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Abstract： In the network for data transmission using CMT， there are multiple paths to choose， and the time delay of each path is not the same， there is a certain issue packet out-of-order. This article studied and analyzed the packet transmission in the sender， for each path assigned specific packet sequence number， in order to reduce the random sequence problem， improve the efficiency of network transmission. In the network for data transmission using CMT， there are multiple paths to choose， and the time delay of each path is not the same， there is a certain issue packet out-of-order. This article studied and analyzed the packet transmission in the sender， for each path assigned specific packet sequence number， in order to reduce the random sequence problem， improve the efficiency of network transmission.
Key words： Concurrent Multipath Transfer； data transfer； path selection； buffer queue
中图分类号：TP393.06 文献标识码：A 文章编号：1009-3044（2016）05-0046-03
1 Introduction
In the network， there are many factors that can affect the data transmission， such as bandwidth， RTT， CWND， hubs， switches， etc.， so that each path transmission time is not necessarily the same.When N path between two hosts transmission delay is not same， how to improve the transmission efficiency of CMT in broad-band network， is a focus in the study of this article.
Set by the SIGTRAN group 2011 SCTP （Stream Control Transmission Prorocol）[1][2]， effectively combine the advantage of TCP and UDP， and have multi-homing and multi-streaming properties.Working principle is to select a path as the main path for data transmission， the other path as the backup path， when the primary path fails， SCTP to select a backup route， as a new main path to transmit data.But there is no multiple concurrent transmission ability of SCTP.
In order to realize the network terminal equipment interface to access more features， put forward the CMT（Concurrent Multipath Transfer）[3]， CMT has multiple parallel transmission capacity， can adapt to host multiple access capability， provide multiple transmission lines between the host and at the same time， effectively improve the efficiency of the network.
2 Related Research
At present， the study of CMT are mainly concentrated in 1M-10M network， such as transmission delay， flow distribution， routing， retransmission strategy， etc.This paper mainly studies the CMT in 5M to 50M（broad-band network） the performance of the network. Using CMT for data transmission， the existing access devices A and B for more than two interfaces.Assumptions， equipment have n interface， A B is m interface， and then between A and B have n * m transmission path.Figure 1 is A simplified network model， only two paths between A and B， is advantageous for the simulation research in the future.
Is the sender of A， B is the receiver.The sender has two interface A1 and A2， A receiver B1 and B2 B has two interfaces.Path is a path between A1 and B1 1， namely path1；A2 and B2 path is a path between the two， namely path2.Path1 delay is D1， path2 delay is D2， assumptions， D1 than D2， namely D1>D2.
Path1 transmission quality is poor， if there is data through， take a long time to arrive at the receiver， or is due to the transmission time delay too long， within the prescribed period of time， not arrived at the receiving end， make the receiver that data loss.And path2 transmission of good quality， through the path of data as soon as possible， and arrive at the receiving end， there is no data delay arrival， or loss of data.
The background of the thesis， it is in high bandwidth （5-50 m） network within the scope of path1 and path2 transmission delay is not the same， D1>D2.In this case， how to improve the transmission efficiency and the feasibility analysis.
3 Problem Description
If the sending end of A buffer queue have 1-9 packets， the nine packet will by sending A，B， transmitted to the receiving end to path selection， determine the distribution of the nine packets， which packets by path1 transmission， which packets by path2 transmission， through the reasonable distribution of packet transmission scheme， to speed up the data transmission efficiency.As shown in figure 2.
At the B receiving end， packet 2， 3， 4 has arrived， and packet 1 haven’t reached， as shown in figure 4.So packets 2， 3， 4 just cached in the receive buffer of B， B， this is bound to take the receiving end of cache resources， reduce B can receive data cache， causing the deterioration of network performance.
Data for the second route choice， assuming that packet 5， choose path1；Packet 6， 7， 8， choose path2 transmission， as shown in figure 5.At this point， the packet 1 B haven’t reached the receiving end.
Due to the poor quality of transmission path1， packets haven’t reached 1 B， the second transmission of packets 6， 7， 8， has reached the B side， as shown in figure 6.B at this point， the receiving end of a buffer for the first time after path2 transmission of packets of 2， 3， 4；And， for the second time after path2 transmission of packets June， July and August.Due to packet loss of 1 and 5 B side rbuf data not up layer of the transfer. Wait for a period of time， by path1 transmission of packets 1， arrived at the receiving end B， as shown in figure 7.B are cached in the receiving end of packet 2， 3， 4， can be together with the packet 1， pass on a layer of a cross， at the same time， the receiving side B， also release packet 1 ～ 4 cache space.Release the space， can be arrived to hold the new data.
Shows， the poor quality of path1， seriously affect the performance of the system， take up the receiver B rbuf， make B arrived there is no more space to receive new data.So need to design a more suitable packet scheduling algorithm， scheduling packet routing， and calculating the distribution of each path data.
4 Conclusion
Research has shown that in high bandwidth network， when the path ShiYanXiang at the same time， increase the receive buffer， can improve the network performance；And when the time delay is not at the same time， increase the receive buffer， will not be able to increase network throughput.However， the actual network transmission environment， the path delay could not have all the same， there are many factors that can affect the time delay， such as sending end processing time， processing time delay， the receiving end back and forth， etc.， so the time delay is not at the same time， how can improve the efficiency of transmission， more research value.
References：
[1] Hung Y， Sieh H， Sivakumar R. A transport layer approach for achieving aggregate bandwidths on multihomed mobile hosts[J]. In Proc. ACM/IEEE MOBICOM. Atlanta， Georgia， USA. September 2002：83-94.
[2] Zhang M， Lai J， Krishnamurthy A， et a1. A transport layer approach for improving end-to-end performance and robustness using redundant paths[C]. Usenix Annual Technical Conference. Boston， MS， USA. June 2004.
