Patent Application
20060013260
The invention relates to communications networks.
The following acronyms may appear in the description below: APON, asynchronous transfer mode (ATM) passive optical network (PON); ASIC, application-specific integrated circuit; ATM, asynchronous transfer mode; B-PON or BPON (broadband PON); CATV, community access television (cable television); CPU, central processing unit (e.g. microprocessor); EPON (Ethernet PON); FPGA, field-programmable gate array; ISDN, integrated services digital network; PON, passive optical network; POTS, plain old telephone service; PPV, pay per view; PSTN, public switched telephone network; RAM, random-access memory; ROM, read-only memory; TDM, time division multiplexed (or multiplexing); VoIP, voice over Internet Protocol; VoATM, voice over ATM; VoD, video on demand.
Optical access systems offer a potentially large bandwidth as compared to copper-based access systems. A broadband optical access system may be used, for example, to distribute a variety of broadband and narrowband communication services from a service provider's facility to a local distribution point and/or directly to the customer premises. These communication services may include telephone (e.g. POTS, VoIP, VoATM), data (e.g. ISDN, Ethernet), and/or video/audio (e.g. television, CATY, PPV, VoD) services.
The OLT may be implemented as a stand-alone unit or as a card in a backplane. The AccessMAX OLT card of Advanced Fibre Communications (Petaluma, Calif.) is one example of a superior OLT product. Other examples of OLTs include the 7340 line of OLTs of Alcatel (Paris, France), the FiberDrive OLT of Optical Solutions (Minneapolis, Minn.), and assemblies including the TK3721 EPON media access controller device of Teknovus, Inc. (Petaluma, Calif.). The OLT may communicate (e.g. via cable, bus, and/or data communications network (DCN)) with a management system or management entity, such as a network element operations system (NE-OpS), that manages the network and equipment.
On the user side, the OLT may be connected to one or more ODNs. An ODN provides one or more optical paths between an OLT and one or more ONUs. The ODN provides these paths over one or more optical fibres. The ODN may also include optional protection fibres (e.g. for backup in case of a break in a primary path).
An optical network unit (ONU) is connected to an ODN and provides (either directly or remotely) a user-side interface of the OAN. The ONU, which may serve as a subscriber terminal, may be located outside (e.g. on a utility pole) or inside a building. One or more network terminations (NTs) are connected to an ONU (e.g. via copper trace, wire, and/or cable) to provide user network interfaces (UNIs), e.g. for services such as Ethernet, video, and ATM. Implementations of such an architecture include arrangements commonly termed Fibre to the Building (FTTB), Fibre to the Curb (FTTC), and Fibre to the Cabinet (FTTCab).
The second architecture example in
The AccessMAX ONT 610 of Advanced Fibre Communications (Petaluma, Calif.) is one example of a superior ONT product. Other examples of ONTs include the Exxtenz ONT of Carrier Access Corporation (Boulder, Colo.), the FiberPath 400 and 500 lines of ONTs of Optical Solutions, the 7340 line of ONTs of Alcatel, and assemblies including the TK3701 device of Teknovus, Inc.
As shown in
An ODN that contains only passive components (e.g. fibre and optical splitters and/or combiners) may also be referred to as a passive optical network (PON). Depending e.g. on the particular protocol used, a PON may also be referred to, for example, as a B-PON (broadband PON), EPON (Ethernet PON), or APON (ATM PON). A OAN may include different OLTs and/or ONUs to handle different types of services (e.g. data transport, telephony, video), and/or a single OLT or ONU may handle more than one type of service. The OLT and/or one or more of the ONUs may be provided with battery backup (e.g. an uninterruptible power supply (UPS)) in case of mains power failure.
