Advanced Internet Research Wim Sjouw Santiago de Compostela 14 February 2003.

Advanced Internet Research Wim Sjouw Santiago de Compostela 14 February 2003


TCP behavior

on

Trans-Atlantic lambda’s

Wim Sjouw, Antony Antony, Hans Blom, Cees de Laat, Jason Lee

EU - IST DataTag project, WP3


LFNT


Long:

RTT > 50 msec


FAT

B > 622 Mbps


Surprise Surprise

Surprise Surprise

TCPthroughput

90 Mbps


UDPmon

Probe the network with trains of UDP packets

Packets are: numbered & time stamped

• variable number of packets• varable packet length• variable inter packet delay


UDPmon


Very precise timing with Pentium proc. clock

Packets are: numbered & time stamped

• number of packets: 5000• packet length: 1000 Bytes• inter packet delay: 0 μsec


UDPmon


Timing: 10 ns


UDPmon


Nb = 1500 Nd = 0 l = 1000

f = 1 Gbps s = 622 Mbps

then M = 0.5 MB


R = 100 ms


Back to TCP

TCP is bursty due to:

• sliding window protocol • slow start algorithm


W= sent segments

Y= advertised window

G= ACK’s

R= retransmits

P= SACK’s


512 packets in 4 ms


So overall pick from this menu:

• flow control

• traffic shaping

• RED (Random Early Discard)


Receiver:

• buffer capacity of NIC

• interupt latency & coalescence

• interupt overhead

• PCI bus width and PCI bus speed

• TCP stack overhead & complexity

• OS overhead


< Mac OS

< Linux


Conclusions:

• ‘old’ TCP does not perform in a “Long Fat Network”

• UDP does perform, but unacceptable

• End system(s) dictate overall performance:

o O.S

o Memory

o NIC


beware of


Thanks!

http://www.science.uva.nl/research/air/


UDPmon:

www.hep.man.ac.uk/~rich/net

Richard Hughes Johnes

Advanced Internet Research Wim Sjouw Santiago de Compostela 14 February 2003.

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