Pw Control Channel Status Notifications (Static Pseudowire Status Signaling) - Alcatel-Lucent 7450 Manual

BFD-based RDI
RDI provides a mechanism whereby the source MEP can be informed of a downstream failure on
an LSP, and can thus either raise an alarm, or initiate a protection switching operation. In the case
of BFD based CC/CV, RDI is communicated using the BFD diagnostic field in BFC CC/CV
messages. The following diagnostic codes are supported:
1 - Control Detection Time Expired
9 - mis-connectivity defect
PW Control Channel Status Notifications (Static Pseudowire Status Signal-
ing)
MPLS-TP introduces the ability to support a full range of OAM and protection / redundancy on
PWs for which no dynamic T-LDP control plane exists. Static PW status signaling is used to
advertise the status of a PW with statically configured labels by encapsulating the PW status TLV
in a G-ACh on the PW. This mechanism enables OAM message mapping and PW redundancy for
such PWs, as defined in RFC6478. This mechanism is known as control channel status signaling
in SR OS.
PW control channel status notifications use a similar model to T-LDP status signaling. That is, in
general, status is always sent to the nearest neighbor T-PE or S-PE and relayed to the next segment
by the S-PE. To achieve this, the PW label TTL is set to 1 for the G-ACh packet containing the
status message.
Control channel status notifications are disabled by default on a spoke-SDP. If they are enabled,
then the default refresh interval is set to zero (although this value should be configurable in CLI).
That is, when a status bit changes, three control channel status packets will be sent consecutively
at one-second intervals, and then the transmitter will fall silent. If the refresh timer interval is non-
zero, then status messages will continue to be sent at that interval. The system supports the
configuration of a refresh timer of 0, or from 10-65535 seconds. The recommended value is 600
seconds.
The system supports the optional acknowledgement of a PW control channel status message.
In order to constrain the CPU resources consumed processing control channel status messages, the
system implements a credit-based mechanism. If a user enables control channel status on a PW[n],
then a certain number of credits c_n are consumed from a CPM-wide pool of max_credit credits.
The number of credits consumed is inversely proportional to the configured refresh timer (the first
three messages at 1 second interval do not count against the credit). If the current_credit <= 0, then
control channel status signaling cannot be configured on a PW (but the PW can still be configured
and no shutdown).
7450 ESS MPLS Guide
MPLS and RSVP
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