Cell Relay Archive

["ronald h. davis" <ronaldd@lucent.com>]

Robin DeFreitas wrote:
> 
> Can someone enlighten me on OAM cells . I always assumed that OAM cells were
> only sent when there was an indication of a problem with a PVC. However some
> one has told me that OAM cells can be sent periocically without there being
> any problems associated with a PVC. Can some one give some explanation on
> how OAM cells really work or maybe some type of document that explains it
> all !?
>

performance monitoring cells are oam cells that are periodically sent
and do not, per force, mean that there is a problem with a vcc/vpc.
the contents of the pm cell could indicate a problem upon further
analysis (e.g. excessive number of lost cells).  continuity cells can
also be sent periodically to verify the integrity of an atm connection 
at the virtual path or virtual circuit level.  cells used for these 
purposes are referred to as f4 and f5 oam flows, respectively (as 
opposed to physical layer information contained in the sonet/pdh header 
which are referred to as f1, f2, and f3 flows - although pdh has no f2 
flow for what it's worth).  failure to receive a continuity cell after
a set interval of time can be used to flag a problem.  i don't think
that continuity cells are used very often in actual practice, however.

alarm indication signal (ais) and remote defect indication (rdi) oam
cells *do* indicate a problem with an atm connection.  loopback oam
cells are often used as a diagnostic tool for trouble location.

-- 
  __  ______  __  / __/ |       lucent technologies, naperville il, usa
_/ (_(_) / (_(_/_/_(_/  .       ronald.h.davis@lucent.com
author of "atm for public networks" published by mcgraw-hill
     http://www.amazon.com/exec/obidos/ASIN/0071344764