6tisch S. Anamalamudi
Internet-Draft Huaiyin Institute of Technology
Intended status: Standards Track M. Zhang
Expires: August 6, 2017 AR. Sangi
Huawei Technologies
C. Perkins
Indian Institute of Science
February 2, 2017

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


This document defines a 6top Scheduling Function called "Scheduling Function One" (SF1) to reserve, label and schedule the end-to-end resources hop-by-hop through the Distributed Resource Reservation Protocol(RSVP). SF1 uses the 6P signaling messages with a global TrackID to add or delete the cells in L2-bundles of isolated traffic flows.

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Table of Contents

1. Introduction

               L3-bundle (Instance-1,Instance-2,...Instance-n)
      nodeA<-------------------------------------------------  nodeB
               L3-bundle (Instance-1,Instance-2,...Instance-n) 

Figure 1: L3-bundle for aggregated traffic flows over 1-hop with SF0.

             L2-bundle(Instance-1)       L2-bundle(Instance-1)
          ----------------------->      ------------------>
         <------------------------      <-------------------
             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) 

Figure 2: Dedicated L2-bundles for end-to-end isolated traffic flows with SF1

Scheduling Function Zero (SF0) [I-D.ietf-6tisch-6top-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 Figure 1 are scheduled in a single L3-bundle (IP link). [I-D.ietf-detnet-use-cases]. For such applications, per-instance L2-bundles need to be scheduled hop-by-hop in between sender and receiver [I-D.ietf-6tisch-architecture]. 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 Figure 2).

2. Operation of Scheduling Function One (SF1)

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: Section 2.1) is triggered to provide end-to-end resource reservations along with scheduling operations.

  1. If Sender has a outgoing bandwidth requirement for a new instance to transmit data to Receiver.
  2. If Sender has a new outgoing bandwidth requirement for an existing instance to transmit data to Receiver.

In both cases, distributed RSVP(explained in

2.1. Resource Reservation Protocol(RSVP)

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).

2.2. RSVP-PATH message

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 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:

   <Path Message> ::=    <Common Header> [ <INTEGRITY> ]
                         [ [<MESSAGE_ID_ACK> | <MESSAGE_ID_NACK> ] ... ]
                         [ <MESSAGE_ID> ]
                         <SESSION> <RSVP_HOP>
                         [ <EXPLICIT_ROUTE> ]
                         [ <SF1 OPERATION REQUEST> ] 
                         [ <6P OPERATION REQUEST> ] 
                         [ <SESSION_ATTRIBUTE> ]
                         [ <NOTIFY_REQUEST> ]
                         [ <ADMIN_STATUS> ]
                         [ <POLICY_DATA> ... ]
                         <sender descriptor> 

  <sender descriptor> ::=  <SENDER_TEMPLATE> <SENDER_TSPEC>
                           [ <ADSPEC> ]
                           [ <RECORD_ROUTE> ]
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |            Length             | Class-Num (19)|  C-Type (4)   |
   | LSP Enc. Type |Switching Type |             G-PID             |
     Value         Type
     -----         ----
      TBD        Timeslot 
     Value               Type
     -----               ----
      100    Time-Division-Multiplex Capable (TDM)
     Value             Type                     Technology
     -----             ----                       ------
      TBD     Wireless Ethernet(802.15.4)         6TiSCH           

  1. LSP Encoding Type (8 bits): Indicates the encoding of the LSP being requested.
  2. Switching Type (8 bits):Indicates the type of switching that should be performed on a particular link.
  3. 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 [RFC3473]. "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.

2.3. RSVP-RESV message

The basic RSVP-RESV messages [RFC2205] 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:

<Resv Message> ::= <Common Header> [ <INTEGRITY> ]
                         [ [<MESSAGE_ID_ACK> | <MESSAGE_ID_NACK> ] ... ]
                         [ <MESSAGE_ID> ]
                         <SESSION> <RSVP_HOP>
                         [ <SF1 OPERATION> ]
                         [ <6P OPERATION> ]
                         [ <RESV_CONFIRM> ]  [ <SCOPE> ]
                         [ <NOTIFY_REQUEST> ]
                         [ <ADMIN_STATUS> ]
                         [ <POLICY_DATA> ... ]
                         <STYLE> <flow descriptor list> 
  <flow descriptor list> ::= <FF flow descriptor>
  <FF flow descriptor> ::= [ <FLOWSPEC> ] <FILTER_SPEC> <LABEL>
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 |            Length             | Class-Num (16)|   C-Type (3)  |
 |  Slotframe ID |                    SlotOffset                 |
 |    .......    |                 ...............               |
 |  Slotframe ID |                    SlotOffset                 |

1. Slotframe ID (1 octet): It represents the specific slotframe of the SlotOffset. A slotframe is defined as the collection of timeslots repeating in time. It is characterized by a slotframe_ID, and a slotframe_size.

