Modeling TCP Throughput: A Simple Model and its Empirical Validation

Transcription

1 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton Jtendra Padhye, Vctor Frou, Don Towsley, Jm Kuros Presenter: Ognjen Vukovc

2 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton Motvaton Steady state throughut for ulk transfer TCP flow o Loss rate o Round tr tme Model catures o Fast retransmt mechansm (related work o Tmeout mechansm o Small recever-sde wndows Model s ased on TCP Reno

3 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton Outlne TCP/TCP Reno Model Descrton Model and xermental Results Concluson and Future ork

4 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 4 TCP Congeston control one of the man TCP asects o Slow-start, congeston avodance o Fast retransmt, fast recovery Slow-start o Starts wth the exonental growth hase o TCP congeston control wndow sze o Increases for each successful ACK receved o Untl a acket loss or the threshold s reached o Congeston avodance lnear growth hase

5 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton TCP Reno Congeston avodance o ncreases y / for each ACK receved o Delayed ACK one ACK for ackets o decreases for each lost acket o Dulcate ACKs or tmeouts Dulcate ACKs o = / o Fast retransmt followed y fast recovery Fast recovery o ats for acknowledgment of the entre transmt wndow o Congeston avodance o Slow start 5

6 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton Throughut and acket loss Throughut o TCP flow starts at t=0 where sender always sends o For any t>0, N t s the numer of transmtted ackets n 0,t o Long-term steady state TCP throughut B lm Packet loss t o If a acket s lost n a round, all consecutve ackets are also lost Router uffer o the roalty that a acket s lost o The roalty does not deend on the wndow sze N t o Goal s to estalsh a relatonsh B( t 6

7 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 7 Trle-dulcate ACK TDP a erod etween two TD loss ndcatons Y numer of ackets sent n TDP erod A duraton of the erod, wndow sze In ths case t holds: B e must exress Y and A Y A

8 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 8 Y α frst acket lost n TDP round where the lost occurs o After acket α, - more ackets are sent efore TD occurs o In + rounds we have Y o Therefore, Y ackets sent

9 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 9 Y, α o Consder a random rocess { } o Packet loss s round ndeendent o { } s a sequence of ndeendent and dentcally dstruted random varales P k ( k ( k, k,,... k k k- successfully acknowledged ackets Y

10 A Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 0 ( r A o r j round tr tme of the j-th round o r j are random varales, ndeendent of the congeston wndow sze (and the round numer j r the average value of round tr tme j A r j o The duraton of TDP s,,..., k k Y / 0 ( ( Y ( β numer of ackets sent n the last round

11 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton o Assumton: { } and { } are mutually ndeendent sequences of ndeendent and dentcally dstruted random varales,,..., Y ( Y β unformly dstruted etween and : 8( 8 for small

12 Long-term steady state TCP throughut Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 6 ( 6 6 ( 6 RTT A ( r A 8( o From,, and o 6 ( 6 8( ( RTT A A Y B o RTT B (

13 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton Model extensons TCP sender tmes-out The mact of wndow lmtaton (recever wndow

14 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 4 Model and xermental Results Measurements o 7 TCP connectons etween 8 hosts across Unted States and uroe o One hour long TCP connectons where sender s an nfnte source o = total numer of loss ndcatons / total numer of ackets sent o One hour sesson dvded nto 6 consecutve 00 second ntervals

15 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 5 Model and xermental Results o TD Only Model s closer to actual data for smaller P o Full roosed model etter descres the actual data than TD only

16 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton 6 Concluson A smle model of the TCP-Reno rotocol Congeston avodance ehavor Model rovdes a very good match to the oserved ehavor n most cases Throughut s overestmated wthout caturng tmeout mechansm and the mact of wndow lmtatons (recever-sde wndow. Future work: fast recovery and fast retransmt

17 Modelng TCP Throughut: A Smle Model and ts mrcal Valdaton Jtendra Padhye, Vctor Frou, Don Towsley, Jm Kuros Presenter: Ognjen Vukovc