Cell Relay Archive

[Paul Koning <pkoning@xedia.com>]

mrityu wrote:
> 
> Hi,
> 
> Actually, I have a related question: can some one please explain how the
> VPI/VCI values are actually managed in a switch. I mean what kind of
> data structures do they use and what is the order of magnitude of their
> search time. Linear allocation is simple, but it also will have to take
> care of random allocations as in the case of PVC creation.

It would depend on who wrote the code; there's no reason to believe
there is any consistent pattern.

(Well, it's likely no one is dumb enough to use linear search...)

The obvious choice is by indexing: look up the VPI in one table,
the VCI in a second table pointed to by the first.  Then again,
some may use a CAM.  Some may use hash lookup.  Whatever works...

Or did you mean the lookup used by the hardware?  If so, the
most likely answer is the double indexing lookup, but I could
imagine it being a single indexed lookup (with the implemented VPI
bits and VCI bits concatenated).  There probably is the occasional
CAM, but probably not a lot of them (too expensive).

	paul