2. slotOffset(3 octets): It identifies a column in the TSCH schedule. SlotOffset is used as an implicit lable to switch the packet through "Track Forwarding".

Upon arrival of the PATH message at an application receiver, the SENDER_TSPEC and ADSPEC objects are interpreted to select the resource reservation parameters. Since RSVP provides receiver initiated resource reservation setup, the scheduling operation has to proceed upstream from receiver to sender. Subsequently, the reserved resources (bandwidth) are mapped into 6tisch cells through Scheduling Function and a corresponding L2-bundle is created. An aggregation of cells is called a "bundle" (the directional link to a next-hop neighbor). Every L2-bundle is associated with a global trackID to dynamically adapt the cells "hop-by-hop" to an scheduled instance. In addition, the TrackID is used as a "packet filter" to switch the incoming tracks to outgoing tracks. The receiver will generate the TrackID with the combination of "Source/Destination IP address" and "RPLInstanceID" that is obtained from "SENDER_TEMPLATE/FILTER_SPEC".

                  next-hop node            Receiver
                 +--------------+       +--------------+
                 |     IPv6     |       |     IPv6     |
                 +--------------+       +--------------+
                 |   6LoWPAN    |       |   6LoWPAN    |
                 +--------------+       +--------------+
                 |     6top     |       |     6top     |
                 +--------------+       +--------------+
                 |   TSCH MAC   |       |   TSCH MAC   |
                 +--------------+       +--------------+
                 |   LLN PHY    |       |   LLN PHY    |
                 +--------------+       +--------------+
                      |                           |
                      |                           | Rspec: Reserves
                      |                           | bandwith
                      |                           |
                      |                           | SF1: Maps
                      |                           | bandwidth to cells
                      | RESV + 6P Request(TrackID)|
                      |<------------------------- |
     Rspec:Reserves   |                           |
     bandwith         |                           |
                      |                           |
   SF1:Maps bandwidth |                           |
   to cells           |6P Response (CellList[..]) |
                      |                           |
                      |                           |
                      |                           |
                      |   6P confirmation         |LABEL SET
                      |   CellList[..]+ Label     |label=Channel+Slot
      Resv state:"Cell|                           |
      label"          |                           |
                      |                           |
                      |                           |
                      |                           |

Figure 3: Operation of RSVP-RESV message with 6P transactions.

	  +--------------+  <-Data transmission in end-to-end Track->
	  |     IPv6     | Sender                             Receiver
	  +--------------+   |                                     |
	  |   6LoWPAN    |   |                                     |
	  +--------------+   |                 nodeB               |
	  |     6top     |   |                +----+               |
	  +--------------+   |                |    |               |
	  |   TSCH MAC   |   |                |    |               |
	  +--------------+   |                |    |               |
	  |   LLN PHY    |   |   L2-Bundle    |    |   L2-Bundle   |
	  +--------------+   +----------------+    +---------------+
	  <--Dedicated cells for each Instance-->

