Added a new Section 3.5 introducing the peering concept in more detail, removing
some of the related terminology details and providing forward pointers to the
relevant normative sections.

New section 3.5:

3.5.  GIST Peering Relationships

   Peering is the process whereby two GIST nodes create message routing
   state which point to each other.

   A peering relationship can only be created by a GIST handshake.
   Nodes become peers when one issues a Query and gets a Response from
   another.  Issuing the initial Query is a result of an NSLP request on
   that node, and the Query itself is formatted according to the rules
   of the message routing method.  For current MRMs, the identity of the
   Responding node is not known explicitly at the time the Query is
   sent; instead, the message is examined by nodes along the path until
   one decides to send a Response, thereby becoming the peer.  If the
   node hosts the NSLP, local GIST and signalling application policy
   determine whether to peer; the details are given in Section 4.3.2.
   Nodes not hosting the NSLP forward the Query transparently
   (Section 4.3.4).

   An exisiting peering relationship can only be changed by a new GIST
   handshake; in other words, it can only change when routing state is
   refreshed.  On a refresh, if any of the factors in the original
   peering process have changed, the peering relationship can also
   change.  As well as network level rerouting, changes could include
   modifications in NSIS signalling functions deployed at a node, or
   alterations to signalling application policy.  A change could cause
   an existing node to drop out of the signalling path, or a new node to
   become part of it.  All these possibilities are handled as rerouting
   events by GIST; further details of the process are described in
   Section 7.1.

From Ted Hardie:

	I am concerned that the peer discovery process is scattered 
throughout the document in ways that will make it difficult for 
implementors.  The document says:

[Adjacent] Peer:      The next node along the data path, in 
the upstream
      or downstream direction, with which a GIST node explicitly
      interacts.  The GIST peer discovery mechanisms implicitly
      determine whether two nodes will be adjacent.  It is possible for
      adjacencies to skip over intermediate nodes which decide not to
      take part in the signaling exchange at the NTLP layer; even if
      such nodes process parts of the signaling messages, they store no
      state about the session and are never visible at the GIST level to
      the nodes on either side.

and

    GIST defines a three-way handshake which
  probes the network to set up the necessary routing state between
  adjacent peers, during which signaling applications can also exchange
  data.

but the details are fairly well distributed in different sections.  
That means some related questions (such as whether an on-path node 
that was not initially part of the GIST layer interaction could insert 
itself later as a peer) are hard to work through.

I am willing to drop this request if there is significant push back, 
but I do believe that a gathered description of this would be a help 
to readers and implementors.