Effective Data Rates???

Posted on 2004-11-14
Last Modified: 2010-04-10
My employer is asking me to check the effective data rates available for users on an 802.3 Network.  I am using random numbers here, they have no meaning just filleres.  

Say on average to read a single email message via web mail, the HTTP protocol sends 1 packet from client to server with 80 bytes and receives one packet with 910.  If the average is one new TCP connection must be established for every email message read. then what is the effective data rate of 802.3 network only using web based email.  

How do I explain this in steps that a user will understand, can anyone walk me through the math.  

What are the total # of packets sent?
What are the total # of data bytes sent?
What is overhead of Ethernet? 26 Bytes
What is the overhead for TCP? 20 Bytes
What is the overhead for IP? 20 Bytes
What is the minimum frame size for ethernet? 64 Bytes
What is the total overhead?
What is the effective data rate?  

I am not sure how to answer these in user terms with simple math.  Can anyone help?  Thanks in advace!  

Question by:wiggs1006
    LVL 3

    Expert Comment

    Well it seems you have a task on you hands!

    A few things that I'd like to say:

    My understanding is that your boss is asking about your 802.3 Network - essentially your internal ethernet network - I wouldn't use web mail to explain because once you leave your network and cross into the realm of the web, its a different ball game, then we start talking about routers and layer 3 protocols galore!

    When explaining it I would go with something like a file from one host to another on the same 802.3 network

    Also, its hard to calculate it that was because one second you may have many frames traveling down the pipe

    Unless you have a lot of network congestion, your network speed is essentially based on your hardware ex 10baseT is 10mbps
    LVL 1

    Expert Comment

    I would advise getting a sniffer...  if you havent already got all the info you need, this will help you gather it properley...

    a good one that is free is Ethereal..

    You could do something like run this sniffer on your network for a few days, and collect data... once you have the data, you can work out how much of your connections are being used in your network...  
    You could do the math for a certain section, and say its a 10Mbps connection, just say to the boss in simple terms, that there is a 10Mbps connection here, and on average, it uses 1Mbps, but at peak times it reaches as much as 7Mbps.. therefore effectively have a 70% effectiveness?
    My 2 cents.. - correct me if im wrong..
    LVL 4

    Accepted Solution

    What, PRECISELY, is your goal? corporate types always have a reason for their questions (even if they are inane) Is he trying to justify upgrading to gigabit network? are they looking for a reason to fry their wiring guy b/c their network isn't up to par in their oppinion? (yes, wiring matters for speed. I've seen companies run their cable-bundles RESTING on their 4 foot Fluorescent lighting fixtures [8 in a row - used em' as wiring trough!]) and then wonder why they had packet loss.

    Also you should note that 802.3 encompases a HUGE breadth - from 802.3 at 10 megaBITS per second to 802.3ae which is the new 10 gigaBIT per second protocol. Could you clarify which they are asking about?

    Ultimately the question seems to be "what is our network speed accross the wire internal to our office?"

    assuming no extra baggage to the question i would advise you to create a real-world scenario, put a 100 meg file on a server and copy it to your workstation, then to another. Use FTP instead of windows file transfer b/c it's slightly more robust and will actually display a speed in kiloBYTES per second. (note bytes, not bits.) you can multiply that speed by 8 and get the effective bit rate. the only reason i suggested 100 MB for a test file is to allow an average to be established over the course of time. You might want to tailor the test to a file size relevant to your application (I. E. accountants copying excel files with last years YTD data might copy 1 MB of information for a busy company or 300 KB for a slower one)

    Or if we're barking up the wrong tree and your boss is way more technically inclined than we're expecting you could get more detailed, but that seems unlikely. usually they're just looking for an executive summary....

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