The layer 4.5 APLS label carries
a stack of application meta-tags representing a sequence of
application segments.
The meta-tags is inserted by the
application end-points, at the egress of an application
segment, an APR pops the next meta-tag and maps it to a
two-tuple of the next application
segment. The two-tuple is placed into the layer 3.5 APLS
header, discussed next.