CN103152128B - Based on the network code connection management method of peer-to-peer communications flow triggering - Google Patents

Abstract

The invention discloses a network coding connection management method triggered based on peer-to-peer communication traffic. The method includes: an optical line terminal OLT discovers optical network units ONUs with peer-to-peer communication traffic, and establishes and removes network coding paired connections for these ONUs. , each ONU only cooperates to participate; ONU marks and caches data frames that may participate in network coding, and OLI performs corresponding caching and coding on data frames participating in network coding, and marks and distributes network coded data frames; ONU Perform network decoding on the received encoded data frame and clear the corresponding buffer. The invention maintains the master-slave relationship between the OLT and the ONU, each ONU does not need to locally learn the LLID and MAC address of the downlink data frame, and does not need to maintain a piece of LLID and the MAC address of the downlink host locally for the entire network ONU For the address pairing table, the present invention also realizes the network coding theory in the passive optical network of tree topology, and is compatible with the main protocols of the existing passive optical network.

Description

Network Coding Connection Management Method Based on Peer-to-Peer Traffic Triggering

technical field

The invention relates to a network coding connection management method triggered based on peer-to-peer communication traffic, and belongs to the technical field of communication.

Background technique

The rise of social networks and peer-to-peer P2P services has put enormous pressure on metro and backbone networks. According to Ipoque, a German Internet research organization, P2P services have completely dominated today's Internet, and 50-90% of the total traffic comes from P2P. A type of business characterized by peer-to-peer communication. In this context, higher requirements are put forward for the local switching capability of the equipment.

Network coding is mostly used to solve the service transmission under the butterfly network, but there is no effective coding mechanism for the tree structure with low connectivity. At the same time, the tree structure on the access network side has caused a serious bandwidth bottleneck. Therefore, how to solve this bottleneck, effectively channel and transmit the bandwidth, integrate the theory of network coding theory to achieve the maximum flow into the passive optical network of the tree topology, and be compatible with the main protocols of the existing passive optical network, so as to strengthen the The exchange efficiency of local peer-to-peer traffic is an important and interesting problem to be solved.

The basic principle of network coding in the passive optical network PON is shown in Figure 1. The optical line terminal OLT schedules the uplink time slots for the optical network unit ONU with peer-to-peer communication, and notifies the ONU to perform corresponding buffer actions. The data packets of the peer-to-peer communication between the two are network-encoded and broadcast, and finally the corresponding ONU receives the encoded data packets, and uses the local previously cached data packets to decode, and obtains the data packets sent by the other ONU to complete the peer-to-peer communication the process of. Compared with the traditional passive optical network communication method without network coding, the network coding scheme can theoretically save half of the downlink bandwidth and increase the network throughput by half. At the same time, network encoding is equivalent to a data encryption process, and ONUs without data frames required for decoding cannot eavesdrop on data that does not belong to them, and the security of communication is also guaranteed consistently.

Therefore, network coding technology can efficiently support peer-to-peer communication services in the access network, effectively save the limited downlink bandwidth in the passive optical network, improve the overall throughput of the network and the robustness in error tolerance and error correction, simplify Routing, while effectively alleviating the bandwidth pressure on the core network.

The current existing network coding schemes in passive optical networks all use the ONU pre-judgment method (only the principle is introduced, no specific detailed implementation scheme), that is, the ONU judges in advance in the local queue and distinguishes whether the destination is in the passive optical network. The data frame inside the network, and then notify the OLT to perform subsequent related operations of network coding. This scheme requires each ONU in the passive optical network to learn the logical link identifier LLID of the local downlink data frame and the MAC address of the medium access control, and maintain an Internet protocol for each ONULLID of the passive optical network and its access host locally. Table corresponding to the IP address, and perform necessary address table learning and aging operations. Since the downlink data frame in the actual passive optical network is encrypted by stirring, each ONU can only learn the MAC address of the LLID and the local matching data frame each time, so this solution has the practical difficulty that the address table needs to be learned many times for a long time and cannot be completely established possibility, and because each ONULLID information is known by all ONUs, communication security issues such as eavesdropping will also be exposed. At the same time, this solution has many disadvantages such as cumbersome mechanism process, relatively large service delay and jitter, so the present invention proposes a network coding method dominated by the OLT in the passive optical network that can solve the above problems, and proposes the The detailed implementation of the method.

