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TCP茻茳å¶åŸ¡ã¢ã«ãŽãªãºã ã®é²å
TCPã®èŒ»èŒ³å¶åŸ¡ã¯é·å¹Žã«ããã£ãŠå€§å¹ ã«é²åããŠãããããããã®æ°ããã¢ã«ãŽãªãºã ã¯å è¡ãããã®ã®éçã«å¯ŸåŠããŠããŸãããããã§ã¯ãããã€ãã®éèŠãªãã€ã«ã¹ããŒã³ãèŠãŠã¿ãŸãããïŒ
1. TCP Tahoe (1988幎)
TCP Tahoeã¯ã茻茳å¶åŸ¡ã®æãåæã®å®è£ ã®äžã€ã§ãããããã¯2ã€ã®åºæ¬çãªã¡ã«ããºã ãå°å ¥ããŸããïŒ
- ã¹ããŒã¹ã¿ãŒãïŒ éä¿¡åŽã¯æåã«å°æ°ã®ãã±ããïŒèŒ»èŒ³ãŠã£ã³ããŠããŸãã¯cwndïŒãéä¿¡ããŸãããã®åŸããã±ãããã¹ãæ€åºããããããããå€ã«éãããŸã§ãcwndã¯ææ°é¢æ°çã«å¢å ããŸãã
- 茻茳åé¿ïŒ ãããå€ã«éããåŸãcwndã¯ç·åœ¢çã«å¢å ããŸãããã±ãããã¹ãçºçãããšãcwndã¯ååã«ãªããã¹ããŒã¹ã¿ãŒãã«åçªå ¥ããŸãã
éçïŒ TCP Tahoeã®ãã±ãããã¹ã«å¯Ÿããç©æ¥µçãªåå¿ã¯ãç¹ã«ã©ã³ãã ãªãã±ãããã¹ããããããã¯ãŒã¯ïŒäŸïŒç¡ç·å¹²æžã«ãããã®ïŒã§ã¯ãäžå¿ èŠãªcwndã®åæžã«ã€ãªããå¯èœæ§ããããŸããããŸãããè€æ°ãã±ãããã¹ãåé¡ã«ãæ©ãŸãããåäžãŠã£ã³ããŠå ã§ã®è€æ°ãã±ããã®ãã¹ãéå°ãªããã¯ãªããåŒãèµ·ãããŸããã
2. TCP Reno (1990幎)
TCP Renoã¯ãé«éåéããã³é«éå埩ã¡ã«ããºã ãå°å ¥ããããšã§ãTCP Tahoeã®ããã€ãã®éçã«å¯ŸåŠããŸããïŒ
- é«éåéïŒ éä¿¡åŽãåãã·ãŒã±ã³ã¹çªå·ã«å¯ŸããŠ3ã€ã®éè€ACKïŒç¢ºèªå¿çïŒãåä¿¡ããå Žåããã®ãã±ããã倱ããããšã¿ãªããã¿ã€ã ã¢ãŠããåŸ ããã«å³åº§ã«åéããŸãã
- é«éååŸ©ïŒ é«éåéã®åŸãéä¿¡åŽã¯é«éå埩ãã§ãŒãºã«å ¥ããåä¿¡ããéè€ACKããšã«cwndã1ã»ã°ã¡ã³ãåå¢å ãããŸããããã«ãããéä¿¡åŽã¯åéãããã»ã°ã¡ã³ãã®ACKãåŸ ã€éãæ°ããããŒã¿ãéä¿¡ãç¶ããããšãã§ããŸãã
å©ç¹ïŒ TCP Renoã¯ãcwndãäžå¿ èŠã«åæžããããšãªããåäžã®ãã±ãããã¹ããè¿ éã«å埩ããããšã§ããã©ãŒãã³ã¹ãåäžãããŸããã
éçïŒ TCP Renoã¯äŸç¶ãšããŠè€æ°ãã±ãããã¹ã«èŠãã¿ãé«åž¯åå¹ ãé«é å»¶ã®ç°å¢ïŒäŸïŒè¡æãããã¯ãŒã¯ïŒã§ã¯ããã©ãŒãã³ã¹ãæªãã£ãã§ãããŸããæ°ãã茻茳å¶åŸ¡ã¢ã«ãŽãªãºã ãšç«¶åããéã®äžå ¬å¹³ãã瀺ããŸããã
3. TCP NewReno
TCP NewRenoã¯Renoã®æ¹è¯çã§ãããç¹ã«åäžãŠã£ã³ããŠå ã§ã®è€æ°ãã±ãããã¹ãããããŸãåŠçããããã«èšèšãããŠããŸãããã¹ãçºçãããšãã«é«éååŸ©ãæ©æã«çµäºããªãããã«ãé«éå埩ã¡ã«ããºã ã倿ŽããŸãã
