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

With Scheduling Function Zero (SF0) [I-D.dujovne-6tisch-6top-sf0], on-the-fly cell scheduling (ADD/DELETE) to 1-hop neighbors can be achieved for aggregated (best-effort) traffic flows. In other words, all the instances from nodeA to nodeB in Fig. 1 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 protect the control/data streams for time-critical applications . For such applications, per-instance based L2-bundles need to be scheduled hop-by-hop in between application sender and receiver nodes . In addition, cells in the scheduled end-to-end L2-bundles of each instance have to be dynamically adapted for bursty time-critical traffic flows. To achieve, end-to-end track has to be installed with a global TrackID that is associated with the L2-bundles of each instance. With 1-hop based SF0 cell scheduling, it is difficult to schedule dedicated end-to-end cells for isolated traffic flows. In addition, global bandwidth estimation through Resource Reservation protocol is required for bandwidth allocation in multi-hop cell scheduling. This draft proposes a Scheduling Function One (SF1) to schedule end-to-end dedicated L2-bundles for each instance, and to dynamically adapt the cells in scheduled L2-bundles of ongoing instance through RSVP protocol(see Fig. 2).

------------------> <------------------------ <------------------- 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, Sender determines when to reserve the 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 ongoing instance through distributed Resource Reservation Protocol (RSVP-lite). The triggering events in SF1 are as follows : If Sender has any Outgoing Bandwidth Requirement for new instance to transmit data to Receiver. If Sender has a New Outgoing Bandwidth Requirement for Ongoing Instance to transmit data to Receiver. In both cases, distributed RSVP-lite (explained in Section .2.1) 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 with reactive P2P-RPL (Storing or non-storing mode) protocols. A distributed Resource Reservation Protocol (RSVP-lite) with 6tisch scheduling capability is designed to schedule the labeled reserved resources hop-by-hop for isolated instance. SF1 of application sender will trigger the RSVP-lite operation, whenever it has time critical traffic flow towards the receiver. The RSVP-lite has two messages namely (1) RSVP-PATH message(Sender to Receiver) and (2) RSVP-RESV message(Receiver to Sender).

The basic RSVP-PATH message [RFC2205] 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 valid to assume other protocol(eg., GMPLS, 6P) as an object in RSVP- PATH messages. The format of PATH message with the support of 6tisch scheduling capabilities (6P and SF1) is as follows :

::= [ ] [ [ | ] ... ] [ ] [ ] [ ] [ ... ] [] [<6P OPERATION REQUEST>] [ ] [ ] [ ] [ ... ] ]]> "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. "Timeslot Switching Capability(TSC)" is used as an implicit labels to switch the cell at intermediate nodes [RFC3473]. The message format of the "TSC" is out-of-scope in this specification. "LABEL_REQUEST" in path message should set to "Timeslot Switching Capability". "RPLInstanceID" is added in the "SENDER_TEMPLATE" to create Global TrackID during 6P transactions of RSVP-RESV message. Whenever the intermediate node won't support the "Timeslot switching Capability" or "6P transactions" or "SF1 operation" then it needs to send a "PathErr" message back to application sender.

The basic RSVP-RESV messages [RFC2205] are transmitted upstream from receiver to sender to provide resource reservation along with "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 RESV message with the support of 6tisch scheduling capabilities (6P and SF1) is as follows :

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