HP J3188A Installation And Reference Manual page 72

Backup Links
Examples of Backup Links
When the primary link is repaired, you must re-enable the primary port. It is
not re-enabled automatically. When the primary port is enabled, the backup
port is automatically disabled and returned to backup mode. See "Reactivating
the Primary Link" later in this appendix.
N o t e
S u g g e s t i o n
The primary link and the backup link cabling should be run over different
paths (through different conduits, for example) to reduce the possibility that
damage will occur to both cables simultaneously.
E-4
Any combination of media types can be used as a backup link by attaching
an external transceiver to the AUI port. This port accepts fiber, thin coax,
twisted-pair external transceivers. For example, a thin coax link from the
ThinLAN port can act as a backup link to a twisted-pair link.
The hub can monitor only one link.
The remote device should have no more than 2 backup links connected
to it from a monitoring hub. If the remote device has more than 2 backup
links functioning, it may not be able to respond to the test packets fast
enough when there is a high level of data traffic on the network segments.
This ability to respond may be improved by increasing the time between
test packet transmissions on the monitoring hubs. For all the backup links
in which the remote device is involved, the time configured on the
monitoring hubs for those links should be increased by one second for
each additional backup link beyond two links. Add one to this count if the
remote device is also functioning as a primary (monitoring) hub for a
different link.