WO2014063014A1 - Duplexage par répartition temporelle pour epoc - Google Patents

Duplexage par répartition temporelle pour epoc Download PDF

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Publication number
WO2014063014A1
WO2014063014A1 PCT/US2013/065613 US2013065613W WO2014063014A1 WO 2014063014 A1 WO2014063014 A1 WO 2014063014A1 US 2013065613 W US2013065613 W US 2013065613W WO 2014063014 A1 WO2014063014 A1 WO 2014063014A1
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Prior art keywords
coax
phy
traffic
subordinate
clt
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PCT/US2013/065613
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English (en)
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David Barr
Michail Tsatsanis
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Entropic Communications, Inc.
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Publication of WO2014063014A1 publication Critical patent/WO2014063014A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q11/0071—Provisions for the electrical-optical layer interface
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/08—Time-division multiplex systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/2854—Wide area networks, e.g. public data networks
    • H04L12/2856—Access arrangements, e.g. Internet access
    • H04L12/2858—Access network architectures
    • H04L12/2861—Point-to-multipoint connection from the data network to the subscribers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/22—Adaptations for optical transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q2011/0086—Network resource allocation, dimensioning or optimisation

Definitions

  • This disclosure is related to a communication system and more
  • Ethernet Passive Optical Networks Protocol over Coax based access networks.
  • EPON is an IEEE 802.3 protocol specification enabling Ethernet Passive Optical Networks.
  • Passive Optical Networks use an Optical Distribution Network (ODN) generally using passive fiber-optic cables and passive optical splitters forming a pomt-to-multipomt topology.
  • ODN Optical Distribution Network
  • 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.
  • QoS Quality of Service
  • SLA Se dee Level Agreement
  • OLT Optical Line Terminal
  • 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.
  • 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.
  • 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.
  • 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)
  • 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 .
  • 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).
  • DDD Wavelength Division Duplex
  • FDD Frequency Division Duplex
  • 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.
  • OLTs use EPON's Multipoint Control Protocol (MPCP) to coordinate and schedule the TDMA upstream bursts.
  • MPCP Multipoint Control Protocol
  • the MPCP protocol relies on constant Round-Trip Time (RTT) as observed and measured by the OLT.
  • RTT Round-Trip Time
  • 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.
  • 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.
  • LLIDs Logical Link Identifiers
  • 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.
  • the ONU 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.
  • 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;
  • 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.
  • MSOs Multiple System Operators
  • TV pay television
  • VoD video on demand
  • VoIP voice over internet protocol
  • SMB small-medium business
  • 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),
  • 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)).
  • MDU multiple dwelling unit
  • FTTB Fiber-to-ttie- basement
  • 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).
  • 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.
  • RF Radio Frequency
  • US from RF electrical signal on coax to RF-modulated optical signal on fiber to the headend;
  • OE Optical-to-Electrical
  • EO Electrical-to-Optical
  • SNR Signal-to-Noise Ratio
  • the topology of the coax plant is a cascade of various active and
  • Cascade lengths vary from:
  • 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.
  • Node+1 with one active amplifier after the Fiber Node (if any);
  • Node+2 with two active amplifiers after the Fiber node (if any);
  • Node+N with N amplifiers (e.g., Node+5 cascades are common among North American MSOs' HFCs).
  • 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 ⁇ 54 ⁇ ) 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.
  • DOCS IS headend equipment is known as a Cable Modem Termination System (CMTS).
  • CMTS Cable Modem Termination System
  • DOCS IS CPEs include Cable Modems, Residential Gateways and Set-Top Boxes.
  • 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
  • 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.
  • DOCSIS Business Class Internet
  • EPON OLTs are significantly less expensive than DOCSIS CMTSs, which can further reduce MSO expenses.
  • EPoC represents a desire for MSOs to have a lower-cost option of using the existing HFC medium for EPON-like services.
  • 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.
  • 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.
  • MAC Medium Access Control
  • EPoC 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 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • CLT Coax Line Terminal
  • 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:
  • 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 .
  • the OCU performs media conversions for both downstream and upstream traffic simultaneously, by using to two different RF channels over coax.
  • PHY- layer Media Conversion can be accomplished with constant processing delay to satisfy EPON protocols' reliance on constant RTT.
  • TDD Time- Division 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.
  • EPON constraints outlined above such as maintaining constant RTT, and the desire to preserve unchanged the MAC sublayer.
  • TDD Time Division Duplex
  • FDD Frequency Division Duplex
  • TDD Time Division Duplex
  • FIG. 1 is an illustration of an OLT to ONU fiber connection and an OCU conversion from a fiber to a coax for CNUs.
  • Fig. 2 illustrates the OCU conversion of Fig, 1.
  • Fig. 3 illustrates a new CLT that resembles the combination of an OLT plus an OCU that interfaces to an analog fiber.
  • Fig. 4 illustrates a CLT that connects directly to a coax.
  • Figs. 5 A and 513 illustrate an embodiment including Subordinate MAC and PHY layers for the coax segments
  • Fig. 6 illustrates the communication and scheduling between the OLT and the OCUs and CNUs of the embodiments of Figs. 5 A and 5B.
  • 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.
  • Fig. 8 depicts an embodiment of proportional mapping applied to downstream traffic over FDD coax.
  • Fig. 9 illustrates an example embodiment enabling reduction of time- iitter.
  • Figs. 10A and 10B depict an embodiment of proportional mapping for TDD downstream.
  • Fig. 11 depicts proportional mapping for upstream traffic via FDD coax.
  • Figs. 12A and 12B depict an embodiment teaching proportional
  • mapping for upstream TDD traffic
  • Fig. 13 shows the preferred embodiment of discovery of TDD CNUs, and the new TDD CNU Discovery Window.
  • the DS delay would comprise:
  • 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.
  • the DS and US channels each are comprised of several links and
  • 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.
  • 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.
  • 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,
  • 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 ⁇ 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 MAC 1 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.
  • 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.
  • 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.
  • 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.
  • 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 MAC 1 134.
  • 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.
  • DS Knob control 130 establishes an overall
  • 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).
  • 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).
  • 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).
  • 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.
  • 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.
  • 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).
  • 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
  • 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.
  • 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).
  • the optical propagation over fiber 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 &
  • the 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).
  • 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.
  • 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 MAC 1 & PHY layers in the CNUs on the CPE ends of the coax plant.
  • 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.
  • 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.
  • 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.
  • AKE Authenticated Key Exchange
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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
  • the Egress Buffers will restore the proper order, as expected by EPON MACs, according to the complementary delays (e.g., derived from
  • 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
  • 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
  • the Subordinate MAC in OCU 106 or EPoC PHY for CLT 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) 2 ⁇ 8 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
  • 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.
  • 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).
  • the Subordinate M AC in OCU 106 (or in the EPoC PHY for CLT) having access to GATE-specified foreknowledge of upstream traffic 140 ?
  • 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.
  • 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).
  • 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).
  • 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.
  • 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).
  • MAP messages e.g., once per TDD Cycle, near the end of each downstream phase
  • 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.
  • 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)).
  • 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).
  • 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.
  • 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
  • An alternative embodiment enables the additional processing time for the Subordinate MAC 1 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.
  • 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.
  • Formation of, and admission into, EPoC networks is rather
  • 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.
  • 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.
  • coax link parameters e.g., LIS Knob or DS Knob control settings
  • 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.
  • the Subordinate MAC & PHY network 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.
  • 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.
  • 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.
  • Medium Access Control for coax is scheduled by the Subordinate MAC layer in the OCU or EPoC PHY for CLT.
  • 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.
  • 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.
  • 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
  • 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).
  • each CNU 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)
  • EPoC-over-MoC A using a Fiber Time Period comprising, for example, 10 MoCA symbols (5.12 ⁇ ,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 x Time_Quanta (16 nanoseconds each) or 128 nanoseconds.
  • Fig. 9 illustrates example embodiments enabling reduction of time- jitter.
  • 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.
  • the usable position comprises not only a subcarrier number, but a combination of ⁇ subcarrier number, and symbol # ⁇ pair.
  • 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.
  • IFG inter-frame gap
  • 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.
  • 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.
  • 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.
  • Fig. 11 depicts proportional mapping for upstream traffic via FDD coax. This embodiment would appear to be similar to that of Fig.
  • EPON ONU MACs in one or more CNUs 326 launch their upstream serial bitstreams as granted 306", 308", 31 ⁇ ", with CNUs each applying FEC coding separately.
  • 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.
  • 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.
  • 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
  • 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.
  • 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.
  • 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.
  • 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.
  • coax e.g., after some CNU block processing
  • 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
  • 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.
  • IFG inter-frame gap
  • Figs. 12A and 12B depict an embodiment teaching proportional mapping for upstream TDD traffic. This embodiment comprises the steps of Fig.
  • the upstream traffic is similar in some respects to a time -reversed downstream TDD transmission.
  • 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.
  • 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.
  • 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.
  • the participating CNUs e.g., the six depicted
  • 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).
  • 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.
  • various clocks e.g., MPCP, XTAL
  • 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).
  • 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.
  • IFG inter-frame gap
  • 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.
  • 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.
  • discoveryWindow > discoverySlot + maxRTT - minRTT > 20Q ( iis where, minRTT and maxRTT describe the range of RTTs expected by the OLT (e.g., 200 ⁇ 8 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.
  • the discov ryWindow interrupts only upstream traffic, leaving the downstream channel and its downstream traffic unaffected.
  • 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]
  • 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.
  • 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).
  • the minRTT can be quite short, even approaching zero, for short fiber/coax plants.
  • maxRTT is generally longer than minRTT due to the additional propagation delay of any longer links in the plant.
  • 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.
  • Fig. 13 depicts an example of a preferred embodiment that has the significant benefit of resolving the problems of discovery identified above.
  • 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 300 ⁇ 8 or more), as described above, where their minRTT 404 ' may exceed the maxRTT 4 ⁇ 6 of ONUs or FDD CNUs.
  • 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.
  • 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.
  • 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.
  • TDD CNUs i.e., TDD CNUs, FDD CNUs and ONUs
  • ONUs i.e., TDD CNUs, FDD CNUs and ONUs
  • 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).
  • 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.
  • 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 3 ⁇ 4 c) ⁇ ), 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:
  • 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.
  • RTTs e.g., including variable and complementary delays
  • TDD CNUs 404 f , 406' compared to those of ONUs or FDD CNUs 404, 406.
  • 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.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
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  • Small-Scale Networks (AREA)

