1、DTN MED平均等待时间计算公式
下面这段代码是在dtnsim2中的packageprotocolStack.globalKnowledge;下的contactschedule中,有一个计算MED时间的函数
/** Computes the MED metric assuming that time begins at startTime. */
public double getMEDWeight(double simTime)
{
if (nextUpTime != null)
{
throw new RuntimeException("ContactSchedule is not closed");
}
double downSquaredSum = 0;
double lastTime = 0;
for (UpTime up : times)
{
if (up.getTimeUp() != 0)
{
assert up.getTimeUp() > lastTime;
double downTime = up.getTimeUp() - lastTime;
assert downTime > 0;
downSquaredSum += downTime * downTime;
}
lastTime = up.getTimeDown();//仅仅统计down的时间长度
}
// Add the very last down time
double downTime = simTime - lastTime;
if (downTime > 0)
{
downSquaredSum += downTime * downTime;
}
double ret = (double) (downSquaredSum / (2 * simTime)) + contact.getLatency();
return ret;
}
在example-simple-readme中有下面情景
This scenario has four nodes: A, B, C, D. Band C are permanently connected to
D. A <-> B has a down interval of 40,and an up interval of 20 (MED = 13.3).
A <-> C has adown interval of 20, and an up interval of 5 (MED = 8).对于AB之间的链路调度如下:
0 40 60 100 120
start up down up down
通过手动计算可以知道0-40期间平均等待时间为40/2=20,而40-60期间平均等待时间是0,所以整个60s的周期中平均等待时间为:20*(40/60)&#43;0*(20/60)=13.3
上面函数中downSquaredSum统计了链路中断持续时间的平方,最后又除以2倍的simTime,让人有点摸不着头脑,其实是这样的:(downtime/2) * (downtime/simtime)即在中断时间的平均等待时间乘以中断时间占整个时间的百分比。在MEED的硕士论文中提到了如何计算。
2、如何运行dtnsim2
在console界面下进入到E:\Network\ONE\Eclipseprj\dtnsim2的examples/simple目录下,运行如下命令行:
java -ea -cp ../../bin/lib simulator.Main-verbose 1 simple_MED
verbose冗长的、啰嗦的,Setthe amount of logging output that should be generated其中ea不知道什么意思,cp表示查找类的路径,后面的-verbose设置输出调试信息的数量,最后的simple_MED表示要读取的配置文件,如下所示:
上述文件设定了带宽、延迟,什么时刻做什么工作,设置node类型、schedule文件、运行文件,最后设置了输出统计数据
其中的simple_Times文件如下:
运行完后,即可在该目录下生成simple_stats统计输出文件:
Algo; Buffer_Size; Message_Size; Bandwidth; Latency; Total_Msgs; Delivered_Msgs; Deliv_Ratio; Avg_Time
MED; 2000; 50; 10; 2; 2; 2; 100.00%; 26.50如果是在Eclipse下运行的话,当前的路径是如下目录
E:\Network\ONE\Eclipseprj\dtnsim2
在设置argument参数时应该设置为:-verbose 1 examples/simple/simple_MED
3、程序解读程序运行流程,simulator包下有一个Main,会读取运行参数:
if (args[i].charAt(0) != ‘-‘)
{
// Until first linewith specified time, all lines in input
// will beinterpreted immediately.
(new InputReader(net, args[i])).runInput(-1);
}
上面这个把simple_MED文件中@0之前的配置读取完毕
runInput函数会对simple_MED文件进行解析,一句话一句话进行解析,语句分为注释#时间@和命令
publicvoid runInput(double curTime)
比如default_cOntactbandwidth= 10 latency = 2
这句话是对contact进行参数配置,是一个命令
会一步一步的测试各种命令:
l 测试是否是本地命令,看是否有interpreter,下是否有run_file
cs = checkLocalCmds(line,curTime);
l 下一步测试cs =line.execCommand();在InputLine类中
1) 测试网络层的命令,network.parseLocalCommand();有network_element,traffic,stats,simulator,network_graph等
2) 测试节点层的命令,parseNodeCommand();有default_node等
3) 测试contact连接的命令,parseContactCommand();,在findContactsForCommand()下有default_contact
在contact,stat类下都有commandparser方法,用于解析配置文件中的命令
运行到如下函数fire处时,将开始执行网络仿真,其实是开始执行@0后的语句命令或配置。
需要执行receiver.receiveEvent(this);,其中receiver定义为EventReceiver,而EventReceiver为一个接口类,找不到其接口实现函数?
