Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 42)

18 Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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Traffic engineering database
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When setting up an LSP, the device actually performs admission control twice: when the Path
message is received and when the Resv message is received. when the LSP passes admission
control after the Resv message is received, bandwidth allocation and LSP preemption take place.
The sections that follow include examples of how admission control, bandwidth allocation, and
preemption work.
Admission control
Admission control examines the LSPs setup priority and mean-rate settings to determine whether
the LSP can be activated. To pass admission control, the reservable bandwidth available at the
LSPs setup priority level must be greater than the value specified by its mean-rate.
For example, when the maximum reservable bandwidth on an interface is 10,000 Kbps and no
LSPs are currently active, the amount of reservable bandwidth on the interface for each priority
level would be as follows:
Priority Unreserved Bandwidth
0 10,000
1 10,000
2 10,000
3 10,000
4 10,000
5 10,000
6 10,000
7 10,000
Active LSPs: None
The LSR receives a Resv message for an LSP that has a configured setup priority of 6 and a hold
priority of 3. The mean-rate specified for this LSP is 1,000 Kbps. For priority level 6, up to 10,000
Kbps can be reserved. Because the configured mean-rate for this LSP is only 1,000 Kbps, the new
LSP passes admission control.
Bandwidth allocation
Once the LSP passes admission control, bandwidth is allocated to it. The bandwidth allocation
procedure examines the LSPs hold priority and mean-rate settings. The amount of bandwidth
specified by the mean-rate is allocated to the LSP, using reservable bandwidth available at the
LSPs hold priority level.
In this example, the LSPs hold priority is three and mean-rate is 1,000 Kbps. On this interface, for
priority level three, up to 10,000 Kbps can be reserved. The amount of bandwidth specified by the
mean-rate (1,000 Kbps) is allocated to the LSP.
After bandwidth is allocated to this LSP, the amount of unreserved bandwidth on the interface is
reduced accordingly. In the example, the reservable bandwidth array for the interface now looks
like this: