JP2008148348A - Pon system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PON system that can effectively use the communication band of a light transmission path that serves as a PON zone. <P>SOLUTION: In a PON system comprising an OLT and a plurality of ONUs, the OLT includes a down-frame processing section that removes the header information of at least a part of a layer 2 header from the down-frame received from a wide area network, and converts the remaining frame into a frame with a header unique to the PON zone and each ONU includes a down-frame processing section that extracts the down-frame transferred from a frame received from a passive optical network to the user terminal, and supplements the layer 2 header information, deleted by the OLT to the down frame. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a passive optical network (PON) system, and more particularly to a PON system that can effectively use a transmission band in an optical transmission line section.

  As the use of the Internet has become widespread and various information services have been provided through the network, the communication network has occupied an important position of the social infrastructure. With the increase in Internet access from general households and business sites in companies, it is necessary to further increase the speed and capacity of access lines connecting these communication sites and carrier network communication stations. ing.

  As one of access networks connected to a wide area network such as the Internet, there is a passive optical network (PON) system in which a plurality of subscriber terminals can share an optical fiber. Each PON system is installed on the user's home side, and is connected to a plurality of subscriber connection devices (ONU: Optical Network Unit) accommodating one or a plurality of user terminals, and these ONUs via an optical fiber network. It consists of a station side device (OLT: Optical Line Terminal). The optical fiber connected to the OLT is coupled by a branch optical fiber connected to each ONU and an optical splitter (optical coupler), and the optical transmission path between the optical splitter and the OLT is shared by a plurality of ONUs (user terminals). By doing so, it is possible to significantly reduce the laying cost of the optical fiber.

  The PON system includes, for example, a B-PON (Broadband PON) that transmits information using a fixed-length ATM cell in an optical fiber section (PON section) and a G-PON (Gigabit PON) that enables high-speed data transfer in the Gigabit class. GE-PON (Giga-Ethernet PON) suitable for information transmission using Ethernet (registered trademark) frames, which are widely used in LAN and metro networks.

  G-PON and GE-PON are capable of transferring variable-length frames in the PON section, and standardization and technical studies are being carried out in ITU-T and IEEE, respectively. As ITU-T recommendations regarding G-PON, for example, there are Non-Patent Documents 1 to 3, and GEM (G is a transmission frame standard for transferring a general variable-length frame that is not limited to an Ethernet frame in the PON section. -PON Encapsulation Mode) Frame standards are defined.

  In the PON system, a downstream frame from the OLT to the ONU is branched into a plurality of branch line optical fibers by a splitter and distributed to all ONUs. Each ONU determines whether or not it is a frame to be received and processed in accordance with destination identification information indicated by a header (for example, GEM header) of the received PON transmission frame. On the other hand, the upstream frame from the ONU side to the OLT is multiplexed on the optical fiber on the OLT side by the optical splitter. In uplink communication, in order to prevent frames from overlapping on the optical fiber, a TDMA scheme is adopted in which frames are transmitted to each ONU in a transmission time zone assigned by the OLT.

  As can be understood from the above configuration, the PON system is an access network suitable for distributing the same service information to a plurality of user terminals by multicast from the OLT side. For this reason, for example, the PON system plays an important role as an access network in the triple play service of broadcasting / telephone / data communication, which has recently been attracting attention, particularly when entering the network infrastructure of the broadcasting industry.

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 PON system, since some optical fiber sections are shared by a plurality of ONUs, while a frame addressed to a specific ONU (or user terminal) is transferred in the PON section, it is addressed to other ONUs. The frame cannot be transferred. Further, when data frames having the same contents are repeatedly transmitted from the OLT, the bandwidth compression rate of the transmission path becomes higher than that of a network constituted by routers and switches that are general communication nodes.

  Therefore, in the PON system, frame transfer that effectively uses the bandwidth of the optical transmission path is required. For example, information that can be shared by many users such as broadcast programs is transmitted individually for each ONU with the same content. Rather than multicasting to a plurality of ONUs, it is desirable to transmit a single frame. In B-PON and GE-PON, when one frame is multicast-delivered to a plurality of ONUs from the OLT side, a destination identifier (multicast port ID or logical link ID) common to a plurality of ONUs defined in advance in the PON section is , Set in the header of the PON transmission frame.

  When the PON system is used as an access network to a wide area network, the OLT is connected to a router belonging to the wide area network or ISP network, and each user terminal is connected to the wide area network via the ONU, the OLT and the router. Communicate with any server (or computer system) above. In this case, the packet addressed to the user terminal transmitted from the server is encapsulated with a data link layer protocol header (hereinafter referred to as an L2 header) of the OSI reference model necessary for communication between the router and the user terminal. In the state, it is input to the OLT.

