Does SPB really replace STP? I have been reading IEEE 802.1Q 2014 about SPB. I also have watched a few videos about SPB on youtube. However I don't understand why no one mentioned that BPDUs are still transmitted in the network, and IEEE 802.1Q have wrote about SPB in many sections in Spanning Tree. If IS-IS controls SPB network, why BPDU are still required? I know Agreement Digest is for preventing temporary loop during topology change. But why is it transmitted inside BPDU?

I just figured it out. Because SPB calculates its CIST for compatibility with STP. So the result of CIST calculation is hashed and put into BPDU agreement digest field.

This way SPB nodes can ensure neighbor SPB nodes have same CIST result.