4. TCP SACK (Selective Acknowledgment)
TCP SACKïŒéžæç確èªå¿çïŒã¯ãåä¿¡åŽãæ£ããåä¿¡ãããéé£ç¶ã®ããŒã¿ãããã¯ã確èªå¿çã§ããããã«ããŸããããã«ãããã©ã®ãã±ããã倱ããããã«ã€ããŠéä¿¡åŽã«ããè©³çŽ°ãªæ å ±ãæäŸãããããå¹ççãªåéãå¯èœã«ãªããŸããSACKã¯ãRenoãNewRenoãšçµã¿åãããŠäœ¿çšãããããšããããããŸãã
5. TCP Vegas
TCP Vegasã¯ãRTT枬å®ã䜿çšããŠãã±ãããã¹ãçºçãã*å*ã«èŒ»èŒ³ãæ€åºãããé å»¶ããŒã¹ã®èŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ã§ããæåŸ ãããRTTãšå®éã®RTTã®å·®ã«åºã¥ããŠéä¿¡ã¬ãŒãã調æŽããŸãã
å©ç¹ïŒ TCP Vegasã¯äžè¬çã«Renoã®ãããªãã¹ããŒã¹ã®ã¢ã«ãŽãªãºã ãããå®å®ããŠãããæ¯åãå°ãªãã§ãããŸããç¹å®ã®ãããã¯ãŒã¯æ¡ä»¶äžã§ã¯ããé«ãã¹ã«ãŒããããéæã§ããŸãã
éçïŒ TCP Vegasã¯RenoãããŒã«å¯ŸããŠäžå ¬å¹³ã«ãªãå¯èœæ§ãããããã®ããã©ãŒãã³ã¹ã¯å¿ ããã茻茳ã瀺ãããã§ã¯ãªãRTTã®å€åã«ææã«ãªãããšããããŸãã
6. TCP CUBIC (2008幎)
TCP CUBICã¯ãé«éãããã¯ãŒã¯åãã«èšèšããããåºãå°å ¥ãããŠãããŠã£ã³ããŠããŒã¹ã®èŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ã§ãã3æ¬¡é¢æ°ã䜿çšããŠèŒ»èŒ³ãŠã£ã³ããŠãµã€ãºã調æŽãããããã¯ãŒã¯ãååã«å©çšãããŠããªãå Žåã¯ããç©æ¥µçã«åž¯åå¹ ãå¢å ãããèŒ»èŒ³ãæ€åºãããå Žåã¯ããä¿å®çã«æžå°ãããŸãã
å©ç¹ïŒ TCP CUBICã¯ãé«åž¯åå¹ ç°å¢ã§ã®ã¹ã±ãŒã©ããªãã£ãšå ¬å¹³æ§ã§ç¥ãããŠããŸããLinuxã®ããã©ã«ãã®èŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ã§ãã
7. TCP BBR (Bottleneck Bandwidth and RTT) (2016幎)
TCP BBRã¯ãGoogleã«ãã£ãŠéçºãããæ¯èŒçæ°ãã茻茳å¶åŸ¡ã¢ã«ãŽãªãºã ã§ããã¢ãã«ããŒã¹ã®ã¢ãããŒãã䜿çšãããããã¯ãŒã¯ãç©æ¥µçã«ãããŒãããŠããã«ããã¯åž¯åå¹ ãšã©ãŠã³ãããªããã¿ã€ã ãæšå®ããŸããBBRã¯ãéä¿¡ã¬ãŒããšãã±ããã®ããŒã·ã³ã°ãæ éã«å¶åŸ¡ããããšã§ãé«ã¹ã«ãŒããããšäœé å»¶ãéæããããšãç®æããŠããŸãã
å©ç¹ïŒ TCP BBRã¯ãé«åž¯åå¹ ãé«é å»¶ç°å¢ãããŒã¹ãçãªãã©ãã£ãã¯ããããããã¯ãŒã¯ãªã©ãæ§ã ãªãããã¯ãŒã¯æ¡ä»¶äžã§åŸæ¥ã®èŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ãšæ¯èŒããŠåªããããã©ãŒãã³ã¹ã瀺ããŠããŸãããã±ãããã¹ãRTTã®å€åã«å¯ŸããŠå ç¢ã§ããããã«èšèšãããŠããŸãã
