CN103747083B - A kind of content delivery method based on CCN - Google Patents

Abstract

The invention relates to a content push method based on CCN. The content pusher initiates communication actively, and the content can be directly pushed to the receiving user without user request, and multiple interactions can be established by triggering a specific interest packet without multiple interactions. The reverse push path of content greatly reduces communication delay and link load. The present invention can be applied to many application scenarios, such as microblog, large file transfer, stock, weather forecast, etc. that are frequently used now, which enriches the practical application of the CCN network.

Description

A CCN-based content push method

technical field

The invention belongs to the technical field of computer networks, and in particular relates to a CCN-based content pushing method.

Background technique

With the continuous development and changes of Internet applications, the existing Internet based on TCP/IP has gradually exposed many inadaptability. At present, the main problems exposed on the Internet are: insecurity, poor mobility, poor reliability, and poor flexibility. The scalability of the Internet and the effective distribution of content have caused an upsurge of research by scholars of Overlay Network and Content Delivery Network. The Internet is gradually changing from a host center to a content center. CCN (content centric network, content centric network) is currently a more mainstream research direction.

Contents of the invention

In order to overcome the deficiencies of the above-mentioned prior art, the present invention proposes a content push method based on CCN, thereby effectively improving the performance of the CCN network, characterized in that:

The pusher constructs a specific interest packet and sends the specific interest packet;

The intermediate node parses the interest packet and judges whether the interest packet contains PIT-specific fields;

The intermediate node modifies the PIT entry if it detects a PIT specific field;

The intermediate node modifies the port and establishes a reverse PIT;

The intermediate node forwards the specific interest packet to the next node according to the FIB route;

The receiver establishes a reverse PIT;

The pusher triggers an Interest packet to query PIT matching entries;

The pusher forwards the content from the port recorded in the PIT.

Preferably, if the result of judging whether the Interest packet contains the PIT specific field is no, continue processing according to the normal CCN process.

Preferably, the normal CCN process is specifically:

When the requester needs to request content, it actively sends an interest packet; after receiving the interest packet, the intermediate node will query the content cache (CS), PIT and FIB in turn;

If there is no content requested by the requester in the CS, the intermediate node records the port number for receiving the Interest packet on the PIT;

The intermediate node forwards the Interest packet according to the FIB; each Interest packet has a random number (nonce); each CCN node judges the name of the Interest packet when receiving the Interest packet, and when receiving an Interest packet with the same name but different nonce , CCN adds the port where the interest packet comes in in the PIT; if the name of the received interest packet is the same as the nonce, the CCN node will discard the duplicate interest packet;

After the content source receives the Interest packet, it searches its own CS. If the content requested by the requester exists in the CS, it will follow the original path according to the port information recorded by the PIT; the content will be returned via the intermediate node;

Intermediate nodes through which the content passes cache content copies in the local CS.

Preferably, the constructed specific interest packet includes one or more of the name of the content recipient, the number of fragments to be pushed, the starting fragment number, and the name of the content.

Preferably, if the intermediate node detects a PIT-specific field, modifying the PIT entry further includes: removing the previous PIT flag and the last component representing the number of PITs;

Construct several new continuous Interests;

Find the forwarding port of the Interest packet, and add the forwarding port of the Interest packet to the PIT entry;

After the PIT entry is added, the Interest packets are not forwarded, and the Interest packets are discarded directly.

Preferably, the pushing party forwarding the content from the port recorded in the PIT further includes:

After searching the CS and finding the matching content, forward the content directly according to the established PIT.

Preferably, the intermediate node forwarding the specific interest packet to the next node according to the FIB route further includes:

The intermediate node forwards the specific interest packet until it reaches the receiver of the content before stopping forwarding.

Preferably, the intermediate node does not forward several Interest packets constructed when adding the reverse PIT, and discards them after the reverse PIT is established.

Preferably, the receiver establishes a reverse PIT specifically as follows:

When a specific interest packet arrives at the receiver, the receiver establishes a PIT, and the name prefix is the same as that of the intermediate node, but the PIT port number is the receiver's local port number;

When the data packet arrives at user B, the PIT port is found to be the local port, and the content will not be forwarded but directly stored in the local CS.

Preferably, the reverse PIT is to reverse the incoming face and outgoing face in the PIT.

The above description is only an overview of the technical solutions of the present invention. In order to understand the technical means of the present invention more clearly and implement them according to the contents of the description, the preferred embodiments of the present invention and accompanying drawings are described in detail below.

Description of drawings

Fig. 1 shows the CCN protocol stack model;

Figure 2 shows the CCN packet format;

Figure 3 shows a flow chart of communication between CCN nodes;

Fig. 4 shows a flow chart of implementing content push in CCN according to an embodiment of the present invention.

Detailed ways

In order to further explain the technical means and effects of the present invention to achieve the intended purpose of the invention, the specific implementation, features and features of a CCN-based content push method proposed according to the present invention will be described below in conjunction with the accompanying drawings and preferred embodiments. Its effect is described in detail below. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

Figure 1 shows the model of the CCN protocol stack. The protocol stack structure based on CCN is similar to the protocol stack structure based on TCP/IP, both are hourglass models. The biggest difference is that the IP protocol is replaced by the Content chunk (content block) protocol. From the perspective of the network, the naming of data replaces the naming of physical entities in the network. In addition, the built-in storage function in the network is used to cache the passing data packets, so as to speed up the response time for other users to access the cached data packets, and at the same time reduce the traffic in the network.

CCN communication is driven by data consumers, and data can be transferred in blocks. There are two types of packets in CCN: Interest Packet and Data Packet. Figure 2 shows the packet format of CCN. The Interest Packet includes the Content Name, which is used to uniquely identify the content; the Selector, which contains some optional parameters, is used to determine the processing method of the Interest Packet. For example, if Scope=0, the Interest Packet It cannot be forwarded to other applications of the host, and Scope=1 cannot be forwarded to the host that initiated the Interest packet; the random number (Nonce) is used to uniquely identify the Interest packet to avoid duplication. The data package includes, content name (Content Name), used to uniquely identify the content name; signature (Signature), used to uniquely identify the content source and content name; signature information (Signed Info), including time, key and other information, used for Set the content parameters; data (Data) refers to the actual transmission data content. Users who need relevant content send requests in multiple directions through interest packets according to their own FIB. If any node that receives this request has content that can satisfy the request, it will send response data to the requesting node through a data packet. This correspondence is based on identifying content, that is, each content has a specific identification. The location of the interest packet and the data packet has nothing to do. On a broadcast medium, requests with the same content requirements can share the same content and network transmission, thereby saving network resources and improving network transmission efficiency.

The identification of the content is actually the address of the CCN. This kind of identification is structured and usually consists of several components (that is, components), where each component is separated by / through this structured address, and can use a mechanism similar to an IP address prefix to quickly locate the required information. For example, /catr.cn/videos/WidgetA.mpg/_v<timestamp>/_s3, where catr.cn is the recognizable name of the whole network, videos is the content type, WidgetA.mpg is the content name, _v<timestamp> is the version time, etc. Information, _s3 is information such as segmentation.

If the content name (Content name) of the interest packet is the prefix of the content name (Content name) of the data packet, it means that the data packet satisfies the request. The content name can be dynamically generated, that is, the application that does not have the requested content temporarily generates the content when receiving the Interest packet. Similar to Dynamic Web, ie mixed support for static content and dynamic generation.

The term Face refers to an interface on a CCN transponder that is coupled to an application or network. Face can be hardware or software based. Such CCN interfaces are called faces to distinguish them from interfaces which are physical network interfaces in router terminology.

When a packet arrives at a Face, it will use the content name to search for the longest prefix match, and three key data will be used to complete the forwarding (FIB, content cache, PIT). FIB (Forwarding information base, forwarding information base) is equivalent to the routing table in the IP protocol, but allows multiple exits instead of being limited to one. The content cache (Content store) can use LRU (least recently used) strategy and time to live (TTL, time to live) strategy to cache forwarded data packets for use by other consumers and improve the hit rate of data packets. PIT (Pending Interesting Table) is used to record the content name and port number of the interest packet that has been forwarded, so that the response data packet can reach its corresponding requester according to the port number. When a packet responding to an Interest is forwarded using an entry in the PIT or when the time-to-live expires, the entry is deleted.

When an Interest packet (Interest packet) arrives at a certain node, first match the content cache according to the Interest packet, if there is a matching content, then use the matching content to respond to the request and discard the Interest packet; if there is no matching content, then indicate The content is not cached or the cache time expires and is replaced. At this time, the PIT is matched. If there is a matching PIT entry, it means that other users may have requested the same content not long ago. Here, PIT aggregation can be performed, that is, in the PIT corresponding Add Face to the entry, and discard the Interest packet; if there is no matching content, match the FIB according to the longest prefix of the Interest packet, forward the Interest packet according to all matching Faces (except the Interest packet arriving at the Face), if there is still no matching Matching Face, discard the Interest packet.

The processing of the data packet (data packet) is relatively simple. When the data packet arrives, the longest prefix match is first performed on the Content Name (content name) field of the data packet, and the match is first performed in the Content Store (content cache). If there is a match content, the returned content is invalid, and the previously requested Interest packet should have been responded, so the data packet is discarded; if there is no matching content, continue to match in the PIT, if there is a matching entry, the content The port number recorded in the PIT is forwarded and cached in the Content Store (content cache). If there is no matching entry, the packet is discarded.

Figure 3 shows the communication flow chart between CCN nodes. There may be several intermediate nodes C between the user A and the content source B, for the sake of brevity, only one intermediate node C is exemplarily shown in FIG. 3 . User A may also be called node A, and content source B may also be called node B or user B. As shown in 301, when user A needs to request content, it actively sends an interest packet; after receiving the interest packet, intermediate node C will query CS (Content Store, content cache), PIT and FIB in sequence. If there is no content requested by user A in the CS, the intermediate node C records the port number for receiving the interest packet on the PIT; as shown in 302, the intermediate node C forwards the interest packet according to the FIB; each interest packet has a nonce (random number ); when each CCN node receives the Interest packet, it will judge the name of the Interest packet. When receiving an Interest packet with the same name but different nonce, CCN will add the port where the Interest packet came in in the PIT; if received If both the name of the Interest packet and the nonce are the same, the CCN node will discard the duplicate Interest packet; as shown in step 303, after receiving the Interest packet, the content source B first searches for its own CS, if there is content requested by user A in the CS , then according to the port information recorded in the PIT, according to the original path, as shown in step 304, the content is reversed via the intermediate node C. At the same time, the intermediate node C through which the content passes will cache the copy of the content in the local CS.

The format of the PIT entry is shown in Table 1 below, where Face0 refers to the port where the Interest packet enters.

Interest name prefix Incoming faces name Face0

Table 1: PIT entry format

The format of the FIB entry is shown in Table 2 below, where Face1 refers to the outgoing port of the Interest packet.

Interest name prefix Outcoming faces name Face1, Face2

Table 2: FIB entry format

Under normal circumstances, only when the user actively sends an interest packet can the acquisition of the corresponding content be triggered. However, many application scenarios need to push content directly to users, such as Weibo, real-time voice communication, large file transfer, stocks, weather forecast, etc., which are widely used now.

CCN can trigger the establishment of a PIT path by sending an Interest packet, and when the content needs to be returned, it can return by searching the PIT path. If user A needs to actively initiate content push to user B, a PIT path needs to be established between user A and user B so that content not requested by user B can be pushed to user B correctly. User A can directly search for CS to push content, without starting to search for CS when receiving an Interest packet. Correspondingly, user B can allow receiving and storing content not requested by him.

In a specific embodiment of the present invention, user A sends a specific interest packet, and after receiving the specific interest packet, the intermediate node C between user A and user B will add a PIT entry and modify the port direction in the PIT, that is, in the user A reverse PIT path is directly established between user A and user B, so that content that has not been requested can be forwarded according to the reverse PIT path, so that content can be directly pushed from user A to user B through data packets without the active request of user B .

