Alcatel-Lucent 7750 SR OS - Port Link Damping; Lacp; LAG Subgroups on Access for DSLAM Aggregation

Interface Configuration
7750 SR OS Interface Configuration Guide Page 113
Port Link Damping
Hold time controls enable port link damping timers that reduce the number of link transitions
reported to upper layer protocols.
The 7750 SR OS port link damping feature guards against excessive port transitions. Any initial
port transition is immediately advertised to upper layer protocols, but any subsequent port
transitions are not advertised to upper layer protocols until a configured timer has expired.
An “up” timer controls the dampening timer for link up transitions, and a “down” timer controls
the dampening timer for link down transitions.
LACP
Generally, link aggregation is used for two purposes: provide an increase in bandwidth and/or
provide redundancy. Both aspects are addressed by aggregating several Ethernet links in a single
LAG.
Under normal operation, all non-failing links in a given LAG will become active and traffic is load
balanced across all active links. In some circumstances, however, this is not desirable. Instead, it
desired that only some of the links are active (for example, all links on the same IOM) and the
other links be kept in stand-by condition.
LACP enhancements allow active lag-member selection based on particular constrains. The
mechanism is based on the IEEE 802.3ax standard so interoperability is ensured.
LAG Subgroups on Access for DSLAM Aggregation
Figure 21 shows interconnection between DSLAM and aggregation node by a LAG. In this
configuration, LAG is used not only to provide higher bandwidth but also to protect against
hardware failure. LAG members are typically distributed across different IOMs to eliminate single
point of failure.
At the same time, QoS SLA enforcement is required. Enforcing QoS policies across links attached
to different IOMs is not possible and therefore it is desirable that traffic always flows through a
single IOM. This can be achieved by selecting only links of a single IOM as active LAG members
and keeping all other LAG members in stand-by condition.
In case of a link failure, Figure 22 and Figure 23, the switch over mechanism must take into
account the above QoS restriction. This means that all lag-members connected to the same IOM as
failing link will become stand-by and lag-members connected to other IOM will become active.