CN114679210A - Self-routing technology of delay tolerant and fault tolerant network based on double-layer satellite network - Google Patents
Self-routing technology of delay tolerant and fault tolerant network based on double-layer satellite network Download PDFInfo
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Abstract
The invention discloses a self-routing technology of a delay tolerant and disconnection tolerant network based on a double-layer satellite network. The method is characterized in that a double-layer network architecture combining a low-earth orbit satellite network and a geosynchronous orbit satellite network is adopted, and a routing solution of a delay-tolerant and interruption-tolerant network application environment is designed based on the architecture, wherein the three applications of the delay-tolerant and interruption-tolerant network, namely transit backhaul, covert communication and interruption continuous transmission, are taken as research backgrounds. The key technology adopted by the method is the law of meeting and link change of spatial information network nodes, a delay-tolerant and disconnection-tolerant routing mechanism based on social network characteristics and message transmission scheduling under the condition of limited network resources. And key links such as time division, group division, routing process, congestion control, autonomous strategy and the like are realized. The invention can deal with the condition that the traditional TCP/IP protocol can not be directly applied to the delay tolerant network and provides a novel routing solution for the delay tolerant network.
Description
Technical Field
The invention belongs to the field of network technology and space satellite communication, and particularly relates to a self-routing technology of a delay tolerant and fault tolerant network based on a double-layer satellite network of a low-earth orbit satellite and a geosynchronous orbit satellite.
Background
Delay-Tolerant Networks (Delay-Tolerant Networks), also known as Delay and Disruption Tolerant Networks (DTNs), are a typical overlay wireless network that lacks end-to-end connections. The delay-tolerant and outage-tolerant network has high flexibility and can be better suitable for complex network environments with high transmission delay, frequent link outage, high error rate and the like. At present, the DTN is widely applied to the network communication fields of space information networks, satellite communication, military operations, remote mountain areas, vehicle-mounted mobile networks and the like.
The DTN is a general message-oriented overlay network architecture, and realizes connection between different subnets by adding a bundle layer between a network layer and an application layer. The traditional TCP/IP protocol is suitable for end-to-end network connection in smooth operation, is suitable for networks with smaller transmission delay, bidirectional path transmission and low error rate, and therefore cannot be directly applied to DTN. The DTN protocol stack is shown in fig. 1. In this protocol, delay or interrupt handling may be performed every DTN "hop count" between the source and destination. The nodes on the path may provide the application data with the temporary storage necessary for it before forwarding it to the next node on the path. The benefit of the DTN architecture protocol is that there is no need to establish simultaneous end-to-end connections for reliable transport of application data. The Bundle Protocol (BP) is a typical implementation of the DTN architecture. The basic unit of data in the BP is the "bundle" which carries the application layer protocol data unit (APDU), sender and destination names, and any additional data messages required for end-to-end delivery.
The DTN network node is a specific entity, and in the spatial information network, the node is a satellite, and other nodes such as a main sentence, a router, a gateway and the like can be used as the network node. The primary role of the node is to implement bundle layer functions for sending, receiving or relaying a bundle.
The DTN is mainly characterized in three aspects of end systems, links and network structures. The challenges facing DTN are illustrated from these three aspects below:
the end system refers to each network terminal facility. Due to energy consumption or environmental factors, their lifetime is limited; under the condition of insufficient energy, the end system periodically collects and transmits data; since the cache capacity of the end system is usually very small, cache overflow is easy to occur; meanwhile, the end system is easy to make mistakes when calculating complex problems due to the limited processing capability of the end system.
A link (path) refers to a channel connecting end systems. The DTN has large delay and low data transmission rate, so that the data transmission is asymmetric; the DTN node is constantly moved, so that the network topology structure is changed, at the moment, the node is possibly failed due to energy consumption or frequent movement, and the end-to-end connection is interrupted; due to the limited processing power of the nodes, the queuing time on the link is longer than that of the traditional network.
The network structure means that the network structure changes all the time because the DTN node moves frequently. The problem faced by network architectures is that interoperability is only effective within this network type, and interoperability issues between heterogeneous networks are not considered; in terms of security, access to the service is not verified.
Disclosure of Invention
The invention aims to provide an autonomous routing technical scheme under a delay tolerant and disconnection tolerant network environment, and meanwhile, the efficiency and the reliability of network data transmission are improved.
The application scenario of the DTN is summarized to solve the problems to be solved at present. When a message is sent, a reliable network connection does not exist between a source node and a destination node. The message can only be transferred in a "store-carry-forward" manner by the potential relay nodes. Since the nodes in the network are sparsely distributed and the movement rules of the nodes are unpredictable, the message may be generated for several hours or even longer before it is finally delivered to the destination node. Therefore, the network needs enough storage space to store the message copies, and the management of the node storage in the whole network is very important.
The delay-tolerant disconnection which is mainly researched by the invention is based on a delay-tolerant disconnection network. The transitive backhaul, which puts high demands on the storage capability of the network node, is shown in fig. 2. One satellite collects the data overseas and stores it in its own storage device. When the satellite runs to an indoor range, a designated ground base station is searched, communication connection is established with the ground base station, and collected data are transmitted back. The covert communication puts high requirements on the delay performance of the DTN, and the application scenario is shown in fig. 3. The ground sending end sends the data information to the satellite of the space-based network, and the ground end is off-line immediately after the data is transmitted from the ground to the space-based network. And then the satellite transmits the data to the domestic ground base station through the space-based network. The interruption of continuous transmission puts higher demand on the link reliability of the DTN, and the application scenario is shown in fig. 4. Due to link interruption caused by network topology change or communication quality problems, in order to avoid extra expenses caused by rerouting and data retransmission, data is stored in a satellite firstly and is transmitted continuously after the link is recovered.
The key method adopted by the technology for realizing the autonomous routing of the delay tolerant disconnection network comprises the rule of network node meeting and link change, a social network characteristic-based delay tolerant disconnection routing mechanism and a message transmission scheduling realization mode under the condition of limited network resources. The autonomous routing technology is researched aiming at the characteristics of limited DTN node storage capacity, prolonged link transmission time, high error rate, frequent network topology change and the like. Firstly, aiming at the characteristics that the track position of the spatial information network node is relatively fixed and the dynamicity and the certainty coexist, the analysis of the meeting and link change rule of the spatial information network node is carried out; secondly, aiming at the characteristics of the connection relationship of the satellite nodes, starting from the perspective of social network analysis, the routing decision is assisted by utilizing the social characteristics of the nodes, and the delay tolerant and break-tolerant network routing technology with the social network characteristics is researched. And finally, aiming at the influence of the satellite node buffer capacity limitation and the node contact time limitation on the network routing performance, researching a node buffer management and message transmission scheduling mechanism and improving the asynchronous routing performance under the network resource constraint condition.
The key links in the process of realizing the autonomous routing technology of the delay tolerant and fault tolerant network comprise time/group division, a routing process, congestion control and an autonomous strategy. The method comprises the following specific steps:
(1) since the network topology changes due to the satellite movement, but the network topology can be considered to be unchanged in a certain time range, it is necessary to perform time/group division on the DTN. By dividing the time segments, the satellite network can be divided into n different topologies, and the routing paths at different times are calculated in sequence.
(2) The network topology can be considered to be basically unchanged in the same time slot, the time slot division in a period can be calculated when satellite tracks in the network are determined, and the route is recalculated when the time slot is updated based on the method.
(3) If a large amount of network traffic is generated in a certain time slot, node congestion is easily caused. In order for the network to operate properly, it is necessary to design a congestion control mechanism. In a double-layer satellite network of a low earth orbit satellite and a geosynchronous orbit satellite, different processing mechanisms are designed aiming at the congestion problem of different layers of satellite nodes.
(4) In the invention, when a new satellite node is added into the network, registration information is firstly sent to the geosynchronous orbit satellite in the area, the geosynchronous orbit satellite does not update the route after receiving the information, the number of members in the group is increased by one, the information is not broadcasted to other satellite nodes in the group, and the route after the network topology is updated is calculated together when the newly added satellite node and other members in the group send link reports after waiting for the next time slice.
Compared with the prior art, the invention has the following remarkable advantages: (1) and a low-orbit satellite and geosynchronous orbit satellite double-layer network architecture is innovatively adopted. Experiments prove that the delay tolerant and break tolerant network autonomous routing technology based on the double-layer network architecture can completely meet established requirements. (2) The routing problem is solved by adopting a typical technical space information network node meeting and link change rule in a delay tolerant and break network, a delay tolerant and break routing mechanism based on social network characteristics and message transmission scheduling under the condition of limited network resources, and the method has universal applicability. (3) The specific processes of realizing the autonomous routing of the delay tolerant disruption tolerant network are detailed, and the specific processes comprise time/group division, a routing process, congestion control and an autonomous strategy. (4) Simulation experiments show that the delay tolerant disruption network autonomous routing technology based on the double-layer network architecture of the low-orbit satellite and the geosynchronous orbit satellite has good effects on the aspects of end-to-end delay, link queue caching and the like, so that the method has practical application significance.
Drawings
Fig. 1 is a content framework diagram of a delay tolerant disruption tolerant network autonomous routing technology based on a low-orbit satellite and geosynchronous orbit satellite dual-layer network architecture in the technology of the present invention.
FIG. 2 is a diagram of a protocol stack of a latency tolerance network in accordance with the present invention.
FIG. 3 is a diagram illustrating a context-based backhaul application scenario for a latency tolerance network in accordance with the present invention.
FIG. 4 is a covert communication application scenario of a delay tolerant network in accordance with the present technology.
FIG. 5 is a block and continue transmission scenario for a latency tolerant network in accordance with the present invention.
FIG. 6 is a schematic diagram of the calculation of the geographic coordinates of the satellite according to the present invention.
Fig. 7 is a logic flow diagram of satellite data transmission in accordance with the present technology.
Fig. 8 is a logic flow diagram of satellite data reception in accordance with the present technology.
FIG. 9 is a diagram illustrating the time/group division and the time/group combination in the present invention.
FIG. 10 is a diagram illustrating a satellite network route update according to the present invention.
Detailed Description
The present invention will be further described in detail with reference to the following drawings for analyzing specific scenes and implementing specific examples.
In the context of the transitive backhaul application of fig. 3, it is assumed that data transmission between different orbiting satellites or between different orbiting satellites is not involved. The satellite firstly acquires necessary data information from abroad, the detected data information is cached in the satellite, and when the satellite moves to the inside coverage range, the data can be transmitted back to the ground base station. The application requires that the satellite has enough large storage space, but the requirement on service real-time performance is not high.
The covert communication scenario of fig. 4 is different from transit backhaul, and first, the ground terminal immediately takes off the line after uploading data information to the satellite network, and the burstiness is strong; second, there is a transmission of information between satellites of the space-based network. The covert communication researched by the invention requires the same data storage capacity as that of the transit backhaul on one hand, and on the other hand, the covert communication scene only aims at the condition that the link from the ground end to the space-based network is disconnected, and the problem of the link disconnection between the space-based network satellites is not involved. In addition, the amount of covert communication data is often small, but burstiness is strong, and communication time is required to be as short as possible and link delay is required to be as low as possible.
The outage continuation scenario of fig. 5 is primarily directed to the case where the space-based network satellite link is frequently interrupted. Due to link interruption caused by topology change of a satellite network or communication quality problems, in order to avoid extra expenses caused by rerouting and data retransmission, data is stored in a satellite firstly and is transmitted continuously after the link is recovered. Such services have high requirements on the reliability of data transmission, but have low requirements on real-time performance.
The problem of large DTN link transmission delay is mainly solved by adopting the spatial information network node encounter and link change rule technology. In the DTN, the spatial information network nodes communicate in a mode of 'storage-carrying-forwarding' by moving on a track. In addition, the relative movement speed between the satellites is high, and the transmission rate and the time delay change of the links between the satellites are large, so that the data forwarding is greatly influenced. Therefore, prior information of satellite operation needs to be fully utilized, the network node encounter rule and the dynamic change mechanism of the link are deeply analyzed, optimization of delay-tolerant and fault-tolerant network data forwarding is achieved, and therefore the data transmission efficiency is improved.
The problem of frequent DTN link interruption is mainly solved by adopting a delay tolerant and disconnection tolerant routing mechanism technology based on social network characteristics. In the DTN, due to the characteristics of its orbit, a satellite node has some stable connection relationships with other satellite nodes, and can be regarded as a social network characteristic in a certain sense. Therefore, the information such as the preference location, the data source, the affinity with other nodes and the like of the satellite is obtained by analyzing from the perspective of the social network and combining the prior calculation and the dynamic sensing, and the information is transmitted on the basis, so that the efficiency of information transmission can be effectively improved.
The problem of insufficient storage capacity of satellite nodes in the DTN is mainly solved by adopting a message transmission scheduling technology under the condition of limited network resources. The buffer capacity limitation of the node and the node contact time limitation not only increase the data forwarding delay, but also have a serious influence on the reliability of the data. In the DTN, the storage capacity of a satellite node is limited, and the inter-satellite link dynamic variability is strong, so that the problem is more prominent. Therefore, on the basis of researching the spatial information network node encounter and link change mechanism, dynamic, autonomous and combined data forwarding service is realized through mechanisms such as pre-allocation and multi-path cooperation, the data forwarding efficiency is improved, and then an efficient transmission service mechanism is established according to diversified business requirements.
The implementation is followed by the determination of the main technique employed. The invention adopts a multilayer network architecture combining a low-orbit satellite and a geosynchronous orbit satellite, and a key problem of multilayer satellite networking is the problem of network topology change caused by satellite motion, which is more important compared with a single-layer satellite network. The main solution adopted for the problem of network topology change is to calculate the routing paths at different times by dividing time/group segments and considering that the network topology is fixed and unchangeable in the same time segment. The process of calculating the route is a key link for implementing the DTN autonomous routing technology, and the process of calculating the route will be described in detail in the example. Meanwhile, a congestion control mechanism and an autonomous policy of the DTN need to be set.
The present invention will be described in further detail with reference to specific examples.
Example 1
The invention relates to a technical solution for autonomous routing of a delay tolerant network based on a double-layer satellite network of a low-orbit satellite and a geosynchronous orbit satellite, which comprises the following steps:
Problem analysis: the satellite moves at a high speed, so that the space-based network topology structure is changed constantly, the information transmission delay is large, the link is interrupted frequently, and the error rate is high. These features are not available in terrestrial networks, and thus the conventional TCP/IP protocol is not suitable for spatial information networks. The delay tolerant network can provide a reliable data transmission protocol spanning terminals, intermittent and dynamic networks, so that the research on the autonomous routing technology based on the delay tolerant network research considers the lack of a stable end-to-end path, high time delay and node storage capacity, and has practical significance for solving a series of problems faced by a spatial information network.
1. Node encounter and link change rule of spatial information network
The satellite moves on a fixed orbit and has a certain operation rule, although the storage capacity of the satellite nodes is limited and the information sharing of a global network cannot be realized, the satellite operation rule is shared in a small range, and the study on the rule of satellite encounter and node change has important significance for improving the network performance. The main contents of the part comprise geographic coordinate calculation, inter-satellite distance and relative change rate, satellite azimuth and change rate thereof, node encounter probability, link change rule modeling and the like.
(1) Geographic coordinate calculation
The earth longitude and latitude is used to represent the satellite node geographical coordinates. The geographical coordinates of the satellite at a certain time (see fig. 6) can be calculated as follows, with the parameter definitions as shown in table 1.
TABLE 1 parameter definition for satellite geospatial coordinate calculation
(2) Inter-satellite distance and relative rate of change thereof
The inter-satellite link is an intra-rail link and an inter-rail link. The inter-satellite distance, azimuth angle, etc. of the in-orbit link are almost unchanged. Because the invention adopts a double-layer network architecture combining a low-orbit satellite and a geosynchronous orbit satellite, the condition of the inter-orbit link needs to be considered. The following provides a calculation method of the distance between any two orbiting satellites, the distance is a straight-line distance between the satellites, and assuming that the occlusion problem of the earth is not considered, the distance between the two orbiting satellites is:
(3) satellite azimuth and its rate of change
The satellite azimuth and its rate of change are for the inter-orbit link. Due to changes in relative position between satellitesThe distance, azimuth and elevation are all varied. In order to accurately locate the exact position of each satellite and its neighbors, it is desirable that the range and azimuth angle between these satellites be as small as possible, with the rate of change being as slow as possible. Azimuth ψ of satellite i to satellite jijThe calculation method comprises the following steps:
(4) satellite node encounter time and link modeling law
The satellite position coordinates are calculated as follows:
the elevation angle theta of the low-orbit satellite relative to the geosynchronous-orbit satellite is greater than the minimum elevation angle epsilonminAnd when the two are in normal communication. Therefore, θ needs to satisfy the following condition:
if the LEO satellite is in the coverage area of the GEO satellite, the critical value of the visible angle λ between the LEO satellite and the GEO satellite is:
and is
Thus:
in the formula (x)l,yl,zl) Is prepared byCoordinates of low orbit satellites, RLIs the LEO satellite orbital radius; (x)g,yg,zg) As coordinates of GEO satellites, RGIs the geosynchronous orbit satellite orbital radius. And comparing the coverage time of the low-level satellite under different high-level satellites, and taking the geosynchronous orbit satellite with the longest connection time as a manager. Therefore, the meeting time of the nodes can be estimated, the performance of the delay tolerant and disconnection tolerant routing is improved, and the network loss is reduced.
2. Spatial information network delay tolerance and disconnection tolerant routing mechanism based on social network characteristics
The social network refers to a network formed by human-to-human interaction, and the network also does not have the characteristic of continuous end-to-end connection, so that the social network is a typical delay tolerant network. The invention researches the autonomous routing technology based on the delay tolerant network, thereby further borrowing the social network routing mechanism for reference, fully utilizing the characteristics of the spatial information network and improving the data transmission performance.
(1) Rules of intra-group forwarding
And when the destination node and the forwarding node are in one group, an intra-group forwarding rule is adopted. According to the nature of the group division, the destination node and the forwarding node are relatively close at this time. Therefore, the intra-group forwarding adopts a multi-copy forwarding mode, the delivery rate is ensured, and too much network overhead is not caused. And by combining with the geographical position information, the intra-group forwarding rule adopts directional forwarding, so that the overhead can be further reduced. The specific method comprises the following steps: if the forwarding node and the destination node are within a one-hop range, the message is directly forwarded in a unicast mode, otherwise, the forwarding node firstly calculates included angles between the forwarding node and the destination node and between the forwarding node and other neighbor nodes (nodes within the one-hop range) in the group, and selects all nodes with included angles smaller than the limit value in the group as the next node for forwarding by setting a threshold (usually 60 degrees).
(2) Rules for intergroup forwarding
When the destination node and the forwarding node are not in a group, an inter-group forwarding rule is adopted. At this time, the distance between the destination node and the forwarding node is relatively long, and a large network overhead is generated in multiple times of forwarding by adopting a multi-copy forwarding mode, so that the performance of the protocol is reduced. Therefore, the inter-group forwarding rule adopts a single copy forwarding mode.
The single copy forwarding mode selects the nodes which are most likely to meet the destination node of the message for forwarding so as to ensure the delivery rate and reduce the propagation delay. The selection of the next hop node is based on some prediction mechanism. As can be seen from the theory of social networking, a node has more time to move between areas where it is familiar and has a greater probability of encountering many times its familiar node. The inter-group forwarding rule adopted by the invention is that when the forwarding node and the destination node are not in the same group, the forwarding node firstly obtains the group in which the destination node is currently positioned through the geographical position information, then traverses all members (including the forwarding node) in the self group, calculates and compares the familiarity of each node to the group in which the destination node is positioned, and selects the node with the maximum familiarity as the next hop node for forwarding.
(3) Data transmission and reception
Fig. 7 and 8 illustrate the logic flow for data transmission and reception, respectively.
In a delay tolerant network, messages are cached in nodes in a routing forwarding process, if the cache of the nodes is small, the number of the messages carried by the nodes is small, so that the number of copies of the same message in the network is relatively small, the probability that the message is finally delivered to a destination node is low, and the transmission delay is relatively high. This may increase the delivery rate of messages and reduce latency if the node's cache is larger. However, at this time, the number of messages forwarded in the network increases, which increases the load on the network. The cache size of the node will have a large impact on the performance of the protocol.
3. Message transmission scheduling under network resource limited conditions
And 2, realizing the self-routing technology of the delay-tolerant disconnection based on the double-layer network architecture of the low-orbit satellite and the geosynchronous orbit satellite.
1. Constructing satellite network topology
The method is characterized in that 3 geosynchronous satellites are arranged in a low orbit by utilizing the characteristic that geosynchronous orbit satellites positioned on the equator are geostationary, so that the global coverage is realized, the problem of managing satellite switching coverage is concentrated to a low orbit satellite layer, management groups are divided through the areas covered by the geosynchronous orbit satellites, and the low orbit satellites are divided into different groups for management. Considering that the geosynchronous orbit satellite is difficult to cover the high-latitude region of the earth, the low-orbit satellite is set as an access layer with the ground, and is responsible for receiving the information from the ground, so that the access problem of the high-latitude region is solved.
2. Time/group division
The time division method mainly comprises equal time division and unequal time division, in an equal time interval, due to the fact that satellite motion can cause great changes of network topology, preset paths can be failed, the problem of network topology changes can be solved through the unequal time division, and huge calculation amount is brought to node calculation routing due to too many divided time segments. The invention adopts an optimized unequal length time division mode, and solves the problem of excessive time segments by merging the time segments.
As shown in fig. 9(a), at time T1, the node a is connected to the node B, and at time T2, the node a is disconnected from the node B, and if only the link in the network is changed during the time period from T1 to T2, the time period is divided into time slices according to a non-equal time division manner. According to the time slice divided in this way, a shorter time slice [ T (4), T (5) ] in the figure may occur, in which the topology of the network is not greatly affected due to the on-off change of only one link, and the problem of recalculating the network route is more serious. For this purpose, the present invention compares the divided time segment length with Td by setting a time length threshold Td, and if the time segment length is less than Td, combines the time segment with the previous time segment and sets the link to be disconnected in advance in the previous time segment, as shown in fig. 9 (b).
3. Routing process
The route update procedure is described with reference to fig. 10, based on the principle that the network topology can be considered as substantially unchanged within the same time slot, and the route is recalculated only at the time of the time slot update.
(1) Each low-orbit satellite acquires and collects connectivity with other nodes, and generates a satellite link report.
(2) The low orbit satellite sends a link report to the grouped management satellite through the interlayer link, the waiting time is tau, if the number of the link reports received in the time tau is the same as the number of members in the group, the step (3) is continued, otherwise, a link failure report is sent to a ground control center, and G is used for simultaneously sending a link failure report to the ground control centeriThe link connectivity for one of the endpoints is set to 0 and then (6) is performed.
(3) When the geosynchronous orbit satellite gathers all the link reports in the group or exceeds time τ, the geosynchronous orbit satellite transmits the gathered link reports to the adjacent geosynchronous orbit satellite through the intra-layer link, if within time δ, GjNot received from GiAnd (4) sending a node failure report to the control center, and executing (6), otherwise, executing (4).
(4) After the geosynchronous orbit satellites exchange link reports, the geosynchronous orbit satellites can obtain a network topology map G (V, E), and then (4) is performed. According to the hop count minimization principle, the geosynchronous orbit satellite calculates the minimum hop count path to all satellites of the low orbit satellite layer for each low orbit satellite in the group, and updates the routing table thereof accordingly.
(5) After the routing table of each low orbit satellite is calculated and updated, the geosynchronous orbit satellite sends the routing table to each low orbit satellite through the interlayer link according to the S _ id of the routing table, and the low orbit satellite sends an ACK (acknowledgement) message. And finishing the updating of the routing calculation.
(6) After receiving the node failure report, the control center firstly judges the type of the failed satellite according to the failure report, and if the failed satellite is a low-orbit satellite, the control center finds out the cause and repairs as soon as possible. If the failed satellite is a geosynchronous orbit satellite, finding out the cause and repairing as soon as possible, and secondly, the failure of the geosynchronous orbit satellite can influence the collection of topology information of a network, so that the control center sends a command to a low orbit satellite in a group of the geosynchronous orbit satellite according to the pre-calculated grouping condition in the time slot, so that the low orbit satellite sends a link report to other geosynchronous orbit satellites, and the normal geosynchronous orbit satellite temporarily processes the report and executes the process again (3).
4. Congestion control
In a low-orbit satellite and geosynchronous orbit satellite dual-layer network architecture, different congestion control mechanisms need to be designed for different levels of satellite networks.
(1) Low orbit satellite congestion control
The low orbit satellite is responsible for access to the ground base station network and most of the data transmission traffic. The congestion of a certain satellite node is mostly large in the area or sudden in the flow. Aiming at different satellite coverage areas of different orbits, the number of satellites in areas with large service volume can be increased by utilizing the characteristic design, and the aim of reasonably distributing network resources is fulfilled. For the flow emergency in the network, the ratio of the self memory number of the node to the maximum buffer number can be used for realizing monitoring.
The threshold value of node congestion judgment can be set to be 85%, when the ratio is larger than 0.85, the current node is considered to be congested, the node sends a congestion report to a grouping manager, the manager sets the satellite to be unreachable in the self storage network topology, recalculates the route and sends the route to the low orbit satellite in the group until the node sends a congestion relief report, resets the satellite to be reachable, and updates the route in the group.
(2) Geosynchronous orbit satellite congestion control
The geosynchronous orbit satellite is a manager of a low orbit satellite group, and is not only responsible for data transmission service, but also responsible for calculating network routing and handling low orbit satellite congestion, so that node congestion is more likely to occur. In practical networks, geosynchronous orbit satellites have superior processing power to low orbit satellites. When the congestion of the geosynchronous orbit satellite occurs, the congestion is mostly caused by the burst of flow in the network, in this case, the time for causing the congestion of the geosynchronous orbit satellite is not long, and the congestion state can be rapidly relieved by using the idea of Bundle layer protocol through temporarily storing the incoming message Bundle into other storage spaces and depending on the processing capacity of the message Bundle. If the geosynchronous orbit satellite in the network is frequently congested, whether the network is attacked or not and needs to be eliminated or the network structure cannot meet the service requirement and needs to be upgraded needs to be considered.
5. Autonomous policy
In the invention, when a new satellite node joins the network, the node firstly sends registration information to a geosynchronous orbit satellite manager in the area, the geosynchronous orbit satellite does not update the route after receiving the information, and executes the operation of adding one to the number of members in the group, but does not broadcast the information to other satellite nodes in the group. And when waiting for the next time slice, newly adding the satellite node and other members in the group to simultaneously send a link report and calculate the route after the network topology is updated. In this way, the newly added satellite node does not need to broadcast the message to all nodes in the network, but the packet manager is responsible for broadcasting, and the autonomy of the network is enhanced.
The invention designs an autonomous routing technology for realizing the delay tolerant and fault tolerant network based on a double-layer network architecture of a low-earth orbit satellite network and a geosynchronous orbit satellite network. The technology can effectively deal with the limitation that the traditional TCP/IP can not be directly applied to the DTN, and adopts a spatial information network node meeting and link change rule, a social network characteristic-based delay-tolerant disconnection routing mechanism and a key technology of message transmission scheduling under the condition of limited network resources. And key links such as time division, group division, routing process, congestion control, autonomous strategy and the like are realized. The technology provides an effective solution for solving the defects of high time delay, frequent link interruption, limited node storage capacity, high error rate and the like in spatial network communication for a delay-tolerant and fault-tolerant network scene, and has a good application effect.
Claims (5)
1. A delay tolerant and disconnection tolerant network autonomous routing technology based on a double-layer satellite network is characterized in that: according to the end system, the link path and the network structure embodied by the delay tolerant disruption network, a specific scheme is provided for solving the problems of application of the delay tolerant disruption network in three aspects of transit return, covert communication and interruption of continuous transmission based on a low-earth orbit satellite and geosynchronous orbit satellite double-layer network architecture. By adopting three core technologies of spatial information network node meeting and link change rules, a delay-tolerant disconnection routing mechanism based on social network characteristics and message transmission scheduling under the condition of limited network resources, the key processes of time/group division, routing process, congestion control, autonomous strategy and the like of satellite network topology change are realized, and finally, the autonomous routing strategy of the delay-tolerant disconnection network is realized. The specific description steps are as follows:
step 1, introducing relevant basic knowledge of a low-orbit satellite and a geosynchronous orbit satellite, and analyzing the necessity of adopting a double-layer network architecture of the low-orbit satellite and the geosynchronous orbit satellite.
And 2, leading out the problem to be solved urgently by three typical application scenes of delay-tolerant and interruption-tolerant networks of transit backhaul, covert communication and intermittent transmission.
And 3, realizing the rule of meeting and link change of the spatial information network nodes of the core technology, a delay-tolerant disconnection routing mechanism based on social network characteristics and a message transmission scheduling mode under the condition of limited network resources.
And 4, realizing the time/group division, the routing process, the congestion control and the autonomous policy core step.
2. The solution of autonomous routing technology for delay-tolerant disruption-tolerant networks based on two-layer satellite networks according to claim 1, wherein step 1 illustrates the application environment of the delay-tolerant disruption-tolerant network. At present, various artificial earth satellites are available, and the artificial earth satellites mainly comprise low orbit satellites, medium orbit satellites, geosynchronous orbit satellites and high elliptic orbit satellites according to the operation orbit division. The technology mainly adopts a double-layer network architecture combining a low-orbit satellite and a geosynchronous orbit satellite, and the specific reasons are as follows:
(1) the low-orbit satellite has the lowest orbit height, so the transmission delay is smaller and the link loss is lower. Because the mobile terminal is closest to the ground, the operation cycle of the mobile terminal is shortest, the connection time with ground nodes is also shortest, and the situation of link interruption is most likely to occur.
(2) The operation period of the geosynchronous orbit satellite is the same as the rotation period of the earth, the transmission delay is higher due to the fact that the geosynchronous orbit satellite is far away from the ground, but the geosynchronous orbit satellite is static relative to the ground, and the performance of large coverage area is a great advantage for a delay tolerant network. Theoretically 3 geosynchronous orbit satellites are required to cover the entire earth.
