- A common misconception is:
- the messages
will be received
reliability
on an end-to-end basis
-
If messages are
received reliably
on a hop-to-hop basis:
then:
The above claim is false !!!
- the messages
will be received
reliability
on an end-to-end basis
- In end-to-end communication,
packets can
be received
out-of-order:
Example:
- Source X transmits
2 messages:
- Packet 1 is
routed into a
congested node B:
- Router A
recomputes routing tables
and toute
packet 2 to
a less congested node:
- The packets will
arrive
out-of-order:
- Source X transmits
2 messages:
- Received
(and acknowledged) packets
can be deleted later
(to make space for
a higher priority
packet) !!!
Example:
- A router received
(and acknowledged)
a packet from
X:
The output queue is almost full
- When some high priority traffic
is received:
Then:
- Some received and acknowledged packet(s) will have to be discarded !!!
Conclusion:
- Hop-to-hop reliability does not ensure end-to-end reliability
- A router received
(and acknowledged)
a packet from
X: