快樂蝦

歡迎轉載，但請保留作者資訊

在first.py中建立了一個點到點的通道，且配置了兩個屬性：

pointToPoint = ns.point_to_point.PointToPointHelper()
pointToPoint.SetDeviceAttribute("DataRate", ns.core.StringValue("2Mbps"))
pointToPoint.SetChannelAttribute("Delay", ns.core.StringValue("100ms"))

在配置DataRate時，first.py傳遞了一個字串”2Mbps”，這個字串最後由下面的C++程式碼進行解析：

bool
DataRate::DoParse (const std::string s, uint64_t *v)
{
  NS_LOG_FUNCTION (s << v);
  std::string::size_type n = s.find_first_not_of ("0123456789.");
  if (n != std::string::npos)
    { // Found non-numeric
      std::istringstream iss;
      iss.str (s.substr (0, n));
      double r;
      iss >> r;
      std::string trailer = s.substr (n, std::string::npos);
      if (trailer == "bps")
        {
          // bit/s
          *v = (uint64_t)r;
        }
      else if (trailer == "b/s")
        {
          // bit/s
          *v = (uint64_t)r;
        }
      else if (trailer == "Bps")
        {
          // byte/s
          *v = (uint64_t)(r * 8);
        }
      else if (trailer == "B/s")
        {
          // byte/s
          *v = (uint64_t)(r * 8);
        }
      else if (trailer == "kbps")
        {
          // kilobits/s
          *v = (uint64_t)(r * 1000);
        }
      else if (trailer == "kb/s")
        {
          // kilobits/s
          *v = (uint64_t)(r * 1000);
        }
      else if (trailer == "Kbps")
        {
          // kilobits/s
          *v = (uint64_t)(r * 1000);
        }
      else if (trailer == "Kb/s")
        {
          // kilobits/s
          *v = (uint64_t)(r * 1000);
        }
      else if (trailer == "kBps")
        {
          // kiloByte/s
          *v = (uint64_t)(r * 8000);
        }
      else if (trailer == "kB/s")
        {
          // KiloByte/s
          *v = (uint64_t)(r * 8000);
        }
      else if (trailer == "KBps")
        {
          // kiloByte/s
          *v = (uint64_t)(r * 8000);
        }
      else if (trailer == "KB/s")
        {
          // KiloByte/s
          *v = (uint64_t)(r * 8000);
        }
      else if (trailer == "Kib/s")
        {
          // kibibit/s
          *v = (uint64_t)(r * 1024);
        }
      else if (trailer == "KiB/s")
        {
          // kibibyte/s
          *v = (uint64_t)(r * 8192);
        }
      else if (trailer == "Mbps")
        {
          // MegaBits/s
          *v = (uint64_t)(r * 1000000);
        }
      else if (trailer == "Mb/s")
        {
          // MegaBits/s
          *v = (uint64_t)(r * 1000000);
        }
      else if (trailer == "MBps")
        {
          // MegaBytes/s
          *v = (uint64_t)(r * 8000000);
        }
      else if (trailer == "MB/s")
        {
          // MegaBytes/s
          *v = (uint64_t)(r * 8000000);
        }
      else if (trailer == "Mib/s")
        {
          // MebiBits/s
          *v = (uint64_t)(r * 1048576);
        }
      else if (trailer == "MiB/s")
        {
          // MebiByte/s
          *v = (uint64_t)(r * 1048576 * 8);
        }
      else if (trailer == "Gbps")
        {
          // GigaBit/s
          *v = (uint64_t)(r * 1000000000);
        }
      else if (trailer == "Gb/s")
        {
          // GigaBit/s
          *v = (uint64_t)(r * 1000000000);
        }
      else if (trailer == "GBps")
        {
          // GigaByte/s
          *v = (uint64_t)(r * 8*1000000000);
        }
      else if (trailer == "GB/s")
        {
          // GigaByte/s
          *v = (uint64_t)(r * 8*1000000000);
        }
      else if (trailer == "Gib/s")
        {
          // GibiBits/s
          *v = (uint64_t)(r * 1048576 * 1024);
        }
      else if (trailer == "GiB/s")
        {
          // GibiByte/s
          *v = (uint64_t)(r * 1048576 * 1024 * 8);
        }
      else
        {
          return false;
        }
      return true;
    }
  std::istringstream iss;
  iss.str (s);
  iss >> *v;
  return true;
}
 

從這一段程式碼也可以明顯看出NS3中速率字串的表達方式及意義，比文件清晰多了，原來還不知道速率可以有這麼多的表達方式，汗一個~~~~

從”DataRate”順藤摸瓜，可以發現其它幾個裝置屬性：

TypeId 
SimpleNetDevice::GetTypeId (void)
{
  static TypeId tid = TypeId ("ns3::SimpleNetDevice")
    .SetParent<NetDevice> ()
    .SetGroupName("Network") 
    .AddConstructor<SimpleNetDevice> ()
    .AddAttribute ("ReceiveErrorModel",
                   "The receiver error model used to simulate packet loss",
                   PointerValue (),
                   MakePointerAccessor (&SimpleNetDevice::m_receiveErrorModel),
                   MakePointerChecker<ErrorModel> ())
    .AddAttribute ("PointToPointMode",
                   "The device is configured in Point to Point mode",
                   BooleanValue (false),
                   MakeBooleanAccessor (&SimpleNetDevice::m_pointToPointMode),
                   MakeBooleanChecker ())
    .AddAttribute ("TxQueue",
                   "A queue to use as the transmit queue in the device.",
                   StringValue ("ns3::DropTailQueue"),
                   MakePointerAccessor (&SimpleNetDevice::m_queue),
                   MakePointerChecker<Queue> ())
    .AddAttribute ("DataRate",
                   "The default data rate for point to point links. Zero means infinite",
                   DataRateValue (DataRate ("0b/s")),
                   MakeDataRateAccessor (&SimpleNetDevice::m_bps),
                   MakeDataRateChecker ())
    .AddTraceSource ("PhyRxDrop",
                     "Trace source indicating a packet has been dropped "
                     "by the device during reception",
                     MakeTraceSourceAccessor (&SimpleNetDevice::m_phyRxDropTrace),
                     "ns3::Packet::TracedCallback")
  ;
  return tid;
}
 

只不過我們目前暫且不管這些屬性。

修改DataRate的值，可以發現在NetAnim中最明顯的表現就是用以表示資料包的箭頭的長度，當DataRate為2Mbps時：

當DataRate變為200Kbps時就變成了：

差別還是很明顯的！