NDT-DEV email list created

[Richard Carlson <>]

Don;

I put the data into the attached spread sheet and sorted the variables 
to do a side-by-side comparison.

First off, the collected data comes from the server-to-client test 
(download).  This means we have some insights but to get more you'll 
need to turn on packet tracing on the server and look at that data off-line.

I'll try and look at the code later this weekend, I still suspect that 
there is a 10x math error in the code that is calculating the upload speed.

In any case I do see that the websocket client is not working as well as 
it should.  As noted in the spreadsheet.

The 1st think I notice is that the both clients are setting (or not 
setting) the TCP options to the same values, except that the flash 
client is using a slightly small receive window.

The websocket client has a theoretical max speed of 311 Mbps, and 
achieves 488 Mbps (or 491 Mbps).  The theoretical value is calculated 
based on the packet size, RTT, and loss rate.  The server noted a loss 
rate of 0 for the flash client and .0000235%.  While that doesn't seem 
like a lot, it does make a big difference on 20 msec paths.  Since you 
wouldn't expect the network loss rate to vary between these 2 tests, I 
would suspect that the client is losing packets.  That is, it can't 
empty the buffer fast enough and packets are dropped.

Next I notice that both clients report the path is an OC-48 (2.4 Gbps) 
path.  The server performs a packet-pair test for every packet it sends 
and receives.  During both test the network is delivering packets at 
line speed (or nearly so)  So I don't suspect a physical path problem.

I also notice that the websocket client reports the PC's receive buffr 
as limiting the throughput to 'NaN Mbps'.  NaN means 'Not a Number' so I 
suspect a bug in the client code not calculating this value correctly.

Looking at the Web100 variables I see the following.

avgrtt (Average RTT) 23.3 msec for both clients

bw (theoretical max) websocket client is limited by loss

CongAvoid (number of times the congestion window was increased by the
congestion avoidance algorithm) Websocket - 120,998: This says that TCP 
was in the congestion avoidance state for a long time! In this state the 
server is increasing the number of packets it sends by 1 every RTT.  A 
very slow process on a 20 msec path and this is another indication of 
why the throughput is so low.

CWNDpeaks: this is a NDT derived number counting the number of time the 
congestion window increased and then dropped back down again.  This is 
what gives TCP its classic sawtooth pattern.  These are the peaks of the 
teeth.  If you have the snaplog option on, you can generate a congestion 
window plot and see these peaks.  Notice that the flash client has 52 
peaks, meaning it is cycling much faster.

loss: again a NDT derived value showing the packet loss rate.

order: another NDT derived value showing how many times packets arrived 
out of order.  The websocket client reported 1.65%.  Again this is 
probably inside the client as it is losing multiple packets.

SndLimTrans{Cwnd, Rwin, Sender}: these are web100 variables that count 
how many times the server switched from one state to another.  Note that 
the flash client toggled rapidly between Congestion window limited and 
sender window limited while the websocket client sat in the congestion 
window state for the majority of the time.

My conclusion is that the websocket client is not processing network 
packets efficiently.  The packets are arriving and the network ring 
buffer is full so they are getting discarded.  The client's TCP stack 
notices this and informs the server of this and the server takes the 
appropriate action and cuts the send rate.

What I can't tell if this is due to the client living inside a VM and 
the virtual NIC just isn't interacting with the client code or if there 
is some other problem.  Have you tried running the clients on real hardware?

That's what I see from the data.  Again if you want some c2s data you 
need to enable packet tracing on the server.

