CN114679385A - LTP protocol parameter optimization configuration method of deep space communication network - Google Patents
LTP protocol parameter optimization configuration method of deep space communication network Download PDFInfo
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Abstract
The invention discloses an LTP protocol parameter optimization configuration method of a deep space communication network, which is used for a complex deep space communication network under a multi-hop scene, and comprises the following steps: establishing an LTP file transmission total time delay theoretical model of a complex deep space communication network according to a communication environment; based on an LTP file transmission total time delay model, providing an LTP parameter optimization design algorithm LTP-PODA; and optimizing segment, block and session parameters in the LTP protocol by an LTP-PODA algorithm to obtain the global optimal solution combination of the three parameters, thereby obtaining the optimal parameter configuration scheme of the LTP protocol. Compared with the existing model established based on a simplified scene, the LTP transmission delay model of the complex deep space communication network established by the invention has higher precision; the method configures reasonable LTP protocol parameters for the DTN-based complex deep space communication network, and improves the LTP protocol transmission performance in a complex scene.
Description
Technical Field
The invention belongs to the technical field of LTP protocol parameter configuration, and particularly relates to an LTP protocol parameter optimization configuration method of a deep space communication network.
Background
LTP (9 tcp) is a DTN (Delay/dispersion Torlrant Network) Protocol designed for point-to-point connections with extremely long propagation Delay and interruptions, and is the main Transmission Protocol of a deep space communication Network based on DTN.
Because different choices of protocol parameters have a great influence on the LTP transmission performance, the LTP protocol parameters need to be configured before a data transmission task using the LTP as a transport layer protocol is performed, but no standard release related to the LTP protocol parameter configuration exists at present. In order to obtain the highest performance possible in data transmission in a deep space communication network using LTP as a transmission protocol, the parameter configuration of LTP needs to be optimally designed.
However, the existing literature focuses on finding a configuration scheme for LTP protocol parameter optimization in a simplified scenario of one to two hops in a simulation experiment manner. Such a research conclusion is not applicable to a complex deep space communication network in a multi-hop scenario, and due to lack of theoretical work, the optimization method proposed by the existing research is not general.
Therefore, in the face of a complex deep space communication network using LTP as a transmission protocol in the future, a general and convenient-to-operate parameter optimization configuration method is urgently needed, and a most appropriate parameter configuration scheme can be provided for LTP in different communication environments, so that the data transmission performance of LTP is improved.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an LTP protocol parameter optimization configuration method of a deep space communication network.
In order to achieve the above object, the present invention provides an LTP protocol parameter optimization configuration method for a deep space communication network, which is used for a complex deep space communication network in a multi-hop scenario, and the method includes:
establishing an LTP file transmission total time delay theoretical model of a complex deep space communication network according to a communication environment;
based on an LTP file transmission total time delay model, providing an LTP parameter optimization design algorithm LTP-PODA; and optimizing segment, block and session parameters in the LTP protocol by an LTP-PODA algorithm to obtain the global optimal solution combination of the three parameters, thereby obtaining the optimal parameter configuration scheme of the LTP protocol.
As an improvement of the above method, the communication environment includes: the deep space communication network comprises the types and the number of communication nodes, the downlink speed of each section of link, a BP (back propagation) hosting mechanism, an aggregation time limit, a file size, MTUs (maximum transmission units), the bundle aggregation speed of the communication nodes, a bundle size, the one-way delay of different links, an error rate and an asymmetric channel speed ratio.
As an improvement of the above method, the LTP file transfer total delay theoretical model is:
Tfile_multihop＝Tformer+Tblock_q_final+Tlatter+Taggre
in the formula, Tfile_multihopTotal delay, T, of LTP file delivery representing complex deep space communication networkformerRepresenting the file from the beginning of the transfer at the source node to the blockq_finalStarting transmission at the q-th hop, wherein the q-th hop represents one hop with the longest one-way link delay, block, in the whole complex deep space communication networkq_finalBlock, T, for last completed transmission on the q-th hopblock_q_finalRepresenting blockq_finalTransmission delay on the q-th hop, TlatterRepresenting slave blocksq_finalTime consumed by the transmission completion on the qth hop until the destination node completely receives the entire file, TaggreRepresents the time consumed for bundle polymerization.
As an improvement of the above method, the building process of the LTP file transfer total delay theoretical model of the complex deep space communication network specifically includes:
step s1) determining the number of pass rounds k experienced in passing only one block on the ith hopmin_iAnd the number of passes k experienced in transferring the entire filemax_iAnd calculating the mean k of the twomean_i；
Step s2) obtaining the time T consumed by the single block completing the transmission on the ith hopblock_i；
Step s3) calculates T of the previous (q-1) hop based on the calculation results obtained in step s1) and step s2)formerMaximum total transfer delay T for a single block transmitted on qthblock_q_finalAnd T of last (n-q) hoplatter；
Step s4) dividing a file into NbundleA bundle for transmission, NbundleEach bundle is combined into NblockBlock;
when N is presentbundle>NblockIn time, the method indicates that one block is formed by aggregating a plurality of bundles, and the time T consumed by aggregating the bundles into the block is calculatedaggre(ii) a When N is presentbundle＝NblockWhile, bundle is in a non-aggregated state, Taggre＝0；
Step s5) summing the calculation results obtained in the step s3) and the step s4) to obtain the LTP file transfer total delay theoretical model of the complex deep space communication network.
