- Assumptions:
- Nodes can
move
at any time....
- Each node
must be able to
forward packets
for other nodes
- Nodes must be
able to
operate promiscuously
- I.e.: nodes will receive frames with physical addresses other than the own physical address
- Wireless communication channels
are assumed to be
asymmetric
- Each node is assigned a unqiue IP address
- Nodes can
move
at any time....
- Source routing:
- Source routing = a routing technique where the message header contain the entire route from the source (sender) node to the destination node
Example:
- Forwarding operation used in
source routing:
Node N receives a message if ( NextRouter == N (mySelf) ) { Rotate the source path in message header Forward the message to the next router in the path } else { Discard message }Example:
- Advantage of
source routing:
- When the destination
receives a message and the
paths are
bi-directional, then:
- The destination can use the reverse path to send messages to the source
Example:
- When the destination
receives a message and the
paths are
bi-directional, then:
- Disadvantage
of source routing:
- The length of
the packet header
in source routing is
variable !!!
(So Source Routing will thus not work with IP routing software)
- The length of
the packet header
in source routing is
variable !!!
- Note:
- Source routing
is well suited for
on demand routing:
- If links are
symmetric,
the destination can use the
reverse route to
reply to the
sender
(And the receiver can skip the (costlier) routing discovering step)
- If links are
symmetric,
the destination can use the
reverse route to
reply to the
sender
- Source routing
is well suited for
on demand routing:
- The DSR protocol
is composed of two mechanisms:
- Route Discovery:
- Route discovery = the algorithm used by a source node S to find a (source) route to a destination node D
- Route Maintenance:
- Route maintenance =
the algorithm used by
by a
source node S when:
- S detected that a source route to the destination does not work anymore.
- The cause
of the failure is
some hop on the
source route
no longer work
(because some node has moved).
Fixing a route:
- Use
an alternate route if the
source node S has
multiple source routes to
the destination
- Use the Route Discovery procedure to find a new route.
- Route maintenance =
the algorithm used by
by a
source node S when:
Note:
- The Route Discovery/Maintenance
procedures are
only used
when:
- The (source) node is actually transmitting a packet to the destination !!!
That's is the nature of on-demand routing !!!
- Route Discovery: