CN105227457A - Towards the protocol Data Unit cross-layer optimizing method under DTN dynamic link - Google Patents

Abstract

The present invention proposes a kind of towards the protocol Data Unit cross-layer optimizing method under DTN dynamic link, according to the predictability of empty sky link, node knows the information of link in advance; The file size transmitted as required estimates the time range of the link of required cost, estimate the average link length in current time frame, average linkage length is put in the middle of the calculation of parameter of SNR, Pe and R as the linkage length value after change simultaneously, and utilize these parameters to obtain the value of the transformation parameter of optimization.Method of the present invention is simple and easy to realize, and effectively can improve network performance, to overcome under dynamic link Parameters variation for the impact of transmission performance.

Description

Towards the protocol Data Unit cross-layer optimizing method under DTN dynamic link

Technical field

The present invention relates to technical field of deep space communication, particularly relate to a kind of towards the protocol Data Unit cross-layer optimizing method under DTN dynamic link.

Background technology

Traditional TCP/IP is applied to has end-to-end link and in the high network of the Loss Rate of data.And existing many networks are subject to the restriction of network environment and the resource use of network own, as: the frequent break-make of link, long propagation delay, high bit-error etc., make TCP/IP cannot be applicable to these networks.DTN network can overcome in network problems such as occurring link break-make and long delay, realizes data and effectively transmits reliably.DTN is the storage forwarding based on point-to-point data, and the transfer of data of point-to-point, by DTN Route Selection via node, connects for end to end, realizes the connection of source node to destination node by data.When the link is broken, node to store data in the memory of node until continue when the connection of link is available to send again, and so just the transfer of data of end-to-end path can be divided into the transfer of data of multiple point-to-point.Owing to being the transfer of data of point-to-point, when data are lost, the re-transmission of data completes between the two nodes, and do not need to retransmit to originating node requests, ensure that the transmitting of data.Each via node has become the transfer station of data, and the data received are transported to next node.

In order to improve the performance of network, reducing propagation delay time, improving throughput, in a static condition, process is optimized to the transmission means of packet bundle and segment and size.For the propagation delay time of a bundle on one hop link, there is an optimal size that it can be made minimum for segment, and for the maximum data size that link can transmit, current ink can be obtained when transmitting data, the size that segment should be arranged.For data from source node to destination node, keep the size of bundle not change, intermediate node only just carries out forwarding effect to data.For bundle, there is an optimum bundle size, the file transmission time of whole piece link can be made minimum in the file transfer time delay in whole multi-hop link.Because segment size is relevant with bundle, bundle size is relevant with segment, trigger the optimization calculating of segment as the initial condition of bundle using the length Lfile of file, the optimization of bundle size is triggered again with the size of segment, can obtain segment and the bundle size of one group of optimum respectively through iteration optimization repeatedly, this size can make the transmission performance of whole piece link optimum as the parameter of Operation system setting during file transfer.

Effectively transmit to realize data in DTN network, transmission be optimized to data, propose many different transmission meanss:

(1) for bundle transmission, the high bit error rate under empty sky environment, causes the repeatedly re-transmission of obliterated data, in order to reduce the number of times retransmitted, when retransmitting beginning, the data doubling to lose are to reduce the Loss Rate of packet, reduce number of retransmissions, reduce propagation delay time.

(2) when bundle is in the process of transmission, the disconnection of link makes bundle be divided into two different bundle blocks, and the continuation be transmitted is transmitted, and the bundle block not completing transmission waits for new transmission opportunity.

(3) time varying channel refers to that the state of channel itself is subject to the impact of environment and changes, and causes the parameter of channel to change.Network code under time varying channel is the size setting encoded packets according to do not calculated in the same time channel status, can obtain optimum network code bag long.

(4) LTP-T transmission means, via node can receive a complete data bundle, as long as the data block successfully received just sends to next node, accelerates the transmission of data.

(5) the multi-hop optimization method of above-mentioned static state is file algorithm to the optimization of transmission data parameters when multi-hop link is transmitted, and algorithm computational process link distance does not change.

