JP2016163069A - Office side device and multicast delivery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an office side device and a multicast delivery method capable of reducing packet copy to effectively utilize a video signal band.SOLUTION: The office side device is an OLT (Optical Line Terminal) 120 of a variable wavelength WDM/TDM-PON (Passive Optical Network) which performs optical signal transmission and reception between with a plurality of ONU (Optical Network Units) 130 in wavelength division multiplexing (WDM) and time division multiplexing (TDM). The office side device includes flow distribution means for distributing a multicast flow delivered from a delivery service provider to user terminals accommodated in the ONU, to a plurality of wavelengths used in the PON.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a station-side apparatus that multicasts video from a distribution provider to viewers in a communication system including wavelength-tunable WDM / TDM-PON and a multicast distribution method thereof.

  Due to the increasing needs for high-speed access services, the spread of FTTH (Fiber To The Home) utilizing the broadband characteristics of optical fibers is progressing worldwide. Most of the FTTH services accommodate a plurality of subscriber side devices (ONU: Optical Network Unit) by time division multiplexing (TDM: Time Division Multiplex), with one accommodation station side device (OLT: Optical Line Terminal), It is provided by an economical passive optical network (PON) system. The current main systems are GE-PON (Gigabit Ethernet (registered trademark) PON) and G-PON (Gigabit-capable PON) having a transmission rate of gigabit.

  On the other hand, as for service trends, the transition from terrestrial analog broadcasting to terrestrial digital broadcasting was completed in Japan in July 2011. Along with this, IP retransmission and IP retransmission services for terrestrial digital broadcasting / BS digital broadcasting by carrier communication carriers are also in full swing. In these IP retransmission services, the network capacity to be delivered is the same as that of broadcasting (expanding the number of users who can view simultaneously, expanding the capacity of channels that can be distributed simultaneously, shortening the channel switching time, ensuring delivery quality, and reliability. On the other hand, on the communication carrier side, there is a problem of cost reduction by efficient distribution. From this point of view, multicast distribution with higher bandwidth utilization efficiency than unicast distribution is generally used.

  FIG. 1 shows the overall configuration of a video distribution system using a TDM-PON system. In this example, it is assumed that ONU # 1 and ONU # 2 are connected to OLT # 1, and ONU # 3 and ONU # 4 are connected to OLT # 2. Further, it is assumed that ONU # 1 and ONU # 3 request flow 1 video distribution, and ONU # 2 and ONU # 4 request flow 2 video distribution. In addition, the distribution system assumed in this paper does not perform packet copying for the number of users at the edge router, but instead performs packet copying for the number of OLTs at the edge router, and performs copying by optical branching in the PON section. (See, for example, Non-Patent Document 1).

  First, a distribution flow of video or the like is transferred from the video distribution server of the distribution company in response to a viewing request of the carrier network. Next, in the core network (NW) of the carrier, the flow is distributed and transferred toward an edge router arranged at the boundary with the access system that accommodates the viewing user. A broadcast VLAN is set and distributed from the edge router to the OLT section. Here, the OLT is provided with an MLD (Multicast Listener Discovery) proxy (or MLD snooping), and performs distribution control of the broadcast VLAN section in cooperation with the edge router. In addition, a broadcast logical link (LLID = 0) is set from the OLT to the ONU section, and broadcast distribution is performed in response to a host request. Here, viewing control is realized by setting a filter (destination MAC address, etc.) for each channel in the ONU and performing frame transmission / discard filter control (see, for example, Non-Patent Document 1).

  In recent years, in addition to the progress of video distribution services, the appearance of applications for uploading / downloading large-capacity files has led to demand for further increase in the capacity of PON systems. On the other hand, in Non-Patent Document 2, a wavelength tunable WDM / TDM that enables wavelength division multiplexing (WDM: Wavelength Division Multiplex) by providing a wavelength variable function in an optical transmitter and an optical receiver mounted in each ONU. -PON has been proposed. In the wavelength tunable WDM / TDM-PON, a terminal unit (OSU: Optical Subscriber Unit) to be logically connected can be changed in units of ONUs by switching transmission / reception wavelengths in each ONU.

  FIG. 2 shows an example of the overall configuration of a video distribution system using a wavelength tunable WDM / TDM-PON system. In this example, the variable wavelength WDM / TDM-PON system is composed of two OLTs and four ONUs. OLT # 1 includes OSU # 1, OSU # 2, a logical connection control unit, and a copy unit. The transmission / reception wavelengths of the optical transceivers in OSU # 1 and OSU # 2 are set to λ1 and λ2, respectively. Assume that the transmission / reception wavelength of the optical transceivers in ONU # 1 and ONU # 2 is set to λ1, and ONU # 1 and ONU # 2 are communicating with OSU # 1. Further, it is assumed that the transmission / reception wavelength of the optical transceivers in ONU # 3 and ONU # 4 is set to λ2, and ONU # 3 and ONU # 4 are communicating with OSU # 2.

  First, a distribution flow of video or the like is transferred from a distribution company's video distribution server in response to a carrier network viewing request. Next, in the core NW of the carrier, the flow is distributed and transferred toward the edge router provided at the boundary with the access system that accommodates the viewing user. A broadcast VLAN is set and distributed from the edge router to the OLT section. Here, the OLT includes an MLD proxy (or MLD snooping), and performs distribution control of the broadcast VLAN section in cooperation with the edge router. Within the OLT, the flow is copied and transferred by the copy unit for the number of OSUs. From the OSU to the ONU section, a broadcast logical link (LLID = 0) is set and broadcast distribution is performed in response to a host request. Here, viewing control is realized by setting a filter (destination MAC address or the like) for each channel in the ONU and performing frame transmission / discard filter control.

  As described above, in the video distribution using the wavelength tunable WDM / TDM-PON system of Non-Patent Document 2, packet copying for the number of OLTs is required at the edge router, and packet copying for the number of OSUs is required at the copy unit in the OLT. It is.

Masakazu Miyamoto, Hiroaki Sato, “Study on IP multicast delivery control method in multi-branch E-PON access with high-speed zapping function”, IEICE Technical Report, 2012-03, 2012 S. Kimura, “WDM / TDM-PON Technologies for Future Flexible Optical Access Networks,” OECC 2010, 6A1-1, 2010.

  As described above, in the multicast video distribution method using the wavelength tunable WDM / TDM-PON, packet copy for the number of OSUs in the OLT is required. For this reason, in Non-Patent Document 2, even if a PON technology is used to increase the capacity of a multicast video distribution method using TDM-PON, packets corresponding to the number of OSUs copied in the OLT are included. There is a problem that the video signal band is used.

  Accordingly, an object of the present invention is to provide an OLT and a multicast distribution method for reducing packet copy and effectively utilizing a video signal band in order to solve the above-described problems.

  In order to achieve the above object, the OLT and the multicast distribution method according to the present invention distribute the multicast flow to a plurality of wavelengths used in the wavelength tunable WDM / TDM-PON.

Specifically, the OLT according to the present invention includes a plurality of subscriber side devices (ONU: Optical Network Unit), wavelength division multiplexing (WDM), and time division multiplexing (TDM). A wavelength-tunable WDM / TDM-PON station side device (OLT: Optical Line Terminal),
A flow distribution means for distributing a multicast flow distributed from a distribution company to a user terminal accommodated in the ONU to a plurality of wavelengths used in the PON;
The flow distribution means includes
A plurality of terminators (OSUs) connected to a plurality of the ONUs and outputting signals of different wavelengths;
A correspondence table describing the OSUs to which the multicast flow is distributed;
A switch that distributes the multicast flow to the OSU based on the correspondence table;
It is characterized by having.

The multicast distribution method according to the present invention is a wavelength-tunable WDM / TDM-PON OLT that transmits and receives optical signals by wavelength division multiplexing and time division multiplexing with a plurality of ONUs. A flow distribution procedure for distributing a multicast flow to be distributed to a user terminal to a plurality of wavelengths used in the PON,
In the flow distribution procedure, the multicast flow is distributed to the OSU based on a correspondence table in which the OSUs to which the multicast flow is distributed are described.

  In the present invention, multicast flows are allocated to each wavelength or OSU, and the ONU is switched to the wavelength of a signal including a desired multicast flow, thereby making it unnecessary to copy packets for the number of OSUs in the OLT. Therefore, the present invention can provide an OLT and a multicast distribution method that reduce packet copy and effectively use video signal bandwidth.

For example, the flow distribution means of the OLT according to the present invention is:
Based on the received flow selection request from the ONU collected by the OSU,
A notification to change the multicast flow toward the ONU is sent to the OSU, and the setting of transparency or discard of the multicast flow of the ONU is changed;
When a logical connection relationship between the ONU and the OSU is determined and the logical connection relationship is changed, the logical connection relationship in which the change has occurred is notified to the OSU, and the logical connection between the ONUs is notified to the OSU. It is possible to further include a logical connection control unit for changing the above.

  The flow distribution unit of the OLT according to the present invention further includes a viewing flow management unit that rewrites the correspondence table based on a reception flow selection request from the ONU collected by the OSU. The degree of freedom of OSU operation can be increased.

  For example, the viewing flow management unit of the OLT according to the present invention may rewrite the correspondence table so that the number of multicast flows allocated to each OSU is uniform.

  The viewing flow management unit of the OLT according to the present invention may rewrite the correspondence table so that the number of ONUs logically connected for each OSU is uniform. Channel switching failure and channel switching time delay can be suppressed.

  The present invention can provide an OLT and a multicast distribution method for reducing packet copy and effectively utilizing a video signal band.

It is a figure explaining the video delivery system using a TDM-PON system. It is a figure explaining the video delivery system using a wavelength variable type WDM / TDM-PON system. It is a figure explaining the video delivery system using the wavelength variable type WDM / TDM-PON system provided with OLT which concerns on this invention. It is a figure explaining the correspondence table with which OLT concerning the present invention is provided. It is a figure explaining the channel switching method in the video delivery system using the wavelength variable type WDM / TDM-PON system provided with OLT which concerns on this invention. It is a figure explaining the channel switching method in the video delivery system using the wavelength variable type WDM / TDM-PON system provided with OLT which concerns on this invention. It is a figure explaining the channel switching method in the video delivery system using the wavelength variable type WDM / TDM-PON system provided with OLT which concerns on this invention. It is a figure explaining the correspondence table with which OLT concerning the present invention is provided. It is a figure explaining the channel switching method in the video delivery system using the wavelength variable type WDM / TDM-PON system provided with OLT which concerns on this invention. It is a figure explaining the correspondence table with which OLT concerning the present invention is provided. It is a figure explaining the video delivery system using the wavelength variable type WDM / TDM-PON system provided with OLT which concerns on this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 3 is a diagram for explaining the structure of the video distribution system 301 of the present embodiment. The video distribution system 301 includes a video distribution server 101, an edge router 102, an OLT 120, an ONU 130, and a user terminal 140. A section from the OLT 120 to the ONU 130 is a wavelength tunable WDM / TDM-PON.

  The OLT 120 is a wavelength-tunable WDM / TDM-PON OLT that transmits and receives an optical signal with a plurality of ONUs 130 by wavelength division multiplexing and time division multiplexing, and is accommodated in the ONU 130 from a distribution provider (video distribution server 101). A flow distribution unit 121 that distributes a multicast flow distributed to the user terminal 140 to a plurality of wavelengths used in the PON is provided.

  The flow distribution unit 121 is connected to a plurality of ONUs 130 and outputs a plurality of OSUs 124 that output signals of different wavelengths, a correspondence table that describes the OSUs to which multicast flows are distributed, and the correspondence table based on the correspondence table And a switch 123 that distributes the multicast flow to the OSU 124.

  This will be described in more detail. In this embodiment, it is assumed that the wavelength tunable WDM / TDM-PON system is composed of two OLTs and four ONUs. The OLT (# 1) 120 includes an OSU (# 1) 124, an OSU (# 2) 124, a logical connection control unit 125, a switch (L2SW) 123, and an NNI (Network-Network Interface) 122. The transmission / reception wavelengths of the optical transceivers in the OSU (# 1) 124 and the OSU (# 2) 124 are set to λ1 and λ2, respectively. The transmission / reception wavelength of the optical transceivers in the ONU (# 1) 130 and the ONU (# 3) 130 is set to λ1, and the ONU (# 1) 130 and the ONU (# 3) 130 communicate with the OSU (# 1) 124. ing. The transmission / reception wavelength of the optical transceivers in the ONU (# 2) 130 and ONU (# 4) 130 is set to λ2, and the ONU (# 2) 130 and ONU (# 4) 130 communicate with the OSU (# 2) 124. ing.

  First, a distribution flow of video or the like is transferred from the video distribution server 101 of the distribution provider in response to a viewing request of the carrier network. Next, in the core NW 103 of the carrier, the flow is distributed and transferred toward the edge router 102 arranged at the boundary with the access system accommodating the viewing user. A broadcast VLAN is set and distributed from the edge router 102 to the OLT 120 section. Here, the OLT 120 includes an MLD proxy (or MLD snooping), and performs distribution control of the broadcast VLAN section in cooperation with the edge router 102. The MLD proxy is a function for terminating an MLD packet received from a multicast terminal (such as the user terminal 140) and transmitting the MLD packet to the video distribution server 101 side on behalf of the terminal. MLD snooping is a technique for specifying a multicast packet transfer destination port by monitoring MLD packet information. The NNI 122122 in the OLT 120 assigns the OSU distribution VID based on the flow. The flow assigned the OSU distribution VID is distributed to each OSU 124 by the L2SW 123 based on the OSU distribution VID. The OSU distribution VID is deleted by the OSU 124. From the OSU 124 to the ONU 130 section, a broadcast logical link (LLID = 0) is set and broadcast distribution is performed in response to a host request. Here, viewing control is realized by setting a filter (destination MAC address or the like) for each channel in the ONU 130 and performing frame transmission / discard filter control.

