JP4926193B2 - Passive optical network system and station side optical transmission line termination device - Google Patents

Description

  The present invention relates to a high-speed optical access network. More specifically, the present invention relates to a passive optical network (PON) system that can provide a high-speed Internet service to each home using an optical fiber, and a station-side optical transmission line applied to the PON system. Terminating device: related to OLT (Optical Line Terminal).

  In IP (Internet Protocol) networks, in addition to voice communication and data services, video distribution services that require high-speed data transfer, such as triple play services that combine broadcasting / telephone / data communication, have become active. ing. Network television in triple play services: IPTV (Internet Protocol Television) is one of the most important broadband applications.

  A passive optical network (PON) system provides high-speed, broadband Internet access using an optical fiber network to user terminals located in each home. Each PON system is arranged on the user's home side, and is connected to a plurality of subscriber connection devices: ONUs (Optical Network Units) that accommodate one or a plurality of user terminals, and these ONUs are connected via an optical fiber network. Station side optical transmission line termination device: OLT (Optical Line Terminal).

  The optical fiber network of the PON system includes a concentrated optical fiber connected to the OLT, a plurality of branch optical fibers connected to each ONU, and an optical splitter (or optical coupler) that couples the branched optical fiber and the concentrated optical fiber. The optical transmission network between the OLT and the optical splitter can be shared by a plurality of ONUs: ODN (Optical Distribution Network).

  The PON system can significantly reduce the cost of installing optical fibers compared to other broadband access technologies. In particular, a G-PON (Gigabit-Capable PON) system can transfer variable-length data frames at a high speed on the gigabit level, and can provide various broadband network applications to end users. G-PON is disclosed in Non-Patent Documents 1 to 3 recommended by ITU-T.

JP 2002-185989 A

ITU-T G.984.1 “Gigabit-capable Passive Optical Networks (GPON): General characteristics” ITU-T G.984.2 `` Gigabit-capable Passive Optical Networks (GPON): Physical Media Dependent (PMD) layer specification '' ITU-T G.984.3 “Gigabit-capable Passive Optical Networks (GPON): Transmission convergence layer specification”

  However, in the conventional PON system, only an ONU having the same signal transmission speed as that of the OLT can be connected to the OLT. Therefore, if an OLT with a high transmission speed is used to realize a high-speed information distribution service, There is a problem that it becomes impossible to connect to a low-speed ONU.

  For example, an ONU that supports 2.4 Gbps of the G-PON standard can communicate only with an OLT that supports 2.4 Gbps. Therefore, when a communication carrier introduces a new 10 Gbps OLT to the Internet connection service, an existing 2.4 Gbps ONU that cannot transmit and receive an optical signal of 10 Gbps due to a difference in clock frequency will install a new 10 Gbps OLT. Connection to the Internet via it becomes impossible. Since many ONUs are installed in the PON system, if the existing low-speed ONU is replaced with a high-speed type as the OLT speeds up, the economic burden becomes enormous.

  In the PON system, the communication speed between the OLT and the ONU is improved from 2.4 Gbps to 10 Gbps due to the advancement of high-speed technology, but once the PON system is in operation, as described above. In addition, the cost of replacing existing ONUs with high-speed ONUs is enormous. Therefore, it is practically difficult for a communication carrier to replace an existing OLT with a new OLT that has been increased in speed even when providing a high-speed information distribution service to a user. That is, the PON system has a problem that it is not possible to connect a plurality of types of ONUs having different signal transmission rates to the OLT.

  As one related prior art, for example, in Japanese Patent Application Laid-Open No. 2002-185989 (Patent Document 1), an upper circuit and a plurality of subscriber circuits are connected by a common data bus, and each subscriber has a common data bus. In a 1-to-M transmission system using time division, in the time domain (time slot) assigned to a high-speed subscriber circuit, a clock of k times the time domain used by other low-speed subscriber circuits It has been proposed to use frequencies. However, this prior art is premised on time division multiplexed communication in which time slots are fixedly assigned to each subscriber circuit, and in a PON system in which the destination ONU is different for each downlink frame transmitted from the OLT. It does not solve the problems described above.

An object of the present invention is to provide a passive optical network (PON) system in which a plurality of types of subscriber connection devices (ONUs) having different signal transmission rates can be connected to one station side optical transmission line termination device (OLT). It is in.
An object of the present invention is to provide a station side optical transmission line termination device (OLT) for a PON system that can connect a plurality of types of subscriber connection devices (ONUs) having different signal transmission rates.

  In order to achieve the above object, in the PON system of the present invention, a station side optical transmission line termination device (OLT) connected to a plurality of types of subscriber connection devices (ONUs) having different signal transmission rates via an optical distribution network is provided. An optical transmission / reception unit coupled to the optical distribution network, a transmission / reception line interface connected to the wide area network, and a downstream frame including a packet received from the wide area network via the transmission / reception line interface in the header portion including identification information of the destination ONU And a downlink transmission control unit that modulates the downlink frame at a rate according to the signal transmission rate of the destination ONU and outputs the modulated signal to the electrical / optical conversion unit connected to the optical transmission / reception unit. It is characterized by that.

