for CLT conveys the downstream traffic over coax frame period 122 during a downstream phase of the TDD Cycle. The C Us receive the OFDMA transmissions over coax from the OCU or EPoC PHY for CLT, then buffer the coax receptions 324 sufficiently to hold coax traffic for at least the duration of a downstream phase of a TDD Cycle, then processing comprises reserializing 316 the receptions, cloaking them out at the EPON rate as expected by the EPON ONU MACs in the CNUs 326. In this embodiment, the CNUs establish complementary delays, so the reserialized traffics arrive at the EPO ONU MACs in CNUs 326 at the expected arrival time after a constant downstream delay. Transmissions on coax are preceded by an optional Preamble, such as is well-known in MoCA, for purposes such as burst-detection, and frequency-offset estimation, and payload identification (e.g., 1.1. ID -. Alternative embodiments could comprise payload headers and/or Pilot subcarriers for substantially the same purposes. Transmissions on coax may be separated by an optional 1FG (inter-frame gap) period, such as is well-known in MoCA, for purposes such as avoiding overlapping or colliding transmissions, or for allowing time periods for transceivers to change state. 9] Fig. 11 depicts proportional mapping for upstream traffic via FDD coax. This embodiment would appear to be similar to that of Fig. 8 for downstream FDD, but the steps are run in reverse time order (e.g., multipoint- to-point). EPON ONU MACs in one or more CNUs 326 launch their upstream serial bitstreams as granted 306", 308", 31Θ", with CNUs each applying FEC coding separately. After a processing period 328, each CNU proportionately maps the temporally-granted location (e.g., {startTime, length}) of its upstream serial bitstream traffics into frequency-domain subcarrier positions 306', 308% 310'withm OFDMA symbols for upstream transmission over corresponding coax frame period 122 to the OCU or EPoC PHY for CLT. In this embodiment, each CNU transmits over coax only those particular subcarriers for which its EPON ONU MAC emits upstream traffic, during consecutive serial bitstream time periods, which map into those subcarriers for corresponding coax frame periods 122. For example, EPON ONU MAC 326' emitting upstream traffic 306" results in CNU#1 transmitting on coax only the subcarriers 306'; similarly, EPON ONU M AC 326" emitting upstream traffic 310" results in CNU#2 transmitting on coax only the subcarriers 310'; and EPON ONU MAC 326"' emitting upstream traffic 308" results in CNU#1 transmitting on coax only the subcarriers 308'. The temporal start and end (i.e., corresponding to position & duration) of the EPON ONU M AC emissions, relative to the consecutive serial bitstream time periods, are proportionately mapped into subcarrier occupations for the OFDM A symbols comprising the corresponding coax frame periods 122 on coax, as shown. Upstream OFDMA transmissions from multiple CNU(s) (i.e., Multipoint-to-point traffic) need to be precisely and accurately synchronized among all the participating CNU(s) so that they arrive at the headend OCU or EPoC PHY for CLT substantially synchronously (e.g., at substantially the same arrival time, and substantially the same subcarrier spacing), in order to preserve the orthogonality of the combined receptions. After reception by the OCU or EPoC PHY for CLT, and after some OCU Processing 330, the individual CNU transmissions 306', 308', and 310' are demultiplexed from the OFDM A symbols then relayed into a serial bitstream comprising upstream payloads 306, 308, and 310 in a corresponding fiber time period 304 (e.g., in their granted TD A sequence) as expected by the OLT 100 or CLT. 0] One benefit of this embodiment is that the behavior among CNU(s) is distributed, with each CNU performing the procedure independently. That is. each of one or more CNU(s) can place its transmission on the coax without colliding with, simultaneous transmissions from other CNUs. This benefit is realized by transposing the OLT's own GATE messages, which precisely separate individual fiber or serial bitstream payloads, into precisely separate subcarriers in one or more OFDMA symbols (i.e., separated in time and frequency) within some Coax Frame Period. Fig. 11 shows how three emissions 306", 308", 310" (e.g., separated in time), from 3 different EPON GNU MACs 326', 326", 326'" in 3 different CNUs (e.g., separated in space), get conveyed onto coax (e.g., after some CNU block processing) as three separate coax frame periods 122 comprising one or more OFDMA symbols 306', 308', 3.1.0', which after propagating over the coax, combine in synchrony to form a single reception upon arrival at the OCU (or EPoC PHY for CLT), carrying all three payloads separated into different frequency-domain subcarrier locations. The synchrony established among all participating CNUs must be sufficiently close that their OFDMA symbols within a Coax Frame Period 122 upon arrival at the OCU or EPoC PHY for CLT share, for example, substantially the same: Cyclic Prefix period, subcarrier spacing, symbol, boundary timing, and any Preamble or IFG (inter-frame gap) periods. The Subordinate MAC & PHYs for coax establish sufficiently close synchrony among the coax transmission from participating CNUs through precise synchronization mechanisms such as: a) closed-loop control of CTC coax time clock counter values or counting rates; b) Timing measurements made by the OCU or EPoC PHY for CLT, that are then fed back as individual Timing Offsets to be established in each CNU; c) CNUs observing or measuring the coax subcarrier frequencies transmitted downstream from the OCU or EPoC PHY for CLT, then matching those subcarrier frequencies precise!)' during CNUs' upstream transmissions to the OCU or EPoC PH Y for CLT; d) exchanging information about the differences between various clocks (e.g., MPCP, XTAL) in CNUs vs. those in the OCU or EPoC PHY for CLT; or, e) other synchronization mechanisms such as may be known to someone skilled in the art. Transmissions on coax are preceded by an optional

