Clarification on sending/receiving epochs

[natevw]

Each epoch is capable of a max throughput of 120bps, or a total of
16k over the full epoch period (about 18 minutes). Every mote has at
least one receiving epoch and one sending epoch per link to another
mote, and will often have multiple epochs with other motes to
increase the bandwidth available.

I'm not sure what this is saying. From the glossary I sort of expected motes to communicate via knocks during windows. What does it mean that a mote has "at least one receiving epoch"? Should this read "receiving window per epoch" and likewise for sending?

[natevw]

As I read further, this is becoming a bit more clear — I think!

Additional MAC-only packet types are defined for exchanging the current set of epochs active between any two motes.

and:

Each mote should actively make use of multiple epochs with more efficient options to optimize the overall energy usage.

…help me [re-]interpret the previous discussion of epoch. I was assuming the whole network would "be in" an epoch for 18 minutes. But now it's becoming a bit more clear that an epoch is [perhaps?] more of a virtual channel, one-way, between exactly 2 motes active for ~18 minutes.

[natevw]

A bit of update in f779a9b