To optimize wire efficiency, Subgroups and Datagrams refer to a track by a numeric identifier, rather than the Full Track Name. Track Alias is chosen by the publisher and included in SUBSCRIBE_OK (Section 9.8) or PUBLISH (Section 9.13).
Objects can arrive after a subscription has been cancelled. Subscribers SHOULD retain sufficient state to quickly discard these unwanted Objects, rather than treating them as belonging to an unknown Track Alias.