TECHNOLOGY

Pseudowire

Frame Relay, IP and ATM

The HSX 6000 supports Frame Relay, ATM, and Ethernet attachment circuit (AC) types. Multiprotocol Label Switching (MPLS) label switch paths (LSPs) are used for the tunneling technology.

For example, as illustrated in Figure 4-3, the attachment circuit (AC) at provider edge one (PE1) could be Frame Relay while the AC at provider edge 2 (PE2) is ATM. A PDU transmitted from CE1 to CE2 is interworked from FR to IP at PE1. At PE2, it is interworked from FR to IP to ATM, which is another key advantage of the ARP technique.

The Layer 2 address is not carried within each PDU between the PE nodes on an IP PW circuit. Therefore, the destination Layer 2 address must be resolved between the CE and PE nodes for the circuit. For the MPLS core to be truly transparent, the PE must translate ARP (and Inverse ARP) requests from the CE and generate ARP (or Inverse ARP) responses. The ARP response contains the mapping of the IP address to the Layer 2 address, which allows the CE to forward unicast IP traffic toward a destination. The PE nodes act as a kind of ARP proxy for the CE nodes associated with peer PE nodes.