  Each flow is distinguished, for example, by using an IP multicast address as an identifier, and an OSU distribution VID determined for each flow is assigned. Further, as in this example, the NLT 122 may be provided in the OLT 120, and the OSU distribution VID may be assigned in the NNI 122, or the OS router distribution may be performed in the edge router 102 without the NNI 122 in the OLT 120. VID may be given.

  FIG. 4 is a diagram for explaining a flow used in the NNI 122 unit and an OSU distribution VID correspondence table. In the present embodiment, a flow prepared in advance and an OSU identification VID correspondence table are used for all flows distributed from the video distribution server 101 of the distributor. In FIG. 4, it is assumed that the flow is 1-2 and the OSU distribution VID is 1-2. When the correspondence table of this example is used, in the L2SW 123, the flow 1 is distributed to the OSU (# 1) 124, and the flow 2 is distributed to the OSU (# 2) 124.

  FIG. 5 is a diagram for explaining a channel switching method according to the present embodiment. In this example, it is assumed that the ONU (# 1) 130 that was viewing the flow 1 switches viewing to the flow 2. In addition, it is assumed that flow 1 is distributed from OSU (# 1) 124 and flow 2 is distributed from OSU (# 2) 124. The ONU (# 1) 130 switches the flow by setting the wavelength of the optical transceiver in the device to the same wavelength as the OSU that distributes the flow in accordance with a viewing request from the user terminal (STB) 140.

  In the multicast method, it is necessary to set a permeation / discard filter for each flow in the ONU. That is, a mechanism for changing the filter setting every time the terminal join / leave transmission is required. An example of this control method is remote centralized control by the OLT 120. This method uses PON's OAM (Operation Administration and Maintenance) function. The OAM function is a maintenance / management function of the Ethernet (registered trademark) network. If the OAM function of the PON is used, for example, it is not necessary to add an MLD proxy that terminates the MLD signal of the host and performs filter control to the ONU. Therefore, it is possible to avoid an increase in cost of adding an IP function to the ONU.

  FIG. 6 is a diagram for explaining a channel switching sequence in the present embodiment. In this example, a channel switching sequence using the PON OAM function is performed by the flow distribution unit 121. Based on the received flow selection request from the ONU 130 collected by the OSU 124, the flow distribution unit 121 transmits a notification for changing the multicast flow to the ONU 130 and sets the ONU 130 to transmit or discard the multicast flow. At the same time, the logical connection relationship between the ONU 130 and the OSU 124 is determined, and when the logical connection relationship is changed, the changed logical connection relationship is notified to the OSU 124, and the logical connection between the ONUs 130 is changed to the OSU 124. The logical connection control unit 125 is further provided.

  The channel switching operation will be described in detail. First, the STB 140 connected to the ONU (# 1) 130 transmits an MLD request for a flow 1 stop (leave) and a flow 2 start (join) (step S601). The OSU (# 1) 124 that has received this stores the settings of flow 1 discard and flow 2 transparency in the extended OAM frame and transmits them to the ONU (# 1) 130 (step S602). Receiving this, the ONU (# 1) 130 changes its own filter setting (step S603). Subsequently, the OSU (# 1) 124 transmits a viewing request change “ONU (# 1) 130 that was viewing Flow 1 switches viewing to Flow 2” to the logical connection control unit 125 (Step S604). ). Upon receiving the viewing request change, the logical connection control unit 125 determines the reception wavelength of the ONU (# 1) 130 based on the flow and the OSU distribution VID correspondence table (step S605). In this example, the logical connection control unit determines the wavelength switching to change the reception wavelength of the ONU (# 1) 130 from λ1 to λ2, and issues a wavelength switching instruction to the OSU (# 1) 124 and the OSU (# 2) 124. (Step S606). Depending on the items described in the correspondence table, there may be no wavelength switching. The OSU (# 1) 124 transmits a wavelength switching instruction to the ONU (# 1) 130 (step S607), and the ONU (# 1) 130 that has received the wavelength switching instruction changes the reception wavelength of the receiver (step S608). ). After the reception wavelength is changed from λ1 to λ2 by the ONU (# 1) 130, the OSU (# 2) 124 registers the ONU (# 1) 130 (step S609) and starts communication. By changing the reception wavelength of the ONU (# 1) 130, the flow that can be received in the ONU (# 1) 130 is changed from the flow 1 to the flow 2. At this stage, channel switching is completed (step S610).

