ndt-users list created

[Christian Reimsbach <>]

Hi,

I am trying to understand how outbound and inbound throughput are being calculated based on the WEB100 kernel variables.

I read Rich's answer to Lize saying that:

"The speeds reported in the Test Results section are the measured speed achieved during this test. The values reported in the More Details section are calculations of the maximum possible speed based on the buffer size and RTT. [...] The NDT report calculates the max possible speed by dividing the appropriate max buffer value (sender, receiver, congestion control) by the average RTT. The theoretical limit is calculated using the Mathis et.al. formula where speed is a function of packet size, RTT, and packet loss." 

I am still confused where in my case the 23.21Mb/s and 927kb/s (see below) come from. Or does Rich's answer mean that the "speeds reported in the Test Results section" cannot be derived out of the WEB100 variable?

Thanks!

Christian



WEB100 Enabled Statistics:
Checking for Middleboxes  . . . . . . . . . . . . . . . . . .  Done.
Checking for firewalls . . . . . . . . . . . . . . . . . . .  Done.
running 10s outbound test (client-to-server [C2S]) . . . . . 927.0kb/s
running 10s inbound test (server-to-client [S2C]) . . . . . . 23.21Mb/s

------  Client System Details------
OS data: Name = Linux, Architecture = amd64, Version = 2.6.32-25-generic
Java data: Vendor = Sun Microsystems Inc., Version = 1.6.0_20

------  Web100 Detailed Analysis  ------
Cable modem/DSL/T1 link found.
Link set to Full Duplex mode
Information: throughput is limited by other network traffic.
Good network cable(s) found
Normal duplex operation found.

Web100 reports the Round trip time =  21.57 ms; the Packet size = 1448 Bytes; and 
69 packets retransmitted, 369 duplicate acks received, and 373 SACK blocks received
The connection stalled 1 times due to packet loss
The connection was idle 0.23 seconds (2.3% of the time)
S2C throughput test: Packet queuing detected: 1.73%
This connection is network limited 99.6% of the time.

Web100 reports TCP negotiated the optional Performance Settings to: 
RFC 2018 Selective Acknowledgment: ON
RFC 896 Nagle Algorithm: ON
RFC 3168 Explicit Congestion Notification: OFF
RFC 1323 Time Stamping: ON
RFC 1323 Window Scaling: ON; Scaling Factors -  Server=7, Client=7

Server 'ndt.iupui.donar.measurement-lab.org' is not behind a firewall. [Connection to the ephemeral port was successful]
Client is probably behind a firewall. [Connection to the ephemeral port failed]
Information: Network Middlebox is modifying MSS variable
Server IP addresses are preserved End-to-End
Information: Network Address Translation (NAT) box is modifying the Client's IP address
Server says [85.168.247.43], but Client says [192.168.0.10]

WEB100 Kernel Variables:
Client: localhost/127.0.0.1
CurMSS: 1448
X_Rcvbuf: 87380
X_Sndbuf: 926744
AckPktsIn: 1854
AckPktsOut: 0
BytesRetrans: 99912
CongAvoid: 1074
CongestionOverCount: 0
CongestionSignals: 6
CountRTT: 1486
CurCwnd: 33304
CurRTO: 232
CurRwinRcvd: 776192
CurRwinSent: 5888
CurSsthresh: 17376
DSACKDups: 2
DataBytesIn: 0
DataBytesOut: 30157608
DataPktsIn: 0
DataPktsOut: 20384
DupAcksIn: 369
ECNEnabled: 0
FastRetran: 5
MaxCwnd: 403992
MaxMSS: 1448
MaxRTO: 1263
MaxRTT: 485
MaxRwinRcvd: 776192
MaxRwinSent: 5888
MaxSsthresh: 201272
MinMSS: 1448
MinRTO: 209
MinRTT: 4
MinRwinRcvd: 5888
MinRwinSent: 5792
NagleEnabled: 1
OtherReductions: 10
PktsIn: 1854
PktsOut: 20384
PktsRetrans: 69
RcvWinScale: 7
SACKEnabled: 3
SACKsRcvd: 373
SendStall: 0
SlowStart: 391
SampleRTT: 26
SmoothedRTT: 29
SndWinScale: 7
SndLimTimeRwin: 0
SndLimTimeCwnd: 10087802
SndLimTimeSender: 40308
SndLimTransRwin: 0
SndLimTransCwnd: 29
SndLimTransSender: 29
SndLimBytesRwin: 0
SndLimBytesCwnd: 29560040
SndLimBytesSender: 597568
SubsequentTimeouts: 0
SumRTT: 32048
Timeouts: 1
TimestampsEnabled: 1
WinScaleRcvd: 7
WinScaleSent: 7
DupAcksOut: 0
StartTimeUsec: 694357
Duration: 10132874
c2sData: 2
c2sAck: 2
s2cData: 8
s2cAck: 4
half_duplex: 0
link: 100
congestion: 1
bad_cable: 0
mismatch: 0
spd: 23.82
bw: 29.86
loss: 0.000294349
avgrtt: 21.57
waitsec: 0.23
timesec: 10.00
order: 0.1990
rwintime: 0.0000
sendtime: 0.0040
cwndtime: 0.9960
rwin: 5.9219
swin: 7.0705
cwin: 3.0822
rttsec: 0.021567
Sndbuf: 926744
aspd: 0.00000
CWND-Limited: 769.73
minCWNDpeak: 1448
maxCWNDpeak: 403992
CWNDpeaks: 6

The theoretical network limit is 29.86 Mbps
The NDT server has a 452.0 KByte buffer which limits the throughput to 327.83 Mbps
Your PC/Workstation has a 758.0 KByte buffer which limits the throughput to 274.58 Mbps
The network based flow control limits the throughput to 142.91 Mbps

Client Data reports link is 'T1', Client Acks report link is 'T1'
Server Data reports link is 'OC-48', Server Acks report link is 'T3'