UNI LSP Graceful Deletion

UNI LSPs can be deleted in either of the following modes:

Graceful deletion: The ingress EN sends a Path message carrying an Admin_Status object with the delete (D) bit of 1 along a UNI LSP. Each node that receives the message along the UNI LSP disables the alarm function and starts a graceful deletion timer. After receiving the message, the egress EN replies with a Resv message carrying the Admin_Status object with the D bit of 1. The Resv message travels through the UNI LSP hop by hop to reach the ingress EN. The ingress EN sends a PathTear message to instruct the nodes to delete the UNI LSP after receiving the Resv message or after the graceful deletion timer expires.
Forcible deletion: Its process is similar to the process for deleting MPLS LSPs. The details are not provided.

The forcible deletion mode used on a transport network leads to a protection switchover and relevant alarms. To prevent unneeded switchovers and alarms, graceful deletion is used.

Graceful deletion is triggered in either of the following modes:

Triggered by configuration: A user runs the shutdown or reset command for a GMPLS UNI LSP, or modifies a GMPLS UNI tunnel attribute on the ingress EN. After this, a UNI LSP is deleted.
Triggered by a Notify message: A Notify message carries an Admin_Status object with the D bit of 1. It originates from internal transport nodes or the NMS and reaches the ingress EN. After receiving the message, the ingress EN deletes a UNI LSP.