Re: [ns] MAC 802_11 Wired-Cum Wireless question

[Huan Pham <huan@cs.jcu.edu.au>]

I think the "bottle neck" in your situation is maybe the BER of the Wireless link.  If
error is reasonable high, TCP througput is limited, and even if you increase the link
capacity, it does not help . Try changing the error rate.



Nilesh Nagraj Rathod wrote:

> > 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
> > > ------------------------------------------------------------------------------
> > >
> > >
> >
> >
> >
> >