/// <summary>
/// Generates a new Message, containing a RREQ for the wanted destination.
/// Implemented according to Section 6.3: Generating Route Requests (RREQ) in the RFC.
///
/// Method also handles buffering of RREQ, to avoid sending a duplicate in next iteration.
/// </summary>
/// <param name="destination">String representation of the destination address.</param>
/// <returns>A Message with the RREQ enclosed. Includes destination address set to broadcast, and TTL adjusted according to the RFC.</returns>
public Message GenerateInitialRreqMessage(string destination)
{
//If RREQ has been sent for this destination by me, and has not yet timed out, dont send a new one
if (RreqAttemptExist(destination, _localAddress) && _time.CurrentTime < GetBufferedRreqAttempt(destination, _localAddress).ExpirationTime)
{
_logger.WriteLine("RREQ has been sent for this destination, and has not yet timed out, so dont send a new one.");
return(null);
}
//Else, no RREQ for this destination waiting for response, send a new one
RoutingTable.IncrementSequenceNumber(); //Must be incremented before sending a RREQ, per section 6.1 and 6.3
var knownEntry = RoutingTable.GetEntry(destination); //Get stale entry if it exists
var rreq = new Rreq
{
G = _conf.AODV_UseGratuitousRREPs,
D = _conf.AODV_DestinationRespondOnlyFlag,
U = knownEntry == null, //True if no current DSN is known, per section 6.3
HopCount = 0,
RouteRequestId = RoutingTable.NextRouteRequestId,
DestinationAddress = destination,
DestinationSequenceNumber = knownEntry?.DestinationSequenceNumber ?? 0, //Known DSN and U=false, or unknown DSN=0 and U=true
OriginatorAddress = _localAddress,
OriginatorSequenceNumber = RoutingTable.SequenceNumber
};
//Any stale routing table entry waiting for a RREP (because of the newly generated RREQ) should not be expunged before current_time + 2 * NET_TRAVERSAL_TIME
if (knownEntry != null)
{
knownEntry.ExpirationTime = _time.GetFutureTime(2 * _aodvParameters.NetTraversalTime);
}
//Create Message to send RREQ in, and adjust RREQ
var msg = new Message(rreq, SimulationConstants.BroadcastAddress, _localAddress, _conf.MessageTtlValue);
msg.Ttl = knownEntry?.HopCount + _aodvParameters.TtlIncrement ?? _aodvParameters.TtlStart; //Per section 6.4, use last known hopcount as initial TTL + TTL_INCREMENT
//Buffer RREQ ID and Originator address, pr. section 6.3 (taken from rreq)
var rreqAttempt = new BufferedRreqAttempt(0, rreq, _conf.AodvConfiguration.PathDiscoveryTime);
rreqAttempt.ExpirationTime = _time.GetFutureTime(_aodvParameters.PathDiscoveryTime);
AddBufferedRreqAttempt(rreqAttempt);
return(msg);
}
/// <summary>
/// Buffers a sent RREQ.
/// </summary>
/// <param name="rreqAttempt">The RREQ attempt to buffer.</param>
public void AddBufferedRreqAttempt(BufferedRreqAttempt rreqAttempt)
{
_bufferedRreqAttempts.Add(rreqAttempt);
}