HEADERS_XML = {'Content-Type': 'application/xml'}
ACCEPT_XML = {'Accept': 'application/xml'}
ACCEPT_JSON = {'Accept': 'application/json'}
+ACCEPT_EMPTY = {} # Json should be default, but no-output RPC cannot have Accept header.
ODL_CONTROLLER_SESSION = None
TOPO_TREE_LEVEL = 2
TOPO_TREE_DEPTH = 3