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Community Member

How to find the bandwidth

WE have Cisco 3640 Routers conneted through the Private Leased line between our two offices. It was 1MB Line and We a day before upgraded the link to 2MB but could not find any wast improvement in speed. Is there any way using Cisco or third part solutions to find out exactly the bandwidth capacity of the link.

Thanks in Advance

7 REPLIES
Bronze

Re: How to find the bandwidth

Unfortunately, there is no means of telling in IOS what the actual speed of the line is. The clocking comes from the DCE device.

You could use the input and output figures under the show interface to determine the speed it is passing data at though.

Community Member

Re: How to find the bandwidth

You can captrue and look into the speed of the line with some third party tools, just like Solarwin, MRTG.

Community Member

Re: How to find the bandwidth

Along with SolarWinds, you could use TTCP to test the throughput of the circuit. Please note that adding bandwidth will not increase speed unless your circuit is overloaded.......bandwidth is the width of the pipe, speed is measured in latency and is distance and hop sensitive.

Blue

Re: How to find the bandwidth

nGenius Real Time Monitor (RTM) is another alternate that you can look at.

Community Member

Re: How to find the bandwidth

Tough question but there are many resources that discuss this on the internet.

Some thoughts are below (including other information in the previous threds)

There are a few options you have. Some that have been mentioned:

You can use a program like mrtg. This program uses snmp to gather data, it will then create a graphical interface for you. It will take a little bit of work but it's pretty easy. Taking the in/out counters every 5mins will give you what bandwidth is being used.

http://people.ee.ethz.ch/~oetiker/webtools/mrtg/

The best way to see if you are getting better bandwidth is to take the average daily usage before the change and compare it to the current situation. If this does not work for you you can use the basic math calculation found in rfc which I can not find I think it's the main tcp rfc BW=RTT/Delay or something like that.

However, this will give a very high over view. Things that you can gain from running a sniffer will help in your analysis. These things are the number of retransmits, mss, acks, windowing, delay etc. will all play into the "theoritical" bandwidth.

Most people use some graphical utility along with RTT or a sniffer to determin how much data is being sent through the wire.

One thing is to think if you have 2 workstations that use a DS1. Then each workstation has 50% of the bandwidth or 768k.

If you have 4 workstations that use a DS1 then each workstation has 512k.

However, since we did not channel out the DS1 per workstation one workstation has the ability to use all the available bandwidth.

Community Member

Re: How to find the bandwidth

Thanks a lot to every one. I will do in accrodance with your advice.

Community Member

Re: How to find the bandwidth

How are you testing the "speed" after the upgrade ? Will depend a lot on the end user operating system and application, network delay.

Try increasing the TCPWindowSize parameter on both side hosts.

Microsoft Windows (except Win2k) have a default of 8760 which will restrict the available bandwidth to less than 1Mb for each session. Try 24820 or higher setting. Here is the link to Microsoft site

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q120642

A simple way to test would be with ftp that will show the transfer rate in bytes.

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