  The communication system according to the present embodiment does not require packet copying for the number of OSUs in the OLT 120 as compared with the technique of Non-Patent Document 2. For example, in the present communication system, when the number of OLT OSUs is M, the downstream bandwidth required for video distribution can be reduced to 1 / M compared to the technique of Non-Patent Document 2. Therefore, compared with the technique of Non-Patent Document 2, this communication system can reduce the downstream bandwidth consumption required for video distribution. Therefore, the required OSU can be increased by increasing the number of multicast channels or improving network distribution efficiency. The maximum transmission rate can be reduced.

  In the present embodiment, as shown in the correspondence table of FIG. 4, the case has been described in which the signal wavelength transmitted from the OSU to the ONU and the flow are associated with each other, but the case where a plurality of flows are associated with one signal wavelength. There is also. In this case, a plurality of flows arrive even if the reception wavelength is selected by the ONU. However, by setting a filter (destination MAC address, etc.) for each channel in the ONU and performing frame transmission / discard filter control. Only the necessary flow can be transmitted to the user terminal side.

(Embodiment 2)
FIG. 7 is a diagram for explaining a channel switching method in the communication system according to the present embodiment. In the communication system of the present embodiment, the OLT 120 described in the first embodiment further includes a viewing flow management unit 126. That is, the flow distribution unit 121 further includes a viewing flow management unit 126 that rewrites the correspondence table based on the received flow selection request from the ONU 130 collected by the OSU 124. That is, the communication system of the present embodiment is newly provided with a function that can change the flow and OSU identification VID correspondence table by an instruction from the viewing flow management unit 126.

  FIG. 7A shows a state before the correspondence table is rewritten. All flows according to the viewing control request from the user terminal 140 group are A to L, the flows A to C from the OSU (# 1) 124, the flows D to F from the OSU (# 2) 124, and the flows from the OSU # 3. Flows J to L are distributed from GI and OSU # 4. A case is assumed in which all flows are changed to A to D due to a change in viewing request from the user terminal 140 group. Here, among the output ports of the L2SW 123, the output ports connected to the OSU (# 1) 124, the OSU (# 2) 124, the OSU # 3, and the OSU # 4 are output port 1, output port 2, and output, respectively. They will be referred to as port 3 and output port 4.

  First, OSU (# 1) 124 to OSU (# 4) 124 receive MLD requests from ONUs under their control. The viewing flow management unit 126 has an MLD snooping function and snoops the MLD requests of the OSU (# 1) 124 to OSU (# 4) 124. In this example, the viewing flow management unit 126 receives that the MLD request has been changed from the flows A to L to the flows A to D, and then displays all the flows according to the MLD request as OSU (# 1) 124 to OSU. (# 4) A flow and OSU identification VID correspondence table is created so that it is evenly distributed to 124. Specifically, as shown in FIG. 8, the flow and the OSU identification VID correspondence table are changed.

  After creating the flow and OSU identification VID correspondence table, the viewing flow management unit 126 transmits the flow and OSU identification VID correspondence table to the NNI 122. The output port from the L2SW 123 is changed in each flow in which the VID assigned by the NNI 122 is changed. In this example, after changing the flow and OSU identification VID correspondence table, the flow A is from the output port 1 of the L2SW 123, the flow B is from the output port 2 of the L2SW 123, the flow C is from the output port 3 of the L2SW 123, and the flow D Is output from the output port 4 of the L2SW 123. In parallel with the transmission of the correspondence table from the viewing flow management unit 126 to the NNI 122, the viewing flow management unit 126 transmits the flow and the OSU identification VID correspondence table to the logical connection control unit 125. The logical connection control unit 125 changes or maintains the OSU to which the ONU logically connects according to the received correspondence table. FIG. 7B shows a state after the correspondence table is rewritten.

  In the present embodiment, the OSU that distributes each flow can be changed according to the viewing control request of the user terminal. For this reason, when the number of flows for which there is a viewing control request is small, the required amount of the downstream band for video distribution can be further reduced. Therefore, since the required downstream bandwidth for video distribution can be reduced, it is possible to increase the number of multicast channels or reduce the required maximum OSU transmission rate by improving the efficiency of network distribution.