(3) In order to adapt to the problems that a delay tolerant and fault tolerant network is large in transmission delay, frequent in link interruption, limited in node storage capacity and the like, a low-orbit satellite and geosynchronous orbit satellite double-layer network architecture is combined to be used for managing the delay tolerant and fault tolerant network. The 3 geosynchronous satellites realize global coverage, the coverage areas of the geosynchronous orbit satellites are divided into management groups, the low orbit satellites are divided into different management groups, and the low orbit satellites are responsible for communication with the ground nodes.
3. The solution of autonomous routing technology for delay-tolerant network based on two-layer satellite network as claimed in claim 1, wherein step 2 illustrates the application scenario of autonomous routing technology for delay-tolerant network and presents the corresponding challenges:
(1) transiting the border back: when the low-orbit satellite returns the overseas investigation data, the ground base station may not be in the coverage range of the low-orbit satellite, at the moment, the data is firstly cached in the low-orbit satellite, and the data is returned when the low-orbit satellite runs above the indoor base station. Such applications do not require much latency performance, but they require large satellite node storage capacity.
(2) Covert communication: and the ground network node uploads the encrypted information to the low-orbit satellite and then immediately takes off the line, and the low-orbit satellite transmits the encrypted information to the target user through the space-based network. The characteristics of covert communication are small data size, strong burstiness, short communication time and high requirement for link delay performance.
(3) Interrupting continuous transmission: due to satellite movement or ground terminal movement, transmission link interruption is caused by human damage and the like. And the data transmission can be continuously completed when the network node moves to the signal coverage range. Generally, the data transmission has high requirements on link reliability and time delay performance.
4. The solution of autonomous routing technology for delay-tolerant network based on two-layer satellite network as claimed in claim 1, wherein the key technologies required for implementing the autonomous routing technology for delay-tolerant network are specified in step 3 as follows:
(1) and (4) the meeting of the nodes of the spatial information network and the change rule of the link. The satellites communicate with each other in a "store-carry-forward" manner. The links may be broken at this time due to changes in the network topology caused by satellite movement. Therefore, the encounter rule between satellite nodes and the link interruption connection rule directly affect the efficiency and success rate of information transmission. Therefore, analysis of the spatial information network node meeting and link change rules is beneficial to improvement of delay-tolerant and interruption-tolerant network data transmission efficiency.
(2) A delay tolerant and disconnection tolerant routing mechanism based on social networking characteristics. Both low orbit and geosynchronous orbit satellites operate in fixed orbits and therefore a network of satellites can be considered to conform to certain characteristics of a social network. From the perspective of a social network, information such as a preference place, a data source, the affinity with other nodes and the like of a satellite is obtained by combining prior calculation and dynamic sensing, and information is transmitted on the basis, so that the efficiency of information transmission can be effectively improved.
(3) And (3) message transmission scheduling under the condition of limited network resources. The storage capacity of the network node is usually limited, and setting a buffer to contact with the node for a limited time will increase data transmission delay to some extent, and usually will also have a certain influence on data reliability. Therefore, on the basis of researching the technology, dynamic, autonomous and combined data forwarding services are realized through mechanisms such as pre-allocation and multi-path cooperation, and the data forwarding efficiency is improved.
5. The solution of autonomous routing technology for delay-tolerant networks based on two-layer satellite networks according to claim 1, wherein step 4 illustrates a key step in the implementation process of autonomous routing technology for delay-tolerant networks based on two-layer satellite networks.
(1) Time/group division: the satellite network is divided into n different network topologies by dividing time segments due to network topology change caused by satellite movement, and topology paths at different moments are calculated according to the different time segments.
(2) And (3) routing process: after the network topology is divided into different time slots (time slots) according to time, the network topology is different in different time slots, and the network topology can be considered to be basically unchanged in the same time slot. When the orbit of the satellite in the network is determined, the time slot division in one period can be calculated, and based on the scheme, the route only needs to be recalculated when the time slot is updated.
(3) And (3) congestion control: since the network route is calculated in time slots, if a large network flow is generated in a certain time slot, node congestion is easily caused. For the network to operate efficiently, it is necessary to design congestion control mechanisms. In a low-orbit satellite/GEO double-layer satellite network, different processing mechanisms are designed aiming at the congestion of different layers of satellite nodes.
(4) And (3) autonomous strategy: when a new satellite node is added into the network, registration information is sent to the geosynchronous orbit satellite in the area, and the routing is not updated after the geosynchronous orbit satellite receives the information, so that the number of members in the group is increased by one. And waiting for the next time slice, the geosynchronous orbit satellite sends the report information of the newly added satellite nodes to other satellite nodes in the group, and simultaneously calculates the route after the network topology is updated.
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