In a specific embodiment of the present invention, the reverse PIT is to reverse the incoming face and outgoing face in the normal PIT. By constructing a reverse PIT, the PIT can be "spoofed", and when the pusher user A has the content, the content can be actively pushed to the receiver user B.

In a specific embodiment of the present invention, the normal Interest packet mentioned in the other invention scheme refers to an Interest packet that does not contain a specific field "PIT", while a specific Interest packet refers to an Interest packet that contains a specific field "PIT", for example ccnx:/B/PIT/B/name/%FD%versionnumber/%pushnumber/n is a specific interest packet, while ccnx:/B/name/%FD%versionnumber/%pushnumber is a normal interest packet. The "PIT" here is only an exemplary description, and other specific fields can be used without departing from the concept of the present invention. It should be noted that since there are only two types of interest packets and data packets in CCN, in order to enrich the application of CCN in some scenarios, specific fields will be added to CCN packets to distinguish them from ordinary interest packets and data packets. Specific fields in CCN generally refer to adding a field similar to "PIT" to the name of the interest packet, so that the interest packet can perform different functions. A "Video" field to construct specific Interests.

Under normal circumstances (that is, when the interest packet sent does not contain a specific field PIT), user A sends an interest packet to user B, and the intermediate node C will first query CS without cache, and then query PIT. If there is no match in PIT, then Start to create a PIT entry. Assuming that the Interest packet arrives from Face2 of the intermediate node C and is forwarded from Face1 of the intermediate node C, the PIT entry added at the intermediate node C is the name of the Interest packet and Face2 (normally, the PIT entry is as shown in Table 3 shown), after adding the PIT, it will be forwarded according to the Face1 port recorded in the FIB, so that when the content is returned from user B to the intermediate node C, the query PIT will be forwarded directly from Face2 to user A to complete the process of obtaining the content.

Interest name prefix Incoming faces ccnx:/B/name/%FD%versionnumber/%pushnumber Face2

Table 3: PIT entries under normal conditions

Reverse PIT means that when adding a port, the forwarding port Face1 will be added to the PIT entry instead of the Interest packet entering the port Face2 (here it is still assumed that the Interest packet arrives from Face2 of the intermediate node C and is forwarded from Face1 to user B). The PIT entry added at C is shown in Table 4 below. In this way, when it is necessary to push content from user A to user B, the content can be directly forwarded from Face1 through the pre-set PIT when passing through user C, so that the content can reach user B, thereby achieving the technical effect of pushing content.

Interest name prefix Incoming faces ccnx:/B/name/%FD%versionnumber/%pushnumber Face1

Table 4: PIT entries in reverse case

The FIB entries of user A and intermediate node C are shown in Table 5 and Table 6 below:

Interest name prefix Outcoming faces B Face1

Table 5: FIB entry for user A

Interest name prefix Outcoming faces B Face1

Table 6: FIB entry for user C

After the above FIB entry is established, the Interest packet sent from user A to user B can be correctly forwarded to node B after finding the FIB.

Fig. 4 is a flow chart of implementing content push in CCN according to an embodiment of the present invention. Step 401, user A (that is, pusher A) constructs a specific interest packet and sends the specific interest packet. The reason for constructing the specific interest packet here is to consider that the processing flow of this interest packet is different from that of a normal interest packet. Considering that the specific interest packet The subsequent processing of interest packets is different from that of normal interest packets. Therefore, the constructed interest packets can: 1) add the name of the content receiver B (user B) in this embodiment, which is B. The purpose is to The interest packet can be correctly routed to the content receiver by searching for the FIB; 2), explain the number of fragments to be pushed and the starting fragment number, large files are fragmented during the transmission process, so in the special interest packet In order to successfully push the required complete content, it is necessary to explain the number of fragments and the starting fragment number; 3), explain the name of the content. In view of the above considerations, the format of the constructed Interest packet is as follows:

ccnx:/B/PIT/B/name/%FD%versionnumber/%pushnumber/n

The meanings of the fields in the Interest package are as follows:

/B/PIT/: B is the communication receiver, "PIT" is the detection field for establishing reverse PIT

/B/name: /B/name is the name of the content to be pushed to B in the CS of pusher A.

/pushnum: pushnum refers to the starting segment number of the content to be sent. Since in the large file push, the push starts from segment 0, so the pushnum is 0 in the large file push; for other scenarios, the starting point is determined according to the specific situation start segment number. In this embodiment, large file transfer is used as an application scenario.

/n: n is the number of reverse PIT entries to be created. During large file transmission, A determines the number of segments to push content by querying its own CS.

"%FD%versionnumber" The component that represents the version number is optional. And the format of the specific interest packet can also be defined as follows: ccnx:/B/PIT/name/%FD%versionnumber/%pushnumber/n, since the component "/B" is only used for routing, it starts with "/B" When querying the FIB, the Interest packet can query the Face corresponding to user B through the longest prefix match, so that the Interest packet can be correctly routed to user B, so only one "/B" can be needed in a specific Interest packet, if so It will only need to remove "/PIT" when receiving special interest packets.

Step 402, parse the Interest packet, and determine whether the Interest packet contains a specific field.

In a specific embodiment of the present invention, the specific field is the "PIT" field; correspondingly, the interest packet containing the "PIT" field is called a specific interest packet; the interest packet without the "PIT" field is called an interest packet. is a normal interest packet.

The parsing process of a specific interest packet is as follows:

User A and the intermediate node C between user A and user B receive the specific interest packet sent by user A, and use string matching to determine whether the second component is "PIT" when parsing the interest packet, so as to determine whether it is detected "PIT" specific field, if the "PIT" specific field is not detected, proceed to step 404, and process the Interest packet according to the flow shown in Figure 3; if the "PIT" specific field is detected, proceed to step 404, remove the preceding Two compnents: /B and /PIT and the last component; step 405, construct n new continuous interest packets:

ccnx:/B/name/%FD%versionnumber/%pushnumber

ccnx:/B/name/%FD%versionnumber/%pushnumber+1

ccnx:/B/name/%FD%versionnumber/%pushnumber+2

ccnx:/B/name/%FD%versionnumber/%pushnumber+n-1;

The processing of these n interest packets is different from that of ordinary interest packets. Ordinary interest packets are forwarded directly after searching the forwarding port. Here, after the n interest packets are established, the interest packets are searched according to the normal process. Forward the port, and then add the forwarding port of the Interest packet to the PIT entry (the normal process is to add the port where the Interest packet comes in to the PIT entry). After adding the PIT entry, there is no need to forward the n Interest packets, and the Interest packet throw away.

The n new interest packets that have been constructed do not contain the PIT string, and the node does not really need to obtain the content. The purpose of constructing the interest packet is only to create a reverse PIT, so that pusher A can follow the correct path to send The content is pushed to receiver B. If the Interest packet is forwarded to one or more nodes, there may be situations where unnecessary content may be returned, which wastes network resources and may cause network congestion. For example: if pusher A needs to push n blocks of content to receiver B, it needs to construct n PIT entries matching the content block at intermediate node C, so that the content at A can be pushed, so at node C n interest packets will be constructed to construct the reverse PIT, but node C does not need to fetch the content, so there is no need to forward the n interest packets.

The specific implementation process is as follows:

According to the constructed n interest packets, it is determined that the entries that need to be added to the PIT are:

ccnx:/B/name/%FD%versionnumber/%pushnumber;

ccnx:/B/name/%FD%versionnumber/%pushnumber+1;

ccnx:/B/name/%FD%versionnumber/%pushnumber+2;

ccnx:/B/name/%FD%versionnumber/%pushnumber+n-1.

Step 406, after the Interest packet entry is added, the port reversal is started, and the reverse port is added to complete the addition of the reverse PIT entry. Record the Forwarding face of the forwarding port of the Interest packet, and add the Forwarding face to the newly created PIT entry. Since the forwarding direction of the Interest packet is consistent with the direction of content push, that is to say, both the forwarding direction of the Interest packet and the push direction of the content are from user A To user B, the path and port passed in the middle are the same, so the forwarding port here is also the forwarding port of the content pushed by user A to user B. After adding the correct port in the PIT entry, when user A pushes content to user B, the content can be forwarded to the target node B correctly by querying the reverse PIT at user A and intermediate node C (that is, receiver B). The reverse PIT format of the intermediate node is as follows: (Among them, Face1 is the outgoing face of the interest packet, that is, the forwarding face, A is the pusher, and B is the receiver, but it is added as the incoming face when adding the PIT, thereby realizing the reverse port Towards).

Interest name prefix Incoming faces

 

Table 7: Intermediate node reverse PIT format

When processing a specific Interest packet, the intermediate node needs to forward the specific Interest packet to the next node in addition to adding the reverse PIT, mainly considering that user B needs to perform corresponding processing after receiving the specific Interest packet, so that the content It can be correctly cached when it reaches user B, so the specific interest packet needs to be forwarded at the intermediate node until the content receiver stops forwarding. However, the n interest packets built when adding the reverse PIT are not forwarded, and are discarded after the reverse PIT is established. When the data packet is forwarded to the destination node B along the reverse PIT, if no special processing is performed, the unrequested data will be discarded according to the CCN protocol B without caching (the main reason is that the PIT entry will be searched for when the content arrives at user B, if not If there is a matching PIT, it will be discarded directly).

In order to avoid the data packet being directly deleted at user B, in a specific embodiment of the present invention, step 407, when the specific interest packet arrives at user B, user B establishes a PIT, and the name prefix is consistent with the processing of the intermediate node, the difference is Here, the PIT port number is the local port number of user B. When the data packet arrives at user B, the PIT port is found to be the local port, and the content will not be forwarded but directly stored in the local CS. The PIT entries established for user B are shown in Table 8.

Table 8: Reverse PIT format for content receivers

In another specific embodiment of the present invention, in order to avoid data packets being directly deleted at Node B, the CCN policy can be further modified so that when the content arrives at the node, the content is not searched for the PIT, and the content is directly cached in the local CS.

In order to enable user A to forward his own CS content according to the port recorded in the PIT, step 408, after the reverse PIT is established, node A retrieves the file in the local CS through ccngetfile ccnx:/B/name to trigger the search CS (please add specific content), the ccngetfile command is a file fetching command under the CCN simulation platform. By executing this command, the user can get the content in the local CS or other user CS and store it locally, but the file fetching operation is still It is completed through interest packets and data packets. When using the ccngetfile command, it will actively send multiple interest packets to the content source (including the local CS) according to the fragmentation of the file, and then obtain multiple content fragments from the content source and return them to the local. Here, when the ccngetfile ccnx:/B/name command is used at node A, since "ccnx:/B/name" does not contain the "PIT" specific field, node A will send the requested content to its local port Normal interest packet, the interest packet will no longer include the "PIT" specific field, node A will first check its own CS to find the matching content when processing the received interest packet, then find the PIT matching entry and record the content from the PIT Forwarding in the port; step 409, since the pusher CS has already cached content, and the PIT entry has been established in advance, after searching the CS and finding the matching content, the content can be forwarded directly according to the established PIT, thereby triggering content push. Step 410, the content is transmitted at the intermediate node according to the established PIT path. After reaching the receiver, since the receiver also has a specific PIT entry (the port is the local face) or a direct cache policy, the receiver will directly cache user A For the pushed content, you can use the packet capture software to capture the packet or directly use the ccndumpnames command to view the CS content and know that the receiver B has cached the content. When user A uses ccngetfile to trigger the search for CS, open the packet capture software at user B. Start to capture the packets passing through user B, and analyze the packet capture results. You can see that n content fragments from node C to user B are displayed in the captured packets, indicating that user A has successfully pushed the content to user C. Next, you need to Check whether user C has cached the content, and if user C uses ccndumpnames to view the content in CS, you can also see n content fragments, which means that user C has successfully cached the content. In addition, if you can use ccngetfile ccnx:/B/name at user B to verify whether there is packet loss during the content push process, if user B can successfully fetch the content, it means that the content push is successful.

Through the technical solution disclosed in the present invention, the content pusher actively initiates communication, and can directly push the content to the receiving user without user request, without multiple interactions, and can establish multiple content feedbacks by triggering a specific interest packet. The forward push path greatly reduces communication delay and link load. The present invention can be applied to many application scenarios, such as phone calls, microblogs, large file transfers, stocks, weather forecasts, etc. that are often used now, which enriches the practical application of the CCN network.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this field Those skilled in the art, without departing from the scope of the technical solution of the present invention, can use the technical content disclosed above to make some changes or modify equivalent embodiments with equivalent changes, but all the content that does not depart from the technical solution of the present invention, according to the present invention Any simple modifications, equivalent changes and modifications made to the above embodiments by the technical essence still belong to the scope of the technical solution of the present invention.

Claims (7)

1. A content push method based on CCN, characterized in that: The pusher constructs a specific interest packet and sends the specific interest packet; The intermediate node parses the interest packet and judges whether the interest packet contains PIT-specific fields; The intermediate node modifies the PIT entry if it detects a PIT specific field; The intermediate node modifies the port and establishes a reverse PIT; The intermediate node forwards the specific interest packet to the next node according to the FIB route; The receiver establishes a reverse PIT; The pusher triggers an Interest packet to query PIT matching entries; The pusher forwards the content from the port recorded in the PIT; If the intermediate node detects a PIT specific field, modifying the PIT entry further includes: Remove the previous PIT flag and the last component indicating the number of PIT; Construct several new continuous Interests; Find the forwarding port of the Interest packet, and add the forwarding port of the Interest packet to the PIT entry; After adding the PIT entry, the interest packets are not forwarded, and the interest packets are directly discarded; The receiver establishes a reverse PIT specifically as follows: When a specific interest packet arrives at the receiver, the receiver establishes a PIT, and the name prefix is the same as that of the intermediate node, but the PIT port number is the receiver's local port number; When the data packet arrives at user B, find the PIT port as the local port, and will not continue to forward the content but directly store it in the local CS; The reverse PIT is to exchange the incoming face and outgoing face in the PIT. 2. The method according to claim 1, characterized in that: If the result of judging whether the Interest packet contains the PIT specific field is no, continue processing according to the normal CCN process. 3. The method according to claim 2, characterized in that: The normal CCN process is specifically: When the requester needs to request content, it actively sends an interest packet; after receiving the interest packet, the intermediate node will query the content cache (CS), PIT and FIB in turn; If there is no content requested by the requester in the CS, the intermediate node records the port number for receiving the Interest packet on the PIT; The intermediate node forwards the Interest packet according to the FIB; each Interest packet has a random number (nonce); each CCN node judges the name of the Interest packet when receiving the Interest packet, and when receiving an Interest packet with the same name but different nonce , CCN adds the port where the interest packet comes in in the PIT; if the name of the received interest packet is the same as the nonce, the CCN node will discard the duplicate interest packet; After the content source receives the Interest packet, it searches its own CS. If the content requested by the requester exists in the CS, it will follow the original path according to the port information recorded by the PIT; the content will be returned via the intermediate node; Intermediate nodes through which the content passes cache content copies in the local CS. 4. The method according to claim 1 or 3, characterized in that: The constructed specific interest packet contains the name of the content receiver, the number of fragments to be pushed, and One or more of the starting segment number and the content name. 5. The method according to claim 4, characterized in that: The forwarding of the content from the port recorded in the PIT by the pushing party further includes: After searching the CS and finding the matching content, forward the content directly according to the established PIT. 6. The method according to claim 5, characterized in that: The intermediate node forwarding the specific interest packet to the next node according to the FIB route further includes: The intermediate node forwards the specific interest packet until it reaches the receiver of the content before stopping forwarding. 7. The method according to claim 6, characterized in that: the intermediate node does not forward the several interest packets constructed when adding the reverse PIT, and discards them after the reverse PIT is set up.