To do this, targeted LDP
sessions are configured between the ABRs in each area and all their local LERs, and a
full mesh of RSVP-TE LSPs is created between all the ABRs and LERs in each area.
Further hierarchical scaling approaches are possible, for example using RSVP-TE to
create forwarding adjacencies over which other RSVP-TE LSPs may be signalled.
MPLS QoS
There are two fundamental aspects to Quality of Service (QoS) in packet-switched
networks:
?– Ensuring the network can meet the QoS requirements before the packet is sent
?– Enforcing QoS in the network elements as packets are forwarded
MPLS 433
The former requirement is addressed in the control plane, and the latter in the forwarding
plane. The forwarding plane mechanisms used for QoS enforcement are generally
based on using multiple queues that are scheduled in strict order of priority,
using some form of round robin mechanism or a combination of both. Packets that are
classified into the same queue will maintain order throughout the network, but order
will not be maintained across queues. Packets may also be marked with an indicator of
their drop precedence to enable the network elements to decide which packets to drop
first during congestion, using algorithms such as Weighted Random Early Detection
(WRED).
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