ATM vs. DS3
Ehud Gavron
GAVRON at ACES.COM
Thu Jul 10 02:52:23 UTC 1997
>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 at connectnet.com
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