  In the conventional PON system, the OLT encapsulates the entire frame received from the router on the wide-area network side with a protocol header unique to the PON section, for example, a GEM header, and transmits it to the optical fiber. That is, the entire frame with the L2 header received from the router is included in the payload of the GEM frame transferred in the PON section. When the received frame includes a PPP header between the L2 header and the IP packet, the payload of the GEM frame also includes the PPP header.

  However, for example, each ONU of the G-PON determines whether the received GEM frame should be discarded or relayed to the user terminal or the ONU control unit based on the value of the port ID indicated by the GEM header of the received frame. The L2 header and PPP header included in the frame payload do not contribute to frame transmission control in the PON section at all.

  An object of the present invention is to provide a PON system that can effectively use a communication band of an optical transmission line serving as a PON section.

  In order to achieve the above object, the PON system of the present invention deletes the header information that can be reproduced by the receiving side device in the PON section and does not contribute to the frame transmission control in the PON section. It is characterized by shortening.

  More specifically, in the PON system of the present invention, the station side device (OLT) removes at least a part of the header information from the downstream frame received from the communication node device of the wide area network, and the remaining frame portion is set in the PON section. A downlink frame processing unit that converts the frame into a frame having a unique header, and each subscriber connection unit (ONU) extracts a downlink frame portion to be transferred to a user terminal from a received frame from a passive optical network; A downlink frame processing unit for supplementing header information deleted by the station side device is provided.

  When the downstream frame received from the communication node device in the wide area network is composed of a layer 2 header and an IP packet in the OSI reference model, and the layer 2 header is, for example, an Ethernet header, the downstream frame processing unit of the station side device At least the destination MAC address, the source MAC address, and the protocol type are removed from the layer 2 header.

  In this case, the downstream frame processing unit of each subscriber connection device supplements at least the destination MAC address of the L2 header, the source MAC address, and the protocol type to the payload content of the received frame from the passive optical network. . If header information other than the layer 2 header can be reproduced by the downlink frame processing unit of the subscriber connection apparatus, the downlink frame processing unit of the station side apparatus also removes header information other than the layer 2 header, thereby It is possible to further reduce the transmission frame length.

  In one embodiment of the present invention, the downlink frame processing unit of the station side device analyzes the downlink frame received from the communication device of the wide area network, removes at least one part of the header information, and outputs the remaining frame part. The frame analysis unit includes a frame generation unit that converts the frame portion output from the frame analysis unit into a frame having a header unique to the PON. The frame analysis unit may remove the header information described above for a specific downlink frame identified by the content of the layer 2 header, for example, a downlink frame including a multicast address as a destination address.

  In the PON system of the present invention, the downlink frame processing unit of each subscriber connection device determines whether or not it includes a downlink frame to be received and processed based on identification information indicated by a header unique to the PON section. The received frame that does not require reception processing is discarded. For example, when the station side apparatus removes header information for a downlink frame including a multicast IP packet, the downlink frame processing unit of the subscriber connection apparatus is based on identification information indicated by a header unique to the PON section. Then, it is determined whether or not the received frame includes a multicast IP packet. When the received frame includes a multicast IP packet, the above-described header information removal operation is performed on the transmission side.

  In one embodiment of the present invention, each subscriber connection device includes a management table storing addresses of participating user terminals for each multicast group, and the downlink frame processing unit of each subscriber connection device has a header unique to the PON section. Whether the received frame includes a multicast IP packet or not. If the received frame includes a multicast IP packet, the management table is referred to based on the destination IP address of the multicast IP packet. If the participating user terminal address is not registered in the multicast group specified by the destination IP address, the received frame is discarded.

  According to the present invention, unnecessary header information is deleted from the transfer frame in the PON section, and the transfer frame length is shortened, thereby enabling communication that effectively uses the communication band 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 device (OLT) 10, a plurality of subscriber connection devices (ONU) 20 (20-1 to 20-k), and an optical fiber network in a PON section that connects these elements. The optical fiber network in the PON section includes an optical fiber 11 connected to the OLT 10 and branch optical fibers 12-i (i = 1 to k) connected to each ONU 20-i. The optical fiber 11 is branched 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. . In the following embodiments, a case where G-PON (Gigabit PON) is applied as a communication protocol in the PON section will be described. However, the present invention is applied to other communication protocols such as GE-PON (Giga-Ethernet PON) in the PON section. ) Is also effective when applied.

Each ONU 20-i has a plurality of user connection lines Lij (j = 1 to m), and accommodates a plurality of user terminals TE through these connection ports. 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.

  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 is Ethernet and the communication protocol between the OLT 10 and the router 40-1 is Ethernet. The format of the downstream GEM frame 70A in the PON section is shown.