Furthermore, the communication system of the present embodiment has the following two effects by using a function capable of changing the OSU that distributes each flow.
The first point is that the service starts with the minimum number of OSUs when the total number of flows viewed by an ONU under one OLT is small, and the decrease in the total number of flows viewed by an ONU under one OLT. By reducing the number of operating OSUs, it is possible to realize OLT power saving.
The second point is that even if an OSU fails, the flow can be moved to another OSU, and a network failure can be dealt with.

(Embodiment 3)
As described with reference to FIG. 6, when filtering control is performed using the PON OAM function, it is necessary to transmit an OAM frame from the OSU to the ONU every time Join / Leave is received. There is a problem to do. The original use of OAM is ONU initial settings (QoS parameters, etc.), statistical information collection, maintenance operations such as firmware update, etc., and is not assumed to be used frequently all the time. Note that the upper limit of OAM traffic is defined by the standard rule of about 10 frames / sec.

  When simultaneous simultaneous distribution requests by a large number of terminals or high-speed zapping by a specific terminal frequently occur, the OSU receives a large number of Join / Leave packet groups in bursts. Therefore, until an OAM frame is generated, the Join / Leave packet is sent to the OSU. Needs to be stored once in the buffer. At this time, if a large number of Join / Leave packets arrive due to frequent zapping, the buffer overflows, packet discard occurs, and channel switching fails. Further, the channel switching time is delayed by the amount of the storage time until the packet stored in the buffer is output from the buffer. Therefore, if a large amount of buffer is set to avoid packet discard, switching failure can be avoided, but channel switching delay increases.

  In the first and second embodiments, when viewing users are biased toward a specific flow, the number of ONUs that are logically connected to a specific OSU increases. As described above, when the number of ONUs logically connected to a specific OSU increases, the frequency of simultaneous simultaneous distribution requests from a large number of terminals increases. Then, due to the frequent occurrence of simultaneous distribution requests by a large number of terminals, channel switching failures and switching delays increase as described above.

  Therefore, in this embodiment, the number of ONUs that are logically connected between a plurality of OSUs is made uniform to suppress channel switching failure and increase in switching delay. Specifically, the viewing flow management unit 126 rewrites the correspondence table so that the number of ONUs logically connected for each OSU is uniform.

  FIG. 9 is a diagram for explaining a channel switching method in the communication system of the present embodiment. FIG. 9A shows a state before the correspondence table is rewritten. Prior to rewriting the correspondence table, the number of viewing users of flows A, B, C, D, E, F, G, H, I, J, K, and L is 20, 4, 4, There are 4, 4, 4, 5, 5, 5, 5, 10, and 10 people. Then, from OSU (# 1) 124 to flows A, B, C, OSU (# 2) 124 to flows D, E, F, OSU (# 3) 124 to flows G, H, I, OSU (# 4) 124 Flows J, K, and L are distributed. In this case, the numbers of ONUs logically connected to the OSU (# 1) 124, the OSU (# 2) 124, the OSU (# 3) 124, and the OSU (# 4) 124 are 28 people, 12 people, and 15 people, respectively. And the number of ONUs that are logically connected to the OSU (# 1) 124 is larger than the number of ONUs that are logically connected to other OSUs. Therefore, when a user who is logically connected to the OSU (# 1) 124 frequently performs zapping, channel switching failure and switching delay increase.

  Therefore, the viewing flow management unit 126 rewrites the flow and OSU distribution VID correspondence table. In this example, the flow and OSU distribution VID correspondence table are determined so that the number of ONUs logically connected to each OSU approaches uniformly.

  The viewing flow management unit 126 has an MLD snooping function and snoops the number of ONUs viewing each flow. Then, the number of ONUs to view each snooped flow and the number of ONUs logically connected to each OSU are calculated using the flow and OSU identification VID correspondence table. Then, the flow and the OSU identification VID correspondence table are rewritten so that the number of ONUs logically connected among a plurality of OSUs becomes uniform. Specifically, the flow and the OSU identification VID correspondence table are changed as shown in FIG. After rewriting the flow and OSU identification VID correspondence table, the viewing flow management unit 126 transmits the flow and OSU identification VID correspondence table to the NNI 122. The output port from the L2SW 123 is changed in each flow in which the VID is changed.

  In this example, after changing the flow and OSU identification VID correspondence table, the flow A is from the output port 1 of the L2SW 123, and the flows B, C, D, E, and F are the flows G, H, and I from the output port 2 of the L2SW 123. , J are output from the output port 3 of the L2SW 123, and flows K and L are output from the output port 4 of the L2SW 123. In parallel with the transmission of the correspondence table to the NNI 122, the viewing flow management unit 126 transmits the flow and the OSU identification VID correspondence table to the logical connection control unit 125. The logical connection control unit 125 changes or maintains the OSU to which the ONU logically connects according to the received correspondence table. In this example, the numbers of ONUs that are logically connected to the OSU (# 1) 124, the OSU (# 2) 124, the OSU (# 3) 124, and the OSU (# 4) 124 are 20, 20 and 20 respectively. The number of ONUs that are logically connected between a plurality of OSUs is uniform, with 20 people and 20 people.