ç°ãªããããã¯ãŒã¯ç°å¢ã«ããã茻茳å¶åŸ¡
ç°ãªã茻茳å¶åŸ¡ã¢ã«ãŽãªãºã ã®ããã©ãŒãã³ã¹ã¯ããããã¯ãŒã¯ç°å¢ã«ãã£ãŠå€§ããç°ãªãããšããããŸãã垯åå¹ ãé å»¶ããã±ãããã¹çããã©ãã£ãã¯ãã¿ãŒã³ãªã©ã®èŠå ããåã¢ã«ãŽãªãºã ã®æå¹æ§ã«åœ±é¿ãäžããå¯èœæ§ããããŸãã
1. æç·ãããã¯ãŒã¯
æ¯èŒçå®å®ãã垯åå¹ ãšäœããã±ãããã¹çãæã€æç·ãããã¯ãŒã¯ã§ã¯ãTCP CUBICã®ãããªã¢ã«ãŽãªãºã ãäžè¬çã«è¯å¥œãªããã©ãŒãã³ã¹ãçºæ®ããŸããããããæç·ãããã¯ãŒã¯ã§ãã£ãŠãããªãŒããŒãµãã¹ã¯ãªãã·ã§ã³ãããŒã¹ãçãªãã©ãã£ãã¯ã«ãã£ãŠèŒ»èŒ³ãçºçããããšããããŸããBBRã¯ããããã¯ãŒã¯ãç©æ¥µçã«ãããŒãããå€åããç¶æ³ã«é©å¿ããããšã§ããããã®ç¶æ³ã§ããã©ãŒãã³ã¹ãåäžãããããšãã§ããŸãã
äŸïŒ é«éã€ãŒãµãããæ¥ç¶ãåããããŒã¿ã»ã³ã¿ãŒç°å¢ã§ã¯ãTCP CUBICã茻茳å¶åŸ¡ã®äžè¬çãªéžæè¢ã§ãããããããªã¢ã«ã¿ã€ã ããŒã¿åæã忣ããŒã¿ããŒã¹ãªã©ãäœé å»¶ãšé«ã¹ã«ãŒããããå¿ èŠãšããã¢ããªã±ãŒã·ã§ã³ã«ã¯BBRãæçãªå ŽåããããŸãã
2. ç¡ç·ãããã¯ãŒã¯
ç¡ç·ãããã¯ãŒã¯ã¯ãæç·ãããã¯ãŒã¯ãšæ¯èŒããŠãããé«ããã±ãããã¹çãšããå€åã®å€§ããé å»¶ãç¹åŸŽãšããŸããããã¯ã茻茳ã®äž»èŠãªææšãšããŠãã±ãããã¹ã«äŸåããåŸæ¥ã®èŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ã«ãšã£ãŠèª²é¡ãšãªããŸãããã±ãããã¹ã«å¯ŸããŠããå ç¢ãªBBRã®ãããªã¢ã«ãŽãªãºã ã¯ãç¡ç·ç°å¢ã§ããè¯ãããã©ãŒãã³ã¹ãæäŸã§ããŸãã
äŸïŒ 4Gã5Gãªã©ã®ã¢ãã€ã«ãããã¯ãŒã¯ã§ã¯ãç¡ç·å¹²æžãã¢ããªãã£ã«ããããã°ãã°é倧ãªãã±ãããã¹ãçºçããŸããBBRã¯ãããå®å®ããæ¥ç¶ãç¶æãããããªã¹ããªãŒãã³ã°ããªã³ã©ã€ã³ã²ãŒã ãªã©ã®ã¢ããªã±ãŒã·ã§ã³ã®é å»¶ãæžããããšã§ããŠãŒã¶ãŒãšã¯ã¹ããªãšã³ã¹ãåäžãããã®ã«åœ¹ç«ã¡ãŸãã
3. é«é å»¶ãããã¯ãŒã¯
è¡æãããã¯ãŒã¯ãå€§éžæšªææ¥ç¶ãªã©ã®é«é å»¶ãããã¯ãŒã¯ã¯ã茻茳å¶åŸ¡ã«ç¹æã®èª²é¡ãæç€ºããŸããé·ãRTTã¯ãéä¿¡è ã茻茳信å·ã«è¿ éã«åå¿ããã®ãããå°é£ã«ããŸããããã«ããã¯åž¯åå¹ ãšRTTãæšå®ããBBRã®ãããªã¢ã«ãŽãªãºã ã¯ããã±ãããã¹ã®ã¿ã«äŸåããã¢ã«ãŽãªãºã ããããããã®ç°å¢ã§å¹æçã§ããå¯èœæ§ããããŸãã