As a modification of the above method, the step s1) specifically includes:
calculating the number k of transfer rounds experienced when only one block is transferred on the ith hop according to the following formulamin_i：
In the formula, pseg_iRepresents the segment loss probability, N, on the ith hopRRepresenting the number of red data segments contained in one block, and m represents the number of all theoretically possible transmission rounds;
the number of transmission rounds k experienced when transmitting the whole file is calculated according to the following formulamax_i：
Where f denotes the red data proportion in a single block to be transmitted, NbundleIndicates that one dimension is LfileIs divided into NbundleOne bundle for transmission, Lbundle_headIndicates the head length, L, of bundleblockSize of a single block, Lseg_payload_iRepresenting the size of the load of a single segment on the ith hop.
As a modification of the above method, the step s3) specifically includes:
obtaining T of the previous (q-1) hop according to the following formulaformer：
In the formula, Ttrans_a_mean、Tprop_a_meanAnd Tex_time_a_meanRespectively represent blockq_finalAverage transmission time, average propagation time and average extra delivery time, T, at hop aformer_aRepresenting blockq_finalAverage total time delay of transmission on the a-th hop, a ∈ [1, q ∈ [ ]]；
Obtaining the maximum total transfer time delay T of a single block when the single block is transmitted on the qth according to the following formulablock_q_final：
Tblock_q_final＝Tprop_q_final+Ttrans_q_final+Tex_time_q
In the formula, Tprop_q_final、Ttrans_q_finalAnd Tex_time_q_finalRespectively represent blockq_finalPropagation time, transmission time and extra delivery time at the q-th hop;
obtaining the T of the last (n-q) hop according to the following formulalatter：
In the formula, Tlater_aThe time interval from the moment that the last block on the (a-1) th hop completes the transfer to the moment that the last block on the a th hop completes the transfer is shown, n represents the time interval of the data transfer from the source end to the destination endTotal number of hops traversed.
As an improvement of the above method, the LTP-based parameter optimization design algorithm LTP-PODA is proposed based on the LTP file transfer total delay model; optimizing segment, block and session parameters in the LTP protocol by an LTP-PODA algorithm to obtain a global optimal solution combination of the three parameters, thereby obtaining an optimal parameter configuration scheme of the LTP protocol; the method specifically comprises the following steps:
step t1) initializing block and segment;
step t2), solving a local optimal solution of the block and the segment according to the optimization basis of the block and the segment by using an iteration mode;
step t3) judging whether a block and a segment which can minimize the total transmission time delay of the LTP file are found, if so, obtaining a global optimal solution of the block and the segment, and temporarily using the global optimal solution as an optimized value of the block and the segment; go to step t 4); otherwise, go to step t 2);
step t4) comparing the obtained block global optimal solution with the actual block size in the data transmission process, thereby adjusting the optimized values of the block and the segment obtained in the step t3) and obtaining the final optimized design values of the block and the segment;
and t5) obtaining an optimal design value of the session according to the optimization basis of the session, and obtaining an optimal parameter configuration scheme of the LTP protocol by combining the optimal design values of the block and the segment.
As a modification of the above method, the step t1) specifically includes:
setting segment frame size L on each segment linkseg_frame_aTo set value, the head length L in combination with segmentseg_headerThe load size L of segment on each link is obtained according to the following formulaseg_payload_aThus, segment initialization is completed:
Lseg_payload_a＝Lseg_frame_a-Lseg_header
mixing L withseg_payload_aIs assigned to Lseg_payload、Lseg_frame_aIs assigned to Lseg_frameSubstituting the following formula to obtain the block size LblockMinimum value L ofb_minThereby completing the initialization of the block；
Wherein L isRS_frameIndicates the frame size, L, of the RSseg_payloadRepresenting the load size, L, of the segmentseg_frameRepresenting the frame size, R, of a segmentdataIndicating the data transmission rate, R, of the data channelACKIndicating a data transmission rate of the ACK channel;
as a modification of the above method, the step t2) specifically includes:
with Lb_minSubstituting for block size to obtain Tformer_a、Tblock_q_finalAnd Tlatter_aWill find the equation Tfile_multihopThe problem of minimum segment size translates to Tformer_a(Lseg_payload_a)、Tblock_q_final(Lseg_payload_q) And Tlatter_a(Lseg_payload_a) Solving the local optimal L meeting the first-order requirement of KKT on each link section by the convex optimization problem of the functionseg_payload_a*，Lseg_payload_aIs a local optimal solution of segment; wherein L isseg_payload_qRepresents the segment load size on the q hop;
mixing L withseg_payload_aIs given to Lseg_payloadSubstituting the following formula to obtain the block size L on each linkblockMinimum value L ofb_min_a：
L from each link segmentb_min_aTaking the maximum value to be given to Lb_min，Lb_minThe method is a local optimal solution of block.
