Alcatel-Lucent 9500 MXC, Руководство пользователя

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Chapter 3. 9500 MXC Nodes
Vol. II-3-62 Alcatel-Lucent
Link Status Propagation
Link Status Propagation is enabled to enhance rapid detection by
externally-connected equipment of the status of a DAC GE channel. It does so by
capturing the channel status (up/down) on the DAC GE ports to force a port
shutdown in the event of a channel failure, such as a radio link failure. A port
shutdown is immediately detected by the connected equipment.
For example, when operating with an external RSTP switch, a failure on a DAC
GE transport channel is reflected directly to the external user device through a
DAC GE port shut-down to support improved link failure detection times for
these devices, compared to the times needed for conventional hello time-out or
polling time-out using control frames.
It also applies to DAC GE L2 link aggregation, when co-located INUs are
installed to provide the physical links. Link aggregation functionality depends
directly on the aggregated port status to confirm the operational status of the
aggregated link.
For more information on link status propagation, refer to Procedure for DAC GE
Configuration, Volume IV, Chapter 7.
Link Aggregation
Link aggregation brings together two or more links to support a single interface
with a traffic capacity that is the sum of the individual link capacities.
Link aggregation also supports redundancy. If one link fails, then capacity
available on the remaining link or links is shared. While the reduced bandwidth
may result in some traffic loss for low-priority traffic, it should ensure security
for all higher priority traffic.
For 9500 MXC two modes of link aggregation can be configured with the DAC
GE, layer 2 (L2) or layer 1 (L1):
• L2 link aggregation uses source and/or destination MAC address data in the
Ethernet frame MAC/LLC header to determine which traffic stream is to be
forwarded over which link.
• The assignment (load balancing) of traffic between links generally ensures
that traffic is distributed equitably so that no one link is overwhelmed. The
weighting mechanism used operates well where there are many MAC
sessions in play. However it is not effective where one source/destination
MAC address is in play, such as between two routers, and has limited
effectiveness where a few (less than 10) concurrent sessions are in play,
especially so where one or two traffic streams dominate throughput on one
link.
• The weighting mechanism operates with link aggregation keys (LAKs),
where 16 such keys are split between the aggregated channels, and/or ports.
In turn, traffic (MAC sessions) are randomly assigned to a LAK.