  More specifically, in the present invention, the OLT includes an ONU management table in which the correspondence between the identification information of each ONU and the signal transmission rate is stored, and the downstream frame transmitted to the optical distribution network is represented by the ONU management table. Modulation is performed at a signal transmission rate corresponding to the identification information of the destination ONU shown.

  In one embodiment of the present invention, the downlink frame processing unit accumulates each downlink frame in a buffer memory for each signal transmission rate indicated by the ONU management table, and the downlink transmission control unit is read from the buffer memory. The downstream frame is modulated at a rate corresponding to the signal transmission rate and output to the electrical / optical converter.

  In the ONU management table, the signal transmission rate and priority are stored in association with the identification information of each ONU, and each downlink frame is signal-transmitted by the ONU management table in the downlink frame processing unit. By storing in the buffer memory for each speed and priority, the downlink transmission controller reads out the downlink frames stored in the buffer memory for each signal transmission speed in order of priority, and modulates at a speed according to the signal transmission speed. It becomes possible to make it.

  According to the present invention, ONUs can be accommodated in a plurality of types having different signal transmission speeds in the same OLT, so that it is possible to replace the OLT of the PON system with a new accelerated PLT during operation.

The figure which shows an example of a structure of the PON system to which this invention is applied. The figure which shows the format of the downstream frame which OLT10 receives from the router by the side of network NW, and the format of the GEM frame transmitted in a PON section. The figure for demonstrating the format of the GTC frame transmitted to the optical fiber network of PON area from OLT10. The block block diagram which shows the 1st Example of OLT10 of this invention. The figure which shows the ONU management table with which OLT10 of this invention is provided. The figure for demonstrating the downlink transmission signal in a 1st Example. The block block diagram which shows the 1st Example of OLT10 of this invention. The figure for demonstrating the downlink transmission signal in a 1st Example. The figure for demonstrating an example of the transmission sequence of the downstream frame in the PON system of this invention. The figure which shows the general message sequence of the discovery and ranging in a PON system. The figure which shows the message sequence of the discovery in the PON system of this invention. The figure which shows the message sequence of the ranging in the PON system of this invention. The figure for demonstrating an example of the method of transmitting a some downlink frame collectively by one time slot.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the case where the present invention is applied to G-PON of the ITU standard will be described. However, the present invention is applicable to information transfer using PON systems other than G-PON, for example, Ethernet (registered trademark) frames. The present invention can also be applied to suitable GE-PON (Gigabit-Ethernet PON) and B-PON (Broadband PON) in which information is transferred by a fixed-length ATM cell in the PON section.

FIG. 1 shows a configuration diagram of a PON system to which the present invention is applied.
The PON system includes a station-side optical transmission line termination unit (OLT) 10, a plurality of subscriber connection units (ONU) 20 (20-1 to 20-k), and an optical distribution network in a PON section that connects these elements. Consists of ODN. The optical distribution network in the PON section is composed of a collecting optical fiber 11 connected to the OLT 10 and branch optical fibers 12-i (i = 1 to k) connected to each ONU 20-i, and the branch optical fibers 12-i. Is branched from the concentrated optical fiber 11 by an optical splitter (optical coupler) 13. The OLT 10 is normally installed in a user line accommodation station owned by a carrier or ISP (Internet Service Provider), and the ONU 20-i (i = 1 to k) is installed in a building such as an office or a condominium, or a user's house. .

Each ONU 20-i has a plurality of user connection lines Lij (j = 1 to m), and accommodates a plurality of user terminals TE via these connection lines. For example, as shown in TE-111, TE-112 (TE-k11, TE-k12), the user terminal transmits an ONU 20-1 (ONU20-) via a home router or a home switch 30-1 (30-k). k) and a case of being directly connected to the ONU 20-2 (ONU 20-k), for example, as shown in TE-21 and TE-2m (TE-km).
NW indicates a wide area network (including an ISP network) composed of a plurality of routers 40 (40-1 to 40-n). Each user terminal TE connected to the PON system communicates with the server 50 (50-1, 50-2) connected to the wide area network NW via the ONU 20-i, the OLT 10, and the router 40-1.

  In FIG. 1, for simplification, the servers 50-1 and 50-2 are directly connected to the router 40-1, but in an actual network, these servers 50-1 and 50-2 and the router 40-1 are connected. There may be another router between the two. In addition to the servers 50-1 and 50-2, the network NW includes a large number of servers accessible from each user terminal, but is omitted in FIG.

  When the OLT 10 receives a frame addressed to the user terminal TE-111 transmitted by the server 40-2 from the communication line L1 via the router 40-1, for example, the OLT 10 conforms to the transmission layer protocol specific to the PON section. It is converted into a frame format (GEM frame in G-PON) and transmitted to the optical fiber 11. In the PON section, the downstream frame transmitted from the OLT 10 to the optical fiber 11 is branched to the branch optical fibers 12-1 to 12-k by the splitter 13 and broadcast to all the ONUs 20-1 to 20-k.

  Each ONU 20-i is assigned a unique port ID within the PON. Each ONU refers to the destination identification information (port ID) indicated by the header part of the received frame (GEM header in G-PON), and the frame in which the destination identification information matches the own port ID or the destination identification information indicates the multicast port ID. The indicated frame is received and the other received frames are discarded. A GEM header including a port ID unique to the ONU 20-1 is attached to a GEM frame including a frame addressed to the user terminal TE-111. Therefore, only the ONU 20-1 receives and processes this GEM frame. The ONU 20-1 removes the GEM header from the GEM frame, and transfers the received frame to the connection line L11 with the user terminal TE-111 according to the destination information indicated by the header of the received frame.

  On the other hand, upstream frames from the ONUs 20-1 to 20-k toward the network NW are transmitted using individual transmission time zones that the OLT 10 previously assigns to each ONU in order to avoid collision on the optical fiber 11. The OLT 10 is reached while being time-division multiplexed on the optical fiber 11. The OLT 10 converts the format as necessary, and then transfers the upstream frame received from the optical fiber 11 to the router 40-1.

  In the present invention, a plurality of ONUs having different signal transmission rates are connected to the OLT 10. In the following description, it is assumed that the ONUs 20-1 to 20-k have a signal transmission rate of either 2.4 Gbps or 10 Gbps.

  FIG. 2 shows the format of the downlink communication frame F1 received by the OLT 10 from the router 40-1 when the communication protocol between the user terminal and the ONU and the communication protocol between the OLT 10 and the router 40-1 are Ethernet. And the format of the downstream GEM frame 70 in the PON section.

The received frame F1 from the router 40-1 is composed of an IP packet 60 and an L2 header 63. The IP packet 60 includes an IP header 61 and an IP payload 62. The IP header 61 includes a source IP address (SA) 611, a destination IP address (DA) 612, and other header information.
Here, the source IP address (SA) 611 of the IP header indicates the IP packet source, for example, the IP address of the server 50-1, and the destination IP address (DA) 612 is the user who is the destination of the IP packet. Indicates the IP address of the terminal.

  In this embodiment, the L2 header 63 is an Ethernet header and includes a destination MAC address (DMAC) 631, a source MAC address (SMAC) 632, a protocol type 634, and other header items 635. In this embodiment, a value indicating that the packet is an IP packet is set in the protocol type 634 indicating the type of packet following the L2 header. Further, DMAC 631 indicates the MAC address of the user terminal that is the destination of the Ethernet frame, and SMAC indicates the MAC address of the router 40-1 that is the transmission source of the Ethernet frame. When the user terminal transmits / receives a frame using a VLAN (Virtual LAN) formed with the router 40-1 in order to enhance the safety of communication, the L2 header 63 includes a VLAN identifier (VID) 633. Is included.

  The downstream GEM frame 70 in the PON section includes a 5-byte GEM header 71 and a variable-length GEM payload 72. The downstream frame of the PON section is subjected to reception control according to the port ID included in the GEM header 71. The OLT 10 sets the reception frame F1 from the router 40-1 in the GEM payload 72, and sets the port ID for designating the ONU that should receive the reception frame F1 in the GEM header 71. When the received frame F1 from the router 40-1 is a multicast frame to be received by all ONUs connected to the optical fiber 11, the OLT 10 sends the received frame F1 from the router 40-1 to the GEM payload 72. Then, a predetermined multicast port ID is set in the GEM header 71.

FIG. 3 shows a format of a TC (Transmission Convergence) downstream frame (GTC frame in G-PON) 80 transmitted from the OLT 10 to the optical fiber 11.
The GTC downstream frame 80 includes a PCBd (Physical Control Block downstream) 81 serving as a header and a GTC payload 82. For example, in the case of G-PON, the maximum length of the GTC downstream frame 80 is 38880 bytes. The GEM frame 70 described in FIG. 2 is mapped to the GTC payload 82 as indicated by GEM (1) and GEM (2) in FIG.

  In this embodiment, a GEM frame addressed to 2.4 Gbps ONU is transmitted by one GTC downstream frame 80, and a GEM frame addressed to 10 Gbps ONU is transmitted by another GTC downstream frame 80.

FIG. 4 shows a first embodiment of the OLT 10 of the present invention that can be connected to a plurality of types of ONUs having different signal transmission rates.
The OLT 10 includes an OLT control unit 100, an optical transmission / reception unit 101 connected to the concentrating optical fiber 11, a transmission line interface 102A and a reception line interface 102B connected to the line L1 on the wide area network side, and an optical transmission / reception unit 101 and transmission. It consists of an upstream signal processing circuit provided between the line interface 102A and a downstream signal processing circuit provided between the optical transmission / reception unit 101 and the reception line interface 102B.

  The upstream signal processing circuit includes an optical / electrical (O / E) conversion unit 110 that converts an optical signal received by the optical transmission / reception unit 101 into an electrical signal, and a 10 Gbps demodulation circuit 111 </ b> A connected to the O / E conversion unit 110 and 2. The demodulating unit includes a 4 Gbps demodulating circuit 111B, a selector 113 that selects one output of the demodulating circuits 111A and 111B, and an upstream frame processing unit 114 connected to the selector 113. The upstream frame processing unit 114 includes an upstream frame termination unit 1141 that reproduces an upstream frame from the output signal of the selector, an upstream frame analysis unit 1142 connected to the upstream frame termination unit 1141, and a frame output from the upstream frame analysis unit 1142. Is composed of an upstream frame generation unit 1143 that converts the data into a format compatible with the protocol on the communication line L1.

  The upstream frame analysis unit 1142 analyzes the upstream reception frame. If the reception frame is a control frame in the PON section, the upstream frame analysis unit 1142 outputs the control frame to the OLT control unit 100 and transfers the reception frame to the user frame or the router 40-1. In the case of a power control frame, this is transferred to the upstream frame generation unit 1143.

  For example, if the protocol on the communication line L1 is ATM, the upstream frame generation unit 1143 converts the received frame into an ATM cell group and transfers it to the transmission line interface 102A. Information necessary for frame format conversion is read from the network configuration information memory 130. In the present embodiment, it is assumed that the protocol on the communication line L1 is Ethernet, and the upstream received frame is also an Ethernet frame. Therefore, the upstream frame generation unit 1143 uses the Ethernet frame output from the upstream frame analysis unit 1142 as a result. What is necessary is just to transfer to the transmission line interface 102A as it is.

  On the other hand, the downlink signal processing circuit includes a reception buffer 120 for temporarily storing downlink frames (or downlink packets) received by the reception line interface 102B from the communication line L1, and a downlink frame read from the reception buffer 120 as a PON section. A downlink frame processing unit 121 that converts the frame format into a specific frame format and outputs it, a buffer memory 122 that temporarily buffers the downlink PON frame output from the downlink frame processing unit 121, a downlink transmission control unit 123, An optical (E / O) converter 124, a switch 130 that selectively distributes the downstream frame read from the buffer memory 122 to either the 10 Gbps modulation circuit 131A or the 2.4 Gbps modulation circuit 131B, and the modulation circuits 131A and 131B Select one of the output signals of Consisting supplies the selector 132. the E / O conversion unit 124. The E / O conversion unit 124 converts the output signal from the selector 132 into an optical signal and outputs the optical signal to the optical transmission / reception unit 101.

  The downlink frame processing unit 121 includes a downlink frame analysis unit 1210 that analyzes a downlink frame read from the reception buffer 120, a buffer memory 1211 that temporarily buffers a frame output from the downlink frame analysis unit 1210, and the OLT control unit 100. And a PON frame generation unit 1212 that converts a downlink user frame read from the buffer memory 1211 into a GEM frame.

  The OLT control unit 100 receives a control frame indicating the transmission data accumulation state or transmission data length from each ONU, and controls the transmission time zone of the uplink frame to be assigned to each ONU by the bandwidth management table 140. The transmission time zone of the uplink frame assigned to each ONU is notified to each ONU by the downlink control frame generated by the OLT control unit.

  The ONU management table 150 stores the correspondence between the ONU identifier (port ID) 151 and the signal transmission speed (clock frequency) 152 as shown in FIG. Further, the header management table 160 includes a plurality of table entries indicating the correspondence relationship between the destination address (DMAC) of the downstream frame and the port ID to be set in the GEM header. For example, the table entry including the MAC addresses of the user terminals TE-111 and TE-112 in FIG. 1 stores the port ID of the ONU 20-1 as the port ID.

  The PON frame generation unit 1212 searches the header management table 160 for a port ID corresponding to the DMAC indicated by the L2 header of the downstream frame, and searches the ONU management table 150 for a signal transmission rate (10 Gbps or 2.. 4 Gbps) and a GEM header including a port ID is generated. The PON frame generation unit 1212 adds the GEM header to convert the downlink user frame read from the buffer memory 1211 and the downlink control frame supplied from the OLT control unit 100 into a GEM frame, and buffers the GEM frame. The memory 122 is buffered for each signal transmission rate.

The downlink transmission control unit 123 forms a TC frame (GTC frame in the present embodiment), and transmits the GEM frame read from the buffer memory 122 using the payload of the TC frame. The downlink transmission control unit 123 selectively distributes the GEM frame read from the buffer memory 122 to the modulation circuit 131A or 131B by the switch 130. The GEM frame read from the buffer area with the clock frequency of 10 Gbps is modulated by the modulation circuit 131A of 10 Gbps, and the GEM frame read from the buffer area with the clock frequency of 2.4 Gbps is the modulation circuit 131B of 2.4 Gbps. Modulated with. The downlink transmission control unit 123 selectively outputs the modulation signals generated by the modulation circuits 131 </ b> A and 131 </ b> B to the E / O conversion unit 124 by controlling the selector 132 in conjunction with the switch 130.

  As described above, by switching the modulation circuit to be applied according to the port ID indicated by the GEM header, for example, as schematically shown in FIG. 6, the frequency in which the GEM frame is adapted to the signal transmission rate of the destination ONU. Can be modulated with. The downstream frame is transferred to all the ONUs through the optical fiber network. With the above configuration, each ONU 20 selects a GEM frame having its own port ID from among the GEM frames matching the respective signal transmission speeds (clock frequencies). It is possible to selectively perform reception processing.

  Since the OLT 10 assigns an upstream frame transmission band to each ONU 20, the OLT 10 can control the selector 113 in accordance with the reception timing of the upstream frame from each ONU. Therefore, when receiving an upstream frame from an ONU with a signal transmission rate of 10 Gbps, the selector 113 selects the output of the 10 Gbps demodulation circuit 111A, and when receiving an upstream frame from an ONU with a signal transmission rate of 4.2 Gbps, the selector 113 By selecting the output of the 4.2 Gbps demodulation circuit 111B at 113, the demodulated uplink frame signal can be supplied to the uplink frame termination unit 1141.

FIG. 7 shows a second embodiment of the OLT 10 of the present invention.
The OLT 10 of the second embodiment uses 10 Gbps as a standard signal transmission rate. In this embodiment, a bit string conversion circuit 133 is provided between the switch 130 and the selector 132 of the downlink signal processing circuit, and the bit string conversion circuit 133 converts the bit string of the downlink frame transmitted to the 2.4 Gbps ONU to 10 Gbps. It is characterized by converting to a bit string.

  The optical signal transmission / reception unit 101 of the OLT 10 uses, for example, 10 Gbps signal transmission / reception in the NRZ (Non Return to Zero) format as a standard mode. FIG. 8A shows a bit string of a frame that is read from the buffer memory 122 and transmitted to an ONU that supports 2.4 Gbps. When the bit string conversion circuit 133 multiplies each bit of the transmission frame by 4 as shown in FIG. 8B and modulates at a clock frequency of 10 Gbps by the modulation circuit 134, as shown in FIG. A 2.4 Gbps signal can be artificially transmitted as a 10 Gbps optical signal.

  On the other hand, an upstream frame transmission signal transmitted from each ONU is demodulated by a 10 Gbps demodulation circuit 111 and then converted to a 2.4 Gbps signal by a bit string conversion circuit 112. When the OLT control unit 100 receives an upstream frame transmitted from a 10 Gbps ONU, the selector 113 selects the output of the demodulation circuit 111 and receives an upstream frame transmitted from a 2.4 Gbps ONU. The selector 113 selects the output of the bit string conversion circuit 112 and supplies it to the upstream frame termination unit 114.

FIG. 9 shows an example of a transmission sequence of a downstream frame from the OLT 10 to the ONU 20.
The OLT 10 transmits each downlink frame at a transmission rate corresponding to the signal transmission / reception rate of the destination ONU of the downlink frame. Therefore, even when a plurality of types of ONUs having different signal transmission / reception speeds are connected to the OLT 10, each ONU 20 can receive an optical signal at a clock frequency suitable for each signal transmission / reception speed. The synchronization speed is usually on the order of 10 to 500 nsec, depending on the clock frequency speed and the receiver performance.

  In the example shown in FIG. 9, the OLT 10 divides the transmission bandwidth of the downstream frame into a slot for 10 Gbps and a slot for 2.4 Gbps, as shown in (A). Each ONU corresponding to 10 Gbps is notified of the start of the downlink communication slot by a communication start notification (control frame) F10-1 transmitted at a signal speed of 10 Gbps, and a communication end notification F12- transmitted at a signal speed of 10 Gbps. 1 notifies the end of the downlink communication slot. The 10 Gbps downlink data frames (GEM frames) F11-1, F11-2,... Are transmitted after the communication start notification F10-1.

  Similarly, each ONU corresponding to 2.4 Gbps is notified of the start of the downlink communication slot by a communication start notification (control frame) F10-2 transmitted at a signal speed of 2.4 Gbps, and the downlink data frame F21-1 , F21-2,..., F21-2 is transmitted at a signal speed of 2.4 Gbps to notify the end of the downlink communication slot.

  Each communication start notification of 10 Gbps and communication start notification of 2.4 Gbps are bandwidth control for notifying the clock synchronization bit and the bandwidth (or the number of transmission bits) of the downlink data frame transmitted in each slot to the ONU. Contains information. In the case of G-PON, PCBd (Physical Control Block downstream) serving as a header of the GTC frame can be used as the communication start notification F10.

  As shown in FIG. 9 (C), each ONT 22 corresponding to 10 Gbps establishes clock synchronization upon reception of the communication start notification F10-1, and the header (GEM) of the downlink data frames F11-1, F11-2,. The port ID indicated by the header) is determined, and the downlink data frame is selectively received. Since the 2.4 Gbps ONU cannot be clock-synchronized with the optical signal of the communication start notification F10-1 of 10 Gbps, as shown in FIG. 9B, the frames F10-1, F11-1, and F12-1 of 10 Gbps are used. Cannot be received.

The OLT 10 causes each ONU corresponding to 10 Gbps to prepare to stop receiving a 10 Gbps downstream optical signal by transmitting a communication end notification F12-1. By notifying the reception stop of the 10 Gbps downstream optical signal, when the downstream optical signal speed is switched from 10 Gbps to 2.4 Gbps in the downstream slot of 2.4 Gbps, each ONU corresponding to 10 Gbps is synchronized. It can prevent falling into an error state. It should be noted that a 10 Gbps communication end notification F12-1 notifies each 10 Gbps ONU of the length of the subsequent 2.4 Gbps downlink slot (bandwidth or number of bits of 2.4 Gbps optical signal). Good. In this case, each ONU can expect the start of the next downlink time slot of 10 Gbps.
In the 2.4 Gbps downlink slot, the OLT 10 repeats the same operation as described above for the 2.4 Gbps compatible ONU.

