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All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 1-
Transport-layer optimizationfor thin-client systems
Yukio OGAWASystems Development Laboratory, Hitachi, Ltd.
E-mail: [email protected]
Go HASEGAWA, Masayuki MURATAOsaka University
2007 International CQR WorkshopMay 15-17, 2007
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 2-
Overview of thin-client systems
office
Internet
data center
thin client
intranet
VPN gateway
server
satellite office, home, ‥
desktop service
without data, apps
thin client
user event
screen updates
Isolating computer resources from users
resource management, user mobility
System performancedepends on network performance
VPN: Virtual Private Network
TCP proxy
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 3-
Research objective and our approach
System performance (usability) depends on network performance. - intranet performance – designed in advance, controllable - Internet performance – uncontrollable
Improve performance of thin-client traffic - especially of flows traversing Internet - thin-client traffic = long-lived interactive TCP data flows - affected by TCP's Nagle algorithm and delayed ACK
- affected by buffering of TCP segments and SSR
Transport layer optimization on basis of actual traffic observations - observation of Hitachi SDL's prototype system - Dec. 20, 2006 to Jan. 25, 2007 - 168 pairs of a server and a thin-client - number of co-existing sessions during office hours: several dozen
research objective
drawback
our approach
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 4-
Characteristics of thin-client traffic- traffic patterns
client server
time time
request
response
large interval
interactive data flow(character information)
client server
time time
bulk data flow(screen update information)
request
response
•distinguished by interarrival time of response packets
size of data segment
time
MSSm ( n MSS + a )
MSS: Maximum Segment Size
•~102
packets•short interval
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 5-
Characteristics of thin-client traffic- interarrival time distribution of request packets
data
segm
ent
size
(lo
g10 b
yte
s)
access from Internet
interarrival time of request packets (log10 sec)-6 -5 -4 -3 -2 -1 0 1 2 3
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 6-
Characteristics of thin-client traffic- interarrival time distribution of response packets
data
segm
ent
size
(lo
g10 b
yte
s)
access from Internet
interarrival time of response packets (log10 sec)-6 -5 -4 -3 -2 -1 0 1 2 3
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.010-2.2( 6.3 m) sec
interactive
bulk (head)
bulk (inside of 'nMSS+a')
bulk(head of 'nMSS+a')
data segment size
time
MSShead
inside
head of 'nMSS+a'inside of 'nMSS+a'
bulk
interactive
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 7-
Proposed methods for improving performance- interactive data flow
client server
time time
request
response
gateway (TCP proxy)
×
Ti
ti
sending copy of data packet
sending interval :
ti = min( RTT – RTTmin , Ti / 2 )
1h
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 8-
Proposed methods for improving performance- bulk data flow
client server
time time
gateway (TCP proxy)
requestresponse
no SSR
data segment size
time
MSSm ( n MSS + a )
data segment size
time
MSSn MSS + a
MSS: Maximum Segment SizeSSR: Slow-Start Restartpaused for buffering
resegmenting TCP data segments
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 9-
Simulation model- system model
R
R
R router
20 Mbps, 5 msec
sender host(server)
gateway(TCP proxy)
receiver host(client)
20 Mbps, 0.1 msec
1 Mbps, 30 – 300 msec
100 Mbps, 0.1 msec
intranet
Internet
receiver hosts
sender hosts
thin-client traffic
background traffic(UDP: 64 bytes, 128 Kbps) x n
packet drop ratio: 0, 3%
tail-drop router(buffer size : 50, 1024 packets)
bottleneck link
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 10-
Simulation model- thin-client traffic for evaluation
interactive
bulk(-0.6, -1.3) : -1.3 = mean - 2 std
(-0.6, -0.6)
access from Internet
aver
age
inte
rarr
ival
tim
e of
resp
onse
pac
kets
(log
10 s
ec )
evaluation traffic•number : 30•duration : 60 sec
-6 -5average interarrival time of response data flows (contiguous packets) (log10 sec)
-4 -3 -2 -1 0 1 2 3
-5
-4
-3
-2
-1
0
1
2
-6
3
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 11-
Simulation results- interactive data flow – packet drop
avera
ge n
um
ber
of
pack
et
dro
ps
(log
10
)
transmission delay of bottleneck link (log10 msec)
(UDP 1024 Kbps)
(UDP 1152 Kbps)
(UDP 1280 Kbps)
bottleneck link - 1 Mbps - 3% drop ratiorouter buffer - 50 packets
send a copy with pause
send a copy without pause
send no copies
bg: background
102
100
10-1
101
101 102 103 101 102 103 101 102 103
102
100
10-1
101
102
100
10-1
101
drop from tail-drop router
random drop from bottleneck link
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 12-
Simulation results- bulk data flow – transfer time
med
ian
tra
nsf
er
tim
e (
log
10
sec)
number of packets in bulk data flow (log10)
buffer size = 1024 packets
bottleneck link - 1 Mbps - 80 msec - 0% drop ratiobackground - 3 UDP flows (= 384 Kbps)
no-SSR, resegmentationno-SSR
101
100
10-1
10-2
101
100
10-1
10-2
100 101 100 101
buffer size = 50 packetsSSR, resegmentation
SSR
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 13-transmission delay of bottleneck link (log10 msec)
Simulation results- bulk data flow – drop from tail-drop router
(UDP 384 Kbps)
no-SSR, resegmentationno-SSR
SSR, resegmentationSSR
bottleneck link - 1 Mbps - 0% drop ratiorouter buffer - 50 packets
(UDP 768 Kbps)
bg: background
avera
ge n
um
ber
of
pack
et
dro
ps
(log
10
)102
101
10-1
10-2
100
102
101
100
101 102 103101 102 103
All Rights Reserved, Copyright(C) 2007, Hitachi, Ltd.- 14-
Conclusion
•for interactive data flows (transferring character information) - send a packet copy with pause
⇒ increases tolerance for packets drops
•for bulk data flows (transferring screen update information) - disable TCP slow-start restart
⇒ increases packet sending rate⇒ increases burstiness of traffic
- resegment TCP data segments⇒ reducees burstiness of traffic
TCP optimization for improving performance of thin-client traffic