The SR OS model supports PBB Epipes and I-VPLS services on the B-VPLS. SPB is added to B-VPLS in place of other control planes (see Table 1). SPB runs in a separate instance of IS-IS. SPB is configured in a single service instance of B-VPLS that controls the SPB behavior (via IS-IS parameters) for the SPB IS-IS session between nodes. Up to four independent instances of SPB can be configured. Each SPB instance requires a separate control B-VPLS service. A typical SPB deployment uses a single control VPLS with zero, one or more user B-VPLS instances. SPB is multi-topology (MT) capable at the IS-IS LSP TLV definitions however logical instances offer the nearly the same capability as MT. The SR OS SPB implementation always uses MT topology instance zero. Area addresses are not used and SPB is assumed to be a single area. SPB must be consistently configured on nodes in the system. SPB Regions information and IS-IS hello logic that detect mismatched configuration are not supported.
SPB Link State PDUs (LSPs) contains B-MACs, I-SIDs (for multicast services) and link and metric information for an IS-IS database. Epipe I-SIDs are not distributed in SR OS SPB allowing high scalability of PBB Epipes. I-VPLS I-SIDs are distributed in SR OS SPB and the respective multicast group addresses are automatically populated in forwarding in a manner that provides automatic pruning of multicast to the subset of the multicast tree that supports I-VPLS with a common I-SID. This replaces the function of MMRP and is more efficient than MMRP so that in the future, SPB scales to a greater number of I-SIDs.
SPB on SR OS can leverage MPLS networks or Ethernet networks or combinations of both. SPB allows PBB to take advantage of multicast efficiency and at the same time leverage MPLS features such as resiliency.