文艾
摘要:針對移動互聯(lián)網(wǎng)環(huán)境下,基于TCP的文件傳輸軟件效率較低的問題,設計并實現(xiàn)了基于RS(Reed-Solomon)編碼的文件傳輸軟件。該軟件基于UDP協(xié)議,利用RS編碼的特性實現(xiàn)文件分塊傳輸?shù)那跋蚣m錯,可容忍一定范圍內(nèi)的數(shù)據(jù)丟失,無需重傳,可有效減少交互開銷,對超出糾錯范圍的分片數(shù)據(jù),利用重傳機制,保證可靠傳輸。實驗結果表明,在高誤碼率,大時延情況下,該軟件的傳輸性能(成功率、傳輸速率)相對傳統(tǒng)的文件傳輸軟件顯著提升。
關鍵詞:RS編碼;文件傳輸;移動互聯(lián)網(wǎng)
中圖分類號:TP393.093 文獻標識碼:A 文章編號:1009-3044(2014)29-6834-05
Abstract: In view of the low efficiency of file transfer software based on TCP in mobile internet environment, a new file transfer software based on RS(Reed-Solomon) code was designed and implemented. The software is based on UPD protocol and it takes advantage of RS code to achieve FEC(forward error correction) of file block transfer. This characteristic can make the software to tolerate a range of block loss and no need to repeat, so it can reduce the communication overhead effectively. For the data which exceeds the error correction range, the retransmission mechanism is used to ensure the reliable transmission. The result of experiment shows that, under the condition of high error rate and long time delay, the transfer performance of the software(success rate, transfer speed)is significantly better than traditional file transfer software.
Key words: RS code; file transfer; mobile internet environment
文件傳輸是一項非常重要的網(wǎng)絡應用。傳統(tǒng)的文件傳輸軟件,如FTP等,通常采用TCP協(xié)議,TCP是面向連接的運輸層協(xié)議,它可以實現(xiàn)數(shù)據(jù)的按序、可靠傳輸。TCP最初是針對有線網(wǎng)絡設計的,該網(wǎng)絡的特點是:低時延、低誤碼率。而在移動互聯(lián)網(wǎng)環(huán)境下,情形相反,大時延,高誤碼率是其特點。TCP原有的一些設計并不能很好地適應這一新的網(wǎng)絡環(huán)境,導致效率低下。其中,TCP協(xié)議的重傳機制和擁塞控制機制是導致其在移動互聯(lián)網(wǎng)環(huán)境下效率低下的兩個主要原因,分析如下。
首先,TCP協(xié)議使用重傳機制來實現(xiàn)數(shù)據(jù)的可靠傳輸。TCP會自動對發(fā)送方所發(fā)出的數(shù)據(jù)進行編號,并且啟動計時器,如果在規(guī)定的時間內(nèi),未收到接收方對該數(shù)據(jù)的ACK,便會觸發(fā)計時器,自動重發(fā)數(shù)據(jù)。如果重傳次數(shù)超過系統(tǒng)所設定的閾值,TCP協(xié)議棧會向上層報告?zhèn)鬏斒 τ谝淮纬晒Φ臄?shù)據(jù)傳輸,包括數(shù)據(jù)發(fā)送和ACK成功兩個部分,缺一不可。……