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 70A 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. In the conventional technique, 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. This is set, and a predetermined multicast port ID is set in the GEM header 71.

  The feature of this embodiment is shown in FIG. 3 when the frame F1 received from the router 40-1 is a multicast frame, and the OLT 10 deletes the L2 header that does not contribute to the downlink frame reception control in the PON section. As described above, the shortened GEM frame 70B including only the IP packet 60 in the GEM payload 72 is transmitted to the ONU 20-1 to ONU 20-k. However, in the L2 header, it is not necessary to delete the entire header, and some header information items may be left. As will be described later, the L2 header deleted by the OLT 10 is reproduced on each ONU 20 side, and the received IP packet 60 is transferred to the user terminal as a frame with the L2 header.

FIG. 4 shows a format of a GTC (G-PON Transmission Convergence) downstream frame 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. In the case of a 2.4 Gbps PON system, the total length of the GTC downstream frame 80 is 38880 bytes.

The GEM frame described with reference to FIGS. 2 and 3 is mapped to the GTC payload 82 as indicated by GEM (1) and GEM (2) in FIG. When the number of GEM frames included in the GTC payload 82 is N, the length of the PCBd area is “30 + 8 × N” bytes, and the length of the GTC payload 82 is “38880-PCBd length”.
According to the present embodiment, since the multicast GEM frame length is shortened by removing the L2 header (Ethernet header) 63, the OLT 10 effectively uses the GTC payload 82 to turn on the ONU 20-1 to ONU 20-k. Can communicate with.

FIG. 5 shows a format of a multicast Ethernet frame Fm reproduced by each ONU 20-i from the multicast GEM frame.
When each ONU 20-i receives the shortened GEM frame 70B including the multicast port ID in the GEM header, each ONU 20-i extracts the IP packet 60 from the received frame, and adds a newly generated L2 header to the multicast Ethernet frame Fm. Play. The generation of the L2 header 63m in the ONU 20-i will be described in detail later. The internal header 64 indicated by a broken line includes internal routing information (line number Nij) necessary for selectively sending the frame Fm to the connection line Lij of the user terminal within each ONT. The frame Fm with the internal header 64 removed is transmitted to the connection line Lij identified by the line number Nij.

FIG. 6 is a configuration diagram showing one embodiment of the OLT 10.
The OLT 10 includes an OLT control unit 100, an optical transmission / reception unit 101 connected to the optical fiber 11, a transmission line interface 102A and a reception line interface 102B connected to the line L1, and an optical transmission / reception unit 101 and a transmission line interface 102A. An upstream signal processing circuit provided therebetween, 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 opto-electric (O / E) converter 110 that converts an optical signal received by the optical transceiver 101 into an electrical signal, and an upstream frame that reproduces an upstream frame from an output signal of the O / E converter 110. Termination unit 111, upstream frame analysis unit 112 connected to upstream frame termination unit 111, and upstream frame generation unit 113 that converts the frame output from upstream frame analysis unit 112 into a format that conforms to the protocol on communication line L1. It consists of.

  The upstream frame analysis unit 112 analyzes the upstream reception frame, and when the reception frame is a control frame in the PON section, outputs the frame to the OLT control unit 100, and forwards 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 113.

  For example, if the protocol on the communication line L1 is ATM, the upstream frame generation unit 113 converts the received frame into an ATM cell and transfers it to the transmission line interface 102A. Information necessary for frame format conversion is read from the network configuration information memory 140. In this embodiment, it is assumed that the protocol on the communication line L1 is Ethernet, and the upstream reception frame is also an Ethernet frame. Therefore, the upstream frame generation unit 113 determines the Ethernet frame output from the upstream frame analysis unit 112 as the Ethernet frame. What is necessary is just to transfer to the transmission line interface 102A as it is.

  However, as will be described later, when an uplink multicast frame is also transferred by removing the L2 header in the PON section, the uplink frame generation unit 113 uses the network configuration information prepared in the memory 140. After generating the L2 header and converting the received frame into an Ethernet frame, the L2 header is transferred to the transmission line interface 102A.

  The downlink signal processing circuit converts the downlink frame read from the reception buffer 120 into a frame format specific to the PON section, and a reception buffer 120 for temporarily storing downlink frames received by the reception line interface 102B from the communication line L1. The downlink frame processing unit 121 to be output, the downlink transmission control unit 124 connected to the frame processing unit 121, and the frame output from the downlink transmission control unit 124 are converted into optical signals and output to the optical transmission / reception unit 101. And an electric light (E / O) conversion unit 125.