Mostly above-mentioned transmission means is in a static condition, and does not consider the impact that the high speed dynamic change of link range brings.High-speed motion due to satellite will make channel parameter change: as SNR, transmission rate R, bit error rate Pe etc.Channel parameter after change will make the Optimal Parameters originally set in the dynamic link transmission process of reality, reduce the performance of network.So when data are transmitted on the link of dynamic change, link range and channel parameter when needing to select to optimize according to the dynamic of link and the transmission of file, so that the performance obtained when data are transmitted on dynamic link.

Summary of the invention

In order to solve the problems of the prior art, the present invention proposes a kind ofly needs situation about transmitting on dynamic link according to file towards the protocol Data Unit cross-layer optimizing method under DTN dynamic link under dynamic link, readjusts the value of optimization.Every suboptimization is all that after optimizing with the last time, the propagation delay time obtained, for interval, calculates the mean value of link range in this interval, asks optimization using this new link range as new optimization distance to Lseg and Lbundle.In dynamic link transmission process, just with the result finally obtained for Optimal Parameters.The method is simple and easy to realize, and effectively can improve network performance, to overcome under dynamic link Parameters variation for the impact of transmission performance.

The present invention is achieved through the following technical solutions:

Towards the protocol Data Unit cross-layer optimizing method under DTN dynamic link, the concrete steps of the method are as follows:

The length Lbundle (0) of step 1: initialization packet loss Pe (0), transmission rate R (0), link average distance d_mean (0) and bundle;

Step 2: to Tbundle and Tfile about Lseg and Lbundle differentiate, obtains the extreme value of Lseg and Lbundle, utilizes mutual interative computation N time of the extreme value of Lbundle and Lseg, obtains Lbundle and Lseg of one group of optimum;

Step 3: the file size transmitted as required, utilizes optimum Lbundle and Lseg to obtain the Link Time scope T needing cost;

Step 4: the Link Time T spent as required estimates the average link length in current time frame, average linkage length is put in the middle of the calculation of parameter of SNR, Pe and R as the linkage length value after change simultaneously, and utilize these parameters to obtain the value of the transformation parameter of optimization.

Accompanying drawing explanation

Fig. 1 is multilayer dummy satellite schematic diagram;

Fig. 2 is multi-hop transmission model schematic;

Fig. 3 is the flow chart of the inventive method;

Fig. 4 (a) is the change schematic diagram of the length of Lbundle Different Optimization number of times in optimizing process;

Fig. 4 (b) is the change schematic diagram of the length of Lseg Different Optimization number of times in optimizing process;

Fig. 5 (a) is the file size different when transmission rate is 1M and the comparison schematic diagram of the file transfer time delay under difference initial bit error rate;

Fig. 5 (b) is the file size different when transmission rate is 2M and the comparison schematic diagram of the file transfer time delay under difference initial bit error rate.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.

First introduce application scenarios of the present invention, as shown in Figure 1, the present invention's application be the transmission system model of multi-hop, be with the multilayer satellite system model of LEO, MEO and GEO satellite composition.LEO layer satellite, as source node and destination node, sends data and receives.And the satellite of MEO and GEO layer is as via node, only storage forwarding is carried out to data and does not change the size of bundle.

When a MEO or GEO satellite node receiving or preserves the complete bundle data of upper satellite node transmission, when link is feasible, data are sent to next satellite node.If the bundle that on satellite node, neither one is complete, wait-receiving mode is just needed to start to transmit bundle to next node to a complete bundle again.And on single satellite node, the transmission of data is after a bundle is transmitted, just then transmit next bundle data.Bundle is transmitted the retransmission delay time that the required time is included in propagation delay time on node and brings due to packet loss, and the transmission system model of file as shown in Figure 2.

In whole multi-hop, the transmission time of data is determined, so carry out the foundation of the model of data transmission period using the longest hop link of bundle propagation delay time as bottleneck link by the link that bundle propagation delay time is the longest.