The protocol for communications between the OLT and the ONUs may be ATM-based (e.g. such that the OLT and ONUs provide transparent ATM transport service between the SNI and the UNIs over the PON), for example. Such embodiments of the invention may be applied to optical access systems that comply with one or more of ITU-T Recommendation G.983.1 (“Broadband optical access systems based on Passive Optical Networks (PON),” dated October 1998 and as corrected July 1999 and March 2002 and amended November 2001 and March 2003, along with Implementor's Guide of October 2003) (International Telecommunication Union, Geneva, CH), and ITU-T Recommendation G.983.2 (“ONT management and control interface [OMCI] specification for B-PON,” dated June 2002 and as amended March 2003, along with Implementor's Guide of April 2000) (International Telecommunication Union, Geneva, CH). Additional aspects of optical access systems to which embodiments of the invention may be applied are described in the aforementioned Recommendations.
An OLT may be capable of delivering one or multiple voice telephony lines to each of a subset of subscribers (possibly to each subscriber) via one or more respective ONTs.
In a TDM “nailed-up” transport approach, the OLT locally decapsulates ATM voice signals to TDM voice signals onto a TDM voice infrastructure that reserves capacity for every subscriber line of the PON. Because transport resources are provided for all possible subscribers, such an approach may be very inefficient in practice. Though OLT systems may have a very high capacity and density of served subscriber lines, in practice subscribers seldom need to concurrently utilize every available voice line.
In an ATM transport approach, ATM voice signals are transported through an OLT to an interface (e.g., a gateway external to the OLT), which terminates the packetized voice signals and decapsulates them into TDM voice signals onto the switch interface to the PSTN. However, if partial cell fill is used for circuit emulation, ATM transport facilities at the OLT must support a much higher bandwidth, even more so as they carry voice traffic for multiple PON networks. In addition, the ATM transport facilities may need to transport all circuits—whether active or not—or, alternatively, address the complexity of dynamically setting virtual circuit connections (VCCs) upon call activity. Switched virtual circuits (SVCs) may be employed to accomplish dynamic allocation, but these require implementation of a complex signaling stack. Such additional complexity increases software development costs and requires processing hardware and ATM switching hardware capable of setting up calls quickly enough to meet stringent timing requirements. Other methods for concentrating voice traffic over. ATM cells (e.g. AAL2 idle channel suppression) also involve higher complexity.
A method of communications processing according to an embodiment of the invention includes receiving idle traffic via each of a plurality of voice ports. The method also includes receiving active traffic via at least one of the plurality of voice ports, while continuing to receive idle traffic via the remainder of the plurality of voice ports, and concentrating the active traffic received via at least one of the plurality of voice ports onto a shared bus.
A method of communications processing according to another embodiment of the invention includes receiving active traffic via each of a first voice port and a second voice port, and receiving a first allocation of resources of a shared bus and a second allocation of resources of the shared bus. The method also includes concentrating the active traffic received via the first voice port onto the shared bus according to the first allocation, and concentrating the active traffic received via the second voice port onto the shared bus according to the second allocation. At least one of the group consisting of the active traffic received via the first voice port and the active traffic received via the second voice port consists essentially of partially filled cells.
A communications apparatus according to an embodiment of the invention includes a shared bus and a cross-connect device. The cross-connect device is configured to receive idle traffic via each of a plurality of voice ports and to transfer, onto an allocated portion of the shared bus, a voice signal based on active traffic received via one of the plurality of voice ports.
A communications apparatus according to another embodiment of the invention includes a shared bus and a cross-connect device. The cross-connect device is configured to receive active traffic via each of a first voice port and a second voice port and to transfer, onto a first allocated portion of the shared bus, a voice signal based on active traffic received via the first voice port. The cross-connect device is also configured to transfer, onto a second allocated portion of the shared bus different from the first allocated portion, a voice signal based on active traffic received via the second voice port, At least one of the group consisting of the active traffic received via the first voice port and the active traffic received via the second voice port consists essentially of partially filled cells.
