[mpls] draft-wijnands-mpls-mldp-in-band-signaling - PIM-Bidir

[Yakov Rekhter <yakov at juniper.net>]

Folks,

Last IETF at MPLS WG meeting I asked the authors to clarify the
procedures for handling PIM-Bidir sender-only branches with mLDP
in-band signaling. The latest (-02) version of the draft still
does not address this in sufficient level of details.

From section 1 of that draft:

                                When an IP multicast tree (either a
   source-specific tree or a bidirectional tree) enters the MPLS
   network, the IP multicast control messages used to set up the tree
   are translated into mLDP messages.  

In the case where we have PIM-Bidir sender-only branches (that do not
originate any PIM Join messages) what are "the IP multicast control
messages used to set up the tree", and how do these messages get 
"translated into mLDP messages" ?

From section 2.2 of that draft:

 2.2.  Transiting IP multicast bidirectional trees

   Bidirectional IP multicast trees [RFC5015] MUST be transported across
   a MPLS network using MP2MP LSPs.  A bidirectional tree does not have
   a specific source address; only the group address and subnet mask are
   relevant for multicast forwarding.  The RP for the group already
   known by IP multicast is used to select the ingress PE and root of
   the LSP.  The group address is encoded in either Section 3.3 or
   Section 3.4, depending on the IP version.  The subnet mask associated
   with the bidirectional group is encoded in the Transit TLV.  There
   are two types of bidirection states in IP multicast, the group
   specific state and the RPA state.  The first type is typlically
   created due to receiving a PIM join and has a subnet mask of 32 for
   IPv4 and 128 for IPv6, the latter is typically created via the RP
   mapping protocol and has a variable subnet mask.  The RPA state is
   used to build a tree to the RP and used for sender only branches.
   Please see [RFC5015] for more details.

The above talks about "the group specific state" and "the RPA state",

Could some of the branches of an MP2MP LSP be associated with just
the RPA state, while other branches of the *same* MP2MP LSP be
associated with the group specific state ? In other words, could
some branches of an MP2MP LSP be signaled using Transit IPv4 Bidir
TLV with mask length less than 32 (the branches associated with the
RPA state), while some other branches of *the same* MP2MP LSP be
signaled using Transit IPv4 Bidir TLV with mask length 32 (the
branches associated with the group specific state) ?

If yes, then what are the procedures at the nodes where the branches
of the MP2MP LSP that are associated with just the RPA state merge
into the part of the *same* MP2MP LSP that is associated with just
the group specific state ? 

Yakov.