Abstract

L'invention concerne un procédé, un système et un programme d'ordinateur pour mettre en œuvre un réseau EPoC et, en particulier, une variante à duplexage par répartition temporelle (TDD). De multiples couches MAC et PHY subordonnées pour câble coaxial (120, 132) ou des segments HFC acheminent un trafic de liaison descendante (114) provenant d'un OLT (100) ou d'un CLT (156), et/ou un trafic de liaison montante (140) vers ceux-ci, la planification dudit acheminement sur le câble coaxial étant subordonnée audit trafic de liaison descendante (114') et/ou de liaison montante (140').
PCT/US2013/065613 2012-10-18 2013-10-18 Duplexage par répartition temporelle pour epoc WO2014063014A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2883318A4 (fr) * 2012-08-10 2016-04-13 Entropic Communications Inc Duplexage par répartition temporelle pour epoc
WO2018113742A1 (fr) * 2016-12-24 2018-06-28 华为技术有限公司 Procédé d'émission de signaux et système de réseau

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6546014B1 (en) * 2001-01-12 2003-04-08 Alloptic, Inc. Method and system for dynamic bandwidth allocation in an optical access network
EP2487824A1 (fr) * 2011-02-14 2012-08-15 Alcatel Lucent Transmission de paquets de données entre neouds de réseau
US20120257892A1 (en) * 2011-04-05 2012-10-11 Broadcom Corporation Method for Sub-Rating an Ethernet Passive Optical Network (EPON) Medium Access Control (MAC) Based Communication Link

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6546014B1 (en) * 2001-01-12 2003-04-08 Alloptic, Inc. Method and system for dynamic bandwidth allocation in an optical access network
EP2487824A1 (fr) * 2011-02-14 2012-08-15 Alcatel Lucent Transmission de paquets de données entre neouds de réseau
US20120257892A1 (en) * 2011-04-05 2012-10-11 Broadcom Corporation Method for Sub-Rating an Ethernet Passive Optical Network (EPON) Medium Access Control (MAC) Based Communication Link

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2883318A4 (fr) * 2012-08-10 2016-04-13 Entropic Communications Inc Duplexage par répartition temporelle pour epoc
WO2018113742A1 (fr) * 2016-12-24 2018-06-28 华为技术有限公司 Procédé d'émission de signaux et système de réseau

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