You're comparing apples to oranges. A 10BaseT LAN is a shared medium,
which explains the oft-quoted-but-not-quite-accurate 40% max usage
figure. The theory is that with CSMA/CD, as traffic increases so do
collisions, which forces retransmits. This is exacerbated in a half
duplex environment.
WAN links, such as a T-1, are synchronous (or isochronous or
pleisochronous or some other x-ochronous word that I don't understand)
full duplex connections. This means that frames are travelling boths
directions over the link at the same speed regardless of the amount of
traffic to be carried. In the case of a T-1, if you have 1.536 Mb/s of
data to send, then go for it. The bandwidth is there if you need it.
For you hair-splitters, I'm purposefully not getting overly detailed.
Of course, you have to factor in packet headers in your calculations.
Any data you have to send has to be encapsulated first. If you're using
IP, then any data packets must be encapsulated with a UDP or TCP header
and then with an IP header. This packet then must be placed inside
whichever datalink frame you're using, whether it's Ethernet, HDLC, PPP,
or whatever. All of this creates overhead that you have to take into
account when calculating how much bandwidth you actually have
available.
But the moral of the story is that point-to-point WAN links suffer from
different issues than CSMA/CD networks.
HTH,
John
>>> "Dana Graesser" 6/26/01 7:39:47
AM >>>
Folks,
Is there a resource somewhere that discusses the theoretical limits of
WAN
links, i.e. for LANs its generally accepted that on a 10Mb LAN, you can
only realistically expect to get 4Mb.
Regards,
Dana
CCNP, CCDP, really want my CCIE written...
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=9966&t=9961
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