Pseudowire Switching - Alcatel-Lucent 7705 Service Manual

Pseudowire Switching

The pseudowire switching feature provides the user with the ability to create a VLL service
by cross-connecting two spoke SDPs.
Services with one SAP and one spoke SDP are created normally on the PE; however, when a
pseudowire originates at customer equipment and not the 7705 SAR, the target destination
of the SDP is the 7705 SAR pseudowire switching node instead of the remote PE. In such
cases, the user must configure a VLL service on the pseudowire switching node (the
7705 SAR, in this case) using the two SDPs and no SAP. This creates a VLL service that
travels over two different types of tunnels. The first pseudowire segment connects the Node
B to the 7705 SAR, and the second segment connects the 7705 SAR to a 7750 SR node.
Figure 29
For the 7750 SR node, there is no implementation change required. The pseudowire segment
is treated as a 7705 SAR-initiated dynamic ATM pseudowire. The 7705 SAR signals for the
ATM pseudowire and negotiates all required parameters, including the pseudowire label,
control word, and VCCV type.
The pseudowire switching node acts in a passive role with respect to signaling of the
pseudowires. The node waits until one or both of the PEs send 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. For example, the 7705 SAR assumes the pseudowire payload from the
Node B, then signals for the ATM pseudowire to the far end and negotiates all required
parameters, including the pseudowire label, control word, and VCCV type.
The switching pseudowire inserts a pseudowire switching point TLV indicating the system
address in the label mapping message. This TLV is useful because it allows for
troubleshooting of the path of the pseudowire, especially if multiple pseudowire switching
points exist between the two PEs. The TLV also helps in loop detection of TLDP signaling
messages, where a switching point receives a label mapping message that it 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. See
Pseudowire Switching TLV
Pseudowire OAM is supported for dynamic switching pseudowires and allows the
7705 SAR pseudowire switching node to relay end-to-end pseudowire status notification
messages between the two PEs. The 7705 SAR can generate a pseudowire status and send it
to one, or both, of the PEs by including its system address in the pseudowire switching point
TLV. This allows a 7705 SAR PE to identify the origin of the pseudowire status notification
message.
7705 SAR OS Services Guide
shows an example of a VLL pseudowire switching service.
for more information.
VLL Services
Page 173