[ns] MAC 802_11 Wired-Cum Wireless question

[Nilesh Nagraj Rathod <rathod@ccs.neu.edu>]

> Hi ppl,
> 
> I have a wired cum wireless network. Senders(TCP) are in the wired domain
> > and receivers(TCPSink) in the wirless domain. I couldnt figure out the
> > bottle neck bandwidth in the wireless doamin. When i check the
> > ns-default.tcl under ..tcl/lib/, I see that the bandwidth value as
> > Phy/WirelessPhy set bandwidth_ 10e6 
> > 
> > No matter what I change this to, and the bandwidths in the wired domain
> > like from 1Mb to 20Mb, goodput per flow that I calculate remains about the
> > same. Number of bytes being sent do not change much. 
> > The backbone bandwidth between the router and the base station is
> > 10MB. And the sources link to the router is of 5Mb bandwidth, but I dont
> > get a goodput of even 0.5Mb.
> > 
> > I changed the wireless domain to a wired one and found reasonable
> > goodput, confirming there is nothing wrong with the script. 
> > 
> 
> Next I added the following in the tcl script:
> Mac set bandwidth_ 1000000, and when I play with values, I do see
> changes. But when I try 10000000, ie 10Mb, it doesnt work and no bytes are
> delivered. 
> 
> It does work with 9Mb. And I get the ollowing result.
> Note for the following backbone abdnwdith is 10Mb and the two sourses to
> the backbone router, are connected to the router via a 5Mb link. 
> 
> Total Bytes Delivered: 24093000 
> Total Bytes Delivered Flow 0 TCPTahoe: 12188000 
> Total Bytes Delivered Flow 1 TCPSack1: 11905000 
> Total Bytes Sent: 24676860 
> Total Bytes Sent Flow 0 TCPTahoe: 12478680 
> Total Bytes Sent Flow 1 TCPSack1: 12198180 
> Goodput of Flow 0 TCPTahoe: 1.0833777777777778  #in Mbps
> Goodput of Flow 1 TCPSack1: 1.1904999999999999  #in Mbps
> % Overhead of Flow 0 TCPTahoe: 2.3849688217919263 
> % Overhead of Flow 1 TCPSack1: 2.4626627467450648 
> Total Retransmit Timeouts of Flow 0 TCPTahoe: 1 
> Total Retransmit Timeouts of Flow 1 TCPSack1: 0 
> 
> When i change 9Mb to 10Mb for the Mac (by using Mac set bandwidth_ 10e6),
> I get the following result:
> 
> num_nodes is set 3
> warning: Please use -channel as shown in tcl/ex/wireless-mitf.tcl
> *** NOTE: no connection pattern specified.
> Loading scenario file...
> Load complete...
> Starting Simulation...
> Total Bytes Delivered: 0 
> Total Bytes Delivered Flow 0 TCPTahoe: 0 
> Total Bytes Delivered Flow 1 TCPSack1: 0 
> Total Bytes Sent: 9180 
> Total Bytes Sent Flow 0 TCPTahoe: 5100 
> Total Bytes Sent Flow 1 TCPSack1: 4080 
> Goodput of Flow 0 TCPTahoe: 0.0 
> Goodput of Flow 1 TCPSack1: 0.0 
> 
> ns: stop: divide by zero          ##Ignore this cos of num of bytes=0
>     while executing
> "expr (double($totalBytesSentFlow($i) -
> $totalBytesDeliveredFlow($i)))/$totalBytesDeliveredFlow($i)"
>     (procedure "stop" line 57)
>     invoked from within
> "stop"
> 
> 
> 
> 
> > Does anyone have any idea how I can work around this one? Thanks in
> advance for
> > your help and time. 
> > 
> > Regards,
> > 
> > Nilesh Rathod
> > E-mail: rathod@ccs.neu.edu
> > ------------------------------------------------------------------------------
> > 
> > 
> 
> 
> 
>