Data Center TCP

1. DCTCP
Data Center TCP
Oded Rotter
oded1233@gmail.com
Based On:
Microsoft Research Stanford University
http://www.stanford.edu/~alizade/Site/DCTCP.html

2. ‫‪TCP‬‬
‫• שכבת ה- ‪ Transport‬המשמעותית ב-‪Data Center‬‬
‫• פופולארי וידוע‬
‫• לא מושלם ....‬

3. ‫דרישות מ-‪ TCP‬בסביבת ‪Data Center‬‬
‫(חשוב מאוד שיתקיימו יחד)‬
‫• התמודדות עם התפרצויות רגעיות של תעבורה‬
‫• שיהוי נמוך‬
‫• ‪ Throughput‬גבוה‬

4. DCTCP is an enhancement to the TCP congestion
control algorithm for data center networks. It
leverages Explicit Congestion Notification (ECN), a
feature which is increasingly becoming available in
modern data center switches. DCTCP sources extract
multi-bit feedback on congestion from the single-bit
stream of ECN marks by estimating the fraction of
marked packets. In doing so, DCTCP sources react to
the extent of congestion, not just the presence of
congestion as in TCP. This finer level of control allows
DCTCP to operate with very low buffer occupancies
while simultaneously achieving high throughput.

5. How …
• Maintain small queues, without loss of
throughput
• Buffer sizing problem :
• A single flow needs buffers for 100%
Throughput.
• Large # of flows: is enough.

6. Data Center TCP Algorithm
B K Don’t
Switch side: Mark
Mark
– Mark packets when Queue Length > K.
Sender side:
– Maintain running average of fraction of packets marked (α).
In each RTT:
 Adaptive window decreases:
– Note: decrease factor between 1 and 2.
19

7. ... ‫סבלנות, עוד קצת גראפים‬
Packets sent in this
Window Size RTT are marked.
W*+1
W*
(W*+1)(1-α/2)
Time
85% Less Buffer than TCP

8. ‫לסיכום‬
‫• ‪ DCTCP‬עונה על הדרישות שלנו‬
‫• אין שינוי מהותי ב-‪TCP‬‬
‫• המתגים מסוגלים לבצע זאת בחומרה קיימת‬
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