Rich



On 07/10/2015 03:17 PM, Don Slaunwhite wrote:
> Hi Rich,
>
> Here is an example of some data from two tests to the Calgary Server. The 
> first is the using the Websocket Client and the second is using the Flash 
> client. They were run one right after the other. These results are indicative 
> of what we are seeing regularly. Websocket Uploads are always much slower.
>
> I am not TCP literate enough to evaluate the results effectively so any help 
> on analysing the logs would be great.
>
> Thanks,
> Don
>
> Websocket Test from VM to Calgary
> ====================================
>
> Upload 52 Mbps Ping 23 ms Download 488 Mbps
>
> Client System Details
> Client version: v1.0.0.0
> OS data:: Windows Server 2012, Architecture:x86
> Flash Info: Version = WIN 18,0,0,203
> The slowest link in the end-to-end path is a 2.4 Gbps OC-48 subnet
> Information: Other network traffic is congesting the link
> This connection is network limited 94.49% of the time
> 2.4 Gbps OC-48 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 = 23.28ms
> the Packet size = 1460bytes
> No packet loss - but packets arrived out-of-order 1.65% of the time
> Web100 reports TCP negotiated the optional Performance Settings to:
> RFC 2018 Selective Acknowledgement:
> ON
> RFC 896 Nagle Algorithm:
> ON
> RFC 3168 Explicit Congestion Notification:
> OFF
> RFC 1323 Time Stamping:
> OFF
> RFC 1323 Window Scaling:
> ON - Server=8, Client=8
> The theoretical network limit is 311.12 Mbps
> The NDT server has a 2048.00 KByte buffer which limits the throughput to 
> 1374.33 Mbps
> Your PC/Workstation has a 6374.50 KByte buffer which limits the throughput to 
> NaN Mbps
> The network based flow control limits the throughput to 939.09 Mbps
> Client Data reports link is OC-48
> Client Acks report link is GigE
> Server Data reports link is OC-48
> Server Acks report link is OC-48
> WEB 100 - Detailed Test Results
>
> AckPktsIn : 130975
> AckPktsOut : 0
> aspd : 0.00000
> avgrtt : 23.28
> bad_cable : 0
> bw : 311.12
> BytesRetrans : 0
> c2sAck : 7
> c2sData : 8
> c2sRate : 51541
> ClientToServerSpeed : 51.541
> CongAvoid : 120998
> congestion : 1
> CongestionOverCount : 0
> CongestionSignals : 1
> CountRTT : 128569
> CurCwnd : 1582640
> CurMSS : 1460
> CurRTO : 223
> CurRwinRcvd : 3785728
> CurRwinSent : 7040
> CurSsthresh : 1432260
> cwin : 21.8657
> CWND-Limited : -nan
> CWNDpeaks : 6
> cwndtime : 0.9449
> DataBytesIn : 573
> DataBytesOut : 625955378
> DataPktsIn : 1
> DataPktsOut : 422956
> DSACKDups : 0
> DupAcksIn : 2159
> DupAcksOut : 0
> Duration : 10183018
> ECNEnabled : 0
> FastRetran : 0
> half_duplex : 0
> Jitter : 51
> link : 0
> loss : 0.000002364
> MaxCwnd : 2865980
> maxCWNDpeak : 2865980
> MaxMSS : 1460
> MaxRTO : 274
> MaxRTT : 74
> MaxRwinRcvd : 6527488
> MaxRwinSent : 7040
> MaxSsthresh : 1432260
> minCWNDpeak : 627800
> MinMSS : 1460
> MinRTO : 223
> MinRTT : 23
> MinRwinRcvd : 0
> MinRwinSent : 5840
> mismatch : 0
> NagleEnabled : 1
> order : 0.0165
> OtherReductions : 5
> PktsIn : 130976
> PktsOut : 422956
> PktsRetrans : 0
> RcvWinScale : 7
> rttsec : 0.023284
> rwin : 49.8008
> rwintime : 0.0221
> s2cAck : 8
> s2cData : 8
> s2cRate : 488203.7666613683
> SACKEnabled : 3
> SACKsRcvd : 35
> SampleRTT : 23
> SendStall : 1
> sendtime : 0.0330
> ServerToClientSpeed : 488.2037666613683
> SlowStart : 2512
> SmoothedRTT : 23
> Sndbuf : 4194304
> SndLimBytesCwnd : 608691440
> SndLimBytesRwin : 586080
> SndLimBytesSender : 16677858
> SndLimTimeCwnd : 9620260
> SndLimTimeRwin : 224548
> SndLimTimeSender : 335983
> SndLimTransCwnd : 70
> SndLimTransRwin : 10
> SndLimTransSender : 65
> SndWinScale : 8
> spd : 491.87
> StartTimeUsec : 822769
> SubsequentTimeouts : 0
> SumRTT : 2993620
> swin : 32.0000
> Timeouts : 0
> timesec : 10.00
> TimestampsEnabled : 0
> waitsec : 0.00
> WinScaleRcvd : 8
> WinScaleSent : 7
> X_Rcvbuf : 87380
> X_Sndbuf : 4194304
>
>
> Flash Test from VM to Calgary
> ====================================
>
> Upload 711 Mbps Ping 21 ms Download 776 Mbps
>
> Client System Details
> Client version: v1.0.0.0
> OS data:: Windows Server 2012, Architecture: x86
> Flash Info: Version = WIN 18,0,0,203
> The slowest link in the end-to-end path is a
> 2.4 Gbps OC-48 subnet
> Information: Other network traffic is congesting the link
> This connection is sender limited 82.56% of the time
> This connection is network limited 17.02% of the time
> 2.4 Gbps OC-48 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 = 23.3ms
> the Packet size = 1460bytes
> No packet loss - but packets arrived out-of-order 0.50% of the time
> C2S throughput test: Packet queuing detected: 0.28%
> S2C throughput test: Packet queuing detected: -2.41%
> Web100 reports TCP negotiated the optional Performance Settings to:
> RFC 2018 Selective Acknowledgement:
> ON
> RFC 896 Nagle Algorithm:
> ON
> RFC 3168 Explicit Congestion Notification:
> OFF
> RFC 1323 Time Stamping:
> OFF
> RFC 1323 Window Scaling:
> ON; Scaling Factors - Server=8, Client=7
> The theoretical network limit is 47808.50 Mbps
> The NDT server has a 2048.00 KByte buffer which limits the throughput to 
> 1373.45 Mbps
> Your PC/Workstation has a 8272.25 KByte buffer which limits the throughput to 
> 2773.81 Mbps
> The network based flow control limits the throughput to 1033.62 Mbps
> Client Data reports link is OC-48
> Client Acks report link is OC-48
> Server Data reports link is OC-48
> Server Acks report link is 10 Gig
> WEB 100 - Detailed Test Results
>
> Timeouts : 0
> waitsec : 0
> PktsRetrans : 0
> timesec : 10
> SndLimBytesSender : 882965584
> CongestionOverCount : 0
> link : 100
> MinRwinRcvd : 64768
> DupAcksIn : 957
> rwintime : 0.0042
> SubsequentTimeouts : 0
> MaxRwinRcvd : 8470784
> sendtime : 0.8256
> MinRwinSent : 5840
> MaxRwinSent : 5888
> cwndtime : 0.1702
> Sndbuf : 4194304
> rttsec : 0.023299
> CongAvoid : 0
> X_Sndbuf : 4194304
> rwin : 64.627
> OtherReductions : 105
> DataPktsOut : 680854
> swin : 32
> minCWNDpeak : 1874640
> FastRetran : 0
> cwin : 24.0823
> X_Rcvbuf : 87380
> AckPktsOut : 0
> spd : 790.47
> DupAcksOut : 0
> SACKsRcvd : 63
> order : 0.005
> MaxMSS : 1460
> CurCwnd : 2823640
> PktsIn : 189616
> CWNDpeaks : 52
> MaxCwnd : 3156520
> maxCWNDpeak : 3156520
> SmoothedRTT : 23
> SndLimTimeRwin : 42777
> StartTimeUsec : 686140
> SndLimTimeCwnd : 1735558
> SndLimTimeSender : 8416704
> Duration : 10195551
> DataBytesOut : 1007364024
> AckPktsIn : 189616
> SendStall : 0
> SndLimTransRwin : 1
> SlowStart : 21762
> SndLimTransCwnd : 1680
> aspd : 0
> SndLimTransSender : 1681
> DataPktsIn : 0
> MaxSsthresh : 0
> CurRTO : 223
> MaxRTO : 231
> SampleRTT : 23
> DataBytesIn : 0
> MinRTO : 221
> CurSsthresh : 2147483647
> MinRTT : 21
> MaxRTT : 43
> DSACKDups : 0
> CurRwinRcvd : 5015040
> SndWinScale : 8
> MinMSS : 1460
> c2sData : 8
> CurRwinSent : 5888
> c2sAck : 8
> s2cData : 8
> s2cAck : 9
> PktsOut : 680854
> ECNEnabled : 0
> mismatch : 0
> NagleEnabled : 1
> congestion : 1
> SACKEnabled : 3
> bad_cable : 0
> TimestampsEnabled : 0
> half_duplex : 0
> SndLimBytesRwin : 79920
> CongestionSignals : 0
> BytesRetrans : 0
> RcvWinScale : 7
> SndLimBytesCwnd : 124318520
> bw : 47808.5
> WinScaleRcvd : 8
> CountRTT : 188334
> loss : 0
> WinScaleSent : 7
> CurMSS : 1460
> avgrtt : 23.3
> SumRTT : 4387999
>
>
>
>
>
>
> -----Original Message-----
> From: 
>
>  
> [mailto:]
>  On Behalf Of Richard Carlson
> Sent: July-08-15 8:28 PM
> To: 
>
> Subject: Re: [ndt-dev] Websocket Client - Upload Speed Problem
>
> Don;
>
> Forgive me for sounding like a broken record on this topic, but the NDT 
> (Network Diagnostic Tool) system was specifically designed to go beyond 
> merely reporting up/down load speeds.  The server captures dozens of TCP 
> variables and analyzes them to identify why a given result was posted.
>
> You don't need to guess if there were packet retransmissions, the NDT server 
