104 lines
3.9 KiB
Markdown
104 lines
3.9 KiB
Markdown
# [EXPERIMENTAL] 6TiSCH Operation Sublayer (6top)
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## Overview
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6TiSCH Operation Sublayer (6top), a logical link layer in the 6TiSCH
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architecture, provides the abstraction of an IP link over a TSCH MAC layer (IEEE
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802.15.4e). The functionality of 6top is to facilitate the dynamic cell
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negotiation with one-hop neighbors.
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This is a Contiki implementation of 6top, developed by:
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- Shalu R, CDAC, shalur@cdac.in, github user: [shalurajendran](https://github.com/shalurajendran)
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- Lijo Thomas, CDAC, lijo@cdac.in
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- Yasuyuki Tanaka
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It supports 6P (6top Protocol) of [draft-03](draft-ietf-6tisch-6top-protocol-03)
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except for concurrent 6P transactions described in [Section
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4.3.3](https://tools.ietf.org/html/draft-ietf-6tisch-6top-protocol-03#section-4.3.3).
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## Code Structure
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| File | Contents |
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|-----------------|--------------------------------|
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| sixtop.[ch] | 6top external APIs |
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| sixp.[ch] | 6P I/O APIs |
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| sixp-nbr.[ch] | 6P Neighbor Management APIs |
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| sixp-pkt.[ch] | 6P Packet Manipulation APIs |
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| sixp-trans.[ch] | 6P Transaction Management APIs |
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| sixp-conf.h | 6P Configuration Parameters |
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## Configuration Paramters
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| Parameter | Meaning | Default Value |
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|--------------------------------------|----------------------------------------------|---------------|
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| SIXTOP_CONF_MAX_SCHEDULING_FUNCTIONS | The maximum number of SFs installed in 6top | 1 |
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| SIXTOP_CONF_MAX_TRANSACTIONS | The maximum number of transactions at a time | 1 |
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## Caveat
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At this moment, allocated 6P neighbor states never be deleted since 6P has no
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way to decide to delete them. 6P neighbor state consists of SeqNum to be used
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for a next reqeust, GTX, and GRX (defined in sixp-nbr.c).
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Once the number of 6P neighbor states reaches to the `SIXTOP_6P_MAX_NEIGHBORS`,
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a transaction with a new neighbor may fail due to failure in allocating a 6P
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neighbor state or schedule generation inconsistency.
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## Example
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An example using 6top is provided under `examples/ipv6/rpl-tsch-sxitop/`.
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A simple Scheduling Function (SF) is implemented in `sf-simple.[ch]`. This SF
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does not have bandwidth monitoring mechanism nor bandwidth adaptation
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mechanism. Instead, the SF provides APIs so that a user process can add or
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remove cells dynamically. A sample user process implementation using the SF is
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found in `node-sixtop.c`, which is tested with `rpl-tsch-sixtop-z1.csc`.
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## Test
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6top or 6P related tests are implemented under `regression-tests/26-6tisch`.
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## Using 6top
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In order to use 6top with your system, `sixtop` module must be built together in
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addition to [TSCH](../).
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Enable TSCH, then set 1 to `TSCH_CONF_WITH_SIXTOP`, typically, in your
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`project-conf.h`:
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```C
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#undef TSCH_CONF_WITH_SIXTOP
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#define TSCH_CONF_WITH_SIXTOP 1
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```
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Next, add `sixtop` into `MODULES` in your Makefile:
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```Makefile
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MODULES += core/net/mac/tsch/sixtop
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```
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For now, the simple SF mentioned above is only one SF shipped in the code
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base. You may have to implement your own SF.
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## Implementing a Scheduling Function
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Scheduling Function (SF) is represented with `sixtop_sf_t`, which defined in
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`sixtop.h`. An SF can be added into 6top by `sixtop_add_sf()`. After the
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addition, a handler defined in `sixtop_sf_t` is invoked on a correspondent
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event, for example, reception of a 6P request or timeout of an ongoing
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transaction.
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SF can send a 6P packet by `sixp_output()`. After every Add or Delete operation,
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SF needs to advance schedule generation counter associated with the peer by
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`sixp_advance_generation()`, counter which is maintaeind by 6P. Otherwise, SF
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will not able to perform any command request other than Clear due to schedule
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generation inconsistency.
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## References
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1. [IETF 6TiSCH Working Group](https://datatracker.ietf.org/wg/6tisch)
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2. [6top Protocol (6P)](https://tools.ietf.org/html/draft-ietf-6tisch-6top-protocol)
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