FIG. 10 shows a general message sequence of discovery and ranging performed between the OLT 1 and the ONU 20.
The OLT 10 (OLT control unit 100) sends a “GATE” message for discovery to all ONUs in order to confirm that a new ONU has been connected or that the connected ONU is operating normally. Broadcast periodically (501). Each ONU that has received the GATE message returns a “REGSITER_REQUEST” message including ONU information to the OLT 10 when a random waiting time has elapsed (502).

  When the OLT 10 receives the REGSITER_REQUEST message from the ONU 20-1, the OLT 10 stores the ONU information, and then returns a “REGSITER” message to the ONU 20-1 (503). Thereafter, the OLT 10 transmits a “GATE” message including the port ID of the ONT to the ONU 20-1 (504). When the ONU 20-1 that has received the GATE message returns a “REGSITER_ACK” message to the OLT 10 (505), the discovery process for the ONU 20-1 is completed. The procedure (502 to 505) similar to the above is repeated for other ONUs.

Next, ranging will be described.
In the PON system, there is a difference in the length of the branch optical fibers that form the optical distribution network ODN. Therefore, a difference occurs in the time until the optical signal transmitted from each ONU 20 arrives at the OLT 10. Therefore, the OLT 10 measures the physical distance (transmission path length) between each ONU 20 by ranging and adjusts the transmission timing of the upstream message from each ONU. In ranging, the OLT 10 transmits a ranging GATE message including an ONU identifier (port ID) and time information to each ONU (510). When each ONU receives a GATE message including its own port ID, it transmits a REPORT message including the port ID and time information to the OLT 10 when a random waiting time has elapsed (511).

In the PON system of the present invention, as described below, the OLT 10 performs discovery and ranging for a plurality of types of ONUs having different signal transmission rates.
FIG. 11 shows an example of a message sequence for discovery executed between the OLT 10 and the ONU 20 of the present invention.
In this embodiment, the OLT 10 executes transmission of a discovery message (GATE) targeted for a 10 Gbps-compatible ONU and transmission of a discovery message (GATE) targeted for a 2.4 Gbps-enabled ONU in different time slots. To do.

  As shown in FIG. 11A, in this embodiment, the OLT 10 transmits a 2.4 Gbps downlink communication start notification F20-1, and then sets the first discovery control frame, that is, the broadcast port ID in the header. In addition, a GATE message F21-1 received by all ONTs compatible with 2.4 Gbps is broadcast. After transmitting the GATE message F21-1, the OLT 10 issues a 2.4 Gbps downlink communication end notification F22-1. Thereafter, the OLT 10 transmits a 10 Gbps downlink communication start notification F20-2, broadcasts a 10 Gbps GATE message F21-2 received by all ONTs compatible with 10 Gbps, and sends a 10 Gbps downlink communication end notification F22-1. .

  The 2.4 Gbps ONU, for example, 20-1 receives the 2.4 Gbps control frames F20-1, 21-1, and 22-1 as shown in FIG. 11B, and receives the 10 Gbps control frame F20. -2, 21-2, and 22-2 are not received. Similarly, an ONU corresponding to 10 Gbps, for example, 20-2, receives control frames F20-2, 21-2, and 22-2 of 10 Gbps as shown in FIG. 11C and receives a control frame of 2.4 Gbps. F20-1, 21-1, and 22-1 are not received.

The ONU 20-1 uses the discovery control frame (GATE message) F21-1 (or the communication end notification F22-1) as a reference, and when the random waiting time RD # 1 has elapsed, the ONU 20-1 includes a REGSITER_REQUEST message F23- containing ONU information. Return # 1 to the OLT 10. As ONU information, for example, the serial number (SN) is applied in the case of G-PON, and the MAC address of the ONU is applied in the case of GE-PON.
Other ONUs 20-n that support 2.4 Gbps also return a REGSITER_REQUEST message F23- # n including ONU information to the OLT 10 when the random waiting time RD # n has elapsed.

  The ONU 20-2 corresponding to 10 Gbps has REGSITER_REQUEST including ONU information when a random waiting time RD # 2 has elapsed with reference to the discovery control frame (GATE message) F21-2 (or the communication end frame F22-2). A message F23- # 2 is returned to the OLT 10.

FIG. 12 shows an example of a ranging message sequence executed between the OLT 10 and the ONU 20 of the present invention.
As shown in FIG. 12A, for example, the OLT 10 sequentially transmits 2.4 Gbps ONUs that have been confirmed by discovery after transmitting a 2.4 Gbps communication start notification F30-1. A ranging control frame, that is, a ranging GATE message including an ONT identifier (port ID) and time information is transmitted, and a response from the ONU is awaited.

  For example, when the OLT 10 transmits a GATE message F31-1 to the ONT 20-1 whose ONT identifier is # 1, as shown in FIG. 12B, the ONT 20-1 sends a REPORT message F32-1 including time information. Return to OLT10. When the OLT 10 receives the REPORT message F32-1, the OLT 10 completes ranging for the ONU 20-1, and transmits a GATE message F31-3 including the ONT identifier of the next ONU corresponding to 2.4 Gbps, for example, the ONU 20-3. , Wait for a response from the ONU. In this case, as shown in FIG. 11C, the ONT 20-1 returns a REPORT message F32-1 including time information to the OLT 10.

In this manner, when ranging is completed for all 2.4 Gbps ONUs, the OLT 10 transmits a 10 Gbps communication start notification F30-2, and then the 10 Gbps compatible ONUs whose existence has been confirmed by discovery. Are sequentially selected, a GATE message for ranging is transmitted, and a response from the ONU is awaited. 10Gbps compatible ONU20-2, as shown in (D) of FIG. 12, the control frame of 2.4Gbps F30-1, F31-1, a no response for F31-3, 10Gbps communication start notification When F30-2 is received, it waits for the reception of a GATE message addressed to its own node. When a GATE message addressed to its own node is received, a REPORT message including time information is returned to the OLT 10.

  FIG. 13 shows an example of a method of transmitting a plurality of downlink frames (GEM frames) having the same signal transmission rate in one time slot (TC frame). FIG. 13A shows a frame queue 122A for 10 Gbps and a frame queue 122B for 2.4 Gbps formed in the buffer memory 122.

  When the PON frame generation unit 1212 of the downlink frame processing unit 121 illustrated in FIGS. 4 and 7 generates a GEM frame including a port ID in the GEM header unit, the PON frame generation unit 1212 refers to the ONU management table 150 and corresponds to the port number. The signal transmission rate (clock frequency) is specified, and the GEM frame is buffered in the frame buffer 122A or 122B corresponding to the signal transmission rate. In the figure, the GEM frame is generated in the order of A, B, C, and D.

  The downlink transmission control unit 123 alternately provides a time slot for 10 Gbps and a time slot for 2.4 Gbps. For example, after transmitting a communication start notification F10-1 of 10 Gbps in the TC header portion in the time slot for 10 Gbps The GEM frame F11-1 is sequentially read out from the 10 Gbps frame queue 122A in the FIFO (First-In First-Out) format, transmitted using the payload of the TC frame, and then the communication ends at 10 Gbps at the end of the TC frame. Notification F12-1 is sent out. Next, the downlink transmission control unit 123 transmits a 2.4 Gbps communication start notification F10-2 in the TC header portion in the 2.4 Gbps time slot, and then transmits the GEM frame F11 from the 2.4 Gbps frame queue 122B. -2 are sequentially read out in the FIFO format, transmitted using the payload of the TC frame, and a 2.4 Gbps communication end notification F12-2 is transmitted at the end of the TC frame.

  Here, the GEM frames for each signal speed stored in the frame queues 122A and 122B are transmitted in the FIFO format. For example, as shown in FIG. 5B, the ONU management table 150 stores the ONU identifier (port number). ), The signal transmission rate (clock frequency) 152 and the priority 153 are registered, and the PON frame generation unit 1212 buffers the GEM frame in the buffer memories 122A and 122B according to the priority. May be. In this case, the downlink transmission control unit 123 sequentially reads the GEM frame from the high priority queue in each time slot, and reads the GEM frame from the low priority queue when the high priority queue becomes empty. It becomes possible to preferentially transmit high priority frames to the ONU.

  In the above embodiment, in each time slot for 10 Gbps and 2.4 Gbps, the OLT 10 continuously transmits a plurality of downlink frames having the same signal speed, but one TC frame is used as a time slot for 10 Gbps. The time slot may be divided into 2.4 Gbps time slots, and the downlink frame transmission described with reference to FIG. 9 may be performed in each time slot.

  In the embodiment, the operation of the PON system of the present invention has been described by taking G-PON as an example, but the present invention can also be applied to other PONs other than G-PON. In the G-PON described in the embodiment, the port ID is an ONU identifier. For example, in the case of a B-PON system, a virtual channel identifier (VPI), and in the case of a GE-PON, a data logic link identifier (LLID). : Logical link Identifier) can be used as the identifier of the ONU, in other words, as the link ID of the PON system. Therefore, by registering the value of VPI or LLID as the ONU identifier (link ID) in the ONU management table 150 and storing the signal transmission rate (clock frequency) 152 in association with this value, B-PON or GE -Even in a PON, a plurality of types of ONUs having different signal transmission rates can be accommodated in one OLT.

In the embodiment, the OLT transmits a communication start notification of 2.4 Gbps and 10 Gbps using the header portion of the TC frame. For example, in the case of GE-PON, these notifications are transmitted as individual frames. it can.
According to the PON system of the present invention, since a plurality of types of ONUs having different signal transmission rates can be accommodated in one OLT, the performance of the OLT can be flexibly upgraded without replacing the existing ONU.

10: OLT, 11, 12: optical fiber network, 13: optical coupler, 20: ONU,
30, 40: router, TE: user terminal,
100: OLT control unit 101: Optical transmission / reception unit 102A: Transmission line interface
102B: reception line interface, 110: O / E conversion unit, 111: demodulation circuit,
114: Upstream frame processing unit, 1141: Upstream frame termination unit,
1142: uplink frame analysis unit, 1143: uplink frame generation unit, 120: reception buffer, 121: downlink frame processing unit, 122: buffer memory, 123: downlink transmission control unit,
124: E / O converter, 130: switch, 131: modulation circuit,
113, 132: selector, 112, 133: bit string conversion circuit.

Claims (8)

A station side optical transmission line termination device (OLT) of a passive optical network (PON) connected to a plurality of types of subscriber connection devices (ONUs) having different signal transmission rates via an optical distribution network,
An optical transceiver coupled to the optical distribution network;
An electrical / optical converter connected to the optical transceiver;
A transmission / reception line interface connected to a wide area network;
An OLT control unit that generates a downlink control frame;
A downlink frame processing unit that converts a downlink control frame generated by the OLT control unit and a frame received from the wide area network through the transmission / reception line interface into a downlink frame including identification information of a destination ONU in a header unit;
When a new downlink frame is transmitted by switching the modulation rate, a communication end notification modulated at the current modulation rate is output to the electrical / optical converter, the modulation rate is switched, and a new signal transmission rate is transmitted. after the output of the communication start notification including a clock synchronization bits, and a downlink transmission control unit for outputting the new downstream frame,
The station-side light characterized in that the electrical / optical conversion unit converts the communication end notification, communication start notification and downlink frame output from the downlink transmission control unit into an optical signal and outputs the optical signal to the optical transmission / reception unit. Transmission line termination equipment. 2. The downlink transmission control unit outputs a plurality of downlink frames having the same signal transmission rate after outputting the communication start notification to the electrical / optical conversion unit. Station side optical transmission line termination equipment. The ONU has a first or second signal transmission rate;
The downlink transmission control unit alternately forms first and second downlink communication slots that start with the communication start notification and end with the communication end notification by switching the modulation rate, respectively. Transmitting a downlink frame group destined for the ONU having the first signal transmission rate in the communication slot, and transmitting a downlink frame group destined for the ONU having the second signal transmission rate in the second downlink communication slot. The station side optical transmission line termination device according to claim 1 or 2, characterized in that The communication start notification includes control information indicating a bandwidth of a downlink frame transmitted in a corresponding time slot, and the communication end notification includes control information indicating a length of a next time slot. Item 4. The station side optical transmission line termination device according to Item 3. An optical / electrical converter connected to the optical transceiver;
A demodulator that demodulates the received signal output from the optical / electrical converter at a rate corresponding to a signal transmission rate;
An uplink frame output from the demodulator, a PON control frame is output to the OLT controller, and other frames are output to the transmission / reception line interface.
The OLT control unit generates a plurality of discovery frames for each signal transmission rate,
After the discovery frame is converted into the downlink frame by the downlink frame processing unit, the discovery frame is supplied to the downlink transmission control unit and modulated at a rate corresponding to the signal transmission rate of the ONU to be discovered, and the electrical / optical The station side optical transmission line termination device according to any one of claims 1 to 4, wherein the station side optical transmission line termination device is output to the conversion unit. The OLT control unit generates a plurality of ranging frames for each signal transmission rate,
The ranging frame generated by the OLT control unit is modulated by the downlink transmission control unit at a rate corresponding to the signal transmission rate of the ONU to be ranged, and is output to the electrical / optical conversion unit. The station side optical transmission line termination device according to claim 5. A station side optical transmission line termination device (OLT) of a passive optical network (PON) connected to a plurality of types of subscriber connection devices (ONUs) having different signal transmission rates via an optical distribution network,
An optical transceiver coupled to the optical distribution network;
An electrical / optical converter connected to the optical transceiver;
A transmission / reception line interface connected to a wide area network;
An OLT control unit that generates a downlink control frame;
A downlink frame processing unit that converts a downlink control frame generated by the OLT control unit and a frame received from the wide area network through the transmission / reception line interface into a downlink frame including identification information of a destination ONU in a header unit;
When the signal transmission rate of the downstream frame destination ONU is slower than the standard signal transmission rate, the bit sequence of the downlink frame is converted into a bit sequence corresponding to the standard signal transmission rate, and then modulated at the standard signal transmission rate. A downlink transmission control unit that outputs to the optical conversion unit,
When the downlink transmission control unit transmits a new downlink frame addressed to an ONU having a different signal transmission rate, a communication end notification is output to the electrical / optical conversion unit at the current signal transmission rate, and a new signal is transmitted. A station-side optical transmission line termination device, which outputs a new downlink frame after outputting a communication start notification including a clock synchronization bit of a transmission rate. Passive light comprising a station-side optical transmission line termination unit (OLT) connected to a wide area network and a plurality of types of subscriber connection units (ONUs) connected to the OLT via an optical distribution network and having different signal transmission rates. Network (PON) system, wherein the OLT
An OLT control unit that generates a downlink control frame;
An optical transceiver coupled to the optical distribution network;
An electrical / optical converter connected to the optical transceiver;
An optical / electrical converter connected to the optical transceiver;
A downlink frame processing unit that converts the control frame generated by the OLT control unit and the frame received from the wide area network into a downlink frame including the identification information of the destination ONU in the header part;
A downlink transmission control unit that modulates the downlink frame at a rate according to a signal transmission rate and sends the modulated signal to the electrical / optical conversion unit;
A demodulator that demodulates the output signal of the optical / electrical converter at a rate corresponding to the signal transmission rate;
An uplink frame processing unit connected to the demodulation unit and outputting an uplink control frame received from each ONU to the OLT control unit;
When the downlink transmission control unit switches the modulation rate and transmits a new downlink frame, it outputs a communication end notification modulated at the current modulation rate to the electrical / optical conversion unit, and switches the modulation rate. Then, after outputting a communication start notification including a clock synchronization bit of a new signal transmission rate, the passive optical network system outputs the new downlink frame.

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