The application as shown in Figure 1 provides access to a VPLS service to Frame Relay and ATM users connected either directly or through an ATM access network to a 7750 SR PE node. The 7750 SR supports a Frame Relay or an ATM VC-delimited Service Access Point (SAP) terminating on a VPLS service.
RFC 2427-encapsulated or RFC 2684-encapsulated untagged Ethernet/802.3 frames (with or without Frame Check Sequence (FCS)) or BPDUs from a customer’s bridge device are received on a specified SAP over an ATM or Frame Relay interface on the 7750 SR. The Frame Relay or ATM-related encapsulation is stripped and the frames (without FCS) are forwarded toward destination SAPs either locally, or using SDPs associated with the VPLS service (as required by destination MAC address VPLS processing). In the egress direction, the received untagged frames are encapsulated into RFC 2427 or RFC 2684 (no Q-tags are added, no FCS in the forwarded frame) and sent over ATM or a FR VC toward the customer CPE.
When AAL5 RFC 2427/2684-encapsulated tagged frames are received from the customer’s bridge on an FR/ATM SAP, the tags are transparent and the frames are processed as described above with the exception that the frames forwarded toward the destinations have the received tags preserved. Similarly in the egress direction, the received tagged Ethernet frames are encapsulated as is (that is, Q-tags are again transparent and preserved) into RFC 2427/2684 and sent over the FR/ATM PVC toward the customer CPE. Because the tagging is transparent, the 7750 SR performs unqualified MAC learning (for example, MAC addresses are learned without reference to VLANs they are associated with). Because of that, MAC addresses used must be unique across all the VLANs used by the customer for a specified VPLS service instance. If a customer wants a per-VLAN separation, the VLAN traffic that needs to be separated must come on different VCs (different SAPs) associated with different VPLS service instances.
All VPLS functionality available on the 7750 SR is applicable to FR and ATM-delimited VPLS SAPs. For example, bridged PDUs received over ATM SAP can be tunneled through or dropped, all FIB functionality applies, packet level QoS and MAC filtering applies, and so on. Also, split horizon groups are applicable to ATM SAPs terminating on VPLS. That is, frame forwarding between ATM SAPs, also referred to as VCI-to-VCI forwarding, within the same group is disabled.
The Ethernet pseudowire is established using Targeted LDP (TLDP) signaling and uses the ether, vlan, or vpls VC type on the SDP. The SDP can be an MPLS or a GRE type.