Wireless LAN Benchmarking with DBS (Distributed benchmarking system)


Why use DBS?
Netperf is a popular tool but it does not provide the change of throughput. DBS can do it.

Installation:
In Linux, it requires  Perl 5 and GNU plot. But this is already associated with red-hat package. Also, it needs XNTP. XNTP is a timeserver that makes it possible to synchronize your local computer-time with an external time-server. Additionally, you can run your own time-server and let other hosts contact you to synchronize your LAN-time. But I guess, with only 2 hosts, xntp is not important. But we should align the hosts' time.
After Download and extracting the sourcecode
  1. go to "src" directory. modify makefile, Line 56, fix a bug, change $(UNAME) to obj ( if Beta1.2.0 version)
  2. make dir
  3. go to ../obj/Linux-2.4.18-14
  4. make
  5. mkdir ../../bin
  6. cp "dbsc dbsd dbs_view" to the new "bin" directory
  7. Edit dbs_view script to change the real location of perl as /usr/bin/perl 
  8. Change the process_flag of "dbs_view" as ON. This will enable throughout calculation

Running:

  1. cd ~/dbs/bin/
  2. compose a command file
  3. runnning dbsd daemon on all hosts. default port is 10710
  4. create the directory to store measurements. such as ./ether/
  5. align the time.
  6. type "dbsc sample1"
  7. after test finished, type " ./dbs_view -f sample1 -sq sr -th r -t 0.3 -title 2" to view sequence number and throughput drawn with GNUPLOT.

Analysis:

The dbsd uses a pair of ports for test control. Command file specify another pair of port for TCP/UDP traffic. If the tcp _trace is set to "OFF" in command file, only a  *.t file will store in the output directory. Throughut is calculated by the subroutine of perl script in dbs_view. So, we need to turn on the "process_flag" if throughput need to be plotted.

"cmd_hostname" is the interface used for commands. Thus, we could use ethernet for exchange commands, and use WLAN for test purpose.

Throughput & Delay....

When DBS is used in wired Ethernet, there will be no duplicated UDP packets becasue CSMA/CD protocol does not retransmit frames. However, IEEE 802.11 does have this mechanism. So, we have to modify the original dbs_view script, especially the calc_throughput sub_routine.

Also, the calculate of delay of UDP traffic is wrong.  What is the delay of  a lost packet?

Write a Sample Command File 
 # Sample 1
  {                                             
          sender {
                  hostname  = 10.0.0.1;
                  hostname_cmd = 192.168.180.249;
                  port      = 20001;
                  so_debug  = OFF;
                  tcp_trace = OFF;
                  send_buff = 65535;
                  recv_buff = 65535;
                  mem_align = 2048;
                  pattern {2048,   2048,     0.0,      0.0}
          }
          receiver {
                  hostname  = 10.0.0.2;
                  hostname_cmd = 192.168.180.21;
                  port      = 20001;
                  so_debug  = OFF;
                  tcp_trace = OFF;
                  recv_buff = 65535;
                  send_buff = 65535;
                  mem_align = 2048;
                  pattern {2048,   2048,     0.0,      0.0}
          }
          file           = ether/test1;
          protocol       = TCP;
          start_time     = 0.0;
          connection_mode= BEFORE;
          end_time       = 30;
          send_times     = 2048;
  }
The file could be srored anywhere.