Contents of the invention

The purpose of the present invention is to provide a network coding connection management method triggered based on peer-to-peer communication traffic. The method adopts a brand-new OLT real-time pre-judgment network coding, led by the OLT, and the ONUs cooperate to complete the discovery of paired ONUs participating in the network coding, paired connection establishment, maintenance and dismantling.

For realizing above-mentioned purpose of the invention, the present invention adopts following technical scheme:

A network coding connection management method triggered based on peer-to-peer communication traffic, characterized in that:

In the passive optical network, the optical line terminal OLT discovers the optical network unit ONU with peer-to-peer communication traffic, and establishes and removes the network coding pairing connection for these ONUs, and each ONU only participates in cooperation;

ONU marks and caches data frames that may participate in network coding, OLT caches and codes data frames that participate in network coding, and marks and sends network coded data frames;

The ONU performs network decoding on the received encoded data frame and clears the corresponding buffer.

The method described above is characterized in that it comprises the following steps:

Step 1: The OLT finds ONUs with peer-to-peer communication traffic. These ONUs are paired ONUs that will be network coded at the OLT. The OLT establishes a paired connection between the paired ONUs through a control frame, and starts the longest effective paired connection. Timing of time; if the OLT cannot detect the peer-to-peer communication data between the paired ONUs within the longest effective time of the paired connection, the connection between the paired ONUs will be removed, and each ONU will receive the control frame issued by the OLT and cooperate to participate in the pairing Connection establishment and teardown;

Step 2: The ONU marks the data frames that may participate in the network and caches them locally; the OLT caches the marked data frames in the data frames of the first upstream party in the paired ONU, and stores the locally cached data waiting for encoding within the cache waiting time Frames and corresponding data are network-coded, and the network-coded data frames are marked and delivered;

Step 3: The ONU performs network decoding on the tagged data frames received in the downlink and the corresponding data in the local cache, and clears the data frames in the cache that have participated in the decoding operation.

The method described in step 1 is characterized in that it comprises the following steps:

Step 1-1: If the OLT detects in real time that there is peer-to-peer communication data between any pair of ONUs in a certain dynamic bandwidth allocation DBA cycle, it can be determined that there is a network coding between the pair of ONUs in the passive optical network Paired, and this pair of ONUs is called a paired ONU;

Step 1-2: OLT assigns a pairing number GroupID to the pair of ONUs within the DBA period, and unicasts the pairing number GroupID and the MAC addresses of all connected terminals under one paired ONU to the other in the form of a Notice frame Pair ONUs and establish a connection between paired ONUs;

Steps 1-3: The OLT saves the Notice frame immediately after delivering the Notice frame through unicast, and starts counting the longest valid time T _max of the pairing number GroupID in the Notice frame. If there is no peer-to-peer communication between the two ONUs corresponding to a certain pairing number within the T _max time period, the OLT sends a Clear frame to the two ONUs corresponding to the pairing number to enable the ONU to delete the record of the pairing number locally, that is, to remove the communication between the pair of ONUs. The pairing connection, and the pairing number needs to wait for a long enough time before it can participate in the allocation of new pairings.