  The communication system according to the present embodiment can eliminate the unevenness of the number of ONUs logically connected to the OSUs by changing the OSUs that distribute the flows so that the number of ONUs logically connected to the respective OSUs approaches uniformly. Therefore, the communication system of the present embodiment can suppress the above-described channel switching failure and channel switching time delay.

(Embodiment 4)
FIG. 11 is a diagram illustrating the communication system according to the present embodiment. The wavelength tunable WDM / TDM-PON system of this embodiment is composed of two OLTs 120 and eight ONUs 130. The OLT (# 1) 120 includes an OSU (# 1) 124, an OSU (# 2) 124, an OSU (# 3) 124, an OSU (# 4) 124, a logical connection control unit (# 1) 125, and a logical connection control unit. (# 2) 125, L2SW 123, and NNI 122 are provided. The transmission / reception wavelengths of the optical transceivers in the OSU (# 1) 124 and the OSU (# 3) 124 are set to λ1, and the transmission / reception wavelengths of the optical transceivers in the OSU (# 2) 124 and the OSU (# 4) 124 are set to λ2. ing. The transmission / reception wavelength of the optical transceiver in the ONU (# 1, # 3, # 5, # 7) 130 is set to λ1. The ONU (# 1, # 3) 130 communicates with the OSU (# 1) 124, and the ONU (# 5, # 7) 130 communicates with the OSU (# 3) 124. The transmission / reception wavelength of the optical transceiver in the ONU (# 2, # 4, # 6, # 8) 130 is set to λ2. The ONU (# 2, # 4) 130 communicates with the OSU (# 2) 124, and the OSU (# 6, # 8) 130 communicates with the OSU (# 4) 124. The ports connected to the OSU (# 1) 124, OSU (# 2) 124, OSU (# 3) 124, and OSU (# 4) 124 of the L2SW 123 are described as port 1, port 2, port 3, and port 4, respectively. To do.

  This communication system is different from the communication system of the first embodiment in that a plurality of OSUs set to the same wavelength are included in one OLT. Therefore, the OLT 120 of this communication system sets a VLAN for each port, with port 1 and port 3 as segment 1 and port 2 and port 4 as segment 2. Then, the correspondence table is set so that the multicast frame to which the OSU distribution VID 1 is assigned is transferred to the segment 1, and the multicast frame to which the OSU distribution VID 2 is assigned is transferred to the segment 2.

  By performing VLAN setting in this manner, even when a plurality of OSUs set to the same wavelength are included in one OLT, packet copying for the number of OSUs in the OLT becomes unnecessary. For this reason, as described in the first embodiment, this communication system also reduces the downstream bandwidth required for video distribution when the number of wavelengths is M to 1 / M compared to the technique of Non-Patent Document 2. be able to. Therefore, compared with the technique of Non-Patent Document 2, this communication system can reduce the downstream bandwidth consumption required for video distribution. Therefore, the required OSU can be increased by increasing the number of multicast channels or improving network distribution efficiency. The maximum transmission rate can be reduced.

  Further, in this communication system, an example of multicast frame distribution is shown, but a unicast frame can also be transmitted together with the multicast frame. In this case, first, the NNI 122 that has received the unicast frame assigns the OSU distribution VID according to the destination ONU. The L2SW 123 that has received the frame to which the OSU distribution VID is assigned transfers the frame to the OSU according to the OSU distribution VID.

[Appendix]
The following describes the communication system of the present embodiment.
When the conventional multicast distribution method by TDM-PON is expanded to WDM / TDM-PON, packet copy for the number of OSUs is required in the copy unit in the OLT, and the downstream bandwidth is multiplied by the number of OSUs of the video signal bandwidth. was there.

Therefore, the communication system of the present embodiment is
(1): Multicast that is distributed from a distribution provider to a user terminal accommodated in the ONU by a wavelength-tunable WDM / TDM-PON OLT that transmits and receives optical signals by wavelength division multiplexing and time division multiplexing with a plurality of ONUs. Flow distribution means for distributing the flow to a plurality of wavelengths used in the PON is provided.