public class Event
{
protected long seq = 0;
protected double time = 0;
protectedEventReceiver receiver = null;
public void fire(Simulator net)
{
if (receiver == null)
return;
receiver.receiveEvent(this);
}
经过调试发现执行的是publicclass InputReader
implements EventReceiver
public void receiveEvent(Eventevent)
{
runInput(event.getTime());
}
在runInput中会simple_MED文件内容,并按照其内容进一步读取其它文件,或执行相关命令。
消息发送
在ProtocolStackNode类下有sendNewMessage方法4、路径计算相关
路由模块的routeForMsg(ProtocolStackMessage msg)方法会调用topology.getRoute(msg);
接着,会调用GKnowledgeTopologyHandler类下的getRoute(msg);
接着,会调用此函数进行计算的初始化lastRouting = new NetworkDijkstra(networkGraph(), parent,network.getCurrentTime(), forMsg);
接着,会调用lastRouting.routeTo((ProtocolStackNode)forMsg.getDestNode());进行真正的路由计算
NetworkGraph,一个抽象类,定义了一些Dijkstra可能会用到的方法:获取邻节点、得到代价
DijkstraGraph,一个接口类,与NetworkGraph差不多
NetworkDijkstra,直接调用的父类Dijkstra的构造函数,这个主要是对Dijkstra计算进行一下初始化
routeTo(NodeTypeendPoint)该函数负责计算到endPoint的路径
该函数又调用了computeShortestPath(endPoint);,此函数是Dijkstra计算所在地
下面的这种HashMap,索引是节点,索引&#20540;是源节点到该节点的路径的信息,一种哈希映射
private HashMap
下面这个GKnowledgeTopologyHandler继承了抽象类TopologyHandler
GKnowledgeTopologyHandler extendsTopologyHandler
GKnowledgeTopologyHandler类下有getRoute方法,此方法会新建NetworkDijkstra类,并调用routeTo方法
在下面RouteRoutingHandler类下有routeForMsg(ProtocolStackMessage msg)方法,此方法调用了route = topology.getRoute(msg);
ProtocolStackNode的方法sendNewMessage
创建一个新的消息:msg = new ProtocolStackMessage(。。destNode, dataLength);
然后,接收新消息:ret = acceptNewMessage(msg);
然后进入RouteRoutingHandler类下的acceptNewOwnMessage方法,新消息、自己产生
然后是addMessage(msg),在这里会判断本地节点还有没有足够的buffer,如果有,那么加入buffer,至此,新消息已经产生
调用父母parent节点ProtocolStackNode的方法notifyNewMessage,在这里会遍历所有的eventHandlers的新消息到达通知,
通过这些又触发路由模块RouteRoutingHandler的notifyNewMessage,在路由模块的新消息到达函数里会执行routeForMsg(msg);ProtocolStackNode::notifyNewMessage(ProtocolStackMessage msg)
{
for (EventHandler handler : eventHandlers)
{
handler.notifyNewMessage(msg);
}
}
public boolean addMessage(ProtocolStackMessage msg)
{
// We are willing to store any message, as long as we have space in
// the buffer:
if (!parent.canAllocateCapacity(msg, this))
{
return false;
}
parent.allocateCapacity(msg, this);
if (orderPolicy == ORDER_CREATION_TIME)
{
}
else
{
buffer.add(msg);
}
msgIDs.put(msg.getId(), msg);
bufSize += msg.getLength();
msg.setEventHandlerID(eventHandlerID());
parent.notifyNewMessage(msg);
return true;
}
ContactSchedule类下有getMEDWeight,getEDWeight,getFirstGoodUpTime
在BasicContact类下,
在读取simple_Times文件后,发现有up命令后,会调用parseCommandPart,
接着会在Contact UP后,会调用processEvent(CONTACT_UP, null);
接着会调用srcNode.contactIdle(this);
public CommandStatus parseCommandPart(ArrayList 获取第一个合适的连接机会,分两部分,是否合适的标准是能否满足msg的发送时间,为什么不考虑传播时间latency和接收时间呢???发出去了,但对面的节点关闭接收机,消息还是无法收到啊??? 1、 当前时间在contact内,判断剩余时间长度是否满足msg的发送时间 2、 当前时间在contact内,但长度不够,或当前时间在contact外,判断时间长度是否满足msg的发送时间 public UpTime getFirstGoodUpTime(double afterTime, Message forMsg) Dtnsim2中只有MEED、MED、ED的代码,没有EDLQ、EDAQ和LP的代码。 Dtnsim2学习笔记,布布扣,bubuko.com
{
String param = part.get(0);
CommandStatus ok = new CommandStatus(CommandStatus.COMMAND_OK);
// Parameters without arguments:
if (param.equals("up"))
{
contactUp();
return ok;
}
{
// Get the time it will take to send this message over the contact
double transferTime = 0;
if (forMsg != null)
transferTime = contact.getTransferTime(forMsg);
// Find the first uptime that we care about
int index = Collections.binarySearch(times, new UpTime(afterTime));
// If the element wasn‘t found, switch the index to the positive
// insertion point
if (index <0)
{
index = -index - 1;
assert index >= 0;
}
if (index > 0 && times.get(index - 1).getTimeDown() > afterTime)
{
// We are in the middle of an interval
double timeRemaining = times.get(index - 1).getTimeDown() - afterTime;
// 这里仅仅是看是否有足够时间发送,没有管接收和传播延时
if (timeRemaining >= transferTime)
{
// There is enough time remaining in this interval: Return
// an iterator at this point
return times.get(index - 1);
}
}
if (index == times.size())
{
// There are no more times!
assert afterTime >= times.get(times.size() - 1).getTimeDown() : "AfterTime: " + afterTime + "; lastTime: "
+ times.get(times.size() - 1).getTimeDown();
return null;
}
assert times.get(index).getTimeUp() >= afterTime;
while (index
UpTime interval = times.get(index);
double up = interval.getTimeUp();
assert up >= afterTime;
double down = interval.getTimeDown();
if (down - up >= transferTime)
{
return interval;
}
// This interval was not long enough for this message
index += 1;
}
return null;
}
5、总结