TECHNOLOGY

Pseudowire

The underlying network of Pseudowire is typically MPLS, meaning that the Pseudowire is built on top of an MPLS tunnel. Each tunnel is capable of carrying a large number of Pseudowires. This aggregation of Pseudowire traffic at the edge provides scalability advantages within the core of the network.

For example, the state of the Pseudowire circuit is not managed in the core, and a few tunnels can be used to carry the traffic of thousands of Pseudowires. At the PE nodes, ingress AC PDUs are re-encapsulated into an MPLS frame which includes a Pseudowire label and a tunnel label. Within the network core, these MPLS frames are switched by the tunnel label until the frame reaches the egress PE node. At the egress PE node, the PWE3 is de-multiplexed by the PW label, and the original Layer 2 service PDU is recovered. The PDU is then transmitted over the attachment circuit (AC) to the customer edge (CE) node. Pseudowire functions implemented in the HSX 6000 platform include:

Encapsulate service-specific bit streams, cells, or PDUs arriving at a logical or physical ingress port.

Carry encapsulated data across a PSN.

Establish the Pseudowire (PWid and Generalized PWid Fec), including the exchange and/or distribution of the Pseudowire identifiers that are used by the PSN tunnel endpoints.

Switch Pseudowires

Manage the signaling, timing, order, or other aspects of the service at the boundaries of the Pseudowire.

Manage service-specific alarm status.

Automatically establish multi segment Pseudowires (MS-PW)

For all service types, Pseudowire frames share a common base format that includes a 4-byte Pseudowire label and a 4-byte control word. The control word contains protocol information and the interpretation of the bits within the control word varies, based on the protocol. For example, for Frame Relay Pseudowire, the FECN, BECN, DE, CLP and Command/Reponse bits are emulated. The payload of the Pseudowire frame is the payload of the FR PDU.