- Flooding:
- Flooding = the basic algorithm to perform broadcasting without the use of routing tables
(If you can use routing tables, there is a more efficient algorithm called: reverse path broadcasting)
- The Flooding algorithm:
Initial flooding operation: Select TTL = "large enough" (depends on network topology); Send packet with TTL value to all neighbor nodes;
Flooding forwarding algorithm: Node receives a packet on link L; Set TTL = TTL - 1; if ( TTL > 0 ) { Send packet with new TTL on all links except link L; } else { Drop packet; }
Example: Flooding
- Reliable flooding:
- Reliable flooding =
a more efficient
flooding algorithm
- Nodes must
maintain:
- A lastest "version" number (similar to a send sequence number)
- A node will only forward a flood message that has a newer (larger) version number than its current version number
- Reliable flooding =
a more efficient
flooding algorithm
- Example:
- Recall that:
- Flooding will broadcast some information to all nodes in the network
- Suppose:
- All nodes broadcast their link cost (state) information
The result will be:
- Every node will know the link costs of every link in the network.
- Example:
- Network:
- After the
flooding is done,
each node will
have this information:
Distance matrix To: From A B C D E ------+--------------------------------- A | * 5 10 * * B | 5 * 3 11 * C | 10 3 * 2 * D | * 11 2 * 3 E | * * * 3 *The matrix contains the cost of all the links
- Network:
- Every node in the network will
have the same information
- Each node will next run the well-known Dijkstra Algorithm on the graph to find the shortest paths.
- I have used symmetric link costs
- In general, the link costs
are asymmetric
(due to different queueing delays)
- The Dijkstra's algorithm will work on networks with asymmetric link costs