  The downlink frame processing unit 121 analyzes a downlink frame read from the reception buffer 120 and removes header information (L2 header in this embodiment) according to the present invention, and a downlink frame analysis unit The frame output from 122 and the control frame supplied from the OLT control unit 100 are converted into a GEM frame, and the TC / GEM frame generation unit 123 outputs the TC frame format (GTC frame in this embodiment) and outputs the frame. .

  As shown in the flowchart of FIG. 7, the downstream frame analysis unit 122 reads the received frame from the reception buffer 120 (161), and determines whether the received frame is a multicast frame or a unicast frame from the DMAC 631 indicated by the L2 header (162). ). If the upper n bits of the DMAC 631 (n = 25 when the subsequent IP packet is IPv4, n = 16 when the IPv6 is IPv6) is a predetermined specific pattern (fixed pattern), the received frame is It is determined as a multicast frame.

  If the received frame is a unicast frame, the downstream frame analysis unit 122 outputs the received frame as it is to the TC / GEM frame generation unit 123 (164). If the received frame is a multicast frame, the downlink frame analysis unit 122 removes the L2 header (163) and then receives the received frame. The frame is output to the TC / GEM frame generation unit 123.

  The OLT control unit 100 receives a control frame indicating the transmission data accumulation state or transmission data length from each ONU-i, and controls the transmission time zone of the upstream frame to be assigned to each ONU by the upstream bandwidth management table 130. The transmission time zone of the uplink frame assigned to each ONU is notified to each ONU by a downlink control frame generated by the OLT control unit 100.

  The TC / GEM frame generation unit 123 refers to the GEM header table 150 illustrated in FIG. 8 and the frame output from the downlink frame analysis unit 122 and the control frame supplied from the OLT control unit 100 (for example, OMCI frame or PLOAM frame) is converted into a GEM frame.

  The GEM header table 150 includes a plurality of table entries indicating the correspondence between the DMAC 151 and the port ID 152 to be set in the GEM header. For example, in the table entry including the MAC addresses “MAC111” and “MAC112” of the user terminals TE-111 and TE-112 shown in FIG. 1 as the DMAC 151, the port ID 152 is the port ID (“ID1”) of the ONU 20-1. In the table entry including the MAC address “MAC21” of the user terminal TE-21, the port ID 152 indicates the port ID (“ID2”) of the ONU 20-2. In addition, in the table entry including the MAC address for multicast as the DMAC 151, the port ID 152 indicates the multicast port ID.

  If there is no L2 header in the frame received from the downstream frame analysis unit 122, the TC / GEM frame generation unit 123 determines that this is a multicast frame, and adds a GEM header including the multicast port ID indicated by the GEM header table 150. The received frame is output to the downlink transfer control unit 124. When the received frame has the L2 header, the TC / GEM frame generation unit 123 searches the GEM header table 150 for the GEM port ID corresponding to the DMAC 631 indicated by the L2 header, and adds the GEM header including the GEM port ID. The received frame is output to the downlink transmission control unit 124.

FIG. 9 is a block diagram showing an embodiment of the ONU 20-i.
The ONU 20-i includes an ONU control unit 200, an optical transmission / reception unit 201 connected to the branch optical fiber 12-i, and a plurality of line interfaces 202-1 to 202-m connected to user terminal connection lines Li1 to Lim, respectively. A downlink transmission control unit 219 and an uplink reception control unit 220 connected to these line interfaces, a downlink signal processing circuit provided between the optical transmission / reception unit 201 and the downlink transmission control unit 219, and an optical transmission / reception unit 201 And an uplink signal processing circuit provided between the uplink reception control unit 220 and the uplink reception control unit 220.

  The downstream signal processing circuit terminates the GTC frame based on an output signal from the O / E converter 210 and an opto-electric (O / E) converter 210 that converts the optical signal received by the optical transceiver 201 into an electrical signal. A TC frame terminating unit 211 that outputs GEM frames extracted from the GTC payload one after another, a downstream frame buffer 212 that temporarily stores GEM frames, and a GEM frame read from the downstream frame buffer 212 as described later. A downlink frame processing unit 213 that analyzes and extracts the Ethernet frame extracted from the GEM frame and the Ethernet frame reproduced from the shortened GEM frame in the frame format with the internal header shown in FIG. 5 to the downlink transmission control unit 219; Consists of. Detailed operation of the downstream frame processing unit 213 will be described later with reference to FIG.

  When the downlink transmission control unit 219 receives a frame from the downlink frame processing unit 213, the downlink transmission control unit 219 specifies at least one connection line Lij as a frame transfer destination according to the line number Nij indicated by the internal header of the received frame, and corresponds to this specific line. The downlink Ethernet frame from which the internal header is removed is transferred to the line interface 202-j.

