Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Local Fault/Remote faults

Before submitting as a comment, I wanted some feedback
from the community.

46.3.4  Fault signalling.  As defined, local fault is declared for any fault
which occurs between the remote RS and the local RS. Remote fault is
defined as any fault which occurs between the local RS and the remote
RS. This signalling is still inadequate for in-system failure correction.
For example: If the remote LAN equipment has a failure in the PCS layer,
this will be declared to the local RS as a local fault. The far end will
still receive data (as defined). Since the local port is in LF, the operator
would query the MDIO (if installed) to determine the source of the
fault. The local RS may or may not be transmitting data at this time.
Discovering no fault, the operator would run local diags to isolate the
source of the local fault. In the meantime, the far end device which is
the source of the error has no why of knowing it has a problem.
When the local operator has gone through the all built-in checks and
found nothing (likely changed the line card just to be sure), the
port is reconnected to discover the LF is still present. The local
operator must then inform the remote operator that the fault
may be in that system even though the remote system displays
no fault condition.
Suggested remedy:  Change the signalling so that LF defines
a failure between the input to the PMD and the RS. RF defines
a failure between the remote RS and the local PMD input. This requires
another bit in table 46-4 defined as far-end fault. Far-end
fault (FEF) is the feedback mechanism in the RS to RS communication.
When the RS receives an RF, it clears the RF and sets the
FEF.  When an RS receives a FEF, it knows the error is in its
transmit path.
Similarly a LF condition is terminated by the RS. The remote
device does not know that the local device is broken, since
there is no corrective action to be taken at the remote site.
This can be communicated in the MAC to MAC layers.

Tim Warland     P.Eng.
Hardware Design Engineer  Broadband Products
High Performance Optical Component Solutions
Nortel Networks                (613)765-6634