$Tfile=Tf\left(Lbundle\right)=\frac{Lfile}{Lbundle-Lbhead}\×({\mathrm{Tbundle}}_{neck}+Tpro)+\underset{i\≠neck}{\overset{n}{\underset{i=1}{\mathrm{\Σ}}}}{\mathrm{Tbundle}}_i$

Wherein, Lbhead is the head length of bundle, and Lfile refers to the length of transfer files, Tbundle _neckrefer to that transmission time of jumping that the bundle transmission required time is maximum in multihop path, Tpro represents the time of single times of light path, and Tbundle is single bundle propagation delay time computation model, contains transmission delay and back off time.

$\begin{array}{c}Tbundle=Ts\left(Lseg\right)=\frac{Lbundle}{Lseg}\×\frac{Lseg+Lshead}{R}\×(1+\frac{Pseg}{(1-\mathrm{Pr}s)(1-Pseg)})+Tpro\\ +\[\frac{EN-1}{1-\mathrm{Pr}s}(2Tpro+Trs)\]+\[-\frac{Pcp}{1-Pcp}(2Tpro+Tcp+Trs)+Tcp\]\end{array}$

In above formula, Lseg and Lshead is respectively the length of segment and segment head, and Pseg is segment packet loss, R transmission rate, and EN is the number of times retransmitted, and Pcp, Prs, Tcp, Trs are respectively packet loss and the propagation delay time of CP and RS data block.

The change of dynamic link is continuous print, for the ease of the propagation delay time of calculation document on physical link, turns to multiple timeslice by discrete for continuous print link, using the propagation delay time of a bundle as a timeslice.At single bundle in single timeslice, the parameter supposition of channel does not change, and only between timeslice and timeslice, channel just changes.

$T=\underset{n=1}{\overset{\frac{Lfile}{Lbundle-Lbhead}}{\mathrm{\Σ}}}\[{\mathrm{Tbundle}}_{neck}\left(n\right)+Tpro\left(n\right)\]+\underset{i\≠neck}{\overset{m}{\underset{i=1}{\mathrm{\Σ}}}}{\mathrm{Tbundle}}_i$

In formula, n represents the n-th bundle and residing timeslice, and wherein Tbundle (n) is:

$\begin{array}{c}Tbundle\left(n\right)=\frac{Lbundle}{Lseg}\×\frac{Lseg+Lshead}{R\left(n\right)}\×(1+\frac{Pseg\left(n\right)}{(1-\mathrm{Pr}s(n\left)\right)(1-Pseg(n\left)\right)})+Tpro\left(n\right)\\ +\[\frac{EN\left(n\right)-1}{1-\mathrm{Pr}s\left(n\right)}\left(2Tpro\right(n)+Trs)\]+\[\frac{Pcp\left(n\right)}{1-Pcp\left(n\right)}\left(2Tpro\right(n)+Tcp+Trs)+Tcp\]\end{array}$

Inside Tbundle and Tfile computing formula, be the convex function about Lseg and Lbundle respectively, Lseg and Lbundle that namely existence one is optimum, makes Tbundle and Tfile minimum.

MinTfile

s.t.Tfile _i＝Ts(Lbundle _i)Lbundle _i∈{Lbhead,Lfile}

Tfile≤Tfile _ii＝0,1,2……n

Lbundle _i＞0i＝0,1,2……n

Tfile _i＞0i＝0,1,2……n

MinTbundle

s.t.Tbundle _i＝Ts(Lseg _i)Lseg _i∈{Lshead,MTU}

Tbundle≤Tbundle _ii＝0,1,2……n

Lseg _i＞0i＝0,1,2……n

Tbundle _i＞0i＝0,1,2……n

To Tbundle and Tfile about Lseg and Lbundle differentiate, extreme point is positioned at the point that differentiate is zero, and the mutual interative computation of Lbundle and Lseg optimal solution several times just can to the solution of Lbundle and Lseg of one group of optimum.

$\begin{array}{c}Fs\left(Lseg\right)=\frac{\∂Tbundle}{\∂Lseg}=\frac{Lbundle}{R}-\frac{-(1-\mathrm{Pr}s+\mathrm{Pr}s\×Pseg)(1-Pseg)\×Lshead+(Lseg+Lshead)\×Lseg\×\frac{\∂Pseg}{\∂Lseg}}{(1-\mathrm{Pr}s)\×{\[Lseg\×(1-Pseg)\]}^2}\\ +\frac{2Tpro+Trs}{1-\mathrm{Pr}s}\×\frac{\∂EN}{\∂Lseg}\end{array}$

$\begin{array}{c}Fl\left(Lbundle\right)=\frac{\∂Tfile}{\∂Lbundle}=\frac{Lfile}{{(Lbundle-Lbhead)}^2}\{s_{neck}\×\[\frac{\∂{\mathrm{EN}}_{neck}}{\∂Lbundle}\×\\ (Lbundle-Lbhead)-{\mathrm{EN}}_{neck}\]-h_{neck}\×Lbhead-\frac{2Tpro+Tcp+Trs}{1-Pcp}-Tcp\}+\underset{i\≠neck}{\overset{n}{\underset{i=1}{\mathrm{\Σ}}}}\[h_i+s_i\×\frac{\∂{\mathrm{EN}}_i}{\∂Lbundle}\]\end{array}$

And t and h is respectively $t=\frac{2Tpro+Trs}{1-\mathrm{Pr}s}$ With $h=\frac{Lseg+Lshead}{v\×Lseg}\×\[1+\frac{Pseg}{(1-\mathrm{Pr}s)(1-Pseg)}\].$

Static lower Problems existing was discussed above, under dynamic link, needs situation about transmitting on dynamic link according to file, readjust the value of optimization.Every suboptimization is all that after optimizing with the last time, the propagation delay time obtained, for interval, calculates the mean value of link range in this interval, asks optimization using this new link range as new optimization distance to Lseg and Lbundle.In dynamic link transmission process, just with the result finally obtained for Optimal Parameters, no longer change the size of Lseg and Lbundle.The false code of the method described is as follows:

Wherein, d_mean is the mean value by all distances of getting during this period of time to the T moment in start time.T be one by optimize obtain the propagation delay time of whole file, the value acquired by every suboptimization is different, and therefore, T is the value of a dynamic change.The method being asked for SNR by d_mean is:

${\mathrm{\ΔL}}_{space}=20\lg \frac{d+\mathrm{\Δ}d}{d}$

SNR＝SNR ₀-ΔL _space

After the value of SNR, Pe and R tends towards stability, just can stop iteration, the value of N and W can be obtained by experiment.

The flow chart of method of the present invention as shown in Figure 3.According to the predictability of empty sky link, node knows the information of link in advance.The file size transmitted as required estimates the time range of the link of required cost, estimate the average link length in current time frame, average linkage length is put in the middle of the calculation of parameter of SNR, Pe and R as the linkage length value after change simultaneously, and utilize these parameters to obtain the value of the transformation parameter of optimization.

Method of the present invention is simple and easy to realize, and effectively can improve network performance, to overcome under dynamic link Parameters variation for the impact of transmission performance.

The Performance Evaluation of method of the present invention is for standard with the propagation delay time of the situation of Lbundle and Lseg size variation in optimizing process on dynamic link and their whole files on physical link.

Accompanying drawing 4 (a) is the situation of change of Lbundle length of Different Optimization number of times in optimizing process, and accompanying drawing 4 (b) is the situation of change of Lseg length of Different Optimization number of times in optimizing process.Using initial distance as initial optimization distance, optimization solution and the optimization solution acquired below of acquired bundle and segment have very large difference.Work as Pe=5*10 ^-4time, for the size of bundle, first time and secondary difference reach 5*10 ⁶byte, when result tends towards stability, stabilization result and primary difference reach 3*10 ⁶.Work as Pe=10 ^-6time, second time difference is 2*10 ⁶byte, stable difference is also 2*10 ⁶.And for the optimizing the size of segment, the error rate is less, and results change is larger.Work as Pe=10 ^-6time, difference reaches 1000Byte, and works as Pe=5*10 ^-4time, acquired result does not have anything to change.