  On the other hand, the upstream signal processing circuit reads the transmission frame from the upstream frame buffer 221 and the upstream frame buffer 221 for temporarily storing the upstream transmission frames received by the upstream reception control unit 220 from the line interfaces 202-1 to 202-m. After analyzing the header information, the upstream frame processing unit 222 that outputs the upstream frame in the PON section, and the transmission frame that is output from the upstream frame processing unit 222 is transmitted in the transmission time zone specified by the ONU control unit 200. The transmission control unit 223 and an electric light (E / O) conversion unit 224 that converts an output signal from the uplink transmission control unit 223 into an optical signal and outputs the optical signal to the optical transmission / reception unit 201.

  The upstream frame processing unit 222 determines the frame type and transmission necessity from the header information of the transmission frame, and discards the frame determined to be unnecessary for transmission. The upstream frame processing unit 222 corresponds to a control frame of a type designated in advance, for example, a multicast frame according to IGMP (Internet Group Management Protocol) or MLD (Multicast Listener Discovery), or a designated IP address. In the case of an ARP packet frame for inquiring about the MAC address to be transmitted, a copy of the transmission frame is notified to the ONU control unit 200. The uplink frame processing unit 222 converts the format of the transmission frame as necessary, and outputs the converted frame to the uplink transmission control unit 223.

  The ONU control unit 200 includes a memory in which a network configuration information table 230, an internal routing table 240, an ARP table 250, a multicast group management table 260, and the like are formed. In the network configuration information table 230, network configuration information required by the ONU 20-i is set by a PON system administrator or a management system (not shown) when the ONU is connected to the OLT 10. The network configuration information includes at least address information of the router 40-1 to which the OLT 10 is connected.

  As shown in FIG. 10, the internal routing table 240 includes a plurality of correspondence relationships between the destination MAC address (DMAC) 241 of the user terminal accommodated in the ONU 20-i and the line number 242 to which the user terminal is connected. It consists of a table entry and a table entry for multicast. In the multicast table entry, a multicast number designating all line numbers is set as the line number 242 corresponding to the multicast MAC address 241. The internal routing table 240 is referred to so that the downstream frame processing unit 213 specifies a line number as a frame transfer destination and generates an internal header 64 to be attached to the downstream frame.

  As shown in FIG. 11, the ARP table 250 includes a plurality of table entries indicating the correspondence between the IP address 251 and the MAC address 252. The table entry of the ARP table 250 indicates that after the user terminal acquires an IP address according to, for example, DHCP (Dynamic Host Configuration Protocol) or RADIUS (Remote Authentication Dial In User Service), the same IP address is duplicated with other user terminals. When the ARP packet frame is transmitted in order to confirm whether or not it is assigned, the Snooping function of the ONU control unit 200 generates based on the contents of the ARP packet. As will be described later, the ARP table 250 is referred to when the downlink frame processing unit 213 selectively transfers the shortened GEM frame to the requesting user terminal.

  As shown in FIG. 12, the multicast group management table 260 includes a multicast group IP address 261, an IP address (participating user IP address) 262 of a participating user of the multicast group, a VLAN identifier (VID) 263, and other header items. Are made up of a plurality of table entries indicating the corresponding relationship. However, the VID 263 is information necessary when the user terminal uses the VLAN, and is not an essential information item in the multicast group management table 260.

  The table entry of the multicast group management table 260 indicates that when the user terminal transmits a multicast group participation request packet to the server according to IGMP / MLD, the ONU control unit 200's Snooping function is based on the content of the participation request packet. To generate. As will be described later, the multicast group management table 260 is referred to so that the downlink frame processing unit 213 determines whether or not the downlink multicast frame needs to be transferred to the user terminal. The multicast group management table 260 is also referred to when the downlink frame processing unit 213 reproduces the L2 header (Ethernet header) from the shortened GEM frame in the improved embodiment of the present invention.

FIG. 13 is a flowchart showing the operation of the downstream frame processing unit 213.
The downlink frame processing unit 213 reads the GEM frame from the downlink frame buffer 212 (271), and compares the port ID included in the GEM header 71 with its own port ID (272). If the port IDs match, the GEM frame includes the Ethernet frame transmitted from the router 40-1 or the PON control frame transmitted from the OLT 10 in the payload 72. In this case, the downstream frame processing unit 213 removes the GEM header 71 from the GEM frame (273), and determines the type of the received frame included in the GEM payload 72 (274).

  If the received frame is a PON control frame, the downlink frame processing unit 213 transfers the received frame to the ONU control unit 200 (275), and then reads the next GEM frame from the downlink frame buffer 212 (271). When the received frame is an Ethernet frame, the downlink frame processing unit 213 searches the internal routing table 240 for the line number 242 corresponding to the DMAC 631 indicated by the L2 header of the received frame, and generates an internal header including this line number ( 282), the received frame with the internal header added is transferred to the downlink transmission control unit 219 (283). Thereafter, the downstream frame processing unit 213 reads the next GEM frame from the downstream frame buffer 212 (271).

