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Documentation: 6TiSCH 6top sub layer

Simon Duquennoy edited this page Apr 27, 2018 · 3 revisions


6TiSCH Operation Sublayer (6top), a logical link layer in the 6TiSCH architecture, provides the abstraction of an IP link over a TSCH MAC layer (IEEE 802.15.4-2015). The functionality of 6top is to facilitate the dynamic cell negotiation with one-hop neighbors.

This is a Contiki-NG implementation of 6top, developed by:

It supports 6P (6top Protocol) of draft-10 except for concurrent 6P transactions described in Section 3.4.3.

Code Structure

File Contents
sixtop.[ch] 6top external APIs
sixp.[ch] 6P I/O APIs
sixp-nbr.[ch] 6P Neighbor Management APIs
sixp-pkt.[ch] 6P Packet Manipulation APIs
sixp-trans.[ch] 6P Transaction Management APIs
sixp-conf.h 6P Configuration Parameters

Configuration Paramters

Parameter Meaning Default Value
SIXTOP_CONF_MAX_SCHEDULING_FUNCTIONS The maximum number of SFs installed in 6top 1
SIXTOP_CONF_MAX_TRANSACTIONS The maximum number of transactions at a time 1


At this moment, allocated 6P neighbor states never be deleted automatically since 6P itself has no way to decide to delete them. 6P neighbor state consists of SeqNum to be used for a next request (defined in sixp-nbr.c as next_seqno).

Once the number of 6P neighbor states reaches to the SIXTOP_6P_MAX_NEIGHBORS, a transaction with a new neighbor may fail due to failure in allocating a 6P neighbor state or schedule generation inconsistency.


An example using 6top is provided under examples/6tisch/sixtop/.

A simple Scheduling Function (SF) is implemented in sf-simple.[ch]. This SF does not have bandwidth monitoring mechanism nor bandwidth adaptation mechanism. Instead, the SF provides APIs so that a user process can add or remove cells dynamically. A sample user process implementation using the SF is found in node-sixtop.c, which is tested with


6top or 6P related tests are implemented under tests/13-ieee802154/.

Using 6top

In order to use 6top with your system, sixtop module must be built together in addition to TSCH.

Enable TSCH, then set TSCH_CONF_WITH_SIXTOP to 1, typically, in your project-conf.h:


Next, add sixtop into MODULES in your Makefile:

MODULES += os/net/mac/tsch/sixtop

For now, the simple SF mentioned above is only one SF shipped in the code base. You may have to implement your own SF.

Implementing a Scheduling Function

Scheduling Function (SF) is represented with sixtop_sf_t, which defined in sixtop.h. An SF can be added into 6top by sixtop_add_sf(). After the addition, a handler defined in sixtop_sf_t is invoked on a correspondent event, for example, reception of a 6P request or timeout of an ongoing transaction.

SF can send a 6P packet by sixp_output().


  1. IETF 6TiSCH Working Group
  2. 6top Protocol (6P)
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