As a modification of the above method, the step t5) specifically includes:
the actual aggregate size L of the blocks during data transmission is determined byblock_actObtaining an optimized set of sessionsEvaluating Nsess_opt：
Nsess_opt＝1.2×(Lfile/Lblock_act)。
Compared with the prior art, the invention has the advantages that:
1. the invention provides a general and easy-to-operate LTP protocol parameter optimal configuration method for a deep space communication network, which can be applied to a complex deep space communication network under a multi-hop scene and also can be applied to a simplified one-to-two-hop simple deep space communication network, so that the defects of the method provided by the existing research on scene applicability and expansibility are overcome, the method is utilized to configure reasonable LTP protocol parameters for the DTN-based complex deep space communication network, and the transmission performance of the LTP protocol under the complex scene is improved;
2. the invention establishes an LTP (time delay of transmission) model of the complex deep space communication network, the model has higher precision than the existing model established based on the simplified scene, and the model is more suitable for the complex deep space communication network;
3. aiming at the problems that the protocol parameter optimization method proposed by the existing research does not have generality and expansibility and cannot be applied to a complex deep space communication scene, the LTP protocol parameter optimization configuration method for the complex deep space communication network provided by the invention configures a proper parameter configuration scheme for LTP, thereby improving the data transmission performance of LTP in the complex deep space communication network;
4. the method can conveniently and rapidly provide a set of optimal parameter configuration scheme for the LTP in different communication environments, and improve the data transmission performance of the LTP in a complex deep space communication network.
Drawings
FIG. 1 is a flow chart of an implementation of an LTP protocol parameter optimization configuration method of a deep space communication network according to the present invention;
FIG. 2 is a schematic diagram of three data transmission paths under a complex deep space communication network simulation scenario, in which (a), (b), and (c) respectively represent the paths passing through one, two, and three UNICON satellites (N)U＝1、NU＝2、NU3) the forwarded data transmission path;
FIG. 3 is the block, segment, and session values of the optimal parameter configuration scheme under different communication conditions;
fig. 4(a) is a graph comparing LTP transmission performance with different parameter configuration schemes under different error rate conditions;
fig. 4(b) is a diagram comparing LTP transmission performance with different parameter configuration schemes under different link delays;
fig. 4(c) is a diagram of LTP transmission performance comparison with different parameter configuration schemes under different channel rate ratio conditions;
fig. 4(d) is a graph comparing LTP transmission performance with different parameter configuration schemes under bundle aggregation and non-aggregation conditions.
Detailed Description
The existing literature focuses on the LTP parameter optimization in a simplified scenario of one to two hops, however, the research result is not applicable to the complex deep space communication network. The invention firstly establishes an LTP transmission delay model of the complex deep space communication network, and then provides an LTP parameter optimization design algorithm of the complex deep space communication network based on the model, thereby configuring reasonable parameters for an LTP protocol and improving the transmission performance of the LTP. The method comprises the following steps:
step 1) establishing an LTP file transfer delay theoretical model of a complex deep space communication network.
Assuming that the whole LTP file is transmitted by n hops in total, the hop with the longest one-way delay is the q-th hop, and the block finally completing transmission on the q-th hop is the blockq_finalThe total time delay of the LTP file in the complex deep space communication network under both bundle aggregation and non-aggregation conditions is considered. Based on the above assumptions and considerations, the total LTP file transfer delay of the complex deep space communication network is divided into four parts: from the beginning of the file transmission at the source node to blockq_finalTime spent starting transmission until qth hop; blockq_finalTransmission delay on the q-th hop; slave blockq_finalTime consumed during the period from the completion of the transmission on the q-th hop to the complete reception of the entire file by the destination node; time consumed for bundle polymerization. The sum of the four parts is the complex deep space communication networkAnd (3) a LTP file transfer delay theoretical model of the network.
Step 1-1) dividing the total time delay of the LTP file transmission of the complex deep space communication network into four parts, namely Tformer、Tblock_q_final、Tlatter、TaggreThe theoretical model expression of the total delay is as follows:
Tfile_multihop＝Tformer+Tblock_q_final+Tlatter+Taggre (1)
in the formula, Tfile_multihopRepresenting the LTP file transfer time in a complex scene; t isformerRepresenting the file from the beginning of the transfer at the source node to the blockq_finalTime spent starting transmission until qth hop; t isblock_q_finalRepresenting blockq_finalTransmission delay on the q-th hop; t islatterRepresenting slave blocksq_finalThe time consumed by the transmission completion on the q-th hop until the whole file is completely received by the destination node; t isaggreRepresents the time consumed for bundle polymerization.
Step 1-2) obtaining the number of transmission rounds experienced when only one block is transmitted and the number of transmission rounds experienced when the whole file is transmitted, and calculating the average value of the two numbers;
step 1-3) calculating the time consumed by all data transmission when a single block is transmitted;
step 1-4) based on the calculation results obtained in step 1-2) and step 1-3), calculating the average total transmission delay T of a single block in one hopformer、TlatterValue of (c), T is calculated from the maximum total propagation delay of a single block over one hopblock_q_finalA value of (d);
step 1-5) calculating T under both conditions of bundle polymerization and non-polymerizationaggreA value of (d);
and 1-6) summing results obtained in the steps 1-4) and 1-5), namely, the LTP file transmission total delay theoretical model of the complex deep space communication network.
