This disclosure is related to a communication system and more particularly to extending Ethernet Passive Optical Networks (EPON) Protocol over Coax based access networks.
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 point-to-multipoint topology. EPON is often deployed by Operator/Service Providers (OSPs) as an Access Network, to provide high-speed access to the internet backbone and Business Services to medium-to-large businesses seeking strict Quality of Service (QoS) Service 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 central 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 point-to-multipoint, 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., OOK 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 of 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.
The OLT produces the downstream serial bitstream at some constant EPON data-rate, such as 1 Gbps or 10 Gbps. 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 TDMA time-division multiple access.
There are three versions of EPON currently specified:
Upstream (US) traffic generally uses the same wavelength for both 1 Gbps and 10 Gbps data-rates. Downstream (DS) traffic generally uses different optical wavelengths for 1 Gbps and 10 Gbps data-rates. It can be deduced that there is interest in supporting both symmetric and asymmetric upstream/downstream data-rates.
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.
OLTs use EPON's Multipoint Control Protocol (MPCP) to coordinate/schedule the TDMA upstream bursts. The MPCP protocol relies on constant Round-Trip Time (RTT) as observed/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 ONU maintains its own MPCP Clock by setting its clock counter value to that of the OLT's timestamp 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 Service 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., fullness) 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/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.
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 RTT 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 1 km effective fiber length, and the other with 20 km 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).
In summary, EPON protocols were designed around assumptions based on FDD simultaneous US and DS optical fiber transmission:
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.
A publicly-available 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/mar12/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 size and footprint of the service group of CPEs, and how distant they may be from the headend (or Hub). For example, in China, the service group is often a multiple dwelling unit (MDU) with dense concentration of the CPEs in the service group, and relatively short distance to the headend often located in the basement (e.g., Fiber-to-the-Basement (FTTB)). For example, in North America, the service 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 particular service and its assigned spectral occupation in the RF band (typically within 5˜1002 MHz). Smaller plants can be serviced by coax alone, so the headend can interface the coax plant directly. Remote headends 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:
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:
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 deployed decades 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 try to anticipate the evolution of future usage. Predicting the future presents its own risks if the MSOs guess wrong, but this is the predicament that MSOs find themselves in having FDD HFCs already deployed.
The coax plants of HFC networks in North America are often operated as FDD within US spectral allocations (typically 5˜42 MHz) and DS spectral allocations (typically from 54 MHz up to 750, 860 or 1002 MHz as examples), with an allowance for a so-called ‘Split’ or guard band (typically 42-54 MHz) 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 an FDD service: data over cable system interface specification (DOCSIS) cable modem service may occupy one or more single-carrier ‘QAM’ channels occupying 6 MHz of spectrum in the DS band, and one or more QAM channels in the US band. DOCSIS headend equipment is known as a cable modem termination system (CMTS). DOCSIS CPEs include Cable Modems, Residential Gateways and Set-Top Boxes.
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 infrastructure 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: EPON Protocol over Coax
MSOs currently must deploy fiber to the premises to support EPON 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 MSO'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.
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). So, 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 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
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 OLT, 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
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:
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 PHY-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.
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, alternating-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, and vice versa. 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.
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 Access Network would have enabled fewer or no splits in some coax plants.
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 sole 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.
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 ease of illustration these drawings are not necessarily made to scale.
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.
In a preferred embodiment, there is a desire to reuse or reapply EPoC's development of a new FDD PHY-layer specification and leverage EPoC's FDD mode of operation towards an optional TDD mode of operation. This is problematic as explained above since OCU Media Conversion would need to include the complication of buffering in either direction to accommodate waiting for the duplexing phase to cycle between upstream and downstream directions. In a preferred embodiment, the OCU media converter used for FDD could be repurposed for a TDD mode of operation by tuning the upstream and downstream repeaters to share the same RF channel over coax (i.e., occupying a single spectral allocation in TDD, as opposed to two different spectral allocations in FDD). For example, the center frequency of the downstream coax channel could be made equal to the center frequency of the upstream coax channel (fdownstream=fupstream). This would otherwise result in traffic collisions on the coax segment, but in a preferred embodiment, the OLT scheduler would segregate upstream and downstream traffic on the coax segment. By aggregating downstream traffic together into periodic intervals, and aggregating upstream traffic into periodic intervals, then segregating and interleaving the periodic intervals such that US and DS traffic do not overlap in time, collisions can be avoided on the coax segment. Since the FDD repeater is substantially reused for the TDD mode of operation, its constant processing delay enables a constant RTT upon which EPON OLTs (and their MPCP protocol) rely. In this preferred embodiment, constant RTT allows EPON's full-duplex MAC sublayer to be preserved, as MSOs prefer. Another specific benefit of the claimed invention is substantially reusing EPoC's FDD PHY layer specification for the TDD mode of operation. Such reuse avoids the lengthy and expensive developments of an entirely new PHY-layer specification and subsequent chip-level PHY implementations.
The OLT scheduler can avoid collisions in the TDD mode of operation by segregating the upstream and downstream traffic phases with a time gap (aka inter-phase gap (IPG)) between TDD phases. An IPG may allow time for transmissions to complete their propagation from transmitter(s) to intended receiver(s), time for the medium to sufficiently quiesce (if necessary) after reception(s), and time for destination transceiver(s) to switch (if necessary) from receive to transmit mode.
The IPG may be adapted for various TDD topologies, such as (but not limited by):
MSOs may install digital fiber 36 overlaying their HFC cascade 34, extending to the OCU(s) 30 that inject RF signals onto passive coax segment(s) between actives. Digital fiber overlays 36 and OCU(s) 30 are not required to reach every passive coax segment, nor are they required to reach every last active to serve the last passive coax segment on a HFC cascade 34. Digital fiber overlays 36 and OCUs 30 are required only to reach those particular passive coax segments for which the MSO wishes to provide EPoC service to (e.g., Business Services) subscribers. Filter 38 may optionally be installed at the downstream end of a passive coax segments in order to filter out EPoC RF signals before the reach any downstream amplifier.
In a preferred embodiment, the OLT or CLT scheduler may arrange an IPG between the US and DS phases allowing time for upstream transmissions from CNU(s) to complete their propagation over a passive coax segment only, to the OCU or CLT. Similarly, the scheduler may also arrange an IPG between the DS and US phases allowing time for its downstream transmissions to propagate from the OCU or CLT, over passive coax, to destination CNU(s). The propagation times in this embodiment are relatively short, because passive coax segments are usually relatively short. The relatively short IPGs that result are highly desirable in TDD applications because these periods represent duplexing overhead when the channel is unavailable to carry traffic in either direction.
A specific benefit of the invention enables shorter IPG durations and higher temporal efficiency of TDD duplexing by confining the TDD domain to only the passive coax segment, i.e., US and DS transmissions are prevented from overlapping and colliding on coax, but the corresponding US and DS transmissions are allowed to overlap on digital fiber. These corresponding US and DS transmissions on digital fiber overlap, but do not collide, because the EPON digital fiber is operated as WDD/FDD, allowing US and DS transmissions to pass each other on fiber on different wavelengths without collision. In this embodiment, the OCU middle box interfaces the WDD/FDD digital fiber to the TDD passive coax segment. By confining the TDD domain to the passive coax segment, and allowing the digital fiber to carry simultaneous overlapping US and DS traffic via WDD/FDD, the claimed invention not only preserves the EPON full-duplex MAC sublayer, but actually leverages it to facilitate short IPG (whose duration is adapted only to the relatively short passive coax segment) and consequently high temporal efficiency.
