diff --git a/src/conf/xp/3_ncpv b/src/conf/xp/3_ncpv
index e912247..7afe0ea 100644
--- a/src/conf/xp/3_ncpv
+++ b/src/conf/xp/3_ncpv
@@ -1,4 +1,10 @@
 xpType:ncpv
 ncClientPort_0:33400
 clientPcap:yes
+ddCount:15000
+pvRateLimit:100k
 sched:roundrobin
+changePv:yes
+changePvAt:5,-L 200k
+changePvAt:10,-L 100k
+changePvAt:15,-L 600k
diff --git a/src/mpExperienceNCPV.py b/src/mpExperienceNCPV.py
index 23bf7f8..9c4c677 100644
--- a/src/mpExperienceNCPV.py
+++ b/src/mpExperienceNCPV.py
@@ -1,5 +1,6 @@
 from mpExperience import MpExperience
 from mpParamXp import MpParamXp
+from mpPvAt import MpPvAt
 
 class  MpExperienceNCPV(MpExperience): 
 	"""
@@ -32,7 +33,47 @@ class  MpExperienceNCPV(MpExperience):
 		if len(self.ncClientPort) == 0:
 			d = self.xpParam.getParam(MpParamXp.NCCLIENTPORT)
 			self.ncClientPort.append(d)
+		self.loadPvAt()
 
+	def loadPvAt(self):
+		self.changePvAt = []
+		self.changePv = self.xpParam.getParam(MpParamXp.CHANGEPV)
+		if self.changePv != "yes":
+			print("Don't change pv rate...")
+			return
+		changePvAt = self.xpParam.getParam(MpParamXp.CHANGEPVAT)
+		if not isinstance(changePvAt, list):
+			changePvAt = [changePvAt]
+		for p in changePvAt:
+			tab = p.split(",")
+			if len(tab)==2:
+				o = MpPvAt(float(tab[0]), tab[1])
+				self.addPvAt(o)
+			else:
+				print("pv wrong line : " + n)		
+	
+	def addPvAt(self, p):
+		if len(self.changePvAt) == 0 :
+			p.delta = p.at
+		else:
+			if p.at > self.changePvAt[-1].at:
+				p.delta = p.at - self.changePvAt[-1].at
+			else:
+				print("Do not take into account " + p.__str__() + \
+						"because ooo !")
+				return
+
+		self.changePvAt.append(p)
+
+	def getPvChangeCmd(self):
+		cmd = ""
+		for p in self.changePvAt:
+			cmd = cmd + "sleep " + str(p.delta)
+			cmd = cmd + " && "
+			cmd = cmd + MpExperienceNCPV.PV_BIN + " -R " + self.pvPid
+			cmd = cmd + " " + p.cmd + " && "
+		cmd = cmd + " true &"
+		return cmd
 
 	def prepare(self):
 		MpExperience.prepare(self)
@@ -64,6 +105,9 @@ class  MpExperienceNCPV(MpExperience):
 				"_" + str(id) + ".log"
 		print(s)
 		return s
+	def getPvPidCmd(self):
+		s = "pgrep -n pv"
+		return s
 
 	def clean(self):
 		MpExperience.clean(self)
@@ -77,6 +121,17 @@ class  MpExperienceNCPV(MpExperience):
 			self.mpTopo.commandTo(self.mpConfig.server, cmd)
 			
 			cmd = self.getNCClientCmd(i)
-			self.mpTopo.commandTo(self.mpConfig.client, cmd)
+			self.mpConfig.client.sendCmd(cmd)
+
+			cmd = self.getPvPidCmd()
+			self.pvPid = self.mpTopo.commandTo(self.mpConfig.server, cmd)[:-1]
+			
+			cmd = self.getPvChangeCmd()
+			print(cmd)
+			self.mpTopo.commandTo(self.mpConfig.server, cmd)
+
+
+			self.mpConfig.client.waitOutput()
+			
 			self.mpTopo.commandTo(self.mpConfig.client, "sleep 1")
 
diff --git a/src/mpMininetBuilder.py b/src/mpMininetBuilder.py
index 4a5e30b..764e254 100644
--- a/src/mpMininetBuilder.py
+++ b/src/mpMininetBuilder.py
@@ -10,7 +10,7 @@ class MpMininetBuilder(Topo):
 		self.net = None
 	
 	def commandTo(self, who, cmd):
-		who.cmd(cmd)
+		return who.cmd(cmd)
 
 	def notNSCommand(self, cmd):
 		p = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE)
diff --git a/src/mpParam.py b/src/mpParam.py
index e761c01..c6a42ac 100644
--- a/src/mpParam.py
+++ b/src/mpParam.py
@@ -21,9 +21,8 @@ class MpParam:
 				k = tab[0]
 				val = tab[1][:-1]
 				if k in self.paramDic:
-					tmp = self.paramDic[k]
-					self.paramDic[k] = []
-					self.paramDic[k].append(tmp)
+					if not isinstance(self.paramDic[k], list):
+						self.paramDic[k] = [self.paramDic[k]]
 					self.paramDic[k].append(val)
 				else:
 					self.paramDic[k] = val
diff --git a/src/mpParamXp.py b/src/mpParamXp.py
index 70ec9ed..2626f13 100644
--- a/src/mpParamXp.py
+++ b/src/mpParamXp.py
@@ -17,6 +17,8 @@ class MpParamXp(MpParam):
 	PVZ        = "pvZ"
 	NCSERVERPORT = "ncServerPort"
 	NCCLIENTPORT = "ncClientPort"
+	CHANGEPV   = "changePv"
+	CHANGEPVAT = "changePvAt"
 
 	# global sysctl
 	sysctlKey = {}
@@ -45,6 +47,7 @@ class MpParamXp(MpParam):
 	defaultValue[PVG] = "10000"
 	defaultValue[NCSERVERPORT] = "33666"
 	defaultValue[NCCLIENTPORT] = "33555"
+	defaultValue[CHANGEPV] = "no"
 
 	def __init__(self, paramFile):
 		MpParam.__init__(self, paramFile)
diff --git a/src/mpPvAt.py b/src/mpPvAt.py
new file mode 100644
index 0000000..9e1af2b
--- /dev/null
+++ b/src/mpPvAt.py
@@ -0,0 +1,9 @@
+class MpPvAt:
+	def __init__(self, at, cmd):
+		self.at = at
+		self.cmd = cmd
+		self.delta = 0
+
+	def __str__(self):
+		return "Pv... at " + str(self.at) + "(" + str(self.delta) + \
+				") will be " + self.cmd
diff --git a/src/mpTopo.py b/src/mpTopo.py
index c1c0b7b..2537f24 100644
--- a/src/mpTopo.py
+++ b/src/mpTopo.py
@@ -24,7 +24,7 @@ class MpTopo:
 
 	def commandTo(self, who, cmd):
 		self.logFile.write(who.__str__() + " : " + cmd + "\n")
-		self.topoBuilder.commandTo(who, cmd)
+		return self.topoBuilder.commandTo(who, cmd)
 
 	def notNSCommand(self, cmd):
 		"""