Alcatel-Lucent 7210 SAS-X - Pseudowire Switching; Figure 14: Pseudowire Service Switching Node

Pseudowire Switching
Page 130 7210 SAS-X, R6 OS Services Guide
Pseudowire Switching
Note: 7210 SAS-X and 7210 SAS-R6 device can be configured as S-PE nodes. 7210 SAS-M and
7210 SAS-T nodes can be configured only as T-PE nodes.
The pseudowire switching feature provides the user with the ability to create a VLL service by
cross-connecting two spoke SDPs. This feature allows the scaling of VLL and VPLS services in a
large network in which the otherwise full mesh of PE devices would require thousands of Targeted
LDP (T-LDP) sessions per PE node.
Services with one SAP and one spoke SDP are created normally on the PE; however, the target
destination of the SDP is the pseudowire switching node instead of what is normally the remote
PE.
The pseudowire switching node acts in a passive role with respect to signalling of the pseudowires.
It waits until one or both of the PEs sends the label mapping message before relaying it to the other
PE. This is because it needs to pass the Interface Parameters of each PE to the other.
A pseudowire switching point TLV is inserted by the switching pseudowire to record its system
address when relaying the label mapping message. This TLV is useful in a few situations:
• It allows for troubleshooting of the path of the pseudowire especially if multiple
pseudowire switching points exist between the two PEs.
• It helps in loop detection of the T-LDP signalling messages where a switching point would
receive back a label mapping message it had already relayed.
• The switching point TLV is inserted in pseudowire status notification messages when they
are sent end-to-end or from a pseudowire switching node towards a destination PE.
Pseudowire OAM is supported for the manual switching pseudowires and allows the pseudowire
switching node to relay end-to-end pseudowire status notification messages between the two PEs.
The pseudowire switching node can generate a pseudowire status and to send it to one or both of
the PEs by including its system address in the pseudowire switching point TLV. This allows a PE
to identify the origin of the pseudowire status notification message.
In the Figure 14, the user configures a regular Epipe VLL service PE1 and PE2. These services
consist each of a SAP and a spoke SPD. However, the target destination of the SDP is actually not
the remote PE but the pseudowire switching node. In addition, the user configures an Epipe VLL
service on the pseudowire switching node using the two SDPs.
Figure 14: Pseudowire Service Switching Node
| PE1 (Epipe)|---sdp 2:10---| PW SW (Epipe)|---sdp 7:15---| PE2 (Epipe)|