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Bundling is a
general-purpose mechanism that allows communication between temporally
disconnected nodes. Imagine this is
your network, with the only “permanent” links in yellow. At some point, there’s a communication
opportunity for a portion of the network [CLICK]. This may be a deep-space communications pass or someone walking
past a kiosk in an airport, for example.
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Now, assuming
the delay is low enough, nodes 1 and 2 can communicate using TCP [CLICK]
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Eventually,
however, that communication session is lost [CLICK]
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Later, some
other portion of the network becomes connected [CLICK]
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Now nodes 2 and
3 can communicate [CLICK] For a
while…[CLICK]
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And this
continues [CLICK] Nodes 2 and 4 can communicate, [CLICK] nodes 3 and 4
[CLICK]
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The essence of
the store-and-forward bundling protocol is that it allows communications
between nodes for which no contemporaneous end-to-end path ever exists, such
as 1 and 4. You can think of this
sort of like the persistence of vision, where first one part of the network
is illuminated [CLICK], then another [CLICK], and another [CLICK]. Bundling provides the “memory” that allows
us to view these pieces not as disconnected islands, but as a connected
whole. [CLICK]
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You might think
this is no big deal, SMTP can sort of handle situations like this, but not
well.
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