I am trying to calculate the bandwidth of the wi-fi system, with these parameters data rate = bandwidth * log2(1+SNR) ; where SNR is the signal to niose ratio. Calculate Bandwidth-delay Product and TCP buffer size. BDP (Bits of data in transit between hosts) = bottleneck link capacity (BW) * RTT throughput <= TCP. So you just lit up your new high-speed link between Data Centers but are unpleasantly surprised to see relatively slow file transfers across this.
You should have already uploaded your SSH keys to the portal. The project lead of the project you belong to must have enabled wireless for the project.
Finally, you must have reserved time on either WITest or a sandbox at ORBIT either sb2, sb3, or sb7and you must run this experiment during your reserved time. Skip to Run my experiment Background The Nyquist formula gives the upper bound for the data rate of a transmission system by calculating the bit rate directly from the number of signal levels and the bandwidth of the system.
How to Calculate TCP throughput for long distance WAN links
Nyquist is only an upper bound, and on the baseband signal bandwidth - the occupied transmission bandwidth for a wireless signal will further depend on how the signal is modulated onto a carrier frequency for wireless transmission. In this experiment, we will use PSK modulationa digital modulation scheme in which the phase of a carrier signal is varied to represent different bits, or different groups of bits, and there are a discrete number of signal "levels" represented by different phase shifts.
In our experiment, the modulated wireless signal at RF will occupy a transmission bandwidth that is double the Nyquist bandwidth at baseband: Doubling the data rate C and keeping the number of signal levels M the same, will double the bandwidth used Band Squaring the number of signal levels M and keeping the data rate C the same, will halve the bandwidth used B. In this experiment, we will send a constant amount of data over a wireless channel, with varying data rates C and number of signal levels M.
We will observe the effect of these variations on two metrics: The total time required to transfer the data, and The transmission bandwidth. We expect to see that there are two ways to increase the speed of data transmission: Results When we send 5 megabytes 40 Mbits of data at a rate of 0.
However, if we change the bitrate to 2 Mbps, 2 MHz of bandwidth is used and the transmission takes about 20 seconds.OSPF Cost Calculation and Configuring Bandwidth/ip ospf cost/reference bandwidth
To reduce the speed of data transfer by a factor of 4, we had to increase the bandwidth by a factor of 4: Finally, on changing the constellation size to 4 points squaring the number of signal levels relative to the first transmissionthe transmission also takes about 20 seconds, but uses only 1 MHz, when transmitting at 2 Mbps: You will have to make your reservation in advance. To reserve WITest, visit http: Then, use the reservation calendar to reserve one or two consecutive hours for this experiment.
For further information, refer to this tutorial on the reservation system. Then, click on "Control Panel". Use the calendar interface to request time on sb2, sb3 or sb7.
Set up testbed At your reserved time, open a terminal and log in to the console of the testbed that you have reserved. This is usually your regular GENI username with a geni- prefix, e. If you are using WITest, log in to witestlab.
TCP Throughput Calculator - Tools - SWITCHlan - SWITCH
Then, you must load a disk image onto the testbed nodes. From the testbed console, run: What size TCP window should you use? We can use the reverse of the calculation above to determine optimal TCP window size. Formula to calculate the optimal TCP window size: One downside to increasing the TCP window size on your servers is that it requires more memory for buffering on the server, because all outstanding unacknowledged data must be held in memory should it need to be retransmitted again.
Another option is to place a WAN accelerator at each end that uses a larger TCP window and other TCP optimizations such as TCP selective acknowledgements just between the accelerators on each end of the link, and does not require any special tuning or extra memory on the servers. The accelerators may also be able to employ Layer 7 application specific optimizations to reduce round trips required by the application.
How is that possible?
Unless you can figure out how to overcome the speed of light there is nothing you can do to reduce the real latency between sites. Because the local server is seeing very fast local acknowledgments, rather than waiting for the far end server to acknowledge, is the very reason why we do not need to adjust the TCP window size on the servers.
Additionally, the WAAS appliances would also remove redundant data from the TCP stream resulting in potentially very high levels of compression.