NS3网络仿真之：DataRate属性

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前言序锦

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本非通信人，却也来瞧瞧这通信的奇妙！由于SRTP项目选的是通信的项目，所以这段时间，也一直在接触与NS3相关的知识，进他就来和大家简单聊一下……

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正文

• 首先我们需要在first.py文件中创建一个点到点的信道，并配置来两个属性：

PointToPoint = ns.point_to_point.PointToPointHelper()
pointToPoint.SetDeviceAttribute("DataRate", ns.core.StringValue("10Mbps"))
pointToPoint.SetChannelAttribute("Delay", ns.core.StringValue("100ms"))

• 上面的代码我们配置了DataRate的属性时，first.py传递来一个字符串“10Mbps”（同时给“Delay”属性值传递来一个字符串”100ms“，这是传入来一个延时，这个不作讨论），这个字符串最后通过C++代码来进行解析：

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;  
}  

从这段代码我们可以很明显的看出，NS3中速率的字符串的表达方式以及其意义
- 我们通过“DataRate”这个属性来看，可以发现其他几个设备的属性，在这里顺便讲一下：

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;  
}  

这也是NS3仿真过程几个比较重要的属性，后面我们会有详细的介绍，这里找出来让大家一起去探讨……

• 通过NetAnim动态演示工具（后面我也会专门来谈一下NetAnim）我们来修改DataRate的属性值来找出异同：
  
  • 当DataRate的的值为：10Mbps
    
  • 当DataRate的值为：200Mbps
    
• 分析： 我们可以发现，在NetAnim中，最明显的能观察出来的就是用以表示数据包的箭头的长度，当DataRate的值修改为200Mbps时，箭头明显变长，是呈现一个正比例的方式增长的！

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好了，今天的简单分享就到此为止了，想学NS3的童鞋们，我们可以一起学习哟，加油！！！