Usage of Config::Set

[Harald Ott]

I'm trying to change the DataRate at runtime, but I just can't get it to work unfortunately.
Yes, I have read the documentation and other discussions in this forum, but I just can't apply it to my case.
Here's my main function:

int
main (int argc, char *argv[])
{
  Address serverAddress;

  CommandLine cmd;
  cmd.AddValue ("useIpv6", "Use Ipv6", useV6);
  cmd.Parse (argc, argv);

  NS_LOG_INFO ("Create nodes.");
  NodeContainer n;
  n.Create (4);

  InternetStackHelper internet;
  internet.Install (n);

  NS_LOG_INFO ("Create channels.");

  CsmaHelper csma;
  csma.SetChannelAttribute ("DataRate", DataRateValue (DataRate (10000)));
  csma.SetChannelAttribute ("Delay", TimeValue (MilliSeconds (2)));
  csma.SetDeviceAttribute ("Mtu", UintegerValue (1400));
  NetDeviceContainer d = csma.Install (n);

  NS_LOG_INFO ("Assign IP Addresses.");

      Ipv4AddressHelper ipv4;
      ipv4.SetBase ("10.1.1.0", "255.255.255.0");
      Ipv4InterfaceContainer i = ipv4.Assign (d);
      serverAddress = Address(i.GetAddress (1));


  NS_LOG_INFO ("Create Applications.");

  uint16_t port = 9;  // well-known echo port number
  TcpStreamServerHelper server (port);
  ApplicationContainer apps = server.Install (n.Get (1));
  apps.Start (Seconds (1.0));
  apps.Stop (Seconds (10.0));


  TcpStreamClientHelper client (serverAddress, port);
  apps = client.Install (n.Get (0));

  IntegerValue integerValueTemp;
  GlobalValue::GetValueByName ("simulationStartTime", integerValueTemp);
  apps.Start (MicroSeconds (integerValueTemp.Get ()));
  apps.Stop (Seconds (5000.0));

  NS_LOG_INFO ("Run Simulation.");
  Simulator::Run ();
  Simulator::Destroy ();
  NS_LOG_INFO ("Done.");
}

I've left out the parts that are not of interest for the question.
I know that I need something like this:

Simulator::Schedule (Seconds(7.5), Config::Set, ".../<container name>/<index>/.../<attribute>/<attribute>",
  DataRateValue (DataRate (1000)));

But I just don't know how I can access the channel attribute I've set at

csma.SetChannelAttribute ("DataRate", DataRateValue (DataRate (10000)));

through a path?
If someone could supply me with the exact path I need to specify, that would be great

[Harald Ott]

In more detail:

What do I have to insert at

".../<container name>/<index>/.../<attribute>/<attribute>"

?

[Konstantinos]

Hi Harald,

For the API you can find the correct config path

ns3::CsmaChannel is accessible through the following paths with Config::Set and Config::Connect:

• "/ChannelList/[i]/$ns3::CsmaChannel"

I do not think you have multiple channels in your scenario, so '0' should work. Otherwise you can use the wildcard '*'. 

In terms of attributes, again from the API you have Delay and DataRate 

• DataRate: The transmission data rate to be provided to devices connected to the channel
  • Set with class: DataRateValue
  • Underlying type: DataRate
  • Initial value: 4294967295bps
  • Flags: construct write read
• Delay: Transmission delay through the channel
  • Set with class: ns3::TimeValue
  • Underlying type: Time –9223372036854775808.0ns:+9223372036854775807.0ns
  • Initial value: +0.0ns
  • Flags: construct write read

Regard,

K

[Harald Ott]

Hi Konstantinos, thanks for your answer.
I've tried for example

Simulator::Schedule (Seconds(7.5), Config::Set, "/ChannelList/*/$ns3::CsmaChannel/DataRate", DataRateValue (DataRate (100)));

changing the original DataRate of 10000 to 100, looking at the debug output at ~7.5 seconds, no changes in throughput, so it doesn't seem to work unfortunately...

[Konstantinos]

Hi,

Please study the documentation of the Simulator (https://www.nsnam.org/docs/manual/html/events.html#simulator) to understand how you use Schedule()

There are two basic ways to schedule events, with and without context. What does this mean?

Simulator::Schedule (Time const &time, MEM mem_ptr, OBJ obj);

vs.

Simulator::ScheduleWithContext (uint32_t context, Time const &time, MEM mem_ptr, OBJ obj);

I would suggest to create a simple static method called "ChangeRate" 

static void ChangeRate()
{
  Config::Set("/ChannelList/*/$ns3::CsmaChannel/DataRate", DataRateValue (DataRate (100)));
  return;
}

then  use the Schedule to call that.

Simulator::Schedule (Seconds(7.5), &ChangeRate);

[Harald Ott]

Hi Konstantinos,

I've implemented what you suggested, added a NS_LOG_CONFIG("TEST") to ChangeRate(), and it definitely gets called at 7.5 seconds, but I still can't see a change in the DataRate, looking at the file which keeps track of the throughput.
It should fall down at 7.5 seconds, because when I put it to 100 from the beginning, it stays down, but when I try to put it that low with simulator::schedule, it somehow doesn't change...

[Harald Ott]

I've now also tried to set the Datarate at my

CsmaHelper csma;

not with (this way it works):

csma.SetChannelAttribute ("DataRate", DataRateValue (DataRate (1300)));

but instead directly with:

Config::Set("/ChannelList/*/$ns3::CsmaChannel/DataRate", DataRateValue (DataRate (1300)));

noticing, that the latter doesn't set the DataRate, but the DataRate seems to remain at the Initial value: 4294967295bps (according to API), so it doesn't do anything.
How is this possible ?