* the new version makes use of MAC-layer feedback so that bad paths
can be identified quicker and then avoided.
* the new code uses transport layer ACKs that contain feedback from
the collect protocol: when a packet cannot be forwarded due to lack
of resources, the ACK contains a flag that indicates that the packet
could not be forwarded. ACKs also contain the routing metric of the
sender, which improves agility in face of rapid path changes.
* loop detection and management has been improved: with higher path
metric agility, the system is more prone to short-lived routing
loops. Instead of dropping looping packets, the new version adjusts
the routing metric for the routes that exhibit loops so that the
risk for future loops is reduced.
* make use of packet attributes to inform the MAC layer of how many
times packets should be retransmitted.
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.