In general, OAN systems employ asynchronous transfer mode (ATM) based protocols for voice calls, while external circuit-switched telephone networks (e.g., PSTNs—public switched telephone networks) employ time division multiplexing (TDM) based protocols. Accordingly, for voice calls spanning both OAN systems and circuit-switched networks, adaptation between the protocols may be necessary, whether within an OLT system or at a location between the OLT system and the circuit-switched network.
Embodiments of the invention provide methods and systems for facilitating such adaptation for voice calls in a highly efficient, practical, and cost-effective manner that may also be applied to achieve high voice quality. Embodiments herein may be useful, for example, to architects, service providers, and other operators of a passive optical network (PON).
According to embodiments of the invention, a common TDM bus is shared between a subscriber interface (e.g., a PON-side interface) and a switch interface (e.g., a PSTN-side interface). The bus may be shared among multiple subscribers (e.g. via subscriber interface line cards), associated with one or more different PONs, and/or among multiple voice switch interface line cards associated with a PSTN. The bus may transport only active calls, and resources otherwise needed for ATM transport may be eliminated. As such, voice capacity aggregated from multiple PONs can be efficiently concentrated. It is estimated that in some cases, the aggregated voice capacity may be statistically reduced by a factor of ten.
In various embodiments of the invention, high bandwidth on a PON (including partial cell fill and/or transport of traffic for inactive calls) may be employed to achieve high quality for voice calls transported over ATM in the PON without the need to introduce complex bandwidth allocation methodologies. Calls to be carried between the PON and an external TDM-based network are concentrated so that only active calls are transported over a shared TDM bus. Such an approach maximizes bandwidth savings, especially in systems that aggregate multiple PONs and thousands of subscribers.
In an embodiment of the invention, a central control module (e.g. a control card) allocates resources on a shared TDM bus. The central control module may be provisioned with the logical mappings from ONT voice ports to OLT voice interface card ports (for example, to enable or facilitate routing of calls to appropriate locations, such as the ONT associated with a particular voice circuit). The subscriber interface line cards decapsulate packetized ATM voice signals onto TDM (e.g., PCM—pulse code modulation) voice signals. Each subscriber interface line card and switch interface line card may enable programmable access to the TDM bus via a programmable TDM cross-connect device. The TDM cross-connect device cross-connects any arbitrary PON side channel to any arbitrary TDM bus channel.
Embodiments herein may complement and coexist with techniques applied in PONs to reduce delays in ATM voice traffic, such as bandwidth over-engineering techniques. Embodiments herein may also'avoid shortcomings of other approaches taken to adapt voice traffic between an asynchronous system (e.g., an ATM-based system) and a synchronous system (e.g., a ITDM-based system).
Task T110 allocates a timeslot of the synchronous bus to the call. In particular, task T110 may assign one or more available synchronous bus timeslots to the call. Task T120 transmits an indication of the allocated bus timeslot to one or both of the synchronous bus terminations associated with the call (e.g. via an OAM channel). (In an embodiment, the transmitting of the indication may be referred to as signaling.) The indication may specify which bus resources should be used at each end of the synchronous bus. The synchronous bus terminations may be respectively associated with, for instance, a subscriber interface and a switch interface.
Interface 710 is an interface between an asynchronous (e.g., ATM-based) system and a synchronous (e.g., TDM-based) bus 720. For example, interface 710 may be included in a subscriber line interface (e.g. a card providing an interface to a PON). Interface 730 is an interface between a shared synchronous bus 720 and a synchronous (e.g., TDM-based) network. For example, interface 730 may be included in a switch interface (e.g. a card or other module providing an interface to the PSTN). Controller 740 (e.g. a control card) allocates resources of synchronous bus 720. Interfaces 710 and 730 connect to shared synchronous bus 720 to use the resources allocated by controller 740.
Receiver 100 receives (e.g. over a circuit trace or control bus) an indication of a voice call to be carried between a PON and a circuit switched network (e.g. a call setup request). Receiver 100 may also receive other call information such as an indication of the origination and/or desired destination for the call (e.g. an originating circuit number, which may be associated with an ONT port). Allocator 110 allocates, to the call, at least one time slot of a shared TDM bus associated with the PON (and possibly with other PONs). Allocator 110 may also identify (e.g. via a port-to-port mapping as described herein, possibly stored in nonvolatile memory such as flash) an appropriate synchronous bus termination to receive the call. Allocator 100 may include an array of logic elements (e.g. an application-specific integrated circuit or programmable device). Transmitter 120 transmits (e.g. over a circuit trace or control bus) an indication of the allocated timeslot to one or both synchronous bus terminations associated with the call.
Controller 800 may be a part of a PON card, management system device, and/or control card internal or external to an OLT. In some embodiments, such a device may be inserted into a backplane of an OLT, and the OLT may include other cards or card assemblies inserted into the same or a different backplane. Such a backplane may include a standardized bus (e.g. ISA, PCI, VME, VxI) and/or a proprietary or otherwise non-standardized bus. For example, the backplane may include a control bus over which controller 800 communicates with interfaces to a shared synchronous bus (e.g. via OAM channels). Alternatively, the management system or entity may be external to the OLT and associated equipment and may also include, for example, a command-line interface (CLI) or operational support system (OSS).
Detector 300 detects a call status (e.g. presence of a call and/or a termination of a call). Detector 300 may also detect other call information such as an indication of the desired destination for the call (e.g. a voice circuit). Transmitter 220 transmits the detected information to, e.g., a control device such as controller 800 (for example, as a call setup or teardown request). In some implementations, the information is transmitted via an OAM channel. Receiver 200 receives an indication of an allocated timeslot of a synchronous (e.g. TDM) bus (for example, from a control device, possibly via an OAM channel). Connection mechanism 210 (e.g. a programmable cross-connect device) connects to the synchronous bus in accordance with the received indication. Connection mechanism 210 also may disconnect from the synchronous bus (or otherwise release the allocated timeslot(s)) based on the detected termination of the call and/or the occurrence of another event or condition, such as receipt of an indication from a control module (e.g. via an OAM channel). In another embodiment, connection mechanism 210 also performs signaling monitoring operations.
PON interface 1000 is an interface between shared TDM bus 1020 and one or more PONs utilizing ATM protocols for voice calls. PON interface 1000 includes a detector 300, a transmitter 220, a receiver 200, and a connection mechanism 210. PON interface 1000 is an implementation of interface 900 of
Switch interface 1010 is an interface between shared TDM bus 1020 and a PSTN utilizing TDM protocols for voice calls. Switch interface 1010 includes a detector 300, a transmitter 220, a receiver 200, and a connection mechanism 210. Switch interface 1010 is an implementation of interface 900 of
Controller 800 allocates timeslots of shared TDM bus 1020 for voice calls and directs usage of such timeslots by PON interface 1000 and switch interface 1010 in order that voice calls may be transferred between the PON(s) and the PSTN. Controller 800 includes a receiver 100, an allocator 1110, and a transmitter 120 and may be embodied as or within a card or card assembly inserted into a backplane.
In an example scenario, a call arrives at either the PON side or PSTN side with respect to shared TDM bus 1020. Assuming, for illustrative purposes, that the call is originated at the PON side, then detector 300 in subscriber interface 300 detects the call. Subscriber interface 1000 transmits an indication thereof (e.g. a call setup request, possibly via an OAM channel) to controller 800, which indication is received by receiver 100. Allocator 110 of controller 800 allocates one or more timeslots of shared TDM bus 1020 to the call. Transmitter 120 transmits an indication thereof to both subscriber interface 1000 and switch interface 1010 (e.g. via OAM channels), whose respective receivers 200 receive such indication. Their respective connection mechanisms 210 connect to shared TDM bus 1020 in accordance with the indication. As such, a call is established over shared TDM bus 1020.
