Newbie Question Followup #2: How much VPN bandwidth is "a lot"?

Posted on 2004-12-01
Last Modified: 2012-05-05
Dear Network Experts,

My application passes 40,000 bytes intermittently over our customers' networks. In worse case scenario, it might happen a few hundred times per day.  The Network Experts have been kind enough to assure me (twice) that 40,000 bytes is very trivial over a LAN or WAN.  However, there is still a concern at my company that 40,000 bytes might be a problem over a VPN.  

What do you think? Would a VPN be a problem?  Is there any other circumstance where 40,000 bytes might be a concern?  

Thanks one more time,

Question by:BrianMc1958
    LVL 13

    Accepted Solution

    When you consider that a T1 line is 1.544Mbits (or 193Kbytes/second) and a LAN line is 10Mbits (or 1.2Mbytes/sec) transferring 40K is trivial. Even over a 128Kbit ISDN line, this would be trivial. Even 1000 times a day this would be trivial. Even with the overhead associated with VPN, this would be trivial.

    It's trivial!
    LVL 13

    Expert Comment

    I suppose that 'LAN line' would be 100Mbits/second nowadays, or even 1Gbit.

    (Showing my age?)

    Assisted Solution

    What sort of VPN are you talking about?  If its ADSL then you've only got a 256K upload from your site to the end user, regardless of their download speed, if it's SDSL then probably not a problem and also how many clients coming in over the VPN?  It is the upload speed that is relevant from your application to their users and that needs to be shared and also any contention taken into account.

    On a standard ADSL VPN upload with a single client you should be looking at (roughly)

    256kbps kbps X 60 seconds = 15360 Kbp per minute

    15360/8 = 1920k per minute
    1920 k per minute X 60 minutes = 115200/1024 = 112.5mb per hour.

    Which is pretty good throughput assuming no contention and a single user.  Which must be nice.

    How resilient is the application, does it timeout if it the data isn't receive in a set time or does it just wait until all the data is received?

    To be honest, 40k is a very minor but passing it a few hundred times a day = 40K * 300 = 11.72Mb during the day which is a little bit more but are we talking over 8.5 hours (including lunch) that most staff work or 24 hours to a remote site VPN?
    8.5 hrs gives a throughput need of 1.38mb per hour.  Which is pretty trivial still.

    However, nothing beats a live test in a real life situation, a proof of concept, if you like to demonstrate feasibility that way you can at least demonstrate success or walk away knowing you've tried it.

    Whatever you do, if the guys with VPN have full web access and are busy downloading MP3 and videos of therr favourite P2P application then you're stuffed before you begin.  
    LVL 3

    Expert Comment

    Just to put it in perspective:

    40,000 Bytes = 39.0625 Kilobytes. In comparison, the capacity of a 3.5" floppy disk is 1.4MB, or 1,468,006.4 Bytes.

    Definately, a trivial amount of traffic.

    Here's a formula for calculating Network Bandwidth Overhead:

                           NETWORK_BANDWIDTH (X) POLLING_INTERVAL

    LVL 1

    Expert Comment

    A chain is only as strong as its weakest link... A network connection is only as fast as its weakest segment... which segment in the vpn is the slowest? That's the real question.

    AND... if 40K come only from one server and go to every possible customer in individual connections then you will actually slow down server access.

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