When the port ID included in the GEM header 71 does not match the own port ID, the downlink frame processing unit 213 determines whether or not the port ID of the GEM header 71 is a multicast port ID (276), and the multicast port ID. Otherwise, the GEM frame is discarded (284), and the next GEM frame is read from the downstream frame buffer 212 in step 271.
When the port ID of the GEM header 71 is a multicast port ID, the GEM frame is a shortened frame from which the L2 header is deleted, and a multicast in which a multicast group IP address is set as the destination IP address (DA) 612 in the GEM payload. Contains IP packets.

  In each ONU that has received the multicast GEM frame, if the IP packet included in the received frame is irrelevant to the user terminal under its control, it is desirable to discard the received packet. Therefore, the downlink frame processing unit 213 refers to the multicast group management table 260 (277), and whether a table entry (participating user IP address) corresponding to the multicast group IP address (DA: 612) of the received IP packet is registered. It is determined whether or not (278).

If the table entry corresponding to the multicast group IP address is not registered, there is no user terminal that should receive the IP packet in this ONU. In this case, the downstream frame processing unit 213 discards the received GEM frame (284) and reads the next GEM frame from the downstream frame buffer 212 (271).
When a table entry corresponding to the multicast group IP address of the received IP packet is registered in the multicast group management table 260, the downlink frame processing unit 213 removes the GEM header from the GEM frame (279), and the table entry is Using the indicated information, the L2 header 62m to be attached to the received IP packet is reproduced (280).

  A multicast MAC address is set in the destination MAC address (DMAC) 631 of the L2 header 63m. In this case, as shown in FIG. 5, the multicast MAC address is the lower M bits of the destination IP address DA (multicast group IP address) 611 of the received IP packet (M = 23 for IPv4, M = 32 for IPv6). ) Can be generated by combining a known fixed bit pattern with the MAC address portion indicated by.

  The MAC address of the router 40-1 stored in advance in the network configuration information table 230 is applied to the source MAC address (SMAC) 632 of the L2 header. Since it is already known that an IP packet (IPv4 or IPv6) follows the L2 header, a value indicating the IP protocol is set in the protocol type 634 of the L2 header. In the other information 635, information 264 indicated by the table entry retrieved from the multicast group management table 260 is set as necessary.

  When the generation of the L2 header 63m is completed, the downlink frame processing unit 213 generates the internal header 64 to be attached to the Ethernet frame composed of the L2 header and the multicast IP packet with reference to the internal routing table 240 (282). A multicast number is set in the internal header generated here. Thereafter, the downlink frame processing unit 213 transfers the multicast frame with the L2 header 63m and the internal header 64 to the downlink transmission control unit 219 (283), and reads the next GEM frame from the downlink frame buffer 212 (271). .

  When the downlink transmission control unit 219 receives the Ethernet frame from the downlink frame processing unit 213, the downlink transmission control unit 219 removes the internal header 64 and transfers the received frame to the line interface 202 specified by the line number indicated by the internal header 64. The multicast frame is transferred to all line interfaces according to the multicast number indicated by the internal header 64.

  In the above embodiment, as a result of referring to the multicast group management table 260, the multicast frame that the downlink frame processing unit 213 determines to be transferred is transferred to all the line interfaces 202 connected to the downlink transmission control unit 219. In this case, since the multicast frame is transmitted to a line other than the line to which the user terminal that should receive the multicast frame is connected, the multicast frame is also distributed to user terminals not participating in the multicast group.

In order to limit the transmission destination of the multicast frame to a specific line to which user terminals participating in the multicast group are connected, the ARP table 250 may be used.
For example, the downlink frame processing unit 213 that generated the L2 header searches the MAC address 252 from the ARP table 250 based on the participating user IP address 262 searched from the multicast group management table 260 as indicated by a broken line in FIG. Then (281), the line number 242 corresponding to the MAC address is searched from the internal routing table 240, and the internal header 64 to be attached to the multicast frame is generated (282).

  When a plurality of participating user IP addresses are registered corresponding to one multicast group IP address 261 in the multicast group management table 260, the downlink frame processing unit 213 searches the internal routing table 240 for a plurality of line numbers. As a result, the internal header 64 including the plurality of line numbers is generated. In this way, by limiting the line to which the multicast frame is transferred by the internal header, the downlink transmission control unit 219 can selectively transfer the received frame to the specific line interface 202.