One or both of the respective detectors 300 of subscriber interface 1000 and switch interface 1010 detect a termination of the call. Subscriber interface 1000 and/or switch interface 1010 respectively transmit an indication thereof (e.g. a call teardown request, possibly via an OAM channel) to controller 800. In response, transmitter 120 of controller 800 may transmit an indication (e.g. via OAM channels) that subscriber interface 1000 and switch interface 1010 should disconnect from shared TDM bus 1020 (or otherwise release the timeslot(s) associated with the terminated call) to free the bus resources. After receipt of the indication by the respective receivers 200, the respective connection mechanisms 210 disconnect from the shared TDM bus 1020 (release the associated timeslot(s)).
PON subscriber line card 1120 includes 100 voice ports and has the requisite bandwidth to service 100 ATM-based voice calls passing through ONTs 1140. TDM cross-connect device 1130 is configured to couple PON subscriber line card 1120 to shared TDM bus 1110 in order to utilize allocated timeslots of shared TDM bus 1110. In the example of
In a representative mode of operation, TDM cross-connect device 1130 detects a call and transmits a notification, via control channel 1150, to the common control module. The common control module allocates one or more appropriate timeslots of shared TDM bus 1110 to the call and transmits, via control channel 1150, an indication of the allocated timeslot(s) to TDM cross-connect device 1130. TDM cross-connect device 1130 then appropriately couples PON subscriber line card 1120 to shared TDM bus 1110 so that the call may be established. Thus TDM cross-connect device 1130 is configured to concentrate active voice calls onto the shared TDM bus 1110.
In this example, PON subscriber line cards 1120 each include 100 voice ports and have the requisite bandwidth to service 100 ATM-based voice calls that involve ONTs 1140. PON subscriber line cards 1120 and switch interface line cards 1220 each can connect to shared TDM bus 1110 in order to utilize allocated timeslots of shared TDM bus 1110. Shared TDM bus 1110 has a 200-voice-call capacity in the example of
In an example scenario, common control module 1210 allocates one or more appropriate timeslots of shared TDM bus 1110 to a detected call and transmits, via control channel 1150 (e.g. over OAM channels), an indication of the allocated timeslot(s) to the appropriate switch interface line card 1220 and PON subscriber line card 1120. The call is established when the cards 1220 and 1120 connect to shared TDM bus 1110.
Two pairs of established voice calls 1230, 1235 are shown in
Certain embodiments herein illustrate interactions between a central control module, a subscriber interface including subscriber interface line cards, and a switch interface including switch interface line cards. It is to be appreciated that, in practice, the actual number of such cards in an implementation is arbitrary, depending on the number of PONs utilizing the shared TDM bus, the capabilities of the cards, and/or the number of served subscriber lines, for example.
It is expressly contemplated that alternative operations and/or configurations of such elements, and that apparatus including additional elements, are disclosed by and may be constructed according to the description provided herein. For instance, the subscriber interface line cards and/or switch interface line cards of
The foregoing presentation of the described embodiments is provided to enable any person skilled in the art to make or use the present invention. While specific embodiments of the invention have been described above, it will be appreciated that the invention as claimed may be practiced otherwise than as described. Various modifications to these embodiments are possible, and the generic principles presented herein may be applied to other embodiments as well.
An embodiment of the invention may be implemented in part or in whole as a hard-wired circuit (e.g. implemented on a computer interface card) and/or as a circuit configuration fabricated into one or more arrays of logic elements arranged sequentially and/or combinatorially and possibly clocked (e.g. one or more integrated circuits (e.g. ASIC(s)) or FPGAs). Likewise, an embodiment of the invention may be implemented in part or in whole as a firmware program loaded or fabricated into non-volatile storage (such as read-only memory or flash memory) as machine-readable code, such code being instructions executable by an array of logic elements such as a microprocessor or other digital signal processing unit.
Further, an embodiment of the invention may be implemented in part or in whole as a software program loaded as machine-readable code from or into a data storage medium (e.g., as shown in
