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Feature Description - MPLS 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - MPLS
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Establishing a CR-LSP Using RSVP-TE

Establishing a CR-LSP Using RSVP-TE

RSVP-TE is an extension to RSVP. RSVP is designed for the Integrated Service model and runs on every node of path for resource reservation. RSVP is a control protocol working at the transport layer, but does not transmit application data. It establishes or tears down LSPs using TE attributes carried in extended objects.

RSVP-TE has the following characteristics:

  • Unidirectional: RSVP-TE only takes effect on traffic that travels from the ingress to the egress.

  • Receive end-oriented: A receive end initiates a request to reserve resources and maintains resource reservation information.

  • Soft state-based: RSVP uses a soft state mechanism to maintain the resource reservation information.

RSVP-TE Messages

RSVP-TE messages are as follows:

  • Path message: used to request downstream nodes to distribute labels. A Path message records path information on each node through which the message passes. The path information is used to establish a path state block (PSB) on a node.

  • Resv message: used to reserve resources at each hop of a path. A Resv message carries information about resources to be reserved. Each node that receives the Resv message reserves resources based on reservation information carried in the message. The reservation information is used to establish a reservation state block (RSB) and to record information about distributed labels.

  • PathErr message: sent upstream by an RSVP node if an error occurs during the processing of a Path message. A PathErr message is forwarded by every transit node and arrives at the ingress.

  • ResvErr message: sent downstream by an RSVP node if an error occurs during the processing of a Resv message. A ResvErr message is forwarded by every transit node and arrives at the egress.

  • PathTear message: sent downstream by the ingress to delete information about the local state created on every node of the path.

  • ResvTear message: sent upstream by the egress to delete the local reserved resources assigned to a path. After receiving the ResvTear message, the ingress sends a PathTear message to the egress.

Process of Establishing an LSP

Figure 4-9 Schematic diagram for the establishment of a CR-LSP

Figure 4-9 shows the process of establishing a CR-LSP. The process is as follows:

  1. The ingress configured with RSVP-TE creates a PSB and sends a Path message to transit nodes.

  2. After receiving the Path message, the transit node processes and forwards this message, and creates a PSB.

  3. After receiving the Path message, the egress creates a PSB, uses bandwidth reservation information in the Path message to generate a Resv message, and sends the Resv message to the ingress.

  4. After receiving the Resv message, the transit node processes and forwards the Resv message and creates an RSB.

  5. After receiving the Resv message, the ingress creates an RSB and confirms that the resources are reserved successfully.

  6. The ingress successfully establishes a CR-LSP to the egress.

Soft State Mechanism

The soft state mechanism enables RSVP nodes to periodically send Path and Resv messages to synchronize states (including states in the PSB and RSB) between RSVP neighboring nodes or to resend RSVP messages that have been dropped. If an RSVP node does not receive an RSVP matching a specific state within a specified period of time, the RSVP node deletes the state from a state block.

A node can refresh a state in a state block and notifies other nodes of the refreshed state. In the tunnel re-optimization scenario, if a route changes, the ingress is about to establish a new LSP. RSVP nodes along the new path send Path messages downstream to initialize PSBs and receive Resv messages responding to create new RSBs. After the new path is established, the ingress sends a Tear message downstream to delete soft states maintained on nodes of the previous path.

Reservation Styles

A reservation style defines how a node reserves resources after receiving a request sent by an upstream node. The NE supports the following reservation styles:

  • Fixed filter (FF): defines a distinct bandwidth reservation for data packets from a particular transmit end.

  • Shared explicit (SE): defines a single reservation for a set of selected transmit ends. These senders share one reservation but assign different labels to a receive end.

Updated: 2019-01-14

Document ID: EDOC1100058933

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