* Added an optional "keep alive" mechanism whereby an idle network is
periodically probed by dummy packets to maintain a recent quality
metric when there is no traffic.
* Bugfix in when new routing metrics should be advertised
* Rewrote the ACK logic so that a queuebuf is not allocated for each
ack, only for those acks generated by the sink node.
* Updated the wrap-around logic for sequence numbers: when a sequence
number wraps, it won't go back to 0. Instead, it wraps to 128. This
allows us to understand when a node has rebooted: when its seqno is <
128, it has recently rebooted.
* Loop detection and untangling. Now uses in-band loop detection that
works.
* Link quality estimation. Now starts with a conservative /
pessimistic estimate for new links.
* Retransmissions. MAC layer and network layer retransmissions are now
decoupled.
* Loss handling. Deals better with losses now.
* Concurrent applications. Each connection now maintains its own
neighbor table with separated cost to sink estimates for each
connection.
* 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.
