H3C Technologies H3C S10500 Series Switches - Manual (Page 99)

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CSPF first prunes TE attribute incompliant links from the TEDB and then performs SPF calculation to
identify the shortest path to an LSP egress.
Establishing paths
When setting up LSP tunnels, you can use two types of signaling: CR-LDP and RSVP-TE. Both can carry
constraints such as LSP bandwidth, some explicit route information, and color and deliver the same
function.
They are different in that CR-LDP establishes LSPs using TCP while RSVP-TE uses raw IP.
RSVP is a well-established technology in terms of its architecture, protocol procedures and support to
services. CR-LDP is an emerging technology with better scalability.
The switch supports only the RSVP-TE signaling protocol.
Forwarding packets
Packets are forwarded over established tunnels.
CR-LSP
Unlike ordinary LSPs established based on routing information, CR-LSPs are established based on criteria
such as bandwidth, selected path, and QoS parameters in addition to routing information.
The mechanism setting up and managing constraints is called Constraint-based Routing (CR).
CR-LSP involves the following concepts:
• Strict and loose explicit routes
• Traffic characteristics
• Preemption
• Route pinning
• Administrative group and affinity attribute
• Reoptimization
Strict and loose explicit routes
An 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 conditions rather than LSRs are
defined.
Traffic characteristics
Traffic is described in terms of peak rate, committed rate, and service granularity.
The peak and committed rates describe the bandwidth constraints of a path.
Preemption
During establishment of a CR-LSP, if a path with sufficient resources cannot be found, the CR-LSP can be
established by preempting the resources of a lower-priority CR-LSP. This is called path preemption.
Two priorities, setup priority and holding priority, are assigned to CR-LSPs for making preemption
decision. Two priorities, setup priority and holding priority, are assigned to paths for making preemption
decision. Both setup and holding priorities range from 0 to 7, with a lower numerical number indicating
a higher priority.