[RPRWG] RPR: packet sequencing between multicast and unicast
Hi all,
Ethernet multicast: according to 802.1D, packet ordering is based on the 3-tuple <source MAC address, destination MAC address, priority>. All packets received by a bridge that can be identified by a given tuple must not be misordered by the bridge when the packet is retransmitted. There is no particular distinction between multicast destination addresses and unicast destination addresses. Thus it is permissible to arbitrarily reorder multicasts with respect to unicasts from the same source, subject of course to the usual limitations of protocol timers.
For RPR, it would be nice to allow arbitrarily reorder multicasts with respect to unicast in a similar way. This can significantly reduce the implementation cost of multicast. Basically, it relaxes the requirement of instantaneous packet replication (multicast packet needs to be put into receive queue and transit queue at the same time). This may be easy to do in some implementations, it may also be very hard to do in others.
- Heng Liao
PMC-Sierra, Inc.