No throughput for a flow because of channel number

[Mahesh]

Hello ns-3 community,

So I am simulating the attached topology where I have 3 flows as follows with static routing:

Flow 0: 0--->1+++>C1+++>C2 (on channel 38)

Flow 2: 2--->1+++>C1+++>C2 (on channel 46)

Flow 3: 3--->2--->1+++>C1+++>C2 (on channel 54)

When I run the code, throughput is 0 for flow 3. However, if I make all flows run on channel 38, then all flows show throughput. But when different channels are assigned, why flow 3 is giving 0 throughput?

Kindly help me understand.

Thanks,

Mahesh

[Mahesh]

I have enabled OnOffApplication logging in my code and when I observe the logs, it shows bytes being sent from source to destination. But why does flow monitor show 0 throughput for flow 3 corresponding to CASE 2?

I have attached logs for the following cases along with the script:
CASE 1: When all flows are on same channel

CASE 2: When all flows are on different channels

Kindly look into this issue.

Thanks,

Mahesh

[Mahesh]

Hi all,

So I used SpectrumWifiPhy Iogging (NS_LOG="SpectrumWifiPhy=level_debug" ./waf --run scratch/multi-channels-no-throughput-script > scratch/test.out 2>&1) and I am getting the following messages:

drop packet because signal power too Small

Received signal from 0 with unfiltered power -26.7045 dBm

Signal power received (watts) before antenna gain: 0

Signal power received after antenna gain: 0 W (-inf dBm)

drop packet because signal power too Small (0<2.51189e-13)

I have already checked the channel numbering corresponding to 40 MHz channel in wifi-phy.cc file. My numbering is correct. I tried increasing the tx power, reducing the inter node distance etc but still one flow out of three flows is giving 0 throughput when channel numbers assigned to different flows are different. However, when all flows are on the same channel, all 3 flows show throughput. 

Can someone please tell about the channel number conflict among various channels in spectrumWifiPhy?

Thanks,

Mahesh

[Mahesh]

UPDATE ON MY FINDINGS:

I removed the P2P & CSMA part of the attached topology. And then made 3 flows (0--->1, 2--->1, 3--->2--->1) on 3 different channels. For this, I am getting throughput for all 3 flows. 

I now suspect that the issue is due to P2P & CSMA backhaul to which the wireless nodes are sending traffic. However, I do not know why the packets are not going through with different channels when I have P2P/CSMA network. I am using static routing. Script is attached again.

Any guidance will be highly helpful.

Thanks,

Mahesh

[Mahesh]

Is this issue because of there being multiple interfaces on node 1 (each using a different channel frequency/number) and only one of the interfaces being connected to P2P link? This way, the packets are not properly hopping between different frequencies on the same node.

Kindly assist me with this issue. Stuck on it since long.

[Mahesh]

Someone please guide me. I think the issue is with static routing and it being unable to handle the point of interconnection between WiFi and P2P/CSMA link.

Been stuck for a long time.

[pdbarnes]

Hello Mahesh,

Please use the list to ask questions, not direct messages.  Other users and experts can't learn from or contribute to conversations happening privately.

In this case I don't have any advice, except it seems like you are on a good track: static routes might be the culprit.

Good luck,

Peter

I am a masters student from India working on ns3. I came across your profile on one of my answers in the ns3 users google group. I know you might be occupied but kindly help me with this issue. I am sure you will figure it out soon. Here is the link to my problem:
https://groups.google.com/d/msg/ns-3-users/4uGuR4PCqcA/fIC9OLV4BwAJ
I have been waiting for a reply since the last 2-3 weeks but no one has replied. I haven't had any success troubleshooting my problem. PLEASE HELP. I'M SURE IT WON'T TAKE YOU LONG. I AM STUCK ON IT SINCE A LONG