main ideas are:
* Separates the Contiki low-layer network stack into four layers:
network (e.g. sicslowpan / rime), Medium Access Control MAC
(e.g. CSMA), Radio Duty Cycling RDC (e.g. ContikiMAC, X-MAC), and
radio (e.g. cc2420).
* Introduces a new way to configure the network stack. Four #defines
that specify what mechanism/protocol/driver to use at the four
layers: NETSTACK_CONF_NETWORK, NETSTACK_CONF_MAC, NETSTACK_CONF_RDC,
NETSTACK_CONF_RADIO.
* Adds a callback mechanism to inform the MAC and network layers about
the fate of a transmitted packet: if the packet was not possible to
transmit, the cause of the failure is reported, and if the packets
was successfully transmitted, the number of tries before it was
finally transmitted is reported.
* NULL-protocols at both the MAC and RDC layers: nullmac and nullrdc,
which can be used when MAC and RDC functionality is not needed.
* Extends the radio API with three new functions that enable more
efficient radio duty cycling protocols: channel check, pending
packet, and receiving packet.
* New initialization mechanism, which takes advantage of the NETSTACK
#defines.
of link-layer and MAC-layer mechanisms to achieve a very low power
consumption: during idle listening the radio is switched off between
99.2% and 99.6% of the time. One unicast transmission typically adds
between 0.07% and 1.2% additional radio time, depending on packet
size.
ContikiMAC uses the standard IEEE 802.15.4 message format and adds no
additional headers.
ContikiMAC is simple: it uses periodic two-shot channel sampling
during idle listening to keep the radio on-time down. Transmissions
are done with repeated transmissions until a link-layer ACK is
received.
of an rtimer for the periodic radio duty cycling. The benefit of this
implementation is that it leaves an rtimer free for user tasks. The
drawback is a slightly higher idle power consumption. This new version
is based on the current rtimer-based X-MAC.
channel_check_interval(). This function returns the interval by which
the duty cycling mechanism checks the radio channel for activity. It
is used by higher layer mechanisms to determine suitable timeouts for
retransmissions.
* the code is simplified, particularly the duty cycling logic
* old unused code has been removed
* Contiki X-MAC now listens before sending a strobe to avoid MAC-level
collisions
* broadcasts are sent directly, without strobes, reducing the power
consumption of receivers
* turn off radio for 1 ms between sending a strobe and expecting the
strobe ack
sicslowpan tags TCP packets with the PACKETBUF_ATTR_PACKET_TYPE_STREAM
flag, which makes the underlying power-saving MAC layer keep the radio
on for some time after transmitting the packet. This allows reply
packets to be processed directly, significantly increasing TCP latency
and throughput.
the packetbuf from packet attributes. Two framer modules are included,
one that creates 802.15.4 frame headers, and one that creates a
minimal "nullmac"-style header that only contains the link-local
addresses.
last were known to be awake. When sending a packet, a sender does not
start to send strobes until the neighbor is expected to be awake. This
reduces power consumption for senders and decreases the contention in
the network as there are less packets in the air. Additionally, the
ACK optimization was improved so that data/ack exchanges now are
more efficient.
