To improve the scalability of a SAP-per-subscriber model in the broadband services aggregator (BSA), the 7450 ESS and 7750 SR support a variant of split horizon groups called residential split horizon groups (RSHG).
A RSHG is a group of split horizon group SAPs with following limitations:
Downstream broadcast traffic is not allowed.
Downstream multicast traffic is allowed when IGMP snooping is configured in the VPLS.
STP is not supported.
Spoke SDPs can also be members of a RSHG VPLS. The downstream multicast traffic restriction does not apply to spoke SDPs.