And 2) selecting segment, block and session in the LTP protocol parameters for optimization design.
And 3) respectively establishing Optimization bases for the block, the segment and the session based on the theoretical model established in the step 1), thereby providing an LTP Parameter Optimization Design Algorithm (LTP-PODA). And substituting the environment condition parameters into the LTP-PODA for the specific communication environment to obtain an LTP protocol parameter configuration scheme which is most suitable for the communication environment.
Step 3-1) establishing an optimization basis of block on the principle of avoiding delayed waiting of the confirmation information of the block on the forward link in the asymmetric channel;
step 3-2) converting the problem of obtaining the segment size which minimizes the total transmission time delay of the LTP file into a convex optimization problem and establishing an optimization basis of the segment;
step 3-3) establishing an optimization basis of the session according to the principle that the number of the sessions can enable all data to be transmitted at one time;
and 3-4) providing an LTP parameter optimization design algorithm (LTP-PODA) according to the optimization basis of the block, segment and session provided in the step 3-1), the step 3-2) and the step 3-3), and carrying out optimization design on the three protocol parameters. Firstly, block and segment are initialized; then, local optimal solutions of the block and the segment are obtained according to optimization bases of the block and the segment in an iteration mode until the block and the segment which can minimize the total transmission time delay of the LTP file are found out and used as global optimal solutions; on the basis, adjusting the values of the obtained block and segment optimal solutions according to the actual block size to obtain the optimal design values of the block and segment optimal solutions; finally, the optimized design value of the session is obtained according to the optimized basis of the session;
and 3-5) combining the optimized design values of the three parameters obtained in the step 3-4) into an optimal parameter configuration scheme of the LTP in the complex deep space communication network.
And 4) configuring the optimal parameter configuration scheme obtained in the step 3) for the LTP protocol for performing data transmission in the complex deep space communication network, so as to improve the data transmission performance of the whole network.
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 1, embodiment 1 of the present invention proposes an LTP protocol parameter optimization configuration method for a deep space communication network.
1. Building LTP file transmission delay theoretical model of complex deep space communication network
The LTP file transfer latency theoretical model can be expressed as:
Tfile_multihop＝Tformer+Tblock_q_final+Tlatter+Taggre (1)
in the formula, Tfile_multihopThe LTP file transfer time under a complex scene is represented; t isformerRepresenting the file from the beginning of the transfer at the source node to the blockq_finalStarting transmission at the q-th hop, which is the longest one-way delay, blockq_finalBlock for last completed transmission on the q-th hop; t isblock_q_finalRepresenting blockq_finalTransmission delay on the q-th hop; t islatterRepresenting slave blocksq_finalThe time consumed by the transmission completion on the q-th hop until the whole file is completely received by the destination node; t isaggreRepresents the time consumed for bundle polymerization.
1) Calculating the number of transmission rounds;
a. calculating the number of pass rounds experienced when passing only one block
The LTP protocol uses block as a transmission unit to perform data transmission, and during the data transmission process, the block is divided into a plurality of segments, so the number of transmission rounds experienced by one block transmission is determined by the maximum value of the number of transmission rounds experienced by all segments in the block, i.e. Gblock＝Gseg_maxIn the present application GblockTo calculate the number of transfer rounds k experienced when only one block is transferred on the ith hopmin_i：
In the formula, kmin_iRepresenting the number of pass rounds, p, experienced in passing only one block on the ith hopseg_iDenote se on i-th hopFragment loss probability, NRIndicating the number of red data segments contained in a block.
Wherein N isRIs calculated as follows. LTP provides two transmission mechanisms-reliable and unreliable transmission, distinguished by aggregating red and green data segments in an LTP block. The red data segment represents that the segment of data adopts a reliable transmission mode, and the green data segment represents that the segment of data adopts an unreliable transmission mode. Assuming that the red data proportion is f and the green data proportion is (1-f) in a single block to be transmitted, the number of red data segments contained in one block is NR＝(Lblock×f)/Lseg_payloadWherein L isblockSize of a single block, Lseg_payloadRepresenting the load size of a single segment.
b. Calculating the number of transmission rounds experienced when transmitting the whole file
Assuming one dimension LfileIs divided into NbundleTransmitting the bundlets, and combining the bundlets into N after being packaged by BP (BP)blockEach block has Nblock＝(Lfile+Lbundle_head×Nbundle)/LblockEach block is transmitted, and according to the transmission mechanism of the LTP, each block occupies one session, that is, N is required in totalblockAnd (4) session. Wherein L isbundle_headIndicating the length of the header of a bundle after BP encapsulation. The number of transfer rounds k experienced in transferring the entire file on the ith hopmax_iIs calculated as follows
In the formula Lseg_payload_iRepresenting the size of the load of a single segment on the ith hop.
