Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 39)

Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide 15
53-1003031-02
Traffic engineering database
1
How RSVP establishes a signaled LSP
The traffic-engineered path calculated by CSPF consists of a sequential list of physical interface
addresses, corresponding to a path from the ingress LER to the egress LER. Using this
traffic-engineered path, RSVP establishes the forwarding state and resource reservations on each
LSR in the path.
As with OSPF, special extensions for traffic engineering are defined for RSVP. These extensions
include the EXPLICIT_ROUTE, LABEL_REQUEST, LABEL, and RECORD_ROUTE objects in addition to
the Fixed Filter (FF) reservation style. These extensions are described in RFC 3209.
The following diagram illustrates how RSVP establishes a signaled LSP.
FIGURE 6 How RSVP establishes a signaled LSP
RSVP signaling for LSPs works as described below.
1. The ingress LER sends an RSVP Path message towards the egress LER.
The Path message contains the traffic engineered path calculated by the CSPF process,
specified as an EXPLICIT_ROUTE object (ERO). The Path message travels to the egress LER
along the route specified in the ERO.
The Path message also describes the traffic for which resources are being requested and
specifies the bandwidth that needs to be reserved to accommodate this traffic. In addition, the
Path message includes a LABEL_REQUEST object, which requests that labels be allocated on
LSRs and tells the egress LER to place a LABEL object in the Resv message that it sends back
to the ingress LER.
Before sending the Path message, the ingress LSR performs admission control on the
outbound interface, ensuring that enough bandwidth can be reserved on the interface to meet
the LSPs requirements. Admission control examines the LSPs configured setup priority and
mean-rate settings. For the LSP to pass admission control, the outbound interface must have
reservable bandwidth at the LSPs setup priority level that is greater than the amount of
bandwidth specified by the LSPs mean-rate setting. Refer to
“Admission control, bandwidth
allocation, and LSP preemption” , for more information and examples of this process.
2. The Path message requests resource reservations on the LSRs along the path specified in the
ERO.