1348 CHAPTER 77: MPLS TE C ONFIGURATIONThey are different in that CR-LDP establishes LSPs using TCP while RSVP-TE usingraw IP.RSVP is a well-established technology in terms of its architecture, protocolprocedures and support to services; while CR-LDP is an emerging technology withbetter scalability.Both CR-LDP and RSVP-TE are supported on your device.Forwarding packetsPackets are forwarded over established tunnels.CR-LSP Unlike ordinary LSPs established based on routing information, CR-LSPs areestablished based on criteria such as bandwidth, selected path, and QoSparameters in addition to routing information.The mechanism setting up and managing constraints is called constraint-basedrouting (CR).CR-LSP involves these concepts:■ “Strict and loose explicit routes” on page 1348■ “Traffic characteristics” on page 1348■ “Preemption” on page 1348■ “Route pinning” on page 1349■ “Administrative group and affinity attribute” on page 1349■ “Reoptimization” on page 1349Strict and loose explicit routesAn LSP is called a strict explicit route if all LSRs along the LSP are specified.An LSP is called a loose explicit route if the downstream LSR selection conditionsrather than LSRs are defined.Traffic characteristicsTraffic is described in terms of peak rate, committed rate, and service granularity.The peak and committed rates describe the bandwidth constraints of a path whilethe service granularity specifies a constraint on the delay variation that the CR-LDPMPLS domain may introduce to a path’s traffic.PreemptionCR-LDP signals the resources required by a path on each hop of the route. If aroute with sufficient resources cannot be found, existing paths may be rerouted toreallocate resources to the new path. This is called path preemption.Two priorities, setup priority and holding priority, are assigned to paths for makingpreemption decision. Both setup and holding priorities range from 0 to 7, with alower numerical number indicating a higher priority.
