An alternative
is to use OAM messages in the MPLS forwarding plane (e.g., BFD) and to send
these along each LSP from the ingress LSR to the egress. This would generally be used
for LSPs provisioned either with static configuration or an out-of-band control plane
such as GMPLS. In either case, there will be no in-band control plane to propagate
fault status. OAM-based fault detection may be used with LSPs provisioned either in a
1:1 mode, where traffic is forwarded over the primary path but is switched to the secondary
path when OAM flows detect a break in the primary path, or in a 1+1 mode where
traffic is forwarded simultaneously over both paths and the egress LSR selects which
traffic to forward, and which to discard, based on receipt of OAM messages. The 1+1
mode is capable of sub-50-ms protection (detection time is a function of the frequency
with which OAM packets are sent??”typically the LSP is declared down after three packets
are missed). However, the 1:1 mode, requires the egress to inform the ingress of the
error condition, and the ingress to switch from the working to the protect path, and thus
incurs at least one roundtrip time of additional delay when compared to the 1+1 mode.
Pages:
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970