How two SFU cooperate while they provide distributed work?

[chinaluochao]

There is one room named testRoom. One client(A) communicates with SFU C in testRoom via signal process, and another one client(B) communicates SFU D in testRoom via signal process. (as far as I understand signal process will find a grpc service with same name random). SFU C will provide it's own publisher's tracks to A, SFU D will provide it's own publisher's tracks to B. So how SFU D provide B's track to A, and how SFU C provide A's track to B?