MPLS and RSVP
7450 ESS MPLS Guide Page 109
Both of these admission decisions are enhanced to be performed at the TE class level when Diff-
Serv TE is enabled. In other words, CSPF in the head-end node will need to check the LSP
bandwidth against the ‘unreserved bandwidth’ advertised for all links in the path of the LSP for
that TE class which consists of a combination of a CT and a priority. Same for the admission
control at SR OS node receiving the Resv message.
Maximum Allocation Model
The admission control rules for this model are described in RFC 4125. Each CT shares a
percentage of the Maximum Reservable Link Bandwidth through the user-configured BC for this
CT. The Maximum Reservable Link Bandwidth is the link bandwidth multiplied by the RSVP
interface subscription factor.
The sum of all BC values across all CTs will not exceed the Maximum Reservable Link
Bandwidth. In other words, the following rule is enforced:
SUM (BCc) =< Max-Reservable-Bandwidth, 0 <= c <= 7
An LSP of class-type CTc, setup priority p, holding priority h (h=<p), and bandwidth B is
admitted into a link if the following condition is satisfied:
B <= Unreserved Bandwidth for TE-Class[i]
where TE-Class [i] maps to < CTc, p > in the definition of the TE classes on the node. The
bandwidth reservation is effected at the holding priority, i.e., in TE-class [j] = <CTc, h>. Thus, the
reserved bandwidth for CTc and the unreserved bandwidth for the TE classes using CTc are
updated as follows:
Reserved(CTc) = Reserved(CTc) + B
Unreserved TE-Class [j] = BCc - SUM (Reserved(CTc,q)) for 0<= q <= h
Unreserved TE-Class [i] = BCc - SUM (Reserved(CTc,q)) for 0<= q <= p
The same is done to update the unreserved bandwidth for any other TE class making use of the
same CTc. These new values are advertised to the rest of the network at the next IGP-TE flooding.
When Diff-Serv is disabled on the node, this model degenerates into a single default CT internally
with eight pre-emption priorities and a non-configurable BC equal to the Maximum Reservable
Link Bandwidth. This would behave exactly like CT0 with eight pre-emption priorities and BC=
Maximum Reservable Link Bandwidth if Diff-Serv was enabled.
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