Figure 4: End-to-end cell scheduling with SF1 Scheduling

From [RFC6997], the application node that initiates the point-to-point (P2P) traffic is called the "Parent node" and the application receiver that receives the data is called the "Child node". Since the child node targets the Scheduling operation upstream towards the sender, the "3-step transaction" of the 6P protocol needs to be triggered at each hop to schedule the reserved resources (see Figure 3). Hence, "6P Request" with an associated TrackID in the metadata field is transmitted in "RESV" message from Receiver to the next-hop node. The "NumCells" field in the 6P Request is set to the required number of cells, and "CellList" should be empty. Once the next-hop node receives the "RESV" message, it checks the service request specification(Rspec) and performs the resource reservation. Subsequently, the Scheduling Function of next-hop neighbor maps the reserved resources into transmit cells. Later, "6P Response" with "CellList" (slotOffset, channelOffset) is transmitted downstream to receiver. When the receiver has cells (to receive data) available with the "CellList" in the "6P Response" then "6P Confirmation" with "IANA_6TOP_RC_SUCCESS" is upstream towards next-hop node. Otherwise, "ResvErr" message SHOULD be sent back to the receiver with the specific error. Since the cell information (slotOffset,channelOffset) is available in the 6P transactions, the next-hop node will store the "SlotOffset(Timeslot)" as a label to switch the traffic flow to receiver. For multiple cells (i.e., a bundle), a generalized label set is created where each label represents one cell to forward data to receiver. Once the 6P transaction is successful between a next-hop node and receiver, a labeled L2-bundle is created with the associated TrackID. Subsequently, "cell label set" is stored in the Resv state block at the next-hop node. Later, SF1 of "next-hop node" maps the reserved bandwidth to the "receiving cells" to receive the data from its upstream node. The "RESV" message with "6P Request" along with TrackID is transmitted upstream towards sender node. In this way, an end-to-end Track is installed with a succession of paired L2-bundles (a receive bundle from the previous hop and a transmit bundle to the next hop) for a specific instance from sender to receiver (See Figure 4). Figure 4). Later, SF1 of the next-hop neighbor identifies the TrackID based on the "Sender/Receiver IP address, RPLInstanceID" of the received data to switch the track towards receiver. In this way, end-to-end data transmission is achieved through "Track forwarding" at the 6top sub-layer (see Figure 4). Using TSC of RSVP-GMPLS [RFC3473], cells in paired L2-bundles are used as implicit labels to switch the data from Sender to Receiver at the 6top sub-layer.

2.4. Reroute and Bandwidth Increase mechanism

Whenever the sender needs to establish a new tunnel that can maintain resource reservations without double counting (at any particular intermediate node) the resources with an existing tunnel, then the "RSVP reroute mechanism" is initiated [RFC3209]. With this operation, bandwidth can be increased or decreased end-to-end in the tunnel. The detailed explanation of the reroute mechanism is explained in [RFC3209].

2.5. Error Codes

The detailed explanation of PathErr and ResvErr with different ERROR_SPEC to handle Scheduling and 6P operation errors will be described in later specification.

3. Scheduling Function Identifier

The Scheduling Function Identifier (SFID) of SF1 is IANA_SFID_SF1(TBD).

4. IANA Considerations

IANA is requested to allocate a new Scheduling Function (IANA_SFID_SF1) from the SF space of Scheduling Functions defined in [I-D.ietf-6tisch-6top-sf0]

5. Security Considerations


6. References

6.1. References

[RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, DOI 10.17487/RFC2205, September 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, DOI 10.17487/RFC3473, January 2003.
[RFC6997] Goyal, M., Baccelli, E., Philipp, M., Brandt, A. and J. Martocci, "Reactive Discovery of Point-to-Point Routes in Low-Power and Lossy Networks", RFC 6997, DOI 10.17487/RFC6997, August 2013.

6.2. Informative References

[I-D.ietf-6tisch-6top-sf0] Dujovne, D., Grieco, L., Palattella, M. and N. Accettura, "6TiSCH 6top Scheduling Function Zero (SF0)", Internet-Draft draft-ietf-6tisch-6top-sf0-02, October 2016.
[I-D.ietf-6tisch-architecture] Thubert, P., "An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4", Internet-Draft draft-ietf-6tisch-architecture-11, January 2017.
[I-D.ietf-detnet-use-cases] Grossman, E., Gunther, C., Thubert, P., Wetterwald, P., Raymond, J., Korhonen, J., Kaneko, Y., Das, S., Zha, Y., Varga, B., Farkas, J., Goetz, F., Schmitt, J., Vilajosana, X., Mahmoodi, T., Spirou, S. and P. Vizarreta, "Deterministic Networking Use Cases", Internet-Draft draft-ietf-detnet-use-cases-11, October 2016.

Authors' Addresses

Satish Anamalamudi Huaiyin Institute of Technology No.89 North Beijing Road, Qinghe District Huaian, 223001 China EMail: satishnaidu80@gmail.com
Mingui Zhang Huawei Technologies No. 156 Beiqing Rd. Haidian District Beijing, 100095 China EMail: zhangmingui@huawei.com
Abdur Rashid Sangi Huawei Technologies No.156 Beiqing Rd. Haidian District Beijing, 100095 P.R. China EMail: rashid.sangi@huawei.com
Charles E. Perkins Futurewei 2330 Central Expressway Santa Clara, 95050 Unites States EMail: charliep@computer.org
S.V.R Anand Indian Institute of Science Bangalore 560012 India EMail: anand@ece.iisc.ernet.in