Confused about network speeds

English Network/Internet
1

I would like some help trying to explain/optimise my network speed.

I have a server currently connected to my router via a powerline LAN supposedly running at 200MB/s (I get confused with units of transfer speed). The network router is only running at 100MB/s. I am trying to replace this with a gigabit LAN router but at the moment the maximum my network can do should be 100MB/s.

This is the speed I get at the moment:

dd if=/dev/zero bs=16000 count=5000 | nc -v 192.168.0.18 12345
Connection to 192.168.0.18 12345 port [tcp/italk] succeeded!
5000+0 records in
5000+0 records out
80000000 bytes (80 MB) copied, 28.3946 s, 2.8 MB/s

Should that be 100 MB/s?

2

Isn’t the MB in Ethernet speed Mbits and the MB in the dd report Mbytes?

3

I think that your router maximum bandwidth is 100 Mbit/s (most of connection bandwidth are still given in Mbit/s in our multi-To hard drive era). The output of dd shows you the bandwidth in MB/s. Here B stands for Byte (1 octet), so 1 MB/s = 8 Mbit/s. Hence, the speed of your copy with dd is 2.8 MB/s = 22,4 Mbit/s.

Where did the 76.6 Mbit/s go? Well… Your network is as fast as the slowest ring in the chain. You transfer bit rate can be limited by each level of the protocol stack and the client side and the server side:

  1. the application layer
  2. transport layer
  3. internet layer
  4. network access layer

Each layer takes its part of the bandwidth.

openSUSE System Analysis and Tuning guide may help you in optimizing your network and detecting the bottlenecks.

4

Thanks for that explination.

That is my question I suppose.

The laptop I used for the previous shown test is connected via Wifi (Connection speed 52 Mbit/s) so I guess I am only missing about 30 Mbit/s :wink:

I’ll run the test again via a wired connection.

Edit:
Now via wired connection:

dd if=/dev/zero bs=16000 count=5000 | nc -v 192.168.0.18 12345
Connection to 192.168.0.18 12345 port [tcp/italk] succeeded!
5000+0 records in
5000+0 records out
80000000 bytes (80 MB) copied, 22.6099 s, 3.5 MB/s

Faster but still kinda slow.

5

On 07/27/2013 12:16 PM, Dexter1979 wrote:
> kalten;2574925 Wrote:
>> Where did the 76.6 Mbit/s go?
> That is my question I suppose.
>
> The laptop I used for the previous shown test is connected via Wifi
> (Connection speed 52 Mbit/s) so I guess I am only missing about 30
> Mbit/s :wink:
>
> I’ll run the test again via a wired connection.

Yes, bits (b) and bytes (B) do make a difference, just as milli (m) and mega (M)
do. It drives me up a wall when someone writes mb/s!

What you have not taken into account is that wireless is a half-duplex medium.
As a result, the throughput is roughly 1/2 the raw data rate. Thus your 802.11g
network running at 54 Mbps will max out at about 27 Mbps throughput. Your 2.8
MBps is 22 Mbps, thus your network is running close to the maximum. The
difference could easily be explained if some other device is on your wireless
network, there was a scan triggered during the transfer, retransmits were
required, or you have neighbors on the same channel.

6

Especially on a Powerline LAN where there can be interference on the line (although filters will try to mitigate problem) in combination with your desire to transfer very large files (>3MByte files), you should benefit by changing your Congestion Control Algorithm.

I’ve written a guide explaining what it is, why it’s important, types of scenarios where this should be https://sites.google.com/site/4techsecrets/optimize-and-fix-your-network-connection

HTH,
TSU

7

Thanks for that explination. I will try a different modem in a few weeks when my internet is upgraded and I can stop using my locked in modem I have now. I was thinking of getting a gigabit switch in the mean time but it may not be worth my while after reading this. I do most my transfers using wifi and this would not change.

8

No… that looks way to technical for me!! :wink: Thanks for the suggestion tho!