The method described in step 2 is characterized in that it comprises the following steps:

Step 2-1: The corresponding paired ONU receives and saves the Notice frame, and the paired ONU judges whether the destination MAC address of each upstream data frame is consistent with the destination MAC address contained in the valid Notice frame saved locally: if not, then Uplink frames do not perform operations related to network coding; if they are consistent, perform steps 2-2;

Step 2-2: The paired ONU locally caches the uplink data frame whose destination MAC address is consistent with the information in the Notice frame, and adds the same cache sequence number and pairing corresponding to the destination MAC address to both the cache frame and such uplink data frame No. GroupID, the cache sequence number and pairing number are regarded as the mark of the data frame that may participate in the network coding at the OLT place;

Step 2-3: The OLT receives the data frame of the ONU that is the first upstream sender in the paired ONU, and judges whether the data frame has a mark: if there is no mark, the operation related to network coding will not be performed; if there is a mark, the steps will be performed 2-4;

Step 2-4: The OLT caches the tagged data frames of ONUn(c), which is the first upstream sender of the paired ONU, according to the number, and detects whether the upstream paired ONU exists within the longest buffer waiting time T _wait of the network coding at the OLT. Paired data: If it does not exist, perform network coding on the data frame waiting for timeout in the cache and the m-bit data specified in the Notice frame of the corresponding paired ONU saved by the OLT, and perform frame sequence numbering and pairing number marking on the network coded data ; If it exists, execute steps 2-5;

Step 2-5: The OLT performs network coding on the marked data frame and the previously cached data in the data of the paired ONUn and the upstream sending party ONUc(n), and the frame queue length is longer. The excess data frame Locally cache and start a new T _wait timing, add the pairing number of the encoded data frame and two buffer sequence number tags to the network encoded data frame, and the pairing number tag and buffer sequence number tag can represent this type of downlink at the ONU The data frame is a network coded data frame; the OLT does not perform operations related to network coding for data frames that are not marked in the data of the upstream sending ONU after pairing;

Step 2-6: The OLT downlinks the coded and non-coded data in the downlink sending queue.

The method described in step 3 is characterized in that comprising the following steps:

Step 3-1: The paired ONU receives the OLT downlink data frame, and judges whether the downlink data frame has a mark: if not, the paired ONU does not perform operations related to network coding for this type of data frame; if there is a mark, the paired ONU pairs The marked data frames are only numbered according to the cache sequence and the corresponding numbered data frames in the local cache or the m-bit data P _mbit in the Notice frame are decoded by network encoding;

Step 3-2: After the decoding is completed, the paired ONU clears the data frames involved in the decoding operation in the cache.

in,

In the steps 1-2,

The pairing number GroupID and the ONU identifier are in the same field, and the value range of the GroupID and the value range of the ONU identifier do not overlap each other; After checking all the verification rules of the character, it will further verify whether the field is a pairing number.

Control frame: Notice adopts a format similar to the control frame related to bandwidth allocation in PON, and distinguishes it from the control frame related to bandwidth allocation through frame identification fields with different values; the frame payload of the Notice frame should be filled with the frame Receive the pairing information related to the ONUs with which the ONUs are paired: the pairing number GroupID between the paired ONUs, and the MAC addresses of all terminals connected to the paired ONUs. In order to ensure that the control frame Notice can completely contain all pairing information under a group of paired ONUs, The frame sum of the Notice frame is not limited, and it is enough to ensure that all pairing information under a group of paired ONUs is in the same Notice frame.

In the steps 1-3,

The control frame Clear adopts a format similar to the control frame related to bandwidth allocation in PON, and is specifically distinguished from the control frame and Notice frame related to bandwidth allocation through frame identification fields with different values; The information of the relationship is the pairing number GroupID; after the OLT sends the Clear frame and the ONU receives the Clear frame, both of them delete the pairing information associated with the GroupID in the Clear frame locally, that is, the pairing number GroupID between the paired ONUs cached locally, and Pair the MAC addresses of all terminals connected to the ONU, and clear the data frames related to the GroupID in the cache.

T _max represents the connection between the paired ONUs established in a certain DBA cycle, that is, the longest valid time of the pairing number GroupID, and the size is set as the lifetime of the transmission control protocol TCP connection.

In the steps 2-4,

The longest buffer waiting time T _wait of the network coding at the OLT specifically indicates the longest buffer waiting time of data at the OLT, and its size is defined as the time length of two DBA cycles.

The present invention has the following advantages and effects: the present invention maintains the master-slave relationship between the OLT and the ONU, each ONU does not need to locally learn the LLID and MAC address of the downlink data frame, and does not need to maintain a whole network locally The pairing table of the LLID of the ONU and the MAC address of the downlink host, the present invention also implements the network coding theory in the passive optical network of the tree topology, and is compatible with the main protocols of the existing passive optical network.

Description of drawings

In order to illustrate the present invention more clearly, the accompanying drawings that need to be used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. As far as personnel are concerned, more drawings can be obtained based on these drawings on the premise of not paying creative labor.

Figure 1 is a schematic diagram of the comparison between traditional PON and PON data transmission methods based on network coding triggered by peer-to-peer communication traffic;

FIG. 2 is a schematic flowchart of a network coding connection management method triggered based on peer-to-peer communication traffic provided by an embodiment of the present invention;

Fig. 3 is a detailed flowchart of a network coding connection management method triggered based on peer-to-peer communication traffic provided by an embodiment of the invention;

Fig. 4 is a schematic diagram of the definition of the Notice frame preamble format provided by an embodiment of the present invention;

Fig. 5 is a schematic diagram of the frame payload definition of the Notice frame provided by an embodiment of the present invention;

Fig. 6 is a schematic diagram of the definition of the Clear frame preamble format provided by an embodiment of the present invention;

Fig. 7 is a schematic diagram of frame payload definition of a Clear frame provided by an embodiment of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Fig. 2 is a schematic flow chart of a network coding connection management method triggered by peer-to-peer communication traffic provided by an embodiment of the present invention, and the executed steps are as follows:

S201: The OLT discovers ONUn and c with peer-to-peer communication traffic, ONUn and c are paired ONUs to be network encoded at the OLT, and the OLT establishes a paired connection between the paired ONUn and c through a control frame, and starts the paired connection Timing of the longest effective time; if the OLT cannot detect the peer-to-peer communication data between the paired ONUn and c within the longest effective time of the paired connection, the connection between the paired ONUn and c is removed, and ONUn and c receive the OLT The issued control frame cooperates to participate in the establishment and removal of the paired connection;

S202: ONUn and c mark the data frames that may participate in the network, and perform local caching; the OLT caches the marked data frames in the data frames of the upstream side of the paired ONUn and c, and waits for the locally cached data within the cache waiting time The encoded data frame and the corresponding data are network-encoded, and the network-encoded data frame is marked and delivered;

S203: ONUn and c perform network decoding on the tagged data frames received in the downlink and the corresponding data in the local cache, and clear the data frames in the cache that have participated in the decoding operation.

Fig. 3 is a detailed flowchart of a network coding connection management method based on peer-to-peer communication traffic triggering provided by an embodiment of the invention, corresponding to each step shown in Fig. 2, the execution steps of the detailed flowchart are as follows:

S3101: If the OLT detects that there is peer-to-peer communication data between ONUn and c in a certain dynamic bandwidth allocation DBA cycle in real time, it will determine that there is a network code pair between ONUn and c in the passive optical network, and call it ONUn and c are paired ONUs;

S3102: The OLT assigns a pairing number GroupID to ONUn and c within the DBA period, and unicasts the pairing number GroupID and the MAC addresses of all downstream terminals under one pairing ONUn(c) to the other in the form of a Notice frame Pair ONUc(n), the corresponding paired ONU receives and saves the Notice frame, and establishes a connection between the paired ONUn and c;

In step S3102 of this embodiment, the pairing number GroupID and the ONU identifier (such as the LLID in the Ethernet passive optical network EPON/10 Gigabit passive optical network 10GEPON, or the distribution identifier in the gigabit passive optical network GPON Alloc-ID) is in the same field in the preamble, and the value range of GroupID and the value range of the ONU identifier do not overlap each other; when the verification result of the field where the OLT/ONU pair number GroupID is located does not meet the OLT/ONU pair ONU identifier After checking all the verification rules of the character LLID, it is further verified whether the field is a pairing number;

