This read-only value identifies the VCI of the uni-directional multicast send connection between the LEC and BUS, paired with busClientMSendVpi. Verifying cell counts specifically on this VCI is how an admin confirms whether a particular client's broadcasts are even reaching the BUS in the first place, before looking at distribution problems further downstream. Correlating a lack of activity on this VCI with a client's complaint that its broadcasts aren't reaching other stations confirms the fault is on the client's send path, not on BUS distribution.