low throughput over High Speed Ethernet

[Zhengchun Liu]

Hi,

I got an issue for several days. Hope anybody could give me a hint. 

I simulate data transfer (using TCP) over high speed ethernet (40 Gbps), but I can only get about 4MBps throughput with NS3. my topology is: client -> switch -> router -> router -> switch -> server. total RTT is 54ms. 

My configuration is:

Config::SetDefault("ns3::TcpSocket::SndBufSize", UintegerValue(67108864));

Config::SetDefault("ns3::TcpSocket::RcvBufSize", UintegerValue(67108864));

Config::SetDefault("ns3::CsmaNetDevice::Mtu", UintegerValue(9000));

Config::SetDefault("ns3::PointToPointNetDevice::Mtu", UintegerValue(9000));

Config::SetDefault("ns3::TcpSocket::SegmentSize", UintegerValue(8930));

Config::SetDefault("ns3::TcpSocket::InitialCwnd", UintegerValue(8));

Config::SetDefault("ns3::TcpL4Protocol::SocketType", StringValue ("ns3::TcpHtcp"));

GlobalValue::Bind ("ChecksumEnabled", BooleanValue (true));

I tried to capture the traffic, I see [TCP Previous segment not captured] when server gets Seq=3679191, then server keeps receiving [TCP Dup Ack] Ack=3688091, it seems that server does not response client's retransmission request. 

I also tried parallel TCP, the performance became worse!  

Thank you very much in advance.

Zhengchun 

[Tommaso Pecorella]

Hi,

we're missing too many details to provide an even remotely right suggestion.

Read the posting guidelines for hints on what we need to provide some help.

Thanks,

T.

[Zhengchun Liu]

Hi Tommaso,

Thank you so much for your reply. I think I almost figured out the reason, it is mostly because of the csma channel I use, it is not full duplex, can not simulate the modern Ethernet I guess. I saw lots of packets are blocked on the first switch (client send data to server, client connect to a switch). CSMA channel was used to connect client to switch and switch to router. But it is still a little strange why the switch can receive fast but just cannot send as fast as receive. (I already let all the csma channel have the same bandwidth and delay).

Thank you!

Zhengchun

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[Tommaso Pecorella]

Hi Zhengchun,

there's a new module for fast ethernet being reviewed. If you want to take a look at it (and eventually provide us some feedback), the link is https://codereview.appspot.com/5615049/

Cheers,

T.

[Zhengchun Liu]

Hi Tommaso,

OK, great! Thank you!

Zhengchun