äŸïŒ å€§è¥¿æŽæšªæå ãã¡ã€ããŒã±ãŒãã«ã¯ããšãŒããããšåç±³ãçµãã§ããŸããç©ççãªè·é¢ãçžåœãªé å»¶ãçã¿åºããŸããBBRã¯ãå€ãTCPããŒãžã§ã³ãšæ¯èŒããŠãããé«éãªããŒã¿è»¢éãšããè¯ããŠãŒã¶ãŒãšã¯ã¹ããªãšã³ã¹ãå¯èœã«ããŸãã
4. 茻茳ãããããã¯ãŒã¯
éåžžã«èŒ»èŒ³ãããããã¯ãŒã¯ã§ã¯ãç«¶åãããããŒéã®å ¬å¹³æ§ãç¹ã«éèŠã«ãªããŸããäžéšã®èŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ã¯ä»ãããæ»æçã§ããå¯èœæ§ãããã垯åå¹ ã®äžå ¬å¹³ãªå²ãåœãŠã«ã€ãªããããšããããŸããå ¬å¹³æ§ãä¿ã¡ãåã ã®ãããŒã®æ¯æžãé²ãããã«èšèšãããã¢ã«ãŽãªãºã ãéžæããããšãéèŠã§ãã
äŸïŒ ããŒã¯æã«ã¯ãè€æ°ã®ãããã¯ãŒã¯ããã©ãã£ãã¯ã亀æãããããã€ã³ã¿ãŒããããšã¯ã¹ãã§ã³ãžãã€ã³ãïŒIXPïŒã茻茳ããããšããããŸãã茻茳å¶åŸ¡ã¢ã«ãŽãªãºã ã¯ããã¹ãŠã®ãããã¯ãŒã¯ã垯åå¹ ã®å ¬å¹³ãªåãåã確å®ã«åãåãäžã§éèŠãªåœ¹å²ãæãããŸãã
TCPæé©åã®ããã®å®è·µçãªèæ ®äºé
TCPããã©ãŒãã³ã¹ã®æé©åã«ã¯ãé©åãªèŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ã®éžæãTCPãã©ã¡ãŒã¿ã®èª¿æŽããããã¯ãŒã¯ã¬ãã«ã®æé©åã®å®è£ ãªã©ãæ§ã ãªèæ ®äºé ãå«ãŸããŸãã
1. é©åãªèŒ»èŒ³å¶åŸ¡ã¢ã«ãŽãªãºã ã®éžæ
茻茳å¶åŸ¡ã¢ã«ãŽãªãºã ã®éžæã¯ãç¹å®ã®ãããã¯ãŒã¯ç°å¢ãšã¢ããªã±ãŒã·ã§ã³èŠä»¶ã«äŸåããŸããèæ ®ãã¹ãããã€ãã®èŠå ã¯æ¬¡ã®ãšããã§ãïŒ
- ãããã¯ãŒã¯ç¹æ§ïŒ 垯åå¹ ãé å»¶ããã±ãããã¹çããã©ãã£ãã¯ãã¿ãŒã³ã
- ã¢ããªã±ãŒã·ã§ã³èŠä»¶ïŒ ã¹ã«ãŒããããé å»¶ãå ¬å¹³æ§ãå®å®æ§ã
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æšå¥šäºé ïŒ äžè¬çãªçšéã«ã¯ãTCP CUBICãå å®ãªéžæã§ãã髿§èœã¢ããªã±ãŒã·ã§ã³ãå°é£ãªç¹æ§ãæã€ãããã¯ãŒã¯ã«ã¯ãBBRãå€§å¹ ãªæ¹åãããããå¯èœæ§ããããŸãã
2. TCPãã©ã¡ãŒã¿ã®èª¿æŽ
åæèŒ»èŒ³ãŠã£ã³ããŠïŒinitcwndïŒãæå€§ã»ã°ã¡ã³ããµã€ãºïŒMSSïŒãTCPãããã¡ãµã€ãºãªã©ã®TCPãã©ã¡ãŒã¿ã¯ãããã©ãŒãã³ã¹ãæé©åããããã«èª¿æŽã§ããŸãããã ãããããã®ãã©ã¡ãŒã¿ããããã¯ãŒã¯ã®å®å®æ§ãšå ¬å¹³æ§ã«äžãã圱é¿ãæ éã«èæ ®ããããšãéèŠã§ãã
äŸïŒ åæèŒ»èŒ³ãŠã£ã³ããŠãå¢ãããšãçåœãªæ¥ç¶ã®åæã¹ã«ãŒããããåäžããå¯èœæ§ããããŸãããããããããã¯ãŒã¯ããã§ã«éãè² è·ãããŠããå Žåã茻茳ã®ãªã¹ã¯ãé«ãŸããŸãã
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