An Architecture for IPv6 over Time Synchronized Channel Hopping
draft-thubert-6tsch-architecture-00
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| Last updated | 2013-03-11 | ||
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draft-thubert-6tsch-architecture-00
6TSCH P. Thubert, Ed.
Internet-Draft cisco
Intended status: Standards Track RA. Assimiti
Expires: September 12, 2013 Nivis
T. Watteyne
Linear Technology / Dust Networks
March 11, 2013
An Architecture for IPv6 over Time Synchronized Channel Hopping
draft-thubert-6tsch-architecture-00
Abstract
This document presents an architecture for an IPv6 multilink subnet
that is composed of a high speed powered backbone and a number of
IEEE802.15.4e TSCH wireless networks attached and synchronized by
Backbone Routers. Route Computation may be achieved in a centralized
fashion by a Path Computation Element, in a distributed fashion using
the Routing Protocol for Low Power and Lossy Networks, or in a mixed
mode. The Backbone Routers perform proxy Neighbor discovery
operations over the backbone on behalf of the wireless device, so
they can share a same subnet and appear to be connected to the same
backbone as classical devices.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2013.
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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview and Scope . . . . . . . . . . . . . . . . . . . . . 3
4. Centralized vs. Distributed Routing . . . . . . . . . . . . . 6
5. Functional Flows . . . . . . . . . . . . . . . . . . . . . . 6
6. Network Synchronization . . . . . . . . . . . . . . . . . . . 6
7. TSCH and 6TUS . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. 6tus . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.2. Slotframes and Priorities . . . . . . . . . . . . . . . . 7
7.3. Centralized Flow Reservation . . . . . . . . . . . . . . 7
7.4. Distributed Flow Reservation . . . . . . . . . . . . . . 7
7.5. Packet Marking and Handling . . . . . . . . . . . . . . . 8
8. Management . . . . . . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 9
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 10
12.3. External Informative References . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
A new breed of Time Sensitive Networks is being developped to enable
traffic that is highly sensitive to jitter and quite sensitive to
latency. Such traffic is not limited to voice and video, but also
includes command and control operations such as found in industrial
automation or in-vehicule sensors and actuators.
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At IEEE802.1, the "Audio/Video Task Group", was rename TSN for Time
Sensitive Networking. The IEEE802.15.4 Medium Access Control (MAC)
has evolved with IEEE802.15.4e which provides in particular the Time
Synchronized Channel Hopping (TSCH) mode for industrial-type
applications. Both provide Deterministic capabities to the point
that a packet that pertains to a certain flow will cross the network
from node to node following a very precise schedule, like a train
leaves intermediate stations at precise times along its path. The
time slotted aspect reduce collisions, and saves energy. The channel
hopping aspect is a simple and efficient technique to get around
statistical interference by WIFI emitters.
This document presents an architecture for an IPv6 multilink subnet
that is composed of a high speed powered backbone and a number of
IEEE802.15.4e TSCH wireless networks attached and synchronized by
backbone routers. Route Computation may be achieved in a centralized
fashion by a Path Computation Element (PCE), in a distributed fashion
using the Routing Protocol for Low Power and Lossy Networks (RPL), or
in a mixed mode. The Backbone Routers perform proxy Ipv6 Neighbor
Discovery (ND) operations over the backbone on behalf of the wireless
device, so they can share a same IPv6 subnet and appear to be
connected to the same backbone as classical devices.
2. Terminology
The draft uses terminology defined in
[I-D.palattella-6tsch-terminology],
[I-D.chakrabarti-nordmark-6man-efficient-nd], [RFC5191] and
[RFC4080].
It conforms to the terms and models described for IPv6 in [RFC5889]
and uses the vocabulary and the concepts defined in [RFC4291] for
IPv6.
3. Overview and Scope
The scope of the present work is a subnet that, in its basic
configuration, is made of a IEEE802.15.4e Time Synchronized Channel
Hopping (TSCH) [I-D.watteyne-6tsch-tsch-lln-context] MAC Route-Over
Low Power Lossy Network (LLN).
+-----+
| | LLN Border
| | router
+-----+
o o o
o o o o
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o o LLN o o o
o o o o
o
Figure 1: Basic Configuration
The LLN devices communicate over IPv6 [RFC2460] using the 6LoWPAN
Header Compression (6LoWPAN HC) [RFC6282]. Neighbor Devices are
discovered with 6LoWPAN Neighbor Discovery (6LoWPAN ND) [RFC6775] and
the Routing Protocol for Low Power and Lossy Networks (RPL) [RFC6550]
enables routing within the LLN. RPL forms Destination Oriented
Directed Acyclic Graphs (DODAGs) within instances of the protocol,
each instance being associated with an Objective Function (OF) to
form a routing topology. A particular LLN device, usually powered,
acts as RPL root, 6LoWPAN HC terminator, and LLN Border Router (LBR)
to the outside.
An extended configuration of the subnet comprises multiple LLNs. The
LLNs are interconnected and synchronized over a backbone, that can be
wired or wireless. The backbone can be a classical IPv6 network,
with Neighbor Discovery operating as defined in [RFC4861] and
[RFC4862]. The backbone can also support Efficiency aware IPv6
Neighbor Discovery Optimizations
[I-D.chakrabarti-nordmark-6man-efficient-nd] in mixed mode as
described in [I-D.thubert-6lowpan-backbone-router].
Security is often handled at layer 2 and Layer 4. Authentication
during the join process is handled with the Protocol for Carrying
Authentication for Network Access (PANA) [RFC5191].
The LLN devices are time-synchronized at MAC level. The MAC
coordinator that serves as time source through Enhanced Beacons (EB)
is loosely coupled with the RPL parent; this way, the time
synchronization starts at the RPL root and follows the RPL DODAGs
with no timing loop.
In the extended configuration, the functionality of the LBR is
enhanced to that of Backbone Router (BBR). A BBR is an LBR, but also
an Energy Aware Default Router (NEAR) as defined in
[I-D.chakrabarti-nordmark-6man-efficient-nd]. The BBR performs ND
proxy operations between the registered devices and the classical ND
devices that are located over the backbone. 6TSCH BBRs synchronize
with one another over the backbone, so as to ensure that the multiple
LLNs that form the IPv6 subnet stay tightly synchronized. If the
Backbone is Deterministic (such as defined by the Time Sensitive
Networking WG at IEEE), then the Backbone Router ensures that the
end-to-end deterministic behavior is maintained between the LLN and
the backbone.
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---+------------------------
| External Network
|
+-----+ +-----+
| | Router | | PCE
| | | |
+-----+ +-----+
| |
| Subnet Backbone |
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
o | | router | | router | | router
+-----+ +-----+ +-----+
o o o o o
o o o o o o o o o o o
o o o LLN o o o o
o o o o o o o o o o o o
Figure 2: Extended Configuration
The main architactural blocks are arranged as follows:
+-----+-----+-----+-----+-----+--------+
|PANA | RPL |RSVP | PCE | IP |
| | |/NSIS| /CNM|/ FORWARDING |
+-----+-----+-----+-----+--------+-----+-------+
| 6LoWPAN | 6LoWPAN ND |
| HC +-------------+
| |
+----------------------------------------------+
| 6TUS |
+----------------------------------------------+
| 802.15.4e TSCH |
+----------------------------------------------+
Figure 3: 6TSCH stack
RPL is the routing protocol of choice. TBD whether there is a need
to define a 6TSCH OF.
PCE => group needs to work with PCE WG to define flows to PCE, and
define how to accomodate PCE routes and reservation.
BBR => group needs to work woth 6MAN to define ND proxy. Also need
BBR sync, time sync between deterministic ethernet and 6TSCH net.
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IEEE802.1TSN => external, maintain liaison.
IEEE802.15.4 => external, maintain liaison.
ISA100.20 Common Network Management (CNM) => external, maintain
liaison.
IoT6 => external, maintain liaison.
4. Centralized vs. Distributed Routing
5. Functional Flows
6. Network Synchronization
The mechanism(s) used for time synchronization is something that we
might have to reconcile with RPL discovery and maintenance traffic.
Time synchronization in TSCH is based on three mechanisms:
Enhanced Beacons
Enhanced ACKs
Frame based synchronization
If a node communicates intermittently (sleepy, battery operated) it
can also proactively ping its time source and receive time stamps.
In order to maximize battery life and network throughput, it is
advisable that RPL ICMP discovery and maintenance traffic (governed
by the trickle timer) be somehow coordinated with the transmission of
time synch packets (especially with enhanced beacons). This could be
a function of the shim layer or it could be deferred to the device
management entity. Any suggestions, ideas on this topic?
7. TSCH and 6TUS
7.1. 6tus
6tus is an adaptation layer which is the next higher layer to TSCH
and which offers a set of commands defining a data and management
interface. 6tus is defines in [I-D.draft-wang-6tsch-6tus]
The management interface of 6tus enables an upper layer to schedule
cells and slotframes in the TSCH schedule.
If the scheduling entity explicitly specifies the slotOffset/
channelOffset of the cells to be added/deleted, those cells are
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marked as "hard". 6tus can not move hard cells in the TSCH schedule.
Hard cells are typically used by an central PCE.
6tus contains a monitoring process which monitors the performance of
cells, and can move a cell in the TSCH schedule when it performs bad.
This is only applicable to cells which are marked as "soft". To
reserve a soft cell, the higher layer does not indicate the
slotOffset/channelOffset of the cell to add, but rather the resulting
bandwidth and QoS requirements. When the monitoring process triggers
an cell reallocation, the two neighbor motes communication over this
cells negociate the new position in the TSCH schedule of this cell.
7.2. Slotframes and Priorities
6tus uses priority queues to manage concurrent data flows of
different prioroties. When a packet is received from an higher layer
for transmission, the I-MUX module of 6tus inserts that packet in the
outgoing queue which matches the packet best (DSCP can therefore be
used). At each schedule transmit slot, the MUX module looks for the
frame in all the outgoing queues that best matches the cells. If a
frame is found, it is given to TSCH for transmission.
7.3. Centralized Flow Reservation
In a centralized setting, a PCE computes the TSCH schedule, and
communicates with the different nodes in the network to configure
their TSCH schedule. Since it has full knowledge of the network's
topology, the PCE can compute a collision-free schedule, which result
in a high degree of communication determinism.
The protocol for the PCE to communicate with the motes is not yet
defined. This protocol typically reserves hard cells on the
transmitter side of a dedicated cell, and the negociation protocol of
6tus takes care of reserving the same cell on the receiver node.
7.4. Distributed Flow Reservation
In a distributed setting, no central PCE in present in the network.
Nodes use 6tus to reserve soft cells with their neighbors. Since no
node has full knowledge of the network's topology and the traffic
requirements, scheduling collisions are possible, for example because
of a hidden terminal problem.
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A schedule collision can be detected if two motes have multiple
dedicated cells schedule to one another. The statistics process of
6tus can be configure to continuously compute the packet delivery
ratio of those cells, and the monitoring process of 6tus can declare
a soft cell to perform bad when that statistics for that cell is
significantly worse than for the other cell to the same neighbor.
When this happens, the monitoring process of 6tus moves the cell to
another location in the 6TSCH schedule, through a re-negociation
procedure with the neighbor.
The entity that builds and maintains the schedule in a distributed
fashion is not yet defined.
7.5. Packet Marking and Handling
---+----------------
Sender Receiver
+-----------+ +----+ +----+ +----+ +-----------+
|Application|---->| R1 |---->| R2 |----->|BBR |----->|Application|
| +--+ | |+--+| |+--+| |+--+| | +--+ |
| |NE|====|=====||NE||=====||NE||======||NE||======|===|NE| |
| +--+ | |+--+| |+--+| |+--+| | +--+ |
| |^ | | |^ | | |^ | | |^ | | |^ |
| v| | | v| | | v| | | v| | | v| |
| +--+ | |+--+| |+--+| |+--+| | +--+ |
| |6T| | ||6T|| ||6T|| ||6T|| | |6T| |
| |us| | ||us|| ||us|| ||us|| | |us| |
| +--+ | |+--+| |+--+| |+--+| | +--+ |
+-----------+ +----+ +----+ +----+ +-----------+
+--+
|NE| = NSIS ==== = Signaling ---> = Data flow messages
+--+ Entity Messages (unidirectional)
+--+
|6T| 6TUS layer
|us| (and IEEE802.15.4e TSCH MAC below)
+--+
Figure 4: NSIS flow
reservation Deterministic flow allocation (hard reservation of time
slots) eg centralized RSVP? metrics? Hop-by-hop interaction with
6TUS. Lazy reservation (use shared slots to transport extra burst
and then dynamically (de)allocate) Classical QoS (dynamic based on
observation)
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8. Management
9. IANA Considerations
This specification does not require IANA action.
10. Security Considerations
This specification is not found to introduce new security threat.
11. Acknowledgements
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S.E. and R.M. Hinden, "Internet Protocol, Version
6 (IPv6) Specification", RFC 2460, December 1998.
[RFC4080] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
Bosch, "Next Steps in Signaling (NSIS): Framework", RFC
4080, June 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
[RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad
Hoc Networks", RFC 5889, September 2010.
[RFC5974] Manner, J., Karagiannis, G., and A. McDonald, "NSIS
Signaling Layer Protocol (NSLP) for Quality-of-Service
Signaling", RFC 5974, October 2010.
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[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
September 2011.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012.
[RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
"Neighbor Discovery Optimization for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
November 2012.
12.2. Informative References
[I-D.chakrabarti-nordmark-6man-efficient-nd]
Chakrabarti, S., Nordmark, E., and M. Wasserman,
"Efficiency aware IPv6 Neighbor Discovery Optimizations",
draft-chakrabarti-nordmark-6man-efficient-nd-01 (work in
progress), November 2012.
[I-D.draft-wang-6tsch-6tus]
Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6tus
Adaptation Layer Specification. draft-wang-6tsch-6tus-00
(work in progress) ", March 2013.
[I-D.palattella-6tsch-terminology]
Palattella, MR., Ed., Thubert, P., Watteyne, T., and Q.
Wang, "Terminology in IPv6 over Time Slotted Channel
Hopping. draft-palattella-6tsch-terminology-00 (work in
progress) ", March 2013.
[I-D.svshah-tsvwg-lln-diffserv-recommendations]
Shah, S. and P. Thubert, "Differentiated Service Class
Recommendations for LLN Traffic", draft-svshah-tsvwg-lln-
diffserv-recommendations-00 (work in progress), February
2013.
[I-D.thubert-6lowpan-backbone-router]
Thubert, P., "6LoWPAN Backbone Router", draft-thubert-
6lowpan-backbone-router-03 (work in progress), February
2013.
[I-D.watteyne-6tsch-tsch-lln-context]
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Watteyne, T., "Using IEEE802.15.4e TSCH in an LLN context:
Overview, Problem Statement and Goals", draft-watteyne-
6tsch-tsch-lln-context-01 (work in progress), February
2013.
12.3. External Informative References
[HART] www.hartcomm.org, "Highway Addressable Remote Transducer,
a group of specifications for industrial process and
control devices administered by the HART Foundation", .
[IEEE802.1TSNTG]
IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networks Task Group", March 2013, <
http://www.ieee802.org/1/pages/avbridges.html>.
[ISA100.11a]
ISA, "ISA100, Wireless Systems for Automation", May 2008,
< http://www.isa.org/Community/
SP100WirelessSystemsforAutomation>.
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems, Inc
Village d'Entreprises Green Side
400, Avenue de Roumanille
Batiment T3
Biot - Sophia Antipolis 06410
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Robert Assimiti
Nivis
1000 Circle 75 Parkway SE, Ste 300
Atlanta, GA 30339
USA
Phone: +1 678 202 6859
Email: robert.assimiti@nivis.com
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Thomas Watteyne
Linear Technology / Dust Networks
30695 Huntwood Avenue
Hayward, CA 94544
USA
Phone: +1 (510) 400-2978
Email: twatteyne@linear.com
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