HP J2415A Installation And Reference Manual page 79

Hub Reference
Chained Hub Operation
HP AdvanceStack hubs (both 100VG and 10Base-T hubs) can be connected
together with standard unshielded twisted-pair cable through their
Extension ports (RJ-45) creating a Distributed Management Chain. The
chain can support up to 16 hubs and can extend up to 185 meters
(end-to-end) so multiple wiring closets can be managed from a single
location (for example, a single PC running HP Stack Manager). Note that
this is not a network connection, it is only a management connection
between the hubs. For information on the cables used on a Distributed
Management Chain, refer to appendix A.
HP AdvanceStack hubs use a Distributed Management Protocol to pass
command and data communications over the Distributed Management
Chain.
4-9