6tsch webex

6TSCH Webex

06/21/2013

Agenda

• draft-thubert-6tsch-architecture-02 [5min]• draft-vilajosana-6tsch-basic-00 [10min]• Architecture with remote BBR [10min]• Soft cell assignment: random or not?[20min]• Track IDs [10min]• AOB [5min]

draft-thubert-6tsch-architecture-02

Not published yet

Centralized vs. Distributed Routing

6TSCH supports a mix model of centralized routes that are computed by

a Path Computation Entity and distributed routes that are computed by

RPL over a common physical LLN.

Both RPL and the PCE may inject routes in the Routing Tables of the

6TSCH routers. In either case, each route is associated with a

topology that is indexed by an instanceID, as defined in RPL

[RFC6550]. RPL and PCE rely on shared sources to define Global and

Local InstanceIDs.

It is possible for RPL and PCE to share a same topology, in which

case the PCE routes have precedence over RPL routes in case of a

conflict.

Inside the 6TSCH domain, the flow label is used to indicate the

topology that must be used for routing and the associated Routing

Tables as discussed in [I-D.thubert-roll-flow-label].

Tunnel Mode In tunnel mode, the frames originate from an arbitrary protocol over

a compatible MAC that may or may not be perfectly synchronized with

the 6TSCH network. An example of this would be a router with a dual

radio that is capable to receive and send Wireless HART or ISA100.11a

frames with the second radio, by presenting itself as an Access Point

or a Backbone Router, respectively.

In that mode, the PCE may coordinate with a WiHART Network Manager or

an ISA100.11a System Manager in order to specify the flows that are

to be transported transparently over the Track.

Tunnel Mode

+--------------+

| IPv6 |

+--------------+

| 6LoWPAN HC |

+--------------+ set restore

| 6TUS | +dmac+ +dmac+

+--------------+ | | | |

| TSCH MAC | | | | |

+--------------+ | | | |

| LLN PHY | +-------+ +--...-----+ +-------+

+--------------+ | ingress egress |

| |

+--------------+ | |

| LLN PHY | | |

+--------------+ | |

| TSCH MAC | | |

+--------------+ | |

|ISA100/WiHART | | v

+--------------+

Tunnel Mode

In that case, the flow information that identifies the Track is

uniquely derived from the information at the receiving end, for

instance the incoming Timeslots, or an ISA100.11a ContractId. At the

ingress 6TSCH router, the packet destination is recognized as self

but the flow information indicates that the frame must be tunneled

over a particular 6TUS Track so the packet is not punted to upper

layer. Instead, it is passed to the 6TUS sublayer for switching.

The 6TUS sublayer in the ingress router overrides the destination MAC

to broadcast and forwards.

At the egress 6TUS router, the reverse operation occurs. Based on

metadata associated to the Track, the frame is passed to the

appropriate link layer with the destination MAC restored.

draft-vilajosana-6tsch-basic-00

Status

• Follow-up on webex discussion on 06/07/2013

• Published on 06/19/2013

• http://tools.ietf.org/html/draft-vilajosana-6tsch-basic-00

• Same ideas as discussed over the phone

• Comments welcome!

http://tools.ietf.org/html/draft-vilajosana-6tsch-basic-00

http://tools.ietf.org/html/draft-vilajosana-6tsch-basic-00

Architecture with remote BBR

Hybrid ---+----------------------- | External Network | +-----+ +-----+ | | Router | | PCE | | +--| | +-----+ | +-----+ | | ^ ^ ^ | | | | | ------------------------ | | | | | | | | | +---------------+ | +----------------+ | | | v v v +-----+ +-----+ +-----+ | | 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

Question

• PCE, ND must be maintained as separate elements

• 6TSCH does not need to define anything to create the connectivity between the BBRs

• Discovery?

soft cell assignment: random or not?

Problem

• Applies to distributed scheduling only• Two neighbor nodes negotiate the allocation of a

cell in the schedule• If this cell already used by other nodes in the

neighborhood collision• Options:

– random allocation. Collisions unlikely. Detect and fix collisions

– Informed allocation. Neighbors maintain state. Collisions less likely. Still detect and fix (less frequent) collisions.

Collision probability

• 10 node neighborhood• Each node sends 3 pk/s• 101 cells• 16 channels• Random cell allocation• Collision detection

Collision occurrence? Collapse?Overhead of re-negotiation?Overhead maintaining state?

Informed allocation

• exchanging the changes in a node’s cell usages bitmap instead of reporting all cell usage bitmap periodically

• Approaches:– Active– Passive– Hybrid

Using Trickle

• RFC6206, used in RPL• To use Trickle, we need to define

– What constitutes a "consistent" transmission.– What constitutes an "inconsistent" transmission.– What "events", if any -- besides inconsistent

transmissions -- reset the Trickle timer.– What information a node transmits in Trickle

messages.– What actions outside the algorithm the protocol takes,

if any, when it detects an inconsistency.

Using track IDs

Proposal

• Use a TrackID to associate incoming cells and outgoing cells

• TrackID is internal only, i.e. is does not appear in the packets

• Add TrackID to cell commands

• Track (switching) table using trackID

• Schedule is union of all track tables

Any Other Business?

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