Vll Resilience With Two Destination Pe Nodes; Figure 48: Vll Resilience - Alcatel-Lucent 7750 SR Manual

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Virtual Leased Line Services

VLL Resilience with Two Destination PE Nodes

illustrates the application of pseudowire redundancy to provide Ethernet VLL service

resilience for broadband service subscribers accessing the broadband service on the service

provider BRAS.

If the Ethernet SAP on PE2 fails, PE2 notifies PE1 of the failure by either withdrawing the

primary pseudowire label it advertised or by sending a pseudowire status notification with the

code set to indicate a SAP defect. PE1 will receive it and will immediately switch its local SAP to

forward over the secondary standby spoke SDP. In order to avoid black holing of in-flight packets

during the switching of the path, PE1 will accept packets received from PE2 on the primary

pseudowire while transmitting over the backup pseudowire. However, in other applications such

as those described in

Access Node Resilience Using MC-LAG and Pseudowire Redundancy on

225, it will be important to minimize service outage to end users.

When the SAP at PE2 is restored, PE2 updates the new status of the SAP by sending a new label

mapping message for the same pseudowire FEC or by sending pseudowire status notification

message indicating that the SAP is back up. PE1 then starts a timer and reverts back to the primary

at the expiry of the timer. By default, the timer is set to 0, which means PE1 reverts immediately.

A special value of the timer (infinity) will mean that PE1 should never revert back to the primary

The behavior of the pseudowire redundancy feature is the same if PE1 detects or is notified of a

network failure that brought the spoke SDP operational status to DOWN. The following are the

events which will cause PE1 to trigger a switchover to the secondary standby pseudowire:

7750 SR OS Services Guide