Scheduling Function One (SF1) for hop-by-hop Scheduling in 6tisch Networks

Scheduling Function Zero (SF0) enables on-the-fly cell scheduling (ADD/DELETE) between 1-hop neighbors for aggregated (best-effort) traffic flows. In other words, all the instances from nodeA to nodeB in are scheduled in a single L3-bundle (IP link).

nodeA<------------------------------------------------- nodeB L3-bundle (Instance-1,Instance-2,...Instance-n) ]]> Some applications (e.g. Industrial M2M) require end-to-end dedicated L2-bundles to support control/data streams for time-critical applications . For such applications, per-instance L2-bundles need to be scheduled hop-by-hop in between sender and receiver . In addition, cells in the scheduled end-to-end L2-bundles of each instance may have to be dynamically adapted for bursty time-critical traffic flows. To achieve this, an end-to-end track has to be installed with a global TrackID for each isolated instance. With 1-hop based SF0 cell scheduling, it is difficult to schedule dedicated end-to-end cells for isolated traffic flows. Moreover, global bandwidth estimation through Resource Reservation protocol is required for bandwidth allocation in multi-hop cell scheduling. This draft specifies a Scheduling Function One (SF1) to schedule end-to-end dedicated L2-bundles for each instance, and to dynamically adapt the cells in already scheduled L2-bundles through the RSVP protocol (see ).

------------------> <------------------------ <------------------- L2-bundle(Instance-1) L2-bundle(Instance-1) L2-bundle(Instance-2) L2-bundle(Instance-2) ----------------------> -----------------> Sender<-----------------------nodeB <----------------- Receiver L2-bundle(Instance-2) L2-bundle(Instance-2) . . . . L2-bundle(Instance-n) L2-bundle(Instance-n) -----------------------> --------------------> <------------------------ <-------------------- L2-bundle(Instance-n) L2-bundle(Instance-n) ]]>

With SF1, the Sender determines when to reserve end-to-end resources, support implicit label switching (GMPLS), schedule the labeled L2-bundles hop-by-hop, associate the global TrackID for labeled L2-bundles, and dynamically adapt the cells in an existing instance through RSVP(Resource Reservation Protocol). The following events may trigger the use of SF1: If Sender has a outgoing bandwidth requirement for a new instance to transmit data to Receiver. If Sender has a new outgoing bandwidth requirement for an existing instance to transmit data to Receiver. In both cases, distributed RSVP(explained in ) is triggered to provide end-to-end resource reservations along with scheduling operations.

In this specification, an end-to-end route path is assumed to be available, for instance by using reactive P2P-RPL (Storing or non-storing mode) routing. GMPLS signaling Resource Reservation Protocol (RSVP) with 6tisch scheduling capability is designed to label, reserve and schedule the resources hop-by-hop for isolated traffic flows. SF1 of the application sender will trigger the RSVP operation, whenever it has time critical traffic. RSVP has two messages, namely (1)RSVP-PATH message (Sender to Receiver) and (2) RSVP-RESV message (Receiver to Sender).

The basic RSVP-PATH message is used to carry the "Sender Traffic Specification" along with "characterization parameters" from sender to receiver. Since RSVP treat objects as opaque data, it is permissible to use another protocol element (e.g.,GMPLS, 6P, SF1) as an object in a RSVP-PATH message. The format of the PATH message that supports 6tisch scheduling capabilities (6P and SF1) is as follows:

::= [ ] [ [ | ] ... ] [ ] [ ] [ ] [ <6P OPERATION REQUEST> ] [ ] [ ] [ ] [ ... ] ]]>

::= [ ] [ ]]]> The format of the Generalized Label Request Object in PATH message is:

The Generalized Label Request describes the requirement of communication characteristics to support the 6TiSCH-LSP being requested. Generalized Label Request object is set by the ingress node (6LR), transparently passed by transit nodes, and used by the egress node(6LR). LSP Encoding Type (8 bits): Indicates the encoding of the LSP being requested.

Switching Type (8 bits):Indicates the type of switching that should be performed on a particular link.

G-PID (8 bits): An identifier of the payload carried by an LSP, i.e., an identifier of the client layer of that LSP.

"SF1 OPERATION REQUEST" and "6P OPERATION REQUEST" are added in the PATH message to check for 6tisch scheduling capabilities within the intermediate nodes from sender to receiver. The "Timeslot Switching Capability" (TSC) is used as an implicit label to switch the cell at intermediate nodes . "LABEL_REQUEST" in path message should be set to "Timeslot Switching Capability". The "RPLInstanceID" is added in the "SENDER_TEMPLATE" to create the Global TrackID during 6P transactions of RSVP-RESV messages. If an intermediate node does not support the TSC or "6P transactions" or "SF1 operation" then it MUST send a "PathErr" message back to application.

The basic RSVP-RESV messages are transmitted upstream from receiver to sender to provide resource reservation as well as "Label Distribution". In this specification, hop-by-hop scheduling is extended to support both resource reservation and label distribution. The current specification is only defined for unicast point-to-point traffic flows, i.e., Fixed Filter (FF) reservation style. The format of the RESV message that supports 6tisch scheduling capabilities (6P and SF1) is as follows:

::= [ ] [ [ | ] ... ] [ ] [ ] [ <6P OPERATION> ] [ ] [ ] [ ] [ ] [ ... ]