Accompanying drawing 5 (a) is the file size different when transmission rate is 1M and the comparison of the file transfer time delay under difference initial bit error rate, and accompanying drawing 5 (a) is the file size different when transmission rate is 2M and the comparison of the file transfer time delay under difference initial bit error rate.As bundle with segment length result the same, second time optimize after the propagation delay time of trying to achieve and first time optimize after the propagation delay time difference of trying to achieve maximum.When transmission rate is 1M, work as Pe=5*10 ^-4time, first time and secondary whole file transfer time delay difference reach 1200s, and for stable simulation result, its difference reaches 1500s.Work as Pe=10 ^-6time, first time and second time also have the difference of 300s.When initial transmission rate is 2M.Work as Pe=5*10 ^-4time, first time and secondary difference arrive 500s, and stabilization result difference is to 600s.Work as Pe=10 ^-4time, the difference of result and second time result is reached for 700s for the first time, and stable difference result is for reaching 900s.Occur that the reason of this result works as Pe=5*10 ^-4time, the propagation delay time of the whole file that first time obtains is little, and the average propagation distance obtained is less, reduces accordingly, so the difference obtained just can be less than work as Pe=10 to transmitting the performance impact brought ^-4time propagation delay time difference.Under the dynamic change of dynamic link distance, according to bundle and the segment size that the transmission situation of link and file resets, can overcome dynamically to the impact that internetworking the subject of knowledge and the object of knowledge brings.

The present invention can instruct the work of DTN data transmission in network improvement in performance, carry out reasonably in different downstream transmission speed ratio and high bit-error situation according to the present invention, carry out polymerization number to the data bundle of transmission targetedly to arrange, be conducive to reducing the stand-by period of transmission data, improving the throughput of transfer of data, improve the performance of DTN data transmission in network.Then modify to the structure of RS, the transmission method that bundle is polymerized also improves the throughput of transfer of data when high bit-error.

Above content is in conjunction with concrete preferred implementation further description made for the present invention, can not assert that specific embodiment of the invention is confined to these explanations.For general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, some simple deduction or replace can also be made, all should be considered as belonging to protection scope of the present invention.

Claims (2)

1., towards the protocol Data Unit cross-layer optimizing method under DTN dynamic link, it is characterized in that:

The concrete steps of described method are as follows:

Step 1: the length Lbundle of initialization packet loss Pe, transmission rate R, link average distance d_mean and bundle;

Step 2: to Tbundle and Tfile about Lseg and Lbundle differentiate, obtains the extreme value of Lseg and Lbundle, utilizes the extreme value of Lbundle and Lseg mutual interative computation N time, obtains Lbundle and Lseg of one group of optimum,

$Tfile=\frac{Lfile}{Lbundle-Lbhead}\×({\mathrm{Tbundle}}_{neck}+Tpro)+\underset{i\≠neck}{\overset{n}{\underset{i=1}{\mathrm{\Σ}}}}{\mathrm{Tbundle}}_i$

Wherein Lbhead is the head length of bundle, and Lfile refers to the length of transfer files, Tbundle _neckrefer to that transmission time of jumping that the bundle transmission required time is maximum in multihop path, Tpro represents the time of single times of light path, and Tbundle is single bundle propagation delay time computation model, contains transmission delay and back off time,

$\begin{array}{c}Tbundle=\frac{Lbundle}{Lseg}\×\frac{Lseg+Lshead}{R}\×\left(1+\frac{Pseg}{\left(1-\mathrm{Pr}s\right)\left(1-Pseg\right)}\right)+Tpro\\ +\[\frac{EN-1}{1-\mathrm{Pr}s}\left(2Tpro+Trs\right)\]+\[\frac{Pcp}{1-Pcp}\left(2Tpro+Tcp+Trs\right)+Tcp\]\end{array}$

Lseg and Lshead is respectively the length of segment and segment head, and Pseg is segment packet loss, R transmission rate, and EN is the number of times retransmitted, and Pcp, Prs, Tcp, Trs are respectively packet loss and the propagation delay time of CP and RS data block;

Step 3: the file size transmitted as required, utilizes optimum Lbundle and Lseg to obtain the Link Time scope T needing cost,

$T=\underset{n=1}{\overset{\frac{Lfile}{Lbundle-Lbhead}}{\Σ}}\[{\mathrm{Tbundle}}_{neck}\left(n\right)+Tpro\left(n\right)\]+\underset{i\≠neck}{\overset{m}{\underset{i=1}{\mathrm{\Σ}}}}{\mathrm{Tbundle}}_i$

