- Route discovery summary:
- A node S that
need to find
a route
to node D will:
- Broadcast a ROUTE REQUEST(S,D) message to all its neighbors
- Then wait for:
- a ROUTE REPLY message which will contain a source route the the destination
- The node will
cache the
source route in its
route cache
- There may be multiple source routes to the same destination in the route cache !!!
Example:
- Node A broadcasts
a RReq(A,G) message:
- The ROUTE REQUEST message will
travel to the
destination
while
recording the
route travelled:
- The destination will then
return a
ROUTE REPLY message containing the
source route:
- The source route is
saved in the
route cache:
- A node S that
need to find
a route
to node D will:
- Basic Route Discover algorithm:
The node N receives a ROUTE REQUEST message. if ( Destination = N (myself) ) { return a ROUTE REPLY message containing the recorded source route to the sender (See note in NEXT section !!!) } else if ( Source = N (myself) ) { /* My neighbor is forwarding my RReq and I got it back....*/ Discard ROUTE REQUEST message; } else if ( RReqID ∈ RReqIDCache ) { /* The node has received this Route Req before !!! */ Discard ROUTE REQUEST message; } else if ( N ∈ Route Record in ROUTE REQUEST message ) { /* The node has also received this Route Req before !!! */ Discard ROUTE REQUEST message; } else { Append N to the Route Record of ROUTE REQUEST message; TTL = TTL - 1; if ( TTL > 0 ) { Broadcast the modified ROUTE REQUEST message; } else { Discard the ROUTE REQUEST message; } } Save RReqID in ROUTE REQUEST message in RReqIDCache;
- Example:
node A wants to
find a route to
node D
- Node A broadcasts
a ROUTE REQUEST message:
(The Request ID is randomly chosen and it's equal to 86)
- The neighbor nodes will then
re-broadcast the
ROUTE REQUEST with their
ID in the
route record:
Note:
- node A will discard the RReq message
- Nodes B and E will forward the RReq message
- Nodes C and
F
will forward the
ROUTE REQUEST message:
Note:
- Nodes B and
E will
discard the
ROUTE REQ message
because:
- The RouteReq ID (86) is in their Route Req ID Cache !!!
- Node C has
received
2 ROUTE REQ messages:
But:
- Node C will
forward
only one
of the 2 received RReq messages
The 2nd copy is discarded because the RReqID (86) is now in the RouteReqID Cache !!!
- Node C will
forward
only one
of the 2 received RReq messages
- Nodes B and
E will
discard the
ROUTE REQ message
- Node D will
send back a
Route Reply message:
Note:
- We have assumed
that the
destination node D has a
source routing to
source A !!!
See next section !!!
- We have assumed
that the
destination node D has a
source routing to
source A !!!
- Node A broadcasts
a ROUTE REQUEST message:
- The paper assumes that the
network diameter is
relatively small:
- TTL = 5 to 10
(See page 2 of the article)