(2): The flow distribution means is
A plurality of terminators (OSUs) connected to a plurality of the ONUs and outputting signals of different wavelengths;
A correspondence table describing the OSUs to which the multicast flow is distributed;
A switch that distributes the multicast flow to the OSU based on the correspondence table;
The OLT according to (1) above, characterized by comprising:

(3): The flow distribution means is
Based on the received flow selection request from the ONU collected by the OSU,
A notification to change the multicast flow toward the ONU is sent to the OSU, and the setting of transparency or discard of the multicast flow of the ONU is changed;
When a logical connection relationship between the ONU and the OSU is determined and the logical connection relationship is changed, the logical connection relationship in which the change has occurred is notified to the OSU, and the logical connection between the ONUs is notified to the OSU. The OLT according to (2), further including a logical connection control unit that changes the function.

(4): The flow distribution means is
The OLT according to (2) or (3), further including a viewing flow management unit that rewrites the correspondence table based on a reception flow selection request from the ONU collected by the OSU.

(5): The viewing flow management unit
The OLT according to (4) above, wherein the correspondence table is rewritten so that the number of multicast flows distributed to each OSU is uniform.

(6): The viewing flow management unit
The OLT according to (4), wherein the correspondence table is rewritten so that the number of ONUs logically connected to each OSU is uniform.

(7): OLT of wavelength tunable WDM / TDM-PON that transmits and receives optical signals by wavelength division multiplexing and time division multiplexing with a plurality of ONUs.
A multicast distribution method, comprising: performing a flow distribution procedure for distributing a multicast flow distributed from a distribution company to a user terminal accommodated in the ONU to a plurality of wavelengths used in the PON.

(8): The OLT includes a plurality of OSUs connected to the plurality of ONUs and outputting signals having different wavelengths,
In the flow distribution procedure,
The multicast distribution method according to (7), wherein the multicast flow is distributed to the OSU based on a correspondence table in which the OSUs to which the multicast flow is distributed are described.

  The communication system of the present embodiment can reduce unnecessary copies in the OLT and effectively use the video signal band.

101: Video distribution server 102: Edge router 103: Core network 120: Station side device (OLT)
121: Flow distribution means 122: NNI (Network-Network Interface)
123: Switch (L2SW)
124: OSU (Optical Subscriber Unit)
125: Logical connection control unit 126: Viewing flow management unit 130: Subscriber side device (ONU)
140: User terminal (STB)

Claims (6)

Wavelength-variable WDM / TDM-PON which transmits and receives optical signals using multiple subscriber-side devices (ONU: Optical Network Unit), wavelength division multiplexing (WDM), and time division multiplexing (TDM: Time Division Multiplex). Station side device (OLT: Optical Line Terminal),
A flow distribution means for distributing a multicast flow distributed from a distribution company to a user terminal accommodated in the subscriber-side device to a plurality of wavelengths used in the PON;
The flow distribution means includes
A plurality of terminating devices (OSU: Optical Subscriber Units) connected to the plurality of subscriber side devices and outputting signals of different wavelengths;
A correspondence table describing the termination device to which the multicast flow is distributed;
A switch that distributes the multicast flow to the terminating device based on the correspondence table;
A station side device characterized by comprising: The flow distribution means includes
Based on the received flow selection request from the subscriber side device collected by the termination device,
A notification of changing the multicast flow to the subscriber side device is transmitted to the termination device, and the setting of transmission or discard of the multicast flow of the subscriber side device is changed, and
The logical connection relationship between the subscriber side device and the termination device is determined, and when the logical connection relationship changes, the logical connection relationship in which the change has occurred is notified to the termination device, and the termination device is notified. The station-side apparatus according to claim 1, further comprising a logical connection control unit that changes a logical connection between the subscriber-side apparatuses. The flow distribution means includes
3. The station side device according to claim 1, further comprising a viewing flow management unit that rewrites the correspondence table based on a reception flow selection request from the subscriber side device collected by the termination device. The viewing flow management unit
4. The station side device according to claim 3, wherein the correspondence table is rewritten so that the number of multicast flows distributed to each terminal device is uniform. The viewing flow management unit
4. The station side device according to claim 3, wherein the correspondence table is rewritten so that the number of the subscriber side devices logically connected to each terminal device is uniform. A wavelength-tunable WDM / TDM-PON station-side device that transmits and receives optical signals by wavelength division multiplexing and time division multiplexing with a plurality of subscriber-side devices.
A flow distribution procedure for distributing a multicast flow distributed from a distribution company to a user terminal accommodated in the subscriber side device to a plurality of wavelengths used in the PON,
A multicast distribution method characterized in that, in the flow distribution procedure, the multicast flow is distributed to the termination device based on a correspondence table in which the termination device to which the multicast flow is distributed is described.

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