In above formula, n represents the n-th bundle and residing timeslice, and wherein Tbundle (n) is:

$\begin{array}{c}Tbundle\left(n\right)=\frac{Lbundle}{Lseg}\×\frac{Lseg+Lshead}{R\left(n\right)}\×\left(1+\frac{Pseg\left(n\right)}{\left(1-\mathrm{Pr}s\left(n\right)\right)\left(1-Pseg\left(n\right)\right)}\right)+Tpro\left(n\right)\\ +\[\frac{EN\left(n\right)-1}{1-\mathrm{Pr}s\left(n\right)}\left(2Tpro\left(n\right)+Trs\right)\]+\[\frac{Pcp\left(n\right)}{1-Pcp\left(n\right)}\left(2Tpro\left(n\right)+Tcp+Trs\right)+Tcp\]\end{array};$

Step 4: the Link Time T spent as required estimates the average link length in current time frame, average linkage length is put in the middle of the calculation of parameter of SNR, Pe and R as the linkage length value after change simultaneously, and utilize these parameters to obtain the value of the transformation parameter of optimization.

2. cross-layer optimizing method according to claim 1, is characterized in that: to Tbundle and Tfile

Be specially about Lseg and Lbundle differentiate:

$\begin{array}{c}\frac{\∂Tbundle}{\∂Lseg}=\frac{Lbundle}{R}-\frac{-(1-\mathrm{Pr}s+\mathrm{Pr}s\×Pseg)(1-Pseg)\×Lshead+(Lseg+Lshead)\×Lseg\×\frac{\∂Pseg}{\∂Lseg}}{(1-\mathrm{Pr}s)\×{\[Lseg\×(1-Pseg)\]}^2}\\ +\frac{2Tpro+Trs}{1-\mathrm{Pr}s}\×\frac{\∂EN}{\∂Lseg}\end{array},$

$\begin{array}{c}\frac{\∂Tfile}{\∂Lbundle}=\frac{Lfile}{{\left(Lbundle-Lbhead\right)}^2}\{s_{neck}\×\[\frac{\∂{\mathrm{EN}}_{neck}}{\∂Lbundle}\×\\ \left(Lbundle-Lbhead\right)-{\mathrm{EN}}_{neck}\]-h_{neck}\×Lbhead-\frac{2Tpro+Tcp+Trs}{1-Pcp}-Tcp\}+\underset{i\≠neck}{\overset{n}{\underset{i=1}{\mathrm{\Σ}}}}\[h_i+s_i\×\frac{\∂{\mathrm{EN}}_i}{\∂Lbundle}\]\end{array}$

Wherein, $\frac{\∂Pseg}{\∂Lseg}=-ln(1-Pe)\×{(1-Pe)}^{(Lseg+Lshead)},\frac{\∂E\left(N\right)}{\∂Lbundle}=-\underset{m=1}{\overset{\mathrm{\∞}}{\Σ}}\frac{ln(1-{\mathrm{Pseg}}^m)}{Lseg}\×{(1-{\mathrm{Pseg}}^m)}^{\frac{Lbundle}{Lseg}},$ $\begin{array}{c}\frac{\∂E\left(N\right)}{\∂Lseg}=-Lbundle\×\underset{m=1}{\overset{\mathrm{\∞}}{\Σ}}\frac{\frac{m\×{\mathrm{Pseg}}^{m-1}\×{(1-Pe)}^{Lseg+Lshead}ln(1-Pe)}{1-{\mathrm{Pseg}}^m}\×Lseg-ln(1-{\mathrm{Pseg}}^m)}{{\mathrm{Lseg}}^2}\\ \×{\left(1-{\mathrm{Pseg}}^m\right)}^{\frac{Lbundle}{Lseg}}\end{array},$ Maximum that of bundle propagation delay time that what neck and i in formula represented respectively is is jumped and other except maximum bundle propagation delay time are jumped, and t and h is respectively with v represents the transmission rate R of channel.