The TE Router ID (reachable and stable IP address) of the
originator of the P2MP sub-group as received on a Path
message by a transit or egress LSR.
This object is interpreted in the context of
cmplsTeP2mpTunnelDestSrcSubGroupOriginType.
The value of the sub-group originator used on outgoing Path
messages is found in cmplsTeP2mpTunnelDestSubGroupOrigin and
is copied from this object unless this LSR is responsible
for changing the sub-group ID.
At an ingress LSR there is no received Path message.
cmplsTeP2mpTunnelDestSrcSubGroupOriginType should return
unknown(0), and this object should return a zero-length
string.