At 10:39 AM 4/27/01 -0400, Stephen Skinner wrote:
>Guys,
>i`m looking for a good explanation of what this is...
>
>i looked on the archives and cisco site,but beleive i am bieng thick .
>
>according to cisco the bit rate comes in various flavours
>
>UBR,VBR,CBR....but am i getting this complete leg-before-arm
>
>i thought the bit rate was a messunment of how fast the link was ???????
>
>i don`t get it ...some-one put me out of my misery....
>
>thanks
>
>steve :-$
They are the types of "QoS". Service classes defined by the ATM
standards. (UNI 4.0)
Unspecified Bit Rate (AAL5, pretty much Best Effort)
Variable Bit Rate (AAL2, for variable bit video, never really took off)
Constant Bit Rate (AAL1, for constant, guaranteed bandwidth)
There is also ABR (available bit rate), (takes left over bandwidth).
For your information, AAL0 is raw ATM cells, and AAL3/4 is combined
together. In theory, AAL3/4 is absolutely obsoleted by AAL5 since the cell
tax would have been higher. (CRCs in EACH cell vs each PDU (9180 octets or
so)).
Also, VBR has two forms, Non-real time and real time. The actual ATM
adaption type I listed above may vary, as ATM is very complicated and the
standards get fuzzed left and right. I hope anyone with more definitive
knowledge can help you fill in the gaps I may have left.
-Carroll Kong
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=2273&t=2256
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