c. Calculating the mean k of the results of steps a. and bmean_iThe calculation formula is as follows:
kmean_i＝(kmin_i+kmax_i)/2 (4)
2) calculating the total time delay of completing the transmission of a single block on one hop;
the total propagation delay of a single block consists of three components: the transmission time, propagation time and extra transmission time consumed in the retransmission of the CP (Check Point) Segment and the RS (Report Segment, RS) due to the loss of the CP Segment and the RS are calculated as follows:
a. calculating the transmission time of a single block on one hop
One block is divided into a plurality of segments for transmission, and if one segment is transmitted according to geometric probability distribution, the probability of successful m-th transmission is Pseg_m＝pseg m-1×(1-pseg) Wherein p issegRepresenting the loss probability of segments, the expected value of the total number of transmissions of each segment on the ith hop is:
let R be the same for each hop of the path when data is transmitted in the networkdata_iThe data transmission rate of a data channel when data is transmitted in the ith hop is represented, and the transmission time T of the block on the ith hop istrans_iThe calculation formula of (A) is as follows:
in the formula, Lseg_frame_iIndicating the size of a segment when transmitted on a physical channel on the ith hop (including the header information size when encapsulated by the respective lower layer protocol).
b. Calculating the propagation time of a single block over one hop
Propagation time TpropMainly by successful transmission of NRThe number of transfer rounds k (k ≧ 1) experienced by each segment. Let T be the same for each hop of the path, since the one-way delay of each hop is not necessarily the same when data is transmitted in the networkdelay_iRepresents a one-way delay in the transmission of data on the ith hop link, thenPropagation time T of a single block on the ith hopprop_iIs calculated as follows:
in the formula, LRS_frameIndicates the size of the RS during physical channel transmission (including the header information size during encapsulation of each lower layer protocol), RACK_iIndicating the data transmission rate of the ACK channel on the ith hop.
c. Calculating the extra delivery time of a single block on a hop
The loss of the CP segment or RS may cause the corresponding timer to expire, causing retransmission of the CP segment or RS, and the time consumed by the expiration of the timer may additionally increase the overall transmission time. Assume that the timer expiration time is Tex(Tex＝2Tdelay+ β, where β is a fixed value and includes at least the transmission time of the RS). Let p beCP_i、pRS_iRespectively representing the loss probability of the CP segment and the RS on the ith hop, and the loss probability of the CP segment or the RS on the ith hop is pCP_RS_i＝1-(1-pCP_i)×(1-pRS_i). The expected value of the sum of each CP segment and the number of RS transmissions on the ith hop can thus be calculated:
the extra delivery time T consumed due to the loss of CP segments and RSex_time_iIs calculated as follows:
d. the total delay T of the single block completing the transfer at the ith hopblock_iComprises the following steps:
Tblock_i＝Ttrans_i+Tprop_i+Tex_time_i (10)
3) calculating Tformer、Tblock_q_final、TlatterA value of (d);
a. calculating Tformer
Will TformerDivided into T according to the number of previous (q-1) hopsformer_1、Tformer_2、…Tformer_a、…、Tformer_q-1A total of (q-1) segments, wherein each segment contains an average total propagation delay for a block to travel over the hop. Since the total transfer delay of a single block consists of three parts of transmission time, propagation time and extra transfer time, the average total transfer delay of a block transmitted on the a-th hop consists of the average transmission time Ttrans_a_meanAverage propagation time Tprop_a_meanAnd average extra delivery time Tex_time_a_meanThe calculation formula of the three components is as follows:
then TformerThe calculation formula of (A) is as follows:
b. calculating Tblock_q_final
Tblock_q_finalThe value of (d) is the maximum total propagation delay of a single block when transmitted on the qth:
c. calculating Tlatter
For TlatterIt can also be divided into T hops according to the number of (n-q) hops after (where n represents n hops in total for data to be transferred from the source end to the destination end)latter_q+1、Tlatter_q+2、…Tlatter_a、…、Tlatter_nA total of (n-q) sections, wherein each section also contains an average total propagation delay of a block transmitted on the hop, TlatterIs calculated as follows:
4) calculating T under both bundle aggregation and non-aggregation conditionsaggreA value of (d);
suppose a file is divided into NbundleTransmitting by each bundle which is combined into NblockBlock, when Nbundle>NblockWhen N is greater than N, it means that one block is formed by aggregating a plurality of bundlesbundle＝NblockWhen the block only contains one bundle, the bundle is in a non-aggregation state. Let T be the time consumed by bundle aggregation to blockaggre。
In the aggregation state, the aggregation time is mainly affected by the rate λ at which each communication node handles the aggregation operation, assuming ω denotes the aggregation time of a block on a single node, tlimRepresents the longest aggregation time of the LTP protocol setting, then T is presentaggreThe calculation is derived as follows:
in the non-aggregated state, i.e. Nbundle＝NblockWhen the polymerization time is 0, TaggreComprises the following steps:
Taggre＝0 (17)
5) calculating the total time delay of LTP file transmission of the complex deep space communication network;
LTP file transfer total time delay T of complex deep space communication networkfile_multihopFrom Tformer、Tblock_q_final、Tlatter、TaggreFour components, then Tfile_multihopCalculation formulaComprises the following steps:
Tfile_multihop＝Tformer+Tblock_q_final+Tlatter+Taggre (18)
in the formula Tformer、Tblock_q_final、Tlatter、TaggreCan be obtained from the calculation results of the steps 1) to 4).