In step S3102 of this embodiment, the control frame Notice adopts a format similar to the control frame related to bandwidth allocation in PON (such as the MPCP frame in EPON/10GEPON), specifically through the frame identification field with different values (such as EPON/10GEPON The length/type Length/Type field and the opcode field of the MPCP frame in the MPCP frame) to distinguish the control frame related to bandwidth allocation; the frame payload of the Notice frame should be filled with the pairing information related to the ONU paired with the frame receiving ONU : That is, the pairing number GroupID between paired ONUs, and the MAC addresses of all terminals connected to the paired ONU. All the pairing information under a group of paired ONUs can be in the same Notice frame;

According to this requirement, in EPON, a feasible definition of the preamble format of the Notice frame is shown in Figure 4, and a feasible definition of the frame payload of the Notice frame is shown in Figure 5. In Fig. 4, Fig. 4-1 is the frame preamble format stipulated by the EPON standard, and Fig. 4-2 is the Notice frame preamble format in the present embodiment, and the field length in each box in the figure is 1 byte, Replace the LLID field in the preamble of the EPON frame with the pairing relationship identification number GroupID to be used as the preamble of the Notice frame; The definition of the field and the Opcode field is similar to but not repeated with the definition of the existing MPCP frame. This embodiment defines Length/Type=0x8808, Opcode=0x0008; the field after the Opcode is used to fill the pairing number between the paired ONUn and c GroupID, and the MAC addresses of all hosts connected to the paired ONU; any m bits in the Notice frame (such as m bits starting from the GroupID field) can be defined as P _mbit , and the m-bit data is used to cache with the paired ONU at the OLT and wait for timeout DataFrame Network encoded data.

S3103: The OLT saves the Notice frame immediately after delivering the Notice frame by unicast, and starts timing the longest valid time T _max of the pairing number GroupID in the Notice frame. If the ONUn and c corresponding to the pairing number GroupID have no peer-to-peer communication within the T _max time period, the OLT sends a Clear frame to the ONUn and c corresponding to the pairing number to enable ONUn and c to delete the pairing number record locally, that is, to remove the pairing ONUn and c The pairing connection between c, and the pairing number needs to wait for a long enough time before it can participate in the allocation of new pairing;

In step S3103 of this embodiment, the value of the longest effective time T _max is specifically set. On the one hand, it should be considered according to the connection-oriented service characteristics provided by actual TCP, because there are such as confirmation, flow control, and connection management in the TCP communication process. Waiting for the steps of round-trip interaction between multiple communication hosts; on the other hand, the limitation of the ONU's local cache capacity must be considered, because the longer the time for the ONU to store the Notice frame locally, that is, a certain pairing number, the data frame going to the paired ONU All will be cached, and then the demand for local cache will be even greater; comprehensively considering the above needs, T _max is set to be set as the time-to-live of the Transmission Control Protocol TCP connection in the present invention, and the typical value is 3 seconds;

In step S3103 of this embodiment, the control frame Clear adopts a format similar to the control frame related to bandwidth allocation in PON (such as the MPCP frame in EPON/10GEPON), specifically through the frame identification field with different values (such as EPON/10GEPON The Length/Type field and Opcode field of the MPCP frame in the MPCP frame) are distinguished from the control frame and Notice frame related to bandwidth allocation; the information used to release the network coding pairing relationship contained in the control frame Clear is the pairing number GroupID; the OLT sends the Clear frame and the ONU After receiving the Clear frame, both delete the pairing information associated with the GroupID in the Clear frame locally, that is, the pairing number GroupID between the paired ONUs in the local cache, and the MAC addresses of all terminals connected to the paired ONU, and clear the cache Data frame related to GroupID;

According to this requirement, in EPON, a feasible definition of the preamble format of the Clear frame is shown in Figure 6, and a feasible definition of the frame payload definition of the Clear frame is shown in Figure 7. In Fig. 6, Fig. 6-1 is the frame preamble format stipulated in the EPON standard, and Fig. 6-2 is the Clear frame preamble format in the present embodiment, and the field length in each box in the figure is 1 byte, The LLID field in the EPON frame preamble is replaced by the pairing relationship identification number GroupID and can be used as the Clear frame preamble; in Fig. 7, the Clear frame destination MAC address is set to the multicast MAC address (802.3 regulation: the 48th bit of the Ethernet MAC address It is used to indicate whether this address is a multicast address or a unicast address. If this bit is 0, it means that this MAC address is a unicast address; if this bit is 1, it means that this MAC address is a multicast address); Clear frame as a A special multicast frame, using a format similar to MPCP frames. This format is mainly reflected in the definition of the Length/Type field and Opcode field. It is similar to but not repeated with the existing MPCP frame and Notice. Type=0x8808, Opcode=0x0009.

S3201: The corresponding paired ONUn and c receive and save the Notice frame, and the paired ONUn and c judge whether the destination MAC address of each uplink data frame is consistent with the destination MAC address contained in the effective Notice frame stored locally: if not, Then the uplink frame does not perform operations related to network coding; if they are consistent, execute step S3202;

S3202: Pair ONUn and c to locally cache the uplink data frame whose destination MAC address is consistent with the information in the Notice frame, and add the same cache sequence number and pairing number corresponding to the destination MAC address to both the cache frame and such uplink data frame GroupID, the cache sequence number and pairing number are regarded as a mark of a data frame that may participate in network coding at the OLT;

S3203: The OLT presses and receives the data frame of the first upstream sending ONU in the paired ONUn and c, and judges whether the data frame has a mark: if there is no mark, the operation related to network coding will not be performed; if there is a mark, execute Step S3204;

S3204: The OLT caches the tagged data frames of the paired ONUn and c that send the ONU upstream first according to the number, and detects whether there is a paired upstream paired ONUn and c within the longest buffer waiting time T _wait of the network coding at the OLT Data: If it does not exist, perform network encoding on the data frame waiting for timeout in the cache and the m-bit data specified in the Notice frame corresponding to ONUn and c stored in the OLT, and perform frame sequence numbering and pairing number marking on the network encoded data ; If it exists, execute step S3205;

In the step S3204 of this embodiment, specifically set the value of the longest buffering time T _wait of the network coding, on the one hand, it is necessary to ensure the fairness of the upstream data frames of the same ONU in different DBA cycles, and to ensure as much as possible At the OLT, when there is a frame of upstream data in a certain DBA cycle that needs to be processed downstream, there will still be a phenomenon that the upstream data frame in the previous DBA cycle is not sent downstream; The paired data of the upstream side and the paired data of the upstream side are just staggered by one DBA cycle, resulting in extremely low coding efficiency; according to the above requirements for the cache waiting time T _wait at the OLT, T _wait is set to meet the requirements. The value is the length of two DBA cycles.

S3205: The OLT performs network coding on the marked data frame and the previously cached data in the data of the paired ONU and the data of the upstream sending ONU. The frame queue length is longer and the excess data frame is cached locally and a new T _wait is started. Timing, adding the pairing number of the encoded data frame and two buffer sequence number marks to the data frame after network encoding, the pairing number mark and the buffer sequence number mark can indicate that this type of downlink data frame is a network encoding data frame at the ONU place; The OLT does not perform operations related to network coding for the unmarked data frames in the data of the upstream sending ONU after the pairing process;

S3206: The OLT downlinks the coded and non-coded data in the downlink sending queue.

In step S3026 of this embodiment, before the OLT downlinks the encoded and non-encoded data in the downlink transmission queue, it performs downlink churn encryption on the non-encoded data frames, and does not perform churn encryption on the encoded data frames.

S3301: Pair ONUn and c to receive the OLT downlink data frame, and judge whether the downlink data frame has a mark: if not, pair ONUn and c to not perform network coding-related operations on such data frames; if there is a mark, pair ONUn and c, the marked data frames are only numbered according to the buffer order and the corresponding numbered data frames in the local buffer or the m-bit data P _mbit in the Notice frame are decoded by network encoding;

S3302: After the decoding is completed, the paired ONUn and c clear the data frames involved in the decoding operation in the cache.

The above descriptions are only preferred embodiments of the present invention, rather than limiting the present invention. Any person skilled in the art can make many possible changes or replacements within the method and technical scope disclosed in the present invention. Therefore, all the contents that do not depart from the method of the present invention are based on the technical essence of the present invention. Any simple modifications and equivalent changes should be covered within the protection scope of the present invention.

Claims (10)

1. The network coding connection management method based on peer-to-peer communication flow triggering is characterized in that:

in a passive optical network, an Optical Line Terminal (OLT) discovers Optical Network Units (ONU) with peer-to-peer communication flow, and establishes and removes network coding pairing connection for the ONUs, and each ONU only participates in cooperation;

the ONU marks and caches data frames which possibly participate in network coding, the OLT correspondingly caches and codes the data frames which participate in the network coding, and marks and transmits the data frames after the network coding;

and the ONU performs network decoding and corresponding cache emptying on the received encoded data frame.

2. The method of claim 1, comprising the steps of:

step 1: the OLT finds the ONUs with peer-to-peer communication flow, the ONUs are paired ONUs to be subjected to network coding at the OLT, the OLT establishes pairing connection between the paired ONUs through a control frame and starts to time the longest effective time of the pairing connection; if the OLT cannot detect peer-to-peer communication data between the paired ONUs within the longest valid time of the paired connection, the connection between the paired ONUs is removed, and each ONU receives a control frame issued by the OLT and participates in the establishment and the removal of the paired connection in a coordinated manner;

step 2: the ONU marks data frames which possibly participate in network coding and carries out local cache; the OLT caches a marked data frame in a first uplink party in a paired ONU, network encodes a data frame to be encoded and corresponding data which are locally cached within cache waiting time, and marks and issues the data frame after network encoding;

and step 3: and the ONU carries out network decoding on the marked data corresponding to the local cache in the data frame received in the downlink and empties the data frame participating in the decoding operation in the cache.

3. The method of claim 2, wherein step 1 comprises the steps of:

step 1-1: if the OLT detects that data of mutual peer-to-peer communication exists between any pair of ONUs in a certain Dynamic Bandwidth Allocation (DBA) period in real time, the OLT can determine that network coding pairing exists between the pair of ONUs in the passive optical network and call the pair of ONUs as a paired ONU;

step 1-2: the OLT allocates a pairing number GroupID to the pair of ONU within the DBA period, unicasts the pairing number GroupID and MAC addresses of all the drop terminals under one paired ONU to the other paired ONU in the form of a Notice frame, and the corresponding paired ONU receives and stores the Notice frame and establishes connection between the paired ONUs;

step 1-3: immediately storing the Notice frame after the OLT issues the Notice frame in a unicast way, and setting the longest effective time T of the pairing number GroupID in the Notice frame_maxStarting timing; if two ONUs corresponding to a certain pairing number are in T_maxAnd if no peer-to-peer communication exists in the time period, the OLT sends Clear frames which enable the ONUs to delete the pairing number records locally, namely, the pairing connection between the pair of ONUs is removed, and meanwhile, the pairing number needs to wait for a long enough time before participating in the new pairing distribution.

4. The method of claim 2, wherein step 2 comprises the steps of:

step 2-1: and the paired ONU judges whether the target media access control MAC address of each uplink data frame is consistent with the target MAC address contained in the locally stored valid Notice frame: if not, the uplink frame does not carry out the operation related to the network coding; if yes, executing step 2-2;

step 2-2: the paired ONU caches an uplink data frame with consistent information in a target MAC address and a Notice frame locally, and adds the same cache sequence number and a pairing number GroupID corresponding to the target MAC address in the cache frame and the uplink data frame, wherein the cache sequence number and the pairing number are used as marks of data frames which possibly participate in network coding at the OLT;

step 2-3: the OLT receives a data frame of an ONU of an upstream sending party in the paired ONUs, and judges whether the data frame is marked: if not, not carrying out the operation related to the network coding; if yes, executing step 2-4;

step 2-4: the OLT caches marked data frames of the ONU of the upstream sending party in the paired ONUs according to the number, and the OLT encodes the longest cache waiting time T_waitWhether paired data exist in the upstream paired ONU after internal detection is as follows: if the data frame does not exist, the data frame with the overtime buffer waiting and the appointed m-bit data in the Notice frame of the corresponding paired ONU stored by the OLT are subjected to network coding, and the data subjected to the network coding is subjected to frame sequence numbering,A pairing number mark; if so, performing step 2-5;

step 2-5: OLT carries out network coding on data frame with mark in data of ONU at back up line sending side in paired ONU and data buffered previously according to frame, data frame of which the length of frame queue is longer and the side exceeds part is buffered locally and starts new T_waitTiming, adding a pairing number and two buffering sequence number marks of the encoded data frame to the data frame after network encoding, wherein the pairing number mark and the buffering sequence number marks can represent that the downlink data frame is the network encoded data frame at the ONU; the OLT does not perform network coding-related operation on data frames which are not marked in data of the ONU at the rear uplink sending party in the pairing process;

step 2-6: and the OLT carries out downlink transmission on the coded data and the uncoded data in the downlink transmission queue.

5. The method of claim 2, wherein step 3 comprises the steps of:

step 3-1: and the paired ONU receives the OLT downlink data frame and judges whether the downlink data frame has a mark: if not, the paired ONU does not perform network coding-related operation on the data frames; if the mark exists, the paired ONU numbers the marked data frame according to the cache sequence only and numbers the data frame with the corresponding number in the local cache or m-bit data P in the Notice frame_mbitCarrying out decoding operation of network coding;

step 3-2: and after the decoding is finished, the paired ONU clears the data frames participating in the decoding operation in the cache.

6. The method of claim 3, wherein:

in the step 1-2, the pairing number GroupID and the ONU identifier are in the same field, and the value range of the GroupID and the value range of the ONU identifier are not overlapped; and when the verification result of the field of the pairing number groupID of the OLT/ONU does not meet all the verification rules of the OLT/ONU for the ONU identifier, further verifying whether the field is the pairing number.

7. The method of claim 3, wherein:

in step 1-2, the control frame Notice adopts a format similar to that of a control frame related to bandwidth allocation in a PON, and is specifically distinguished from the control frame related to bandwidth allocation by frame identification fields with different values; the pairing information related to the ONU paired with the frame receiving ONU should be filled in the frame payload of the note frame: namely, the pairing number GroupID between the paired ONUs and the MAC addresses of all the terminals hung under the paired ONUs, in order to ensure that the control frame Notice can completely contain all the pairing information under a group of paired ONUs, the frame length of the Notice frame is not limited, and it is sufficient to ensure that all the pairing information under a group of paired ONUs are in the same Notice frame.

8. The method of claim 3, wherein:

in step 1-3, the control frame Clear adopts a format similar to that of a control frame related to bandwidth allocation in a PON, and is specifically distinguished by frame identification fields with different values and control frames related to bandwidth allocation and a note frame; the information contained in the control frame Clear and used for releasing the network coding pairing relationship is a pairing number GroupID; after the OLT sends the Clear frame and the ONU receives the Clear frame, the OLT and the ONU both locally delete pairing information associated with the GroupID in the Clear frame, namely a pairing number GroupID between paired ONUs cached locally and all terminal MAC addresses hung under the paired ONUs, and empty data frames related to the GroupID in the cache.

9. The method of claim 3, wherein: in step 1-3, T_maxThe maximum effective time of the connection between the paired ONUs established in a certain DBA period, namely the pairing number GroupID, is represented, and the maximum effective time is set as the survival time of the TCP connection.

10. The method of claim 4, wherein:

in steps 2-4, network coding at the OLT maximum buffer latency T_waitSpecific body surfaceShowing the longest buffer latency of data at the OLT, the size being defined as the length of time of two DBA cycles.