ns3_AODV 源码阅读1:RouteOutput和RouteInput是什么

运行脚本aodv.cc 可以得到以下log输出

RouteOutput：

主动发包时调用的（它在找到路由的时候返回路由地址）

而这里没有找到路由，所以返回了loopback，也就是本机地址，于是数据包又发回了本机。

RouteInput：

收到包转发时调用的，在这里调用loopback发给自己后

node0就从发包着变成了收包者，然后再进行转发

以及调用DeferredRouteOutput（它又调用SendRequest）发送RREQ

这样复用了RouteInput，从而简化了RouteOutput的操作，只进行路由查询，查询不到的情况下和转发函数合并为RouteInput，不需要在主动发起时考虑如何发出去了（广播啥的）

将发包和收包时的路由请求过程合并

Ptr<Ipv4Route>
RoutingProtocol::RouteOutput (Ptr<Packet> p, const Ipv4Header &header,
                              Ptr<NetDevice> oif, Socket::SocketErrno &sockerr)
{
  NS_LOG_FUNCTION (this << header << (oif ? oif->GetIfIndex () : 0));
  if (!p)
    {
      NS_LOG_DEBUG("Packet is == 0");
      return LoopbackRoute (header, oif); // later
    }
  if (m_socketAddresses.empty ())
    {
      sockerr = Socket::ERROR_NOROUTETOHOST;
      NS_LOG_LOGIC ("No aodv interfaces");
      Ptr<Ipv4Route> route;
      return route;
    }
  sockerr = Socket::ERROR_NOTERROR;
  Ptr<Ipv4Route> route;
  Ipv4Address dst = header.GetDestination ();
  RoutingTableEntry rt;
  if (m_routingTable.LookupValidRoute (dst, rt))
    {//找到路由则返回路由
      route = rt.GetRoute ();
      NS_ASSERT (route != 0);
      NS_LOG_DEBUG ("Exist route to " << route->GetDestination () << " from interface " << route->GetSource ());
      if (oif != 0 && route->GetOutputDevice () != oif)
        {
          NS_LOG_DEBUG ("Output device doesn't match. Dropped.");
          sockerr = Socket::ERROR_NOROUTETOHOST;
          return Ptr<Ipv4Route> ();
        }
      UpdateRouteLifeTime (dst, m_activeRouteTimeout);
      UpdateRouteLifeTime (route->GetGateway (), m_activeRouteTimeout);
      return route;
    }

  // 没有找到有效的路由，在这种情况下我们返回loopback。Valid route not found, in this case we return loopback. 
  //实际路径请求将被推迟，直到包将完全形成， Actual route request will be deferred until packet will be fully formed, 
  // 路由到loopback，从loopback接收并传递到RouteInput（见下文）routed to loopback, received from loopback and passed to RouteInput (see below)
  uint32_t iif = (oif ? m_ipv4->GetInterfaceForDevice (oif) : -1);
  DeferredRouteOutputTag tag (iif);
  NS_LOG_DEBUG ("Valid Route not found");
  if (!p->PeekPacketTag (tag))
    {
      p->AddPacketTag (tag);
    }
  return LoopbackRoute (header, oif);
}

bool
RoutingProtocol::RouteInput (Ptr<const Packet> p, const Ipv4Header &header,
                             Ptr<const NetDevice> idev, UnicastForwardCallback ucb,
                             MulticastForwardCallback mcb, LocalDeliverCallback lcb, ErrorCallback ecb)
{//CALLBACK，回调函数就是一个通过函数指针调用的函数。
    //(虽然这里是类)
    //如果你把函数的指针（地址）作为参数传递给另一个函数，
    //当这个指针被用为调用它所指向的函数时，我们就说这是回调函数。
    //回调函数不是由该函数的实现方直接调用，而是在特定的事件或条件发生时由另外的一方调用的，用于对该事件或条件进行响应。
  NS_LOG_FUNCTION (this << p->GetUid () << header.GetDestination () << idev->GetAddress ());
  if (m_socketAddresses.empty ())
    {
      NS_LOG_LOGIC ("No aodv interfaces");//没有aodv接口
      return false;
    }
  NS_ASSERT (m_ipv4 != 0);
  NS_ASSERT (p != 0);
  // 检查输入设备是否支持IP Check if input device supports IP
  NS_ASSERT (m_ipv4->GetInterfaceForDevice (idev) >= 0);
  int32_t iif = m_ipv4->GetInterfaceForDevice (idev);

  Ipv4Address dst = header.GetDestination ();
  Ipv4Address origin = header.GetSource ();

  // 延迟的路由请求Deferred route request
  if (idev == m_lo)
    {
      DeferredRouteOutputTag tag;
      if (p->PeekPacketTag (tag))
        {
          DeferredRouteOutput (p, header, ucb, ecb);
          //当一个节点无法找到一个可用的到某个节点的路由时，它就会广播一条 RREQ 消息。
          return true;
        }
    }

  // 重复自己的数据包 Duplicate of own packet
  if (IsMyOwnAddress (origin))
    return true;

  // AODV不是多播路由协议 AODV is not a multicast routing protocol
  if (dst.IsMulticast ())
    {
      return false; 
    }

  // 广播本地交付/转发 Broadcast local delivery/forwarding
  for (std::map<Ptr<Socket>, Ipv4InterfaceAddress>::const_iterator j =
         m_socketAddresses.begin (); j != m_socketAddresses.end (); ++j)
    {
      Ipv4InterfaceAddress iface = j->second;
      if (m_ipv4->GetInterfaceForAddress (iface.GetLocal ()) == iif)
        if (dst == iface.GetBroadcast () || dst.IsBroadcast ())
          {
            if (m_dpd.IsDuplicate (p, header))
              {//重复数据包p from Source,Drop
                NS_LOG_DEBUG ("Duplicated packet " << p->GetUid () << " from " << origin << ". Drop.");
                return true;
              }
            UpdateRouteLifeTime (origin, m_activeRouteTimeout);
            Ptr<Packet> packet = p->Copy ();
            if (lcb.IsNull () == false)
              {//广播本地交付to  iface.GetLocal 
                NS_LOG_LOGIC ("Broadcast local delivery to " << iface.GetLocal ());
                lcb (p, header, iif);
                // 通过追加处理 Fall through to additional processing
              }
            else
              {//由于null callback ，无法在本地传递数据包 
                NS_LOG_ERROR ("Unable to deliver packet locally due to null callback " << p->GetUid () << " from " << origin);
                ecb (p, header, Socket::ERROR_NOROUTETOHOST);
              }
            if (!m_enableBroadcast)
              {
                return true;
              }
            if (header.GetProtocol () == UdpL4Protocol::PROT_NUMBER)
              {
                UdpHeader udpHeader;
                p->PeekHeader (udpHeader);
                if (udpHeader.GetDestinationPort () == AODV_PORT)
                  {
                    // 广播发送的AODV数据包已经被管理 AODV packets sent in broadcast are already managed
                    return true;
                  }
              }
            if (header.GetTtl () > 1)
              {//转发广播。 TTL=header.GetTtl ()
                NS_LOG_LOGIC ("Forward broadcast. TTL " << (uint16_t) header.GetTtl ());
                RoutingTableEntry toBroadcast;
                if (m_routingTable.LookupRoute (dst, toBroadcast))
                  {
                    Ptr<Ipv4Route> route = toBroadcast.GetRoute ();
                    ucb (route, packet, header);
                  }
                else
                  {//没有路由转发广播。 丢弃数据包
                    NS_LOG_DEBUG ("No route to forward broadcast. Drop packet " << p->GetUid ());
                  }
              }
            else
              {//TTL超出。 丢弃数据包
                NS_LOG_DEBUG ("TTL exceeded. Drop packet " << p->GetUid ());
              }
            return true;
          }
    }

  // 单播本地交付Unicast local delivery
  if (m_ipv4->IsDestinationAddress (dst, iif))
    {
      UpdateRouteLifeTime (origin, m_activeRouteTimeout);
      RoutingTableEntry toOrigin;
      if (m_routingTable.LookupValidRoute (origin, toOrigin))
        {
          UpdateRouteLifeTime (toOrigin.GetNextHop (), m_activeRouteTimeout);
          m_nb.Update (toOrigin.GetNextHop (), m_activeRouteTimeout);
        }
      if (lcb.IsNull () == false)
        {//单播本地交付到dst
          NS_LOG_LOGIC ("Unicast local delivery to " << dst);
          lcb (p, header, iif);
        }
      else
        {//由于null回调，无法在本地交付数据包
          NS_LOG_ERROR ("Unable to deliver packet locally due to null callback " << p->GetUid () << " from " << origin);
          ecb (p, header, Socket::ERROR_NOROUTETOHOST);
        }
      return true;
    }

  // 检查输入设备是否支持IP转发Check if input device supports IP forwarding
  if (m_ipv4->IsForwarding (iif) == false)
    {
      NS_LOG_LOGIC ("Forwarding disabled for this interface");
      ecb (p, header, Socket::ERROR_NOROUTETOHOST);
      return true;
    }

  // 转发Forwarding
  return Forwarding (p, header, ucb, ecb);
}