  According to the above embodiment, the downlink frame processing unit 213 uses the ARP table 250 and the internal routing table 240 to generate the internal header, so that the requesting user terminal is connected to the downlink frame having the multicast DMAC. It can be selectively transferred to a specific line. However, even in this case, if a plurality of user terminals are connected to the line through which the multicast frame is transmitted via the home router 30, the multicast frame may be transferred to a user terminal that is not the multicast request source. is there.

  In order to forward the multicast frame only to the multicast request source user terminal, the downstream frame processing unit 213 of the ONU 20 uses the participating user IP address 262 and the ARP table 250 indicated by the multicast group management table 260. The multicast IP packet may be converted into a unicast Ethernet frame.

  That is, in the above-described embodiment, the multicast MAC address generated from the destination IP address 612 of the received packet is applied as the destination MAC address (DMAC) 631 of the L2 frame, but the DMAC 631 corresponds to each participating user IP address of the multicast. When the individual MAC address is applied and there are a plurality of multicast participating users under the ONU, a plurality of different Ethernet frames of the DMAC 631 may be generated. In this case, the downlink frame processing unit 213 applies the MAC address of the participating user IP address retrieved from the ARP table 11 instead of the multicast MAC address, and transmits a plurality of Ethernet frames with internal headers each including a different line number. Generate.

  In a network configuration in which the user terminal and the router 40-1 communicate Ethernet frames using a VLAN in order to increase the safety of communication, by storing the VID 263 in the multicast group management table 260, it is possible to The frame processing unit 213 can reproduce the L2 header including the VID 633. When VID is used, even when the same frame is multicast to a plurality of user connection lines, only the user terminal specified by VID can receive the frame.

  In the above embodiment, the case where the OLT 10 removes the L2 header from the downlink multicast frame, converts it into a shortened GEM frame, and multicasts it to the ONUs 20-1 to 20-k has been described. However, the OLT 10 Similarly to the multicast frame, the L2 header may be removed and converted into a shortened GEM frame. In this case, when each ONU receives a GEM frame having a unicast port ID, the destination IP address (DA) 612 is extracted from the IP packet included in the GEM payload, and the destination IP retrieved from the ARP table 250 is extracted. By applying the MAC address corresponding to the address to the DMAC 631 of the L2 header, the L2 header can be reproduced in the same manner as the multicast frame.

  In the embodiment, the case has been described in which the length of the transfer frame in the PON section is shortened by effectively removing the bandwidth by removing the L2 header from the downlink multicast frame from the OLT 10 toward the ONU 20. For upstream multicast frames from ONU 20 to OLT 10, for example, ARP frames and IGMP / MLD frames, the L2 header is removed on the ONU side, and the L2 header is generated on the OLT side, thereby enabling the upstream bandwidth of the PON section to be effective. It can be used.

In the embodiment, the OLT 10 removes the L2 header from the received frame from the wide area network side, converts it to a GEM frame with a shortened frame length, and multicasts it to the PON section. May be deleted, and specific information items required for header playback on the ONU side may be left in the GEM frame.
In the embodiment, the operation of the PON system when a frame composed of the IP packet 60 and the Ethernet header 63 is received as a downstream frame has been described. However, the present invention provides a connection between the IP packet 60 and the Ethernet header 63. The present invention can also be applied to downlink frames including tunnel-type network relay protocol information such as PPP session identification information or L2TP tunnel identification information.

  For example, during a period in which a protocol procedure for establishing a PPP session is being executed between a user terminal connected to the ONU 20 and the router 40-1, the ONU 20 acquires the PPP session information by the Snooping function, If this can be stored in association with the user terminal identification information, the OLT can generate a GEM frame with the PPP session identification information removed. If it is difficult for the ONU 20 to generate PPP session information, the OLT 10 may generate a GEM frame including PPP session identification information and an IP packet in the GEM payload.

  As mentioned above, although the case where this invention was applied to G-PON was demonstrated as an Example, this invention is applicable also to GE-PON. In this case, LLID (Logical Link ID) is applied to the header of the transmission frame in the PON section instead of the port ID.

1 is a configuration diagram of a PON system to which the present invention is applied. The figure which shows the format of the downstream GEM frame 70A transferred in the Ethernet frame F1 which OLT10 receives from a wide area network, and a PON section. FIG. 4 is a format diagram illustrating an example of a shortened GEM frame according to the present invention. The figure for demonstrating the relationship between the GTC downstream frame of a PON section, and a GEM frame The figure which shows the format of the Ethernet frame reproduced | regenerated by ONU. The block block diagram which shows one Example of OLT10 by this invention. The flowchart which shows operation | movement of the downstream frame analysis part 122 of OLT10. The figure which shows the GEM header table which the downstream frame analysis part 122 refers. The block block diagram which shows one Example of ONU20-i by this invention. The figure which shows an example of the internal routing table 240 which ONU20-i refers. The figure which shows an example of the ARP table 250 which ONU20-i refers. The figure which shows an example of the multicast management table 260 which ONU20-i refers. The flowchart which shows operation | movement of the downstream frame process part 213 of ONU20-i.