2. Optimizing parameter selection
The parameters in the LTP protocol that most affect the performance of the LTP protocol include the size of "block," the size of "segment," and the number of "session," and therefore these three parameters are selected for optimal design.
3. Parameter optimization design and optimization configuration scheme selection
1) Establish block optimization basis
When LTP transmits data, the confirmation information RS is sent in block units, namely one block corresponds to one RS, in order to deal with the asymmetric characteristic of a link in a deep space communication environment and avoid the delay waiting of the confirmation information RS of the block on a forward link, the sending time of the block is longer than the sending time of the RS. In addition, LTP specifies that the block is divided into a plurality of segments and then subsequently transmitted, and therefore the block size should be at least larger than the segment size, and the block optimization is based on the following:
2) establishing segment optimization basis
The segment selection problem can be transformed into a convex optimization problem, with the following expression:
in the formula, Lseg_payload_aIndicates the size of the segment load, L, on hop aseg_headerThe header information size of the segment is represented. For each link section before the link with the maximum time delay of the one-way link in the data transmission process, Ta(Lseg_payload_a)＝Tformer_a(Lseg_payload_a) (ii) a For the link with the largest one-way link delay, Ta(Lseg_payload_a)＝Tblock_q_final(Lseg_payload_q) (ii) a T for each link section after the link with the maximum time delay of the one-way linka(Lseg_payload_a)＝Tlatter_a(Lseg_payload_a). In addition, LMTURepresents the MTU size, L, of the link layer MTU1500 bytes; due to LblockIs generally larger than the MTU, so L can be ignored hereblockAnd (4) size constraint.
The optimal solution of the convex optimization problem should meet the first-order necessary condition of Karush-Kuhn-Tucker (KKT), and let the KKT multiplier be mu1*，μ2Then, the optimal solution L of segment on each segment of link is solvedseg_payload_aThe calculation formula is as follows:
3) establishing session optimization basis
Considering both bundle polymerization and non-polymerization, the calculation formula of the optimized design of session is as follows:
Nsess_opt＝1.2×(Lfile/Lblock_act) (23)
in the formula Lblock_actRepresenting the actual aggregate size of the block, Nsess_optThe optimal selection value for session is represented.
4) LTP parameter optimization design algorithm (LTP-PODA)
The LTP-PODA algorithm steps are as follows:
first, let L on each link sectionseg_frame_aSubstituting 1500bytes into formula (19) to obtain LblockMinimum value L ofb_min；
Second, the step of dissolving Lb_minSubstituting equations (12), (13), (14), finding the local optimum L satisfying the first-order requirement of KKT on each link segment by solving equation (21)seg_payload_aThis is the local optimal solution for segment; l obtained by the formula (21)seg_payload_aSubstitution (19) for minimum value L of block size on each linkb_min_aAnd taking the maximum of these values and assigning L to the maximumb_minThis is the local optimal solution of block;
thirdly, judging whether a messenger T is foundfile_multihopMinimum Lseg_payload_a*、Lb_minIf so, let L be the final valueseg_payload_a*、Lb_minRespectively has a value of Lsegment_opt_temp、Lblock_opt_tempAnd go to the fourth step; if not, turning to the second step;
fourthly, calculating L according to the formula (22)block_actIt is reacted with Lblock_opt_tempMaking a comparison if Lblock_act＝Lblock_opt_tempIf the optimal design value of block and segment is Lsegment_opt＝Lsegment_opt_temp、Lblock_opt＝Lblock_opt_temp(ii) a If L isblock_act<Lblock_opt_tempAnd the optimal design value of block is Lblock_opt＝Lblock_opt_tempHowever, since the actual block size is Lblock_actThus will Lblock_actNew L obtained by substituting formulae (12), (13) and (14) and then solving formula (21)seg_payload_aOptimized design value L for segmentsegment_opt；
Fifthly, the optimized design value N of the session can be obtained according to the formula (23)sess_opt。
5) Obtaining LTP parameter optimization configuration scheme under different communication environments
L obtained by substituting the environmental conditions into LTP-PODA for different communication environmentsblock_opt、Lsegment_opt、Nsess_optThe values are combined into an optimized configuration scheme of the LTP parameters in the communication environment.
4. Configuring the optimal parameter configuration scheme obtained in the step 5) in the step 3 for the LTP protocol for performing data transmission in the complex deep space communication network, thereby realizing the improvement of the data transmission performance of the whole network.
The technical effect of the application is shown through simulation.
The simulation scenario is as follows:
the simulation scene is a complex deep space Communication Network scene of mars-UNICON-GEO-earth (Universal inter-satellite Communication Network, UNICON);
the network includes 1 Mars finder, 6 UNICON satellites, 1 GEO satellite and 1 ground station, and nine communication nodes, and the schematic diagram of the data transmission path is shown in FIG. 2, in which U1-U6 represent six UNICON satellites;
the simulation parameter configuration is shown in table 1.
TABLE 1 simulation experiment parameter configuration of LTP protocol parameter optimization configuration method of complex deep space communication network
In the complex deep space communication network scenario, according to different link environments shown in table 1, the configuration method provided by the present application is used to provide a parameter configuration optimization scheme in a corresponding scenario for LTP, and performance comparison is performed with other parameter configuration schemes in different environments, so as to verify the effectiveness of the configuration method provided by the present application in the aspect of LTP performance improvement.
The simulation experiment designs 8 configuration schemes. Scheme 1 represents a parameter configuration scheme in which all three parameters are optimized. Scheme 2, scheme 3, scheme 4 represent schemes where only block or segment is not optimized, respectively. Scheme 5, scheme 6, scheme 7 represent schemes where only block or segment or session is optimized, respectively. Scheme 8 represents a scheme in which none of the three parameters were optimized.
In the schemes 2-8, 500KB is selected as the unoptimized size of the block, and L is selectedMTU-100 ═ 1400bytes as unoptimized segment size, if Lblock1bundle, 1/2 × (L)file/Lblock) (wherein LblockAnd Lblock_actEqual to) to calculate NsessThe value is used as the value of the unoptimized session number, if Lblock>1bundle, at 1.2 × (L)file/Lblock)(Lblock≠Lblock_act) Calculate NsessAs an unoptimized value of session. The optimized values of the block, the segment and the session in different link environments are obtained by the configuration method described in the present application, as shown in fig. 3.
And (3) simulation results: fig. 4(a) is a comparison graph of LTP transmission performance under different bit error rate conditions with different parameter configuration schemes; fig. 4(b) is a diagram comparing LTP transmission performance for different parameter configuration schemes under different link delays; fig. 4(c) is a diagram comparing LTP transmission performance with different parameter configuration schemes under different channel rate ratios; fig. 4(d) is a graph comparing LTP transmission performance for different parameter configuration schemes under bundle aggregation and non-aggregation conditions. As can be seen from the four diagrams, in any link environment, the LTP parameter optimization configuration scheme obtained by using the parameter configuration method described in the present application is configured to the LTP, and compared with configuring other parameter configuration schemes for the LTP, better transmission performance can be obtained.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A method for optimally configuring LTP protocol parameters of a deep space communication network is used for a complex deep space communication network under a multi-hop scene, and comprises the following steps:
establishing an LTP file transmission total time delay theoretical model of a complex deep space communication network according to a communication environment;
based on an LTP file transmission total time delay model, providing an LTP parameter optimization design algorithm LTP-PODA; and optimizing segment, block and session parameters in the LTP protocol by an LTP-PODA algorithm to obtain the global optimal solution combination of the three parameters, thereby obtaining the optimal parameter configuration scheme of the LTP protocol.
2. The LTP protocol parameter optimal configuration method of the deep space communication network according to claim 1, wherein the communication environment comprises: the deep space communication network comprises the types and the number of communication nodes, the downlink speed of each section of link, a BP (back propagation) hosting mechanism, an aggregation time limit, a file size, an MTU (maximum transmission unit), the bundle aggregation speed of the communication nodes, the bundle size, the one-way time delay of different links, the error rate and the channel speed asymmetry ratio.
3. The LTP protocol parameter optimization configuration method of the deep space communication network according to claim 1, wherein the LTP file transfer total delay theoretical model is:
Tfile_multihop＝Tformer+Tblock_q_final+Tlatter+Taggre
in the formula, Tfile_multihopTotal delay, T, of LTP file delivery representing complex deep space communication networkformerRepresenting the file from the beginning of the transfer at the source node to the blockq_finalStarting transmission at the q-th hop, wherein the q-th hop represents one hop with the longest one-way link delay, block, in the whole complex deep space communication networkq_finalBlock, T, for last completed transmission on the q-th hopblock_q_finalRepresenting blockq_finalTransmission delay on the q-th hop, TlatterRepresenting slave blocksq_finalTime consumed by the transmission completion on the qth hop until the destination node completely receives the entire file, TaggreRepresents the time consumed for bundle polymerization.
4. The LTP protocol parameter optimization configuration method of the deep space communication network according to claim 3, wherein the building process of the LTP file transfer total delay theoretical model of the complex deep space communication network specifically comprises:
step s1) finds the number k of transfer rounds experienced when only one block is transferred on the ith hopmin_iAnd the number of passes k experienced in transferring the entire filemax_iAnd calculating the mean k of the twomean_i；
Step s2) obtaining the time T consumed by the single block completing the transmission on the ith hopblock_i；
Step s3) calculates T of the previous (q-1) hop based on the calculation results obtained in step s1) and step s2)formerMaximum total transfer delay T for a single block transmitted on qthblock_q_finalAnd T of last (n-q) hoplatter；
Step s4) dividing a file into NbundleA bundle for transmission, NbundleEach bundle is combined into NblockBlock;
when N is presentbundle>NblockIn time, the method indicates that one block is formed by aggregating a plurality of bundles, and the time T consumed by aggregating the bundles into the block is calculatedaggre(ii) a When N is presentbundle＝NblockWhile, bundle is in a non-aggregated state, Taggre＝0；
Step s5) summing the calculation results obtained in the step s3) and the step s4) to obtain the LTP file transfer total delay theoretical model of the complex deep space communication network.