Preamble, such as is well-known in MoCA, for purposes such as burst- detection, and frequency-offset estimation, and pay!oad identification (e.g., LLID). Alternative embodiments could comprise payload headers and/or Pilot subcarriers for substantially the same purposes. Transmissions on coax may be separated by an optional IFG (inter-frame gap) period, such as is well- known in MoCA, for purposes such as avoiding overlapping or colliding transmissions, or for allowing time periods for transceivers to change state. 1] Figs. 12A and 12B depict an embodiment teaching proportional mapping for upstream TDD traffic. This embodiment comprises the steps of Fig. 1 1 , but further comprises the step of buffering upstream traffic in CNUs, sufficient to hold each CNU's traffic for at least the duration of a downstream phase of a TDD Cycle. In this embodiment, the upstream traffic is similar in some respects to a time -reversed downstream TDD transmission. In Fig. 12B, six CNUs are participating during one or more consecutive MAC Serial Emission Time Periods, whose EPON ONU MACs 326 are separately emitting six different serial bitstream payloads 306", 308", 310", 332", 334", 336", with all six payloads substantially separated (e.g., in time) according to their GATE-specified grants. Each CNU, after FEC coding or other processing 328, transposes the temporal position and duration of its emission (s) into subcarrier locations within one or more OFDMA symbols comprising a corresponding coax frame period 122, according to where each CNU's emissions fall within consecutive MAC Serial Emission Time Periods, leaving any remaining subcarriers empty (i.e., not transmitted over coax) for other CNUs to possibly occupy. In this depiction, two such consecutive MAC Serial Emission Time Periods 340, 342 result in the formation of one or more OFDMA symbols comprising corresponding coax frame period 122, depicted having roughly double the carrying capacity as shown previously for FDD transmission over coax. In this depiction, each CNU performs processing, and provides buffering 344, sufficient to hold CNU's upstream traffic for at least the duration of a downstream phase of a TDD Cycl e, This step of buffering 344 results in the suffering of vari able delays in each CNU. When the TDD Cycle progresses into an upstream phase, the participating CNUs (e.g., the six depicted) each transmit one or more OFDMA symbols to the OCU or EPoC PHY for CLT. When these individual transmissions over coax 306', 308% 310', 332' 334' 336' arrive in sufficient synchrony at the OCU or EPoC PHY for CLT, they appear substantially as a single reception 122' aggregating six pavloads into different frequency-domain subcarrier locations. In Fig. 12 A. the OCU or EPoC PHY for CLT receives reception 122' comprising one or more OFDMA. symbols from the participating CNU(s), and provides buffering 346, sufficient to hold coax traffic for at least the duration of an upstream phase of a TDD Cycle, thereby comprising complementary delays (i.e., complementary to the CNUs' variable delays). Following some OCU processing period 348, the OCU or EPoC PHY for CLT demultiplexes the individual pavloads from the reception 122' comprising one or more OFDMA symbols, and relays them to the OLT or CLT as individual serial bitstream pa loads 306, 308, 310, 332, 334, 336 (e.g., in their granted TDMA sequence) as expected by OLT 100 or CLT. The Subordinate MAC & PHYs for coax establish sufficiently close synchrony among the coax transmission from participating CNUs through precise synchronization mechanisms such as: a) closed-loop control of CTC coax time clock counter values or counting rates; b) Timing measurements made by the OCU or EPoC PHY for CLT, that are then fed back as individual Timing Offsets to be established in each CNU; c) CNUs observing or measuring the coax subcarrier frequencies transmitted downstream from the OCU or EPoC PHY for CLT, then matching those subcarrier frequencies precisely during CNUs' upstream transmissions to the OCU or EPoC PHY for CLT; d) exchanging information about the differences between various clocks (e.g., MPCP, XTAL) in CNUs vs. those in the OCU or EPoC PHY for CLT; or, e) other synchronization mechanisms such as may be known to someone skilled in the art. Transmissions on coax are preceded by an optional Preamble, such as is well-known in MoCA, for purposes such as burst-detection, and frequency-offset estimation, and payload identification (e.g., LLID). Alternative embodiments could comprise payload headers and/or Pilot subcarriers for substantially the same purposes.

Transmissions on coax may be separated by an optional IFG (inter-frame gap) period, such as is well-known in MoCA, for purposes such as avoiding overlapping or colliding transmissions, or for allowing time periods for transceivers to change state.

TDD Discover

[0082] Discovery of ONUs in EPON comprises the OLT advertising a

Discovery GATE message to ail uninitialized ONUs (e.g., ONUs for which no RTT has been yet measured). This Discovery GATE message specifies a disco veryS lot, having a length greater than the 64 Byte response expected by the OLT. In addition, the OLT reserves a discoveryWindow for responses (such as REG 1STE __REQ messages) from uninitialized ONUs (which generally remains unknown outside the OLT), during which the OLT does not schedule u pstream traffic from initialized ONUs. The duration of this discoveryWindow is commonly described by the following expression: discoveryWindow > discoverySlot + maxRTT - minRTT > 20Q₍iis where, minRTT and maxRTT describe the range of RTTs expected by the OLT (e.g., 200μ8 is common). Uninitialized ONUs that respond to the Discovery GATE add a random delay to the start time of the discoverySlot before responding in order to minimize the likelihood that their response collides with a response from some other uninitialized ONU, particularly from other uninitialized ONUs that have substantially the same RTT and would otherwise persistently collide even upon retries. This EPON procedure raises a quandary for EPoC, and in particular for TDD embodiments over coax. In an FDD embodiment, the discov ryWindow interrupts only upstream traffic, leaving the downstream channel and its downstream traffic unaffected.

Consequently, there are no additional constraints on the OLT's (or CLT's) duration of discovery Window. However, a problem arises for TDD embodiments, because the duration of the discoveryWindow can extend beyond an upstream phase of a TDD Cycle, thereby overlapping the subsequent downstream phase of a TDD Cycle. This problem is further complexified because the EPoC PHYs 126, 158 of Figs. 5 A. and 5B are generally unaware of the duration of the OLT's (or CLT's) discoveryWindow, and furthermore because a minimally augmented OLT would preferably be unaware of any underlying TDD Cycle phasing confined to the EPoC PHYs 126, 158. If the discoveryWindow extends beyond the upstream phase of a TDD Cycle, then collisions with, or some other disruption of, downstream traffic could result. In one embodiment, the OLT or CLT could begin the discoveryWindow' at the start of an upstream phase of the TDD Cycle, although this would force the OLT or CLT to be made aware of the underlying TDD Cycle phasing, which might represent more than a minimally augmented OLT (e.g., more than modifying only OLT's software), or even a layer violation. 4] In the presently-claimed invention, minRTT has substantial duration, even for short coax, HFC, and/or fiber plants, since it includes variable delays, and complementary delays in the EPoC PHYs 126, 158. This implies that a value for minRTT spans roughly the same time period as the duration of a TDD Cycle (e.g., constant coax downstream delay 162 has roughly similar duration as an upstream phase of a T DD Cycle, and constant coax upstream delay 174 has roughly similar duration as a downstream phase of a TDD Cycle). Whereas in EPON, or in FDD EPoC, the minRTT can be quite short, even approaching zero, for short fiber/coax plants. Similarly, maxRTT is generally longer than minRTT due to the additional propagation delay of any longer links in the plant. In this embodiment, the difference maxRTT - minRTT, representing the range of expected RTTs expected by the OLT or CLT, does not grow problematically long, even for a TDD embodiment, since the processing delays, variable delays, and complementary delays cancel each other during the subtraction. Consequently, in this TDD embodiment, the duration of a discoveryWindow only for CNUs in EPoC is not substantially longer than that for ONUs in EPON. Unfortunately, there's still a potential problem if the OLT or CLT were to schedule a single discoveryWindow for both CNUs and ONUs, because the discoveryWindow duration would need to span short RTTs approaching zero (as describe above), as well as long TDD RTTs greater than maxRTT for ONUs or FDD CNUs, which in the case of TDD can be longer than the duration of a TDD Cycle. In other words, if the OLT or CLT were to schedule a single discoveryWindow for both CNLIs and ONUs, then its duration would overlap a downstream phase, thereby overlapping or interfering with downstream traffic, or the discoveryWindow would otherwise need to somehow span two upstream phases. 5] Fig. 13 depicts an example of a preferred embodiment that has the significant benefit of resolving the problems of discovery identified above. In this embodiment, traditional Discovery GATE message 412 and

