Physical-Link Failure Indicator; Link Failure - 3Com CoreBuilder 7000 Operation Manual

128 C 5: E
HAPTER STABLISHING
automatic retry
Physical-Link
Failure Indicator

Link Failure

ATM C
HANNELS


No VCC available — Number of VCCs exceed a limit


No rate available — No available bandwidth


Resources unavailable — Node internal resource problem
The crankback mechanism eliminates the need for the original
transmitting station to release and re-establish the call.
The crankback mechanism works as follows: If a virtual channel fails to be
established along one of the links, a RELEASE message will be sent back
to the switch that sent the SETUP message.
After receiving the RELEASE message, the source CoreBuilder 7000 family
ATM switch again attempts to establish a virtual channel but this time via
an alternate path. The switch determines the alternate path automatically
with the routing table that was established during the first connection
attempt. The routing table holds all the connection alternatives. The
CoreBuilder 7000 family ATM switch remembers which connection was
used in the failed attempt and chooses a different connection the second
time, resulting in a new and different path to the destination.
The availability of alternate paths for connections depends on the
addressing scheme that was used in setting up the network. Alternate
connections need to have the same match type (see "Alternate Routes"
on page 63 in the Management Guide).
For more information and examples of the crankback mechanism, see
publications of the 3Com Technical Education Services.
This section discusses the operation and configuration of the physical-link
failure indicator of the CoreBuilder 7000 family ATM switch. It includes
the following topics:


Link Failure


Link Failure Detection


Link-Failure Detection Sensitivity Control
When a physical link between a CoreBuilder 7000 family ATM switch and
a neighboring device fails, the virtual channels that carry calls through
that link are affected. The network acts to establish an alternate virtual
channel over the network to enable the call to continue.