[3] Iyengar J R， Amer P D ，Stewart R. Concurrent multipath transfer using SCTP multihoming over independent end-to-end paths [J]. IEEE/ACM Trans. On Networking ，2006，14（5）：951-964.
Key words： Concurrent Multipath Transfer； data transfer； path selection； buffer queue
中图分类号：TP393.06 文献标识码：A 文章编号：1009-3044（2016）05-0046-03
1 Introduction
In the network， there are many factors that can affect the data transmission， such as bandwidth， RTT， CWND， hubs， switches， etc.， so that each path transmission time is not necessarily the same.When N path between two hosts transmission delay is not same， how to improve the transmission efficiency of CMT in broad-band network， is a focus in the study of this article.
Set by the SIGTRAN group 2011 SCTP （Stream Control Transmission Prorocol）[1][2]， effectively combine the advantage of TCP and UDP， and have multi-homing and multi-streaming properties.Working principle is to select a path as the main path for data transmission， the other path as the backup path， when the primary path fails， SCTP to select a backup route， as a new main path to transmit data.But there is no multiple concurrent transmission ability of SCTP.
In order to realize the network terminal equipment interface to access more features， put forward the CMT（Concurrent Multipath Transfer）[3]， CMT has multiple parallel transmission capacity， can adapt to host multiple access capability， provide multiple transmission lines between the host and at the same time， effectively improve the efficiency of the network.
2 Related Research
At present， the study of CMT are mainly concentrated in 1M-10M network， such as transmission delay， flow distribution， routing， retransmission strategy， etc.This paper mainly studies the CMT in 5M to 50M（broad-band network） the performance of the network. Using CMT for data transmission， the existing access devices A and B for more than two interfaces.Assumptions， equipment have n interface， A B is m interface， and then between A and B have n * m transmission path.Figure 1 is A simplified network model， only two paths between A and B， is advantageous for the simulation research in the future.
Is the sender of A， B is the receiver.The sender has two interface A1 and A2， A receiver B1 and B2 B has two interfaces.Path is a path between A1 and B1 1， namely path1；A2 and B2 path is a path between the two， namely path2.Path1 delay is D1， path2 delay is D2， assumptions， D1 than D2， namely D1>D2.
Path1 transmission quality is poor， if there is data through， take a long time to arrive at the receiver， or is due to the transmission time delay too long， within the prescribed period of time， not arrived at the receiving end， make the receiver that data loss.And path2 transmission of good quality， through the path of data as soon as possible， and arrive at the receiving end， there is no data delay arrival， or loss of data.
The background of the thesis， it is in high bandwidth （5-50 m） network within the scope of path1 and path2 transmission delay is not the same， D1>D2.In this case， how to improve the transmission efficiency and the feasibility analysis.
3 Problem Description
If the sending end of A buffer queue have 1-9 packets， the nine packet will by sending A，B， transmitted to the receiving end to path selection， determine the distribution of the nine packets， which packets by path1 transmission， which packets by path2 transmission， through the reasonable distribution of packet transmission scheme， to speed up the data transmission efficiency.As shown in figure 2.
At the B receiving end， packet 2， 3， 4 has arrived， and packet 1 haven’t reached， as shown in figure 4.So packets 2， 3， 4 just cached in the receive buffer of B， B， this is bound to take the receiving end of cache resources， reduce B can receive data cache， causing the deterioration of network performance.
Data for the second route choice， assuming that packet 5， choose path1；Packet 6， 7， 8， choose path2 transmission， as shown in figure 5.At this point， the packet 1 B haven’t reached the receiving end.
Due to the poor quality of transmission path1， packets haven’t reached 1 B， the second transmission of packets 6， 7， 8， has reached the B side， as shown in figure 6.B at this point， the receiving end of a buffer for the first time after path2 transmission of packets of 2， 3， 4；And， for the second time after path2 transmission of packets June， July and August.Due to packet loss of 1 and 5 B side rbuf data not up layer of the transfer. Wait for a period of time， by path1 transmission of packets 1， arrived at the receiving end B， as shown in figure 7.B are cached in the receiving end of packet 2， 3， 4， can be together with the packet 1， pass on a layer of a cross， at the same time， the receiving side B， also release packet 1 ～ 4 cache space.Release the space， can be arrived to hold the new data.
Shows， the poor quality of path1， seriously affect the performance of the system， take up the receiver B rbuf， make B arrived there is no more space to receive new data.So need to design a more suitable packet scheduling algorithm， scheduling packet routing， and calculating the distribution of each path data.
4 Conclusion
Research has shown that in high bandwidth network， when the path ShiYanXiang at the same time， increase the receive buffer， can improve the network performance；And when the time delay is not at the same time， increase the receive buffer， will not be able to increase network throughput.However， the actual network transmission environment， the path delay could not have all the same， there are many factors that can affect the time delay， such as sending end processing time， processing time delay， the receiving end back and forth， etc.， so the time delay is not at the same time， how can improve the efficiency of transmission， more research value.
References：
[1] Hung Y， Sieh H， Sivakumar R. A transport layer approach for achieving aggregate bandwidths on multihomed mobile hosts[J]. In Proc. ACM/IEEE MOBICOM. Atlanta， Georgia， USA. September 2002：83-94.
[2] Zhang M， Lai J， Krishnamurthy A， et a1. A transport layer approach for improving end-to-end performance and robustness using redundant paths[C]. Usenix Annual Technical Conference. Boston， MS， USA. June 2004.
[3] Iyengar J R， Amer P D ，Stewart R. Concurrent multipath transfer using SCTP multihoming over independent end-to-end paths [J]. IEEE/ACM Trans. On Networking ，2006，14（5）：951-964.