corresponding discoveryWindow 402 is employed for initializing any ONUs or FDD CNUs because they have similar RTTs (e.g., roughly 200_,us or less). TDD CNUs have much longer RTTs (e.g., roughly 300μ8 or more), as described above, where their minRTT 404 ' may exceed the maxRTT 4Θ6 of ONUs or FDD CNUs. in this embodiment, a new TDD CNU Discovery GATE message 412', and a new TDD CNU Discovery Window 402^?, are established separately from those used for ONUs or FDD CNUs, and dedicated for initializing TDD CNUs, if any. The TDD CNU Discovery GATE message 412 specifies a TDD CNU discoverySlot during the TDD CNU Discovery Window, but the TDD CNU discoverySlot and Discovery Window both begin and end significantly later than those for ONUs and FDD CNUs, as depicted in Fig. 13. For example, as shown in Figs. 5 A and 5B, the TDD CNU Discovery GATE messages undergo variable delays in the OCU 106 or EPoC PHY for CLT 158, followed by complementary delays in the EPoC PHY for CNUs 126, comprising a constant coax downstream delay 162 approximately the same duration as an upstream phase of the TD D Cycle. Similarly, for example, the upstream responses from TDD CNUs (e.g., REGISTER REQs) 408 (e.g., from near and far CNUs) undergo variable delays in the EPoC PHY for CNUs 126, followed by complementary delays in the OCU 106 or EPoC PHY for CLT 158, comprising a constant coax upstream delay 174 approximately the same duration as a downstream phase of the TDD Cycle. This preferred embodiment becomes beneficial because there is a Catch-22 if an attempt is made to use a single longer Discovery Window for both TDD CNLis and FDD CNUs/ONUs, namely that attempting to increase the duration of an upstream phase to accommodate a longer Discovery Window would simultaneously increase the RTT of TDD CNLis by a corresponding amount, thereby remaining out of reach. Another benefit of this embodiment enables ail types of CNLis (i.e., TDD CNUs, FDD CNUs and ONUs) to initialize and coexist on the same OLT or CLT, wh le preserving the goal of "minimal augmentation to MPCP." Furthermore, the embodiment enables multiple QCLJs, each with possibly different TDD Cycle parameters or phasing, to coexist under a given OLT. TDD CNUs would be implemented to ignore the traditional Discovery GATE messages, and the new TDD CNU Discovery GATE messages could be designed such that they are ignored by ONUs and FDD CNUs (e.g., using a different multicast destination address from that in traditional Discovery GATE messages). 6] TDD CNU Discovery Window 402/ has substantially similar duration to that of traditional discovery windows 402, since, for example, it is determined by the propagation delays due to length of coax and fiber (if any), consequently enabling TDD CNU Discovery Window 402 ' to fit within an upstream phase of the TDD Cycle. For example, the TDD CNU Discover}' Window might he roughly up to 2Q4iis (e.g., 2* {(<20km fixed fiber length)÷(c-^'--1.48) + (<750m variable coax path)÷(0.83 ^¾c)}), implying that the TDD Cycle would allocate an upstream ph ase duration of at least that long, when CNUs are being initialized. This relationship between duration of upstream phase, propagation times, and TDD CNU Discovery Window can be expressed as follows:

(duration of US phase) > (duration of new disco very Window) > (maxRTT-minRTT) + discoverySlot

New TDD CNU Discovery Window 402'' begins later after the corresponding new TDD CNU Discovery GATE message 412, as depicted in Fig. 13, due to longer RTTs (e.g., including variable and complementary delays) for TDD CNUs 404^f, 406', compared to those of ONUs or FDD CNUs 404, 406. 83] While various embodiments of the disclosed method and apparatus have been described above, it should be understood that they have been presented by way of example only, and should not limit the claimed invention. Likewise, the various diagrams may depict an example architectural or other configuration for the disclosed method and apparatus. This is done to aid in understanding the features and functionality that can be included in the disclosed method and apparatus. The claimed invention is not restricted to the illustrated example architectures or configurations, rather the desired features can be implemented using a variety of alternative architectures and

configurations. Indeed, it will be apparent to one of skill in the art how alternative functional, logical or physical partitioning and configurations can be implemented to implement the desired features of the disclosed method and apparatus. In addition, a multitude of different constituent module names other than those depicted herein can be applied to the various partitions.

Additionally, with regard to flow diagrams, operational descriptions and method claims, the order in which the steps are presented herein shall not mandate that various embodiments be implemented to perform the recited functionality in the same order unless the context dictates otherwise.

[0084] Although the disclosed method and apparatus is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described. Thus, the breadth and scope of the claimed invention shoul d not be limited by any of the above- described exemplary embodiments.

[0085] Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term "including" should be read as meaning "including, without limitation" or the like; the term "example" is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms "a" or "an" should be read as meaning "at least one," "one or more" or the like; and adjectives such as "conventional," "traditional," "normal," "standard," "known" and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.

[0086] A group of items linked with the conjunction "and" should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as "and/or" unless expressly stated otherwise.

Similarly, a group of items linked with the conjunction "or" should not be read as requiring mutual exclusivity among that group, but rather should also be read as "and/or" unless expressly stated otherwise. Furthermore, although items, elements or components of the disclosed method and apparatus may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated.

[0087] The presence of broadening words and phrases such as "one or more," "at least," "but not limited to" or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. The use of the term "module" does not imply that the components or functionality described or claimed as part of the module are all configured in a common package. Indeed, any or al l of the various components of a module, whether control logic or other components, can be combined in a single package or separately maintained and can further be distributed in multiple groupings or packages or across multiple locations.

[0088] Additionally, the various embodiments set forth herein are described in terms of exemplary block diagrams, flow charts and other illustrations. As will become apparent to one of ordinary skill in the art after reading this document, the il lustrated embodiments and their various alternatives can be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular architecture or configuration.

Claims

1 . A method for implementing an EPoC Ethernet Passive Optical Network (EPON) Protocol over Coax network, the method comprising the steps of:

a) providing MAC and PHY layers (120, 132) for coax links for conveying downstream traffic ( 1 14) from, and/or upstream traffic (140) to, an OLT (100) or CLT (156), wherein the PHY^" layers are subordinate to MAC layers for the coax links; and

b) scheduling the conveyance over coax via the MAC¹ layers for coax links' PHY layers (146, 150) wherein the schedule is subordinate to said downstream (114') and/or upstream traffic (140').

2. A system for implementing an EPoC Ethernet Passive Optical Network (EPON) Protocol over Coax network comprising:

a) means for providing M AC and PHY layers (120, 132) for coax links for conveying downstream traffic ( 1 14) from, and/or upstream traffic (140) to, an OLT (100) or CLT, wherein the PHY" layers (146, 150) are subordinate to MAC layers for the coax links; and

b) means for scheduling said conveyance over coax via the MAC layers for coax links' PHY layers ( 120, 132) wherein the schedule is subordinate to said downstream (1 14') and/or upstream traffic ( 140').

3. A non-transitory computer-executable storage medium comprising program instructions which are computer-executable to implement an EPoC Ethernet Passive Optical Network (EPON) Protocol over Coax network comprising:

a) program instructions that cause MAC and PHY⁷ layers (120, 132) for coax links be provided for conveying downstream traffic ( 1 14) from, and/or upstream traffic ( 140) to, an OLT (100) or CLT, wherein the PHY layers (146,150) are subordinate to MAC layers for the coax links; and

b) program instructions that cause a schedule said conveyance over coax via the MAC layers for coax links' PHY layers (146, 150) wherein the schedule is subordinate to said downstream (114') and/or upstream traffic (140').

4. The method system, or storage medium according to any one of claims 1-3, wherein the step of, or means or program instructions comprise Time-Division Duplex (TDD) scheduling and/or, wherein the Subordinate MAC¹ and PHY layers (120) comprises an OCU (106) or EPoC PHY for CLT (158) and further comprises creating subordinate schedules for traffic over coax; and distributing the subordinate schedules to one or more CNUs (12.4) each with a corresponding Subordinate MAC & PHY layer (132) and/or, wherein the OCU (106) or EPoC PHY for CLT (158) further comprise receiving the downstream traffic (114') into a downstream ingress buffer (118); and conveying the downstream traffic (114') over coax through its Subordinate MAC & PHY layers (120), comprising variable delays (160); and wherein CNU(s) (124) comprise receiving downstream traffic (114) over coax from the OCU (106) or EPoC PHY for CLT (158) through its Subordinate MAC & PHY layers (132); buffering downstream traffic into a downstream egress buffer (128); establishing downstream egress delays which are complementary (164) to the variable delays ( 160); and relaying downstream traffic (1 14") to its minimally augmented EPON ONU MAC (134) after the complementary egress delays (164) and/or, wherein CNU(s) (124) comprise receiving upstream traffic from its EPON ONU MAC (134) into an upstream ingress buffer (144); conveying the upstream traffic (140) over coax (122) through its Subordinate MAC & PHY layers(132), comprising variable delays ( 168); and the OCU (106) or EPoC PHY for CLT (158) comprise receiving upstream traffic (140) over coax (122) from the CNU(s) (124) through its Subordinate MAC & PHY layers (120); buffering upstream traffic into an upstream egress buffer (152); establishing upstream egress delays which are complementary (172) to the variable delays (168); and, relaying upstream traffic (140'") to a minimal ly augmented EPON OLT ( 100) or CLT (156) after the complementar egress delays (172) and/or further comprising deriving the subordinate schedules for traffic over coax comprising a fullness of ingress buffers ( 1 18, 144) and/or, further comprising deriving the subordinate schedules for upstream traffic (140) over coax (122) comprising requests sent to the coax scheduler in the OCU (106) or EPoC PHY for CLT ( 158) from the Subordinate MAC & PHY (132) in the one or more CNUs (124) and/or, further comprising deriving the subordinate schedules for upstream traffic (140) over coax (122) comprising GATE messages (200) observed in the downstream traffic (114') from the OLT (100) or CLT (156) and/or, comprising scheduling at least as much traffic as the OLT (100) has scheduled in the subordinate schedules and/or, further comprising reordering of traffic, or aggregating of traffic, or other processing of traffic for optimized conveyance over coax in the

subordinate schedules and/or further comprising providing grants ((210, 220) in the form of MAP Media Access Plan messages, or coax-specific GATE messages in the subordinate schedules and/or, further comprising the OCU (106) or EPoC PHY for CLT (158) filtering out downstream traffic ( 1 14) not destined for its o wn CNU(s) ( 124) and out of the

subordinate schedules and/or wherein the filtering comprises discrimination according to LLID values and/or, further comprising traffic shaping by the CLT (156) or OLT (100) or OCU (106) of the downstream or upstream traffic to avoid congesting the coax l ink (122) or overflowing Ingress Buffers (118, 144).

5. The method system, or storage medium according to claim 4, wherein the step of, or means or program instructions further comprise timestamping downstream traffic (116) upon reception at the OCU (106) or EPoC PHY for CLT (158) or downstream ingress buffer (1 18) and/or wherein the timestamping (1 16) comprises establishing a coax time clock ( 192) by the Subordinate MAC & PHY layers (120) and/or wherein establishing downstream egress delays which are complementary (164) to the variable delays (160) comprises providing a DS Knob (130) control setting and/or further comprising establishing a constant delay (162) by the DS Knob (130) control setting and comprising a header or indication of tirnestamped arrival time and/or further comprising establishing a constant delay by the DS Knob (130) control setting and comprising a header or indication of Lateness or variable delays suffered in the OCU (106) or EPoC PHY for CLT (158) and/or, further comprising establishing a constant delay (162) by the DS Knob (130) control setting and comprising a header or indication of the complementary delays (164 ) to be established by the EPoC PH Y for C NU (126) and/or wherein the establishing downstream egress delays which are complementary (164) to the variable delays (160); and relaying downstream traffic (114") to its minimally augmented EPON ONU MAC (134) after the complementary egress delays (164) comprises providing a MPCP Clock ( 186) from the minimally augmented EPON ONU MAC ( 134), or a crystal-disciplined oscillator (186) and/or further comprising establishing a constant delay by the DS Knob (130) control setting and comprising a header or indication of tirnestamped arrival time and/or further comprising establishing a constant delay by the DS Knob (130) control setting and comprising a header or indication of Lateness or variable delays suffered in the OCU ( 106) or EPoC PHY for CLT (158) and/or further comprising establishing a constant delay by the DS Knob (130) control setting and comprising a header or indication of the complementary delays to be established by the EPoC PHY for CNU (126),

6. The method system, or storage medium according to claim 5, wherein the step of or means or program instructions further comprising timestamping upstream traffic (142) in the CNUs (124) upon reception from the EPON ONU MAC ( 134), or upon reception at the EPoC PHY for CNU (126), or upon reception at the upstream ingress buffer (144) and/or wherein the timestamping (142) comprises providing a coax time clock (190) established by the Subordinate MAC & PHY layers (120, 132) and/or wherein the establishing upstream egress delays which are complementary (172) to the variable delays (168) comprises the step of providing an US Knob (154) control setting and/or further comprising establishing a constant delay by the US Knob (154) control setting and comprising a header or indication of timestamped arrival time and/or further comprising establishing a constant delay by the US Knob (154) control setting comprising a header or indication of the Lateness or variable delays suffered by the EPoC PHY for CNU ( 126) and/or further comprising establishing a constant delay by the US Knob (154) control setting comprising a header or indication of the complimentary delays to be established by the OCU (106) or EPoC PHY for CLT (158) and/or wherein establishing upstream egress delays which are complementary (172) to the variable delays (168) or relaying upstream traffic (140) to a minimally augmented EPON OLT (100) or CLT (156) after the complementary egress delays (172) comprises providing a PLL (184) disciplined by the downstream traffic (114') and/or comprises providing an MPCP Clock in the OCU ( 106) or EPoC PHY for CLT (158) and/or further comprising decrypting GATE messages (218) and/or further comprising receiving decryption key information the CNUs (124), from the OLT ( 100), or from the CLT (156) and/or further comprising the step of authenticated key exchange to obtain decryption key information and/or further comprising adjusting a DS Knob (130) control setting to allow sufficient processing time to create and distribute the subordinate schedules for upstream traffic over coax (140) and/or further comprising distributing the created subordinate schedules substantially coincident with, or before, the corresponding GATE messages (218) reach the EPON ONU MAC (134) and/or further comprising a CLT (156) or minimally augmented OLT (100) transmitting its GATE messages (218) downstream to EPON ONU MACs (134) in C Us (124) substantially in advance of their startTime, allowing sufficient processing time to create and distribute the subordinate schedules for upstream traffic over coax (140) and/or further comprising deriving the subordinate schedules for upstream traffic over coax (140) comprising substantially those GATE messages (218) that will produce upstream traffic (140') from EPON ONU MACs (134) in the CNU(s) (124) ready to be conveyed in corresponding coax scheduling periods and/or the CNU(s) (124) informing the Subordinate MAC scheduler in the OCU (120) or EPoC PHY in CLT (158) how to compensate for their individual clock differences.

7. A method for implementing an EPoC Ethernet Passive Optical N etwork (EPON) Protocol over Coax network, the method comprising the steps of:

a) searching, discovering, forming or joining a coax network ( 122, 146, 150) with an OCU ( 106) or EPOC PHY for CLT (158);

b) receiving or negotiating coax link parameters to form or join a Subordinate MAC & PHY network ( 120, 132); and

c) establishing a constant TT rangeable by an OLT (100) or CLT (156) during admission or other MPCP protocols (182),

8. A system for implementing an EPoC Ethernet Passive Optical Network (EPON) Protocol over Coax network, the method comprising the steps of:

a) means for searching, discovering, forming or joining a coax network (122, 146, 150) with an OCU (106) or EPOC PHY for CLT (158);

b) means for recei ving or negotiating coax link parameters to form or join a Subordinate MAC & PHY^" network (120, 132); and

c) means for establishing a constant RTT rangeable by an OLT (100) or CLT (156) during admission or other MPCP protocols (182).

9. A non-transitory computer-executable storage medium comprising program instructions which are computer-executable to implement an EPoC Ethernet Passive Optical Network (EPON) Protocol over Coax network comprising:

a) program instructions that cause a search, discovery, the formation or jomder of a coax network (122, 146, 150) with an (X I (106) or EPOC PHY for CLT (158);

b) program instructions that cause a receipt or negotiation of coax link parameters to form or join a Subordinate MAC & PH Y network (120, 132); and

c) program instructions that cause an establishment of a constant RTT rangeable by an QUI (100) or CLT (156) during admission or other MPCP protocols (182),

10. The method system, or storage medium according to any one of claims 7-9, wherein the step of, or means or program instructions further comprise maintaining the coax link by adapting PHY & MAC parameters to evolving channel and traffic conditions, while remaining substantially transparent to EPON network layers.