5. The LTP protocol parameter optimal configuration method for the deep space communication network according to claim 4, wherein the step s1) specifically comprises:
calculating the number k of transfer rounds experienced when only one block is transferred on the ith hop according to the following formulamin_i：
In the formula, pseg_iRepresents the segment loss probability, N, on the ith hopRRepresenting the number of red data segments contained in one block, and m represents the number of all theoretically possible transmission rounds;
calculating a transfer integer according toNumber of pass k experienced per filemax_i：
Where f denotes the red data proportion in a single block to be transmitted, NbundleIndicates that one dimension is LfileIs divided into NbundleA bundle for transmission, Lbundle_headIndicates the head length, L, of bundleblockSize of a single block, Lseg_payload_iRepresenting the size of the load of a single segment on the ith hop.
6. The method for optimal configuration of LTP protocol parameters for deep space communication networks according to claim 5, wherein the step s3) specifically comprises:
obtaining T of the previous (q-1) hop according to the following formulaformer：
In the formula, Ttrans_a_mean、Tprop_a_meanAnd Tex_time_a_meanRespectively represent blockq_finalAverage transmission time, average propagation time and average extra delivery time, T, at hop aformer_aRepresenting blockq_finalAverage total time delay of transmission on the a-th hop, a ∈ [1, q ∈ [ ]]；
Obtaining the maximum total transfer time delay T of a single block when the single block is transmitted on the qth according to the following formulablock_q_final：
Tblock_q_final＝Tprop_q_final+Ttrans_q_final+Tex_time_q
In the formula, Tprop_q_final、Ttrans_q_finalAnd Tex_time_q_finalRespectively represent blockq_finalPropagation time, transmission time and extra delivery time at the q-th hop;
according to the formulaObtaining the T of the last (n-q) hoplatter：
In the formula, Tlater_aAnd n represents the total hop number of data transmitted from the source end to the destination end.
7. The LTP protocol parameter optimization configuration method of the deep space communication network according to claim 6, wherein the LTP file transfer total delay model is based on providing a LTP parameter optimization design algorithm LTP-PODA; optimizing segment, block and session parameters in the LTP protocol by an LTP-PODA algorithm to obtain a global optimal solution combination of the three parameters, thereby obtaining an optimal parameter configuration scheme of the LTP protocol; the method specifically comprises the following steps:
step t1) initializing block and segment;
step t2), solving a local optimal solution of the block and the segment according to the optimization basis of the block and the segment by using an iteration mode;
step t3) judging whether a block and a segment which can minimize the total transmission time delay of the LTP file are found, if so, obtaining a global optimal solution of the block and the segment, and temporarily using the global optimal solution as an optimized value of the block and the segment; go to step t 4); otherwise, go to step t 2);
step t4) comparing the obtained block global optimal solution with the actual block size in the data transmission process, thereby adjusting the optimized values of the block and the segment obtained in the step t3) and obtaining the final optimized design values of the block and the segment;
and t5) obtaining an optimal design value of the session according to the optimization basis of the session, and obtaining an optimal parameter configuration scheme of the LTP protocol by combining the optimal design values of the block and the segment.
8. The LTP protocol parameter optimization configuration method for the deep space communication network according to claim 7, wherein the step t1) specifically comprises:
setting segment frame size L on each segment linkseg_frame_aTo set value, the head length L in combination with segmentseg_headerThe load size L of segment on each link is obtained according to the following formulaseg_payload_aThereby, the initialization of segment is completed:
Lseg_payload_a＝Lseg_frame_a-Lseg_header
mixing L withseg_payload_aIs assigned to Lseg_payload、Lseg_frame_aIs assigned to Lseg_frameSubstituting the following formula to obtain the block size LblockMinimum value L ofb_minThus completing the block initialization;
wherein L isRS_frameIndicates the frame size, L, of the RSseg_payloadRepresenting the load size, L, of the segmentseg_frameRepresenting the frame size, R, of a segmentdataIndicating the data transmission rate, R, of the data channelACKIndicating the data transmission rate of the ACK channel.
9. The LTP protocol parameter optimization configuration method for the deep space communication network according to claim 8, wherein the step t2) specifically comprises:
with Lb_minSubstituting for block size to obtain Tformer_a、Tblock_q_finalAnd Tlatter_aWill find the equation Tfile_multihopThe problem of minimum segment size translates to Tformer_a(Lseg_payload_a)、Tblock_q_final(Lseg_payload_q) And Tlatter_a(Lseg_payload_a) Solving the local optimal L meeting the first-order requirement of KKT on each link section by the convex optimization problem of the functionseg_payload_a*，Lseg_payload_aIs a local optimal solution of segment; wherein L isseg_payload_qRepresents the segment load size on the q hop;
mixing L withseg_payload_aIs given to Lseg_payloadSubstituting the following formula to obtain the block size L on each linkblockMinimum value L ofb_min_a：
L from each link segmentb_min_aTaking the maximum value and assigning it to Lb_min，Lb_minThe method is a local optimal solution of block.
10. The LTP protocol parameter optimization configuration method for the deep space communication network according to claim 9, wherein the step t5) specifically includes:
the actual aggregate size L of the blocks during data transmission is determined byblock_actObtaining an optimized design value N of sessionsess_opt：
Nsess_opt＝1.2×(Lfile/Lblock_act)。
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