- Consider the following
scenario:
- Initially:
- Then node D
moves:
- Suppose node C
transmits a packet to
D:
and does not get back an ACK....
- Node C will then
transmit a
ROUTE REQUEST:
And get back a new source route:
Notice that:
- The ROUTE REPLY is
only received by
node C !!!!
- Furthermore, Node G
still has
the old route to
node D:
- Initially:
- Suppose that
node D
moves again:
- Now consider what will
happen if we
salvage a
packet:
- Again:
node A transmits a
message to
node D using the
broken source route:
- Then node C will
detect the
error
(no ACK):
- Node C will transmit
an ERROR report, but will
also
salvage the
packet:
because node C has a source route to D that does not use the link CD !!!
- However,
node G will
fail to
deliver the
packet and
detect the
error
(no ACK):
- If
Node G
salvage the
packet,
node G will
send the
packet back to C:
because node C has a source route to D that does not use the link CD !!!
- Again:
node A transmits a
message to
node D using the
broken source route:
- Caveat:
- We have a routing loop !!!
- Solution:
- A salvaged packet is
marked
as having been salvaged
- A salvaged packet cannot be salvaged again !!!!
- A salvaged packet is
marked
as having been salvaged