Re: ATM vs. DS3

[Ehud Gavron <GAVRON () ACES COM>]

> Hello,
>       I just thought of something. We are in the process of purchasing a
> 4 Mb CIR from another backbone. Now, we have the choice of ATM or standard
> T3 delivery (over a DS3 either way). Now, if we get ATM, that 4 Mb CIR
> turns into:

> [ (53-5)/53 ] * 4 Mb/s = 48/53 * 4 Mb/s = 3.62 Mb/s

> Because an ATM cell is 53 bytes, but 5 bytes of that is header. Thus we
> pay for 4 Mb/s and get 3.62 Mb/s.

> Now, the question is, what is the overhead of the serial (ppp?) protocol
> running over the T3? Since it is point to point, and not addressed, it
> should be less, or is this not the case?

        <24 bytes per MTU.  If your MTU is 4000, your large frames
        buy you 3976/4K, which conveniently multiplies by 4M to give you
        3.9+M.

        Also, don't forget that ATM switching introduces a latency that
        a p2p connection doesn't.

        If you're truly having a point-to-point application, and you have
        a choice of a non-switched/routed protocol vs a p2p protocol...
        um... go with b :)

        E

> Any input would be appreciated!

> Josh Beck                                           jbeck () connectnet com
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