As an example of this benefit, consider an OCU connected to an OLT via 20 km of digital fiber, having one-way propagation time of ˜100 μs=20 km÷{c÷1.48}. The OCU interfaces to a passive coax segment of several hundred meters in length, having one-way propagation time of (for example) 2 μs=500 m÷{c×0.83}. Coax plants often exhibit multipath propagation, making the coax channel somewhat time-dispersive, so the IPG may include allowance for any such echoes on the coax channel to quiesce after intended reception(s). Such echoes commonly decay sufficiently in less than a couple microseconds. The IPG may also include a few microseconds to allow destination TDD transceiver implementation(s) to switch between from receive to transmit mode. Using the claimed invention to accomplish TDD over the entire domain, including the digital fiber, would require an IPG duration of approximately ˜107 μs (e.g., 100+2+2+3). Two such IPGs would be used for each TDD Cycle (one between the US-to-DS transition, and another between the DS-to-US transition). TDD Cycle periods are adjustable, but for this example we can consider a TDD Cycle period, for example of 500 μs. The consequent temporal efficiency of the TDD duplexing would be only 57% because the IPG overhead amounts to 43% ({107 μs+107 μs}÷500 μs). However, using the claimed invention to accomplish TDD while confining the TDD domain to only the passive coax segment, leaving the digital fiber to operate full-duplex, then the IPG duration need not include any (100 μs) contribution from the digital fiber segment, allowing the IPG to be kept as short as 7 μs. In this embodiment, the claimed invention greatly improves the temporal efficiency to 97% because the IPG overhead now amounts to only 3% ({7 μs+7 μs}÷500 μs).
The explanatory depiction (above) of two separate IPGs per TDD Cycle (one between the US-to-DS transition, and another between the DS-to-US transition) is a matter of perspective. Alternate explanations of TDD duplexing overhead could be depicted from some other perspective, such as that from a CLT or OCU. In that alternate explanation, the CLT or OCU would launch its DS traffic, then wait for the downstream propagation, then wait for quiescence at the destination, then wait for the destination CNUs to switch their TDD transceiver implementations from receive mode to transmit mode before launching their upstream traffic, then wait for upstream traffic to propagate towards the CLT or OCU. After receiving that US traffic, the CLT or OCU could almost immediately begin transmitting DS traffic (perhaps after waiting for its TDD transceiver to switch modes, but NOT having to wait for any propagation time). From such perspective, the TDD duplexing overhead could be depicted as a single IPG, but having twice the duration (i.e., including both a DS propagation time plus an US propagation time). It will be obvious to someone skilled in the art that such alternate explanations of TDD duplexing overheads are equivalent, resulting in the same temporal efficiency, and that the claimed invention and its benefits apply congruently to any such alternate depictions or perspectives.
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Another specific benefit of the claimed invention allows the OLT or CLT to schedule the TDD traffic on each passive coax segment independently. That is, each serviced passive coax segment and its CNUs form an independent scheduling domain, where traffic on one coax segment can be scheduled simultaneously with traffic on another coax segment without collision between the segments. Such independent scheduling domains would, for example, enable for each domain: differing TDD Cycle periods or duty cycles, differing IPG duration optimizations, differing modulation types or modulation orders, and/or differing spectral allocations or channel-widths. This enables MSOs to reuse the same EPoC RF spectrum (e.g., the RF spectrum above MSOs' existing CATV services, say from 860 MHz to 1.2 GHz) for each passive coax segment serviced. This spectral reuse multiplies the EPoC throughput capacity which now scales with the number of coax segments serviced, compared to alternative FDD approaches or other TDD architectures that establish a shared scheduling domain spanning the length of a coax or HFC cascade and all the CNUs on that cascade. That is, the full TDD coax datarate gets shared among a smaller number of CNU(s) that are located on, and share a passive coax segment (e.g., a passive coax segment might pass by premises of only ⅕th as many subscribers as a Node+5 coax cascade might pass), such that each CNU has access to a larger fraction of the shared throughput available.
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. Also, 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.
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 should not be limited by any of the above-described exemplary embodiments.
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.
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.
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 all 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.
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 illustrated 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.
This application claims the benefit of U.S. Provisional Application No. 61/650,855, filed May 23, 2012, the specification of which is incorporated herein by reference.
Number | Date | Country | |
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61650855 | May 2012 | US |