1. Field of the Invention
The present invention relates to a signal processing apparatus, a signal processing method, and a signal frame structure for a gigabit passive optical network (GPON), more particularly to its transmission convergence structure.
2. Description of the Related Art
Known systems that provide access to networks such as the Internet through optical fibers include fiber-to-the-home, fiber-to-the-curb, fiber-to-the-node, fiber-to-the-premises, and other such systems, all of which may be conveniently denoted FTTx. A passive optical network (PON) is one type of network that can be used to implement these FTTx systems.
The wavelength of the downstream optical signals used on the PON in transmission to the ONUs differs from the wavelength of the upstream optical signals used on the PON in transmission to the OLT. Bidirectional communication can accordingly be performed on a single strand of optical fiber.
Downstream transmission from the OLT to the ONUs is point-to-multipoint. The OLT 701 sends downstream signal frames Fd addressed to individual ONUs, as indicated by the characters 2, 3, 1, . . . , n in the downstream frames Fd in the drawing, to all of the ONUs 704-1 to 704-n. Each of the ONUs 704-1 to 704-n extracts the frames addressed to it from the received data stream by a method such as decryption, and discards the other frames.
Upstream transmission from the ONUs 704-1 to 704-n to the OLT is point-to-point. Upstream frames Fu, numbered 1 to n in the drawing, are transmitted to the OLT 701 from the ONUs at timings assigned by the OLT. The timings are assigned so that the frames from different ONUs do not collide in the splitter 702. The timing assignments take into consideration the different round-trip (upstream and downstream) transmission delays between the OLT and the ONUs 704-1 to 704-n, which are due to different distances between the splitter 702 and the ONUs.
GPON, standardized as Recommendation G.984 of the Telecommunication Standardization Sector of the International Telecommunications Union (ITU-T), is one of several known varieties of PON. GPON is an optical access network system capable of carrying Ethernet, time-division multiplexing (TDM), and asynchronous transfer mode (ATM) communication. The Ethernet communication system is used in the Internet and in local area networks, TDM is used in existing telephone networks, and ATM is usable in all sorts of voice, data, and video communication media. Known documents that disclose GPONs include Japanese Patent Application Publication Nos. 2004-320745 and 2004-320746, and ‘Series G: Transmission System And Media, Digital System And Networks’, February 2004, International Telecommunications Union, compiled by ITU-T Study Group 15.
Ethernet, incidentally, is a registered trademark.
The methods by which the three types of communication systems (Ethernet, TDM, and ATM) are accommodated in a GPON will be described below, first for downstream communication, then for upstream communication.
The overhead section, which is necessary for communication control, maintenance, and operation, includes a frame header known as a downstream physical control block (PCBd) that gives a variety of information about the GTC frame. Part of the PCBd is an upstream bandwidth map that gives information for controlling upstream transmission by the ONUs 704-1 to 704-n. In the example in
The payload section, which carries user's signals, includes an ATM partition and a GPON encapsulation mode (GEM) partition. The ATM partition carries unaltered ATM cells. The GEM partition accommodates a GEM frame. The GEM frame may include Ethernet or TDM signals as described below. The PCBd in the overhead gives information indicating the boundary between the ATM and GEM partitions.
In upstream transmission, each ONU sends a frame including overhead and a payload. If the upstream signal is an ATM signal, one or more ATM cells are directly mapped onto the payload as in the ATM partition in a downstream signal. If the upstream signal is an Ethernet signal or a TDM signal, the signal is mapped onto a GEM frame, and the GEM frame is mapped onto the payload.
The transmit and receive processing in the ONU is carried out in a series of layers referred to as a protocol stack.
A downstream GTC frame is received by a GTC framing sublayer 910 of the GTC frame layer in each of the ONUs 704-1 to 704-n. In the GTC framing sublayer 910, an ATM signal is read from the ATM partition in the GTC frame or a GEM frame is read from the GEM partition, according to the ONU's allocation identifier, and the ATM signal or GEM frame is passed to a transmission convergence (TC) adaptation sublayer 920. When the GTC framing sublayer 910 reads an ATM signal, it is received by an ATM TC adapter 922 in the TC adaptation sublayer 920, and a VPI/VCI filter 925 identifies the logical path of the signal from the virtual path identifier (VPI) and virtual channel identifier (VCI) given as connection information in each cell, before outputting the signal to an ATM client that provides ATM service to the subscriber. When the GTC framing sublayer 910 reads a GEM signal, it is received by a GEM TC adapter 921 in the TC adaptation sublayer 920, and a port-ID and PTI filter 923 identifies its logical path from the port identification (ID) value and payload type indicator (PTI) code given as connection information in the signal, before outputting the signal to a GEM client, which may provide either Ethernet service or TDM service.
In upstream transmission, the GTC framing sublayer 910 in each of the ONUs 704-1 to 704-n generates a container corresponding to the ONU's allocation identifier, maps the ATM signal or the GEM frame onto the payload of the container, and transmits the container (see
In downstream transmission, the GTC deframing function 1050, GEM extraction function 1052, and ATM extraction function 1053 in
The distribution function 1054, GEM-to-Ethernet conversion function 1062, and GEM-to-TDM conversion function 1064 correspond to the port-ID and PTI filter 923 in the TC adaptation sublayer 920, the conversion functions forming a GEM interface (IF). The ATM interface 1076 corresponds to the VPI/VCI filter 925. Although no blocks are shown N corresponding to the GEM TC adapter 921 and ATM TC adapter 922 in
In upstream transmission, the GTC framing function 1034, GEM mapping function 1032, and ATM mapping function 1033 in
The conventional apparatus in
In ITU-T Recommendation G.984, a GEM frame accommodates Ethernet and TDM signals as described above. A single Ethernet or TDM signaling unit (e.g., an Ethernet packet) may be mapped onto a single GEM frame, or may be divided among a plurality of GEM frames. A single Ethernet or TDM signaling unit is mapped onto a single GEM frame in the example shown in
As described above, ITU-T Recommendation G.984 maps the unaltered ATM cells of an ATM signal onto an ATM partition of a GTC frame, and maps Ethernet and TDM signals onto a GEM partition (see
ATM communication service is currently provided in fewer countries and territories than Ethernet and TDM communication service. Furthermore, since ATM communication service is not heavily used, when GPONs are constructed, many of them may not support ATM communication. Accordingly, there is a need for a method of processing ATM signals at a low cost.
An object of the present invention is to provide a simple, low cost ATM-capable signal processing apparatus for use in GPON equipment such as an OLT or ONU.
Another object of the invention is to provide a signal processing method and a GTC frame for use in the invented signal processing apparatus.
The invented signal processing apparatus comprises an Ethernet-to-GEM conversion function, a TDM-to-GEM conversion function, a non-GEM-to-GEM conversion function, a GEM-to-Ethernet conversion function, a GEM-to-TDM conversion function, a GEM-to-non-GEM conversion function, a GTC input section, a GTC output section, and a mapping information management function.
The Ethernet-to-GEM conversion function converts an input Ethernet signal to a GEM frame. The TDM-to-GEM conversion function converts an input TDM signal to a GEM frame. The non-GEM-to-GEM conversion function converts a non-GEM signal to a GEM frame.
The GTC output section assigns GEM frames generated by the Ethernet-to-GEM conversion function, the TDM-to-GEM conversion function, and the non-GEM-to-GEM conversion function to output time slots, based on mapping information generated by the mapping information management function, adds overhead to the assigned GEM frames to create GTC frames, and outputs the GTC frames.
The GTC input section extracts GEM frames from received GTC frames, determines which one of an Ethernet signal, a TDM signal, and a non-GEM signal is included in each GEM frame, and sends GEM frames including Ethernet signals to the GEM-to-Ethernet conversion function, GEM frames including TDM signals to the GEM-to-TDM conversion function, and GEM frames including non-GEM signals to the GEM-to-non-GEM conversion function.
The GEM-to-Ethernet conversion function converts GEM frames to Ethernet signals. The GEM-to-TDM conversion function converts GEM frames to TDM signals. The GEM-to-non-GEM conversion function converts GEM frames to non-GEM signals.
A non-GEM signal is a signal, such as an ATM signal, that is not placed in a GEM frame under the conventional GPON practice. A TDM signal with a different bandwidth from the TDM signals input to the TDM-to-GEM conversion function and output from the GEM-to-TDM conversion function may also be treated as a non-GEM signal.
The mapping information management function generates mapping information from the overhead of the GTC frame input to the GTC input section and sends the mapping information to the GTC output section.
In a preferred embodiment of the above signal processing apparatus, the GTC input section includes a GTC deframing function, a GEM extraction function, and a distribution function, and the GTC output section includes a bandwidth management buffer function, a GEM mapping function, and a GTC framing function.
The GTC deframing function disassembles input GTC frame into overhead and a payload, and sends the overhead to the mapping information management function and the payload to the GEM extraction function. The GEM extraction function extracts a GEM frame from the payload and sends the GEM frame to the distribution function.
The distribution function determines which one of an Ethernet signal, a TDM signal, and a non-GEM signal is included in the GEM frame, and sends the GEM frame to the GEM-to-Ethernet conversion function if it includes an Ethernet signal, to the GEM-to-TDM conversion function if it includes a TDM signal, and to the GEM-to-non-GEM conversion function if it includes a non-GEM signal.
The bandwidth management buffer function stores GEM frames received from the Ethernet-to-GEM conversion function, the TDM-to-GEM conversion function, and the non-GEM-to-GEM conversion function temporarily in a buffer, awaiting output, and sends the GEM frames to the GEM mapping function responsive to commands from the GEM mapping function.
The GEM mapping function assigns the GEM frames received from the bandwidth management buffer function to the output time slots of GTC frames according to the mapping information received from the mapping information management function.
The GTC framing function generates a frame header, attaches the frame header as overhead to one or more GEM frames or fragments thereof to generate a GTC frame, and outputs the GTC frame in the time slot to which the GEM frame or frames in its payload were assigned.
In a preferred embodiment, the GTC input section, GTC output section, mapping information management function, Ethernet-to-GEM conversion function, GEM-to-Ethernet conversion function, TDM-to-GEM conversion function, and GEM-to-TDM conversion function are implemented in a chip set, and the non-GEM-to-GEM conversion function and GEM-to-non-GEM conversion function are implemented outside the chip set.
Alternatively, the GTC input section, GTC output section, and mapping information management function may be implemented in a chip set, and the Ethernet-to-GEM, GEM-to-Ethernet, TDM-to-GEM, GEM-to-TDM, non-GEM-to-GEM, and GEM-to-non-GEM conversion functions may be implemented outside the chip set.
The invention provides a signal processing method for use in generating GTC frames. First, in a conversion step, an input Ethernet signal TDM signal, or non-GEM signal is converted to a GEM frame. Next, in a mapping step, the GEM frame is assigned to a time slot, or is divided into fragments which are assigned to different time slots. Next, in a GTC framing step, overhead is generated for the GEM frames and/or fragments assigned to each time slot, and these GEM frames and/or fragments are output together with the overhead as a GTC frame in the assigned time slot.
The invention also provides a signal processing method for use in receiving GTC frames. First, in a GTC deframing step, a GTC frame is input and disassembled into overhead and a payload. A GEM frame is then extracted from the payload. Whether the GEM frame includes an Ethernet signal, a TDM signal, or a non-GEM signal is determined, and the GEM frame is converted to an Ethernet signal, a TDM signal, or a non-GEM signal, accordingly.
The GTC frame provided by the present invention for use in a gigabit passive optical network comprises an overhead section accommodating information necessary for control, maintenance, and operation, and a payload accommodating user signals. The payload one or more GEM frames, or fragments thereof. A GEM frame may encapsulate an Ethernet signal, a TDM signal, or a non-GEM signal.
In the novel signal processing apparatus and method and GTC frame, Ethernet, TDM, and ATM signals or other non-GEM signals are all converted to GEM frames, thereby providing a more unified form of signal processing than in conventional GPON systems, which convert only Ethernet and TDM signals to GEM frames and do not convert ATM signals to GEM frames.
Consequently, the invented signal processing apparatus does not require a separate bandwidth management buffer function for ATM, a separate ATM mapping function, and a separate ATM extraction function, and has a correspondingly simpler circuit configuration.
If the GTC input section, GTC output section, mapping information management function, Ethernet-to-GEM conversion function, GEM-to-Ethernet conversion function, TDM-to-GEM conversion function, and GEM-to-TDM conversion function are implemented in a chip set, and the non-GEM-to-GEM conversion function and GEM-to-non-GEM conversion function are implemented outside the chip set, then the chip set can be used in signal processing apparatus that does not support ATM service without burdening the apparatus with unnecessary ATM signal-processing circuitry. In this case, the non-GEM-to-GEM and GEM-to-non-GEM conversion functions can be used to process time-division multiplexed signals having a different bandwidth (bit rate) from the TDM signals processed by the TDM interfaces in the chip set.
Alternatively, the chip set may include only the GTC input and output sections and the mapping information management function, forming a core that is independent of the types of communication service being supported. The low-cost core chip set can then be used in all GPON systems, and can be supplemented with only the necessary additional chips in each system in which it is used, where the additional chips provide the Ethernet-to-GEM conversion function, GEM-to-Ethernet conversion function, TDM-to-GEM conversion function, GEM-to-TDM conversion function, non-GEM-to-GEM conversion function, and GEM-to-non-GEM conversion function as necessary.
In the attached drawings:
An embodiment of the invention will now be described with reference to the attached drawings, in which like elements are indicated by analogous reference characters. When the same function appears in different apparatus, reference characters with three numeric digits will be used, the last two numeric digits identifying the function, the first numeric digit identifying the apparatus. For example, the bandwidth management buffer function 130 in the signal processing apparatus 100 in
The description will refer back to
The signal processing apparatus 100 in
The signal processing apparatus 100 in
The signal processing apparatus 100 also comprises an Ethernet interface 102 for output of Ethernet signals, a TDM interface 104 for output of TDM signals, an ATM interface 106 for output of ATM signals, an Ethernet interface 172 for input of Ethernet signals, a TDM interface 174 for input of TDM signals, and an ATM interface 176 for input of ATM signals.
The signal processing apparatus 100 may be used in any of the ONUs 704 in
Ethernet interface 102 converts a received Ethernet signal to a format internal to the ONU, and sends the converted Ethernet signal to the Ethernet-to-GEM conversion function 112. The Ethernet-to-GEM conversion function 112 converts the converted Ethernet signal to a GEM frame. In this process, the Ethernet-to-GEM conversion function 112 receives the port identifier (ID) necessary for generation of the GEM frame from the port-ID manager 120, and uses the port ID to generate the GEM frame.
TDM interface 104 converts a received TDM signal to a format internal to the ONU, and sends the converted TDM signal to the TDM-to-GEM conversion function 114. The TDM-to-GEM conversion function 114 converts the converted TDM signal to a GEM frame. In this process, the Ethernet-to-GEM conversion function 112 receives the port identifier (ID) necessary for generation of the GEM frame from the port-ID manager 120, and uses the port ID to generate the GEM frame.
The ATM interface 106 converts a received ATM signal to a format internal to the ONU, and sends the converted ATM signal to the ATM-to-GEM conversion function 116. The ATM-to-GEM conversion function 116 converts the converted ATM signal to a GEM frame. In this process, the Ethernet-to-GEM conversion function 112 receives the port identifier (ID) necessary for generation of the GEM frame from the port-ID manager 120, and uses the port ID to generate the GEM frame.
In each case, the generated GEM frame is sent to the bandwidth management buffer function 130, where it waits in a predetermined buffer being until to the OLT 701.
In signal processing apparatus according to the present invention, ATM signals as well as Ethernet and TDM signals are mapped onto GEM frames. An ATM signal may be mapped onto a GEM frame, that is, encapsulated in a GEM frame, by any preferred method.
The bandwidth management buffer function 130 sends each GEM frame awaiting output in the predetermined buffer to the GEM mapping function 132 responsive to a command from the GEM mapping function 132.
The GEM mapping function 132 sends the command to the bandwidth management buffer function 130 according to mapping information received from the mapping information extraction function 140, which operates as the mapping information management function, and assigns the GEM frame to an appropriate output time slot for output in a GTC frame. The upstream transmission timings of GTC frames are determined according to the mapping information so as to multiplex the transmissions of different ONUs. The functions of the mapping information extraction function 140 will be described in more detail below.
The GTC framing function 134 generates GTC frames. More specifically, the GTC framing function 134 maps each GEM frame assigned to an output time slot onto the payload of a GTC frame, generates a frame header for the GTC frame, and places the header in the overhead part of the frame.
In upstream transmission, a GTC frame generated in the GTC framing function 134 is converted to an optical signal in the PON interface (not shown) of the ONU, and sent to the OLT.
In downstream transmission, the ONU receives a GTC frame from the OLT. The GTC frame is converted from an optical signal to an electrical signal in the PON interface (not shown) and sent to the GTC deframing function 150.
The GTC deframing function 150 disassembles the GTC frame into overhead and a payload. The GTC deframing function 150 sends the payload of the GTC frame to the GEM extraction function 152, and the overhead to the mapping information extraction function 140.
The mapping information extraction function 140 (the mapping information management function) generates GEM mapping information by extracting an upstream bandwidth map, added by the OLT 701 (
The GEM extraction function 152 extracts a GEM frame from the payload of the GTC frame. The extracted GEM frame is sent to the distribution function 154.
The distribution function 154 determines which one of an Ethernet signal, a TDM signal, and an ATM signal is included in the GEM frame, according to the port ID information received from the port-ID manager 120. The distribution function 154 sends a GEM frame including an Ethernet signal to the GEM-to-Ethernet conversion function 162, a GEM frame including a TDM signal to the GEM-to-TDM conversion function 164, and a GEM frame including an ATM signal to the GEM-to-ATM conversion function 166.
Upon receiving a GEM frame, the GEM-to-Ethernet conversion function 162 converts the GEM frame to an Ethernet signal, and sends the Ethernet signal to the Ethernet interface 172. The Ethernet interface 172 converts the Ethernet signal, which is formatted in the internal ONU format, to an appropriate Ethernet signal format, and outputs the converted Ethernet signal to the subscriber's communication terminal 706.
Similarly, upon receiving a GEM frame, the GEM-to-TDM conversion function 164 converts the GEM frame to a TDM signal, and sends the TDM signal to the TDM interface 174. The TDM interface 174 converts the TDM signal, which is in the internal ONU format, to an appropriate TDM signal format, and outputs the converted TDM signal to the communication terminal 706.
The GEM-to-ATM conversion function 166, when it receives a GEM frame, converts the received GEM frame to an ATM signal, and sends the ATM signal to the ATM interface 176. The ATM interface 176 converts the ATM signal, which is also in the internal ONU format, to an appropriate ATM signal format, and outputs the converted ATM signal to the communication terminal 706.
The novel GTC frame includes an overhead section (not shown), which includes information necessary for communication control, maintenance, and operation, and a payload section, which accommodates user signals. A detailed description of the overhead section of the novel GTC frame will be omitted, since it is the same as in the conventional GTC frame described with reference to
The payload section includes only a GEM partition, which accommodates one or more GEM frames or fragments thereof. Each GEM frame includes only one type of signal: an Ethernet signal, a TDM signal, or a non-GEM signal.
The difference between the GTC frame used in the present invention and the conventional GTC frame is that the payload section is not divided into an ATM partition and a GEM partition. The entire payload section is treated as a GEM partition; there is no ATM partition. The ATM cells that were mapped onto the ATM partition in a conventional GTC frame are mapped onto the GEM frame partition in the novel GTC frame. More precisely, ATM signals, like TDM and Ethernet signals, are encapsulated in GEM frames, which are mapped onto the GEM partition of the GTC frame (see
In the downstream direction, the novel GTC frame has the conventional physical control block, specifying the start and end of each ONU's bandwidth allocation. The overhead section of the frame complies with ITU-T Recommendation G.984, so the frame can be transported on a GPON complying with ITU-T Recommendation G.984.
Downstream GTC frames are received by a GTC framing sublayer 310 in the ONU, and GEM frames read from the payloads of according to the ONU's bandwidth allocation, which is identified in the frame overhead. The GTC deframing function 150 and GEM extraction function 152 in
When the GTC framing sublayer 310 reads a GEM frame, it is received by a GEM TC adapter 321 in the TC adaptation sublayer 320, and a port-ID and PTI filter 323 identifies its logical path from the port ID value and PTI code. If the GEM frame includes an Ethernet or TDM signal and is destined to a GEM client, the port-ID and PTI filter 323 sends the frame signal to the GEM client.
When the GEM frame includes an ATM signal, the port-ID and PTI filter 323 sends the signal to a VPI/VCI filter 325. The VPI/VCI filter 325 identifies the logical path of the signal from the VPI and VCI in the ATM header information encapsulated in the frame, and sends the signal to an ATM client.
The distribution function 154, GEM-to-Ethernet conversion function 162, GEM-to-TDM conversion function 164, and GEM-to-ATM conversion function 166 in
Although no block in
In upstream transmission, the GTC framing function 134, GEM mapping function 132, and bandwidth management buffer function 130 in
Although there is no block in
The OLT receives Ethernet, TDM, and ATM signals from, for example, an IP based network.
The OLT comprises an Ethernet interface 402, a TDM interface 404, and an ATM interface 406. The Ethernet interface 402 converts a received Ethernet signal to a format internal to the OLT, and sends the converted Ethernet signal to an Ethernet-to-GEM conversion function 412. The TDM interface 404 converts a received TDM signal to the internal OLT format, and sends the converted TDM signal to a TDM-to-GEM conversion function 414. The ATM interface 406 converts a received ATM signal to the internal OLT format, and sends the converted ATM signal to an ATM-to-GEM conversion function 416.
The Ethernet-to-GEM conversion function 412, TDM-to-GEM conversion function 414, ATM-to-GEM conversion function 416, a port-ID manager 420, bandwidth management buffer function 430, GEM mapping function 432, and GTC framing function 434 cooperate to generate GTC frames from the Ethernet, TDM, and ATM signals in the same way as the corresponding ONU elements in
In downstream transmission, GTC frames generated in the GTC framing function 434 are output from the PON interface in the OLT to the ONUs.
In upstream transmission, the OLT receives GTC frames as optical signals from the connected ONUs. The PON interface in the OLT converts the GTC frames to electrical signals and sends them to the GTC deframing function 450.
The GTC deframing function 450, GEM extraction function 452, distribution function 454, GEM-to-Ethernet conversion function 462, GEM-to-TDM conversion function 464, GEM-to-ATM conversion function 466, Ethernet interface 472, TDM interface 474, and ATM interface 476 in the OLT in
A mapping information generation function 441, which controls mapping and multiplexing, generates upstream GEM mapping information by calculating bandwidth allocations from the bandwidth control information in the overhead of the GTC frames received from the ONUs. The mapping information generation function 441 sends the generated GEM mapping information to the GEM mapping function 432, thereby operating as the mapping information management function.
The ONU and OLT signal processing apparatus described above converts Ethernet signals, TDM signals, and ATM signals to GEM frames for use in GPON systems, thereby providing a more unified form of signal processing than in conventional GPON systems. As the signal processing apparatus does not require a separate bandwidth management buffer function for ATM, a separate ATM mapping function, and a separate ATM extraction function, it has a simpler configuration than the conventional apparatus in
The novel signal processing apparatus may be implemented as a chip set, that is, a set of two or more monolithic integrated circuits designed to operate together. Such a chip set may include all of the functional elements shown in
Referring to
The signal processing apparatus 500 in
If the signal processing apparatus 500 does not need to support ATM communication, then the GEM interfaces 508, 578 can be used for other purposes. For example, the ATM-to-GEM conversion function and GTM-to-ATM conversion function can be replaced with a TDM-to-GEM conversion function and a GEM-to-TDM conversion function. The TDM interfaces 504, 574, the TDM-to-GEM conversion function 514, and the GEM-to-TDM conversion function 564 in the chip set 580 can then be used to process TDM signals having one bandwidth, and the GEM interfaces, the external TDM-to-GEM conversion function, and the external GEM-to-TDM conversion function can be used to process TDM signals having a different bandwidth.
Alternatively, if only Ethernet signals and one type of TDM signals need to be processed, the GEM interfaces 508, 578 in the chip set 580 can be left unused.
The invention can also be practiced as shown in
The present invention can accordingly provide a low-cost core chip set can then be used in all GPON systems, and can be supplemented with only the necessary additional chips in each system in which it is used.
In addition to these variations of the embodiment shown in
Number | Date | Country | Kind |
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2006-349340 | Dec 2006 | JP | national |