one photo on a web page
cut into small pieces
#1 of 6
TO 203.0.113.7
#2 of 6
TO 203.0.113.7
#3 of 6
TO 203.0.113.7
#4 of 6
TO 203.0.113.7
#5 of 6
TO 203.0.113.7
#6 of 6
TO 203.0.113.7
header: where it is going, and which piece it is
payload: up to about 1,500 bytes of the page
A
page
becomes
numbered
packets
you
the server
1
2
3
4
ROUTER R4 TABLE: 203.0.113.0/24 → R6
R4
each router reads the address and passes the packet on
Routers
pass
them
on,
hop
by
hop
you
the server
link down
1
2
3
4
no switchboard in charge: routers just pick another working hop
pieces of one page can travel by different paths
A
broken
link?
They
go
around
it
1
2
3
4
5
6
arriving, in whatever order the network delivered them
put back in order by number
#3
#1
#5
#2
#6
#4 missing: ask the server to send it again
#4
page rebuilt
Your
device
puts
them
back
in
order
How
does
the
internet
work?