> tells you that.  You don't need to guess if the delay is high, low, or 
> varying, just look at the test results.  You don't need to guess if the 
> client's configuration is limiting throughput, just look at the test results.
>
> If the results given at the end of the test aren't enough, then turn on more 
> diagnostics, capture the packet trace, get TCP variables at 5 msec intervals 
> for the 10 sec test.  Use the data that's being collected, and reported, to 
> better understand what is going on.
>
> If you need help reading the test results, post a question to the ndt-dev 
> email list.  We'll be glad to help walk you through the results.
>
> What I would start looking at is,
>
> What is the TCP window size set to?  The 100% increase in speed between 
> Calgary and Montreal probably means the receive window is the limited factor. 
>  (assuming the RTT to Montreal is 2x the RTT to Calgary). Then look at the 
> time spend in the various states.  Sitting in the send or
> receive states indicates a host resource issue.   Look at the number of
> packets sent/ack's received.
>
> Given that the Websocket Upload numbers are 10x lower than the others, I'd 
> wonder if there isn't a math error in the code somewhere and you are simply 
> seeing a reporting error, not a testing error.  Looking at the packet traces 
> and other diagnostic data will quickly point out that type of code bug.
>
> Rich (NDT grandfather).
>
> On 07/08/2015 01:38 PM, Don Slaunwhite wrote:
> > Hi Jordan,
> >
> > It seems we may have multiple email threads going on about this issue. I'll 
> > respond with details on the other thread. 8) But to help clarify for the 
> > people here.
> >
> > We were running a Windows 2012 Server  as the Amazon VM. At first we chose one with 
> > "Low" network bandwidth, but we also created another with "High" network 
> > bandwidth. On those Windows machines we have testing software which runs our IPT test through the 
> > Chrome browser. It basically just goes flash then websocket etc. The times between runs is 
> > roughly 30 seconds and we let it run overnight.
> >
> > We did see slower values coming from the Toronto site, so we ran the same 
> > tests to Calgary and Montreal. Those sites gave us much better results (in 
> > both Flash and Websocket) but still Flash was significantly faster. I'm not 
> > sure if it is our implementation of the Flash/websockets client or what.
> >
> > For instance in Montreal
> >
> > Flash Upload - 304Mbps
> > Flash Download - 220Mbps
> > Websocket Upload - 45Mbps
> > Webscoket Download - 230Mbps
> >
> > And in Calgary
> >
> > Flash Upload - 616Mbps
> > Flash Download - 542Mbps
> > Websocket Upload - 44Mbps
> > Webscoket Download - 472Mbps
> >
> > So even on other servers we are definitely seeing a degradation of Websocket 
> > upload. Now perhaps it truly is something with the VM. But even then it seems 
> > a bit odd. We have no firewall/anti-virus on. What sort of things have you 
> > seen gone wrong with VM testing?
> >
> > We did do some external real life testing via our employee's home
> > systems (not through VPN etc) and we still saw slower Websocket
> > speeds. (But not anything of this magnitude of difference.)
> >
> > For example:
> >
> > (about 200 tests from around Ottawa)
> >
> > 20.8 Mbps - Flash Chrome Download Avg
> > 3.034 Mpbs  - Flash Chrome Upload Avg
> > 21.2 Mpbs - Websocket Chrome Download Avg
> > 2.56 Mpbs - Websocket Chrome Upload Avg
> >
> > So not as big a difference, but still large enough to wonder. Then combined 
> > with the VM testing above.
> >
> > Do you have a dataset from your testing that we could look at?
> > Honestly if you have a good sample size of data that we can feel
> > comfortable with, then we can start looking at what exactly on our
> > implementation is going wrong. (if it is indeed our implementation.)
> >
> > Thanks,
> > Don
> >
> >
> > -----Original Message-----
> > From: Jordan McCarthy 
> > [mailto:]
> > Sent: July-07-15 3:53 PM
> > To: Don Slaunwhite
> > Cc: 
> > ;
> >  
> >
> > Subject: Re: [ndt-dev] Websocket Client - Upload Speed Problem
> >
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA512
> >
> > Hi everybody,
> >           We've also been monitoring the performance characteristics of the 
> > WebSockets client closely, both before and after the client's official 
> > publication in NDT 3.7.0, and we haven't been able to reproduce the disparity 
> > that CIRA has encountered.  We've run Websocket-based tests from several 
> > different browser combinations on a variety of operating systems and 
> > consumer-grade connections, during various times of the day, and haven't 
> > encountered any appreciable differences (within any given 
> > machine/connection/time of day combination).  Additionally, for the sake of 
> > thoroughness we've run C-client tests from the same connections, and the 
> > numbers we got from the C client runs were pretty comparable with what we 
> > were getting out of all of the Websockets tests.
> >
> > Don: could you tell us a little bit more about your testing methodology?  I'm 
> > guessing you spun up a Linux VM, and used X-forwarding to get access to an 
> > instance of the browser running on the VM?
> >
> > Off the top of my head that sounds reasonable, but we've definitely seen 
> > weird artifacts introduced by running tests out of VM environments, so 
> > perhaps that could be throwing things off somewhat.
> >
> > Jordan
> >
> > Jordan McCarthy
> > Open Technology Institute @ New America Public Key: 0xC08D8042 | 4A61
> > 3D39 4125 127D 65EA DDC2 BFBD A2E9 C08D 80
> > 42
> >
> > On 07/06/2015 02:45 PM, Don Slaunwhite wrote:
> > > Hi Everyone,
> > >
> > >
> > >
> > > My name is Don Slaunwhite and I’m a Product Manager at CIRA. We have
> > > been utilizing the NDT tests as part of our Internet Performance Test
> > > up here in Canada.
> > >
> > >
> > >
> > > We have been working on transitioning to the Websocket client with
> > > our test, but we have been seeing some very different results in
> > > upload speeds as compared to the flash client.
> > >
> > >
> > >
> > > We did a lot of internal/external testing and in every case the
> > > upload speeds for the websocket version were lower (most times
> > > significantly) than our current flash client. The download speeds are
> > > comparable, with websocket usually coming in a bit faster
> > >
> > >
> > >
> > > For example we setup a VM at Amazon to run some (hopefully!)
> > > controlled tests. Using Chrome and Firefox.
> > >
> > >
> > >
> > > Chrome Averages based on ~200 tests
> > >
> > > Flash 19.3Mpbs Upload
> > >
> > > Flash 49.8Mpbs Download
> > >
> > > Websocket  9.3Mpbs Upload
> > >
> > > Websocket  54.3Mpbs Download
> > >
> > >
> > >
> > > Firefox Averages based on ~300 tests
> > >
> > > Flash 27.4 Mpbs Upload
> > >
> > > Flash 50.1 Mpbs Download
> > >
> > > Websocket  11.1 Mpbs Upload
> > >
> > > Websocket  57.2 Mpbs Download
> > >
> > >
> > >
> > > In each case the websocket upload is significantly lower. I’m trying
> > > to determine if this is expected behaviour with the websocket code.
> > > If not what possible items might be causing this type of speed
> > > degradation.
> > >
> > >
> > >
> > > We are running with client versions 3.7.0 (Flash has a buffer size of
> > > 32K) against mlab servers in Toronto.
> > >
> > >
> > >
> > > I realize there will be new functionality/capability with the
> > > multiple stream releases, but right now I’d like to try and focus on
> > > one major change at a time, so any ideas on speed differences between
> > > Flash and Websocket using just 3.7.0 would be really helpful.
> > >
> > >
> > >
> > > Thanks,
> > >
> > > Don
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Attachment: canada-ndt.xls
Description: MS-Excel spreadsheet