Explanation of symbols

TE: user terminal, 10: OLT, 11: optical fiber, 12: branch optical fiber,
13: Splitter, 20: ONU, 30: Home switch (router), 40: Router
50: Server, 61: IP header, 62: IP payload, 63: L2 header,
64: internal header, 71: GEM header, 72: GEM payload, 81: PCBd,
82: GTC payload, 100: OLT control unit, 101: optical transmission / reception unit, 102A: transmission line interface, 102B: reception line interface, 110: O / E conversion unit,
111: Upstream frame termination unit, 112: Upstream frame analysis unit, 113: Upstream frame generation unit, 120: Reception buffer, 121: Downstream frame processing unit, 122: Downstream frame analysis unit, 123: TC / GEM frame generation unit, 124 : Downlink transmission control unit, 125: E / O conversion unit, 130: uplink bandwidth management table, 140: network configuration control information memory,
150: GEM header table, 200: ONU control unit, 201: optical transmission / reception unit,
202: Line interface, 210: O / E conversion unit, 211: TC frame termination unit,
212: Downlink frame buffer, 213: Downlink frame processing unit, 219: Downlink transmission control unit, 220: Uplink reception control unit, 221: Uplink frame buffer, 222: Uplink frame processing unit, 223: Uplink transmission control unit, 224: E / O conversion unit, 230: network configuration information table, 240: internal routing table, 250: ARP table, 260: multicast group management table.

Claims (6)

A subscriber connection device (ONU) that accommodates user terminals, a station side device (OLT) connected to a wide area network, and a passive optical network that connects between the subscriber connection device and the station side device, The station side device transfers a downlink frame received from the communication node device on the wide area network side to the subscriber connection device via the passive optical network, and the subscriber connection device transmits the downlink frame to the user terminal. In the PON (Passive Optical Network) system that transfers to
The downlink frame includes a layer 2 header and an IP packet,
The station side device
A frame analysis unit that removes at least part of the information in the layer 2 header of the downlink frame and outputs as a downlink frame from which at least part of the information in the layer 2 header is removed;
A frame generation unit that generates a PON frame by adding a header specific to the PON to a downstream frame from which at least part of the information in the layer 2 header output from the frame analysis unit has been removed;
The subscriber connection device is
Holding the correspondence between the IP address and MAC address of the user terminal,
Based on the identification information indicated by the header specific to the PON in the PON frame received from the station side device, it is determined whether or not the PON frame includes a frame to be received by the own device. If it is determined that it is necessary, a downlink frame from which at least part of the information in the layer 2 header has been removed is extracted from the PON frame received via the passive optical network, and the IP of the downlink frame is extracted. Layer 2 including the MAC address of the user terminal specified by the destination IP address in the IP packet with reference to the destination IP address in the packet and the IP address of the user terminal held in the correspondence relationship A PON system comprising a downlink frame processing unit that generates header information by itself and adds the header information to the extracted downlink frame. Beam. The downstream frame analysis unit of the station side device,
It is determined whether the downlink frame received from the communication node apparatus is a multicast frame or a unicast frame. If the downlink frame is determined to be a unicast frame, at least a part of information in the layer 2 header of the downlink frame is removed. The PON system according to claim 1, wherein a downstream frame from which at least a part of information in the layer 2 header is removed is output to the frame analysis unit. The downstream frame analysis unit of the station side device,
3. The method according to claim 2, wherein, based on a destination address of a layer 2 header of a downlink frame received from the communication node, it is determined whether the downlink frame received from the communication node device is a multicast frame or a unicast frame. PON system. The downlink frame generation unit of the station side device,
When it is determined that the downlink frame received from the communication node apparatus is a unicast frame, the downlink frame in which at least part of the information in the layer 2 header output from the frame analysis unit is removed is specific to the PON. The PON system according to claim 1, wherein a PON frame is generated by adding a header of The downlink frame processing unit of the subscriber connection device,
Based on identification information indicated by a header unique to the PON in the PON frame received from the station side device, it is determined whether or not the PON frame includes a frame to be received by the own device, and no reception processing is required. 2. The PON system according to claim 1, wherein the PON frame is discarded when it is determined.   The PON system according to any one of claims 1 to 5, wherein a downlink frame received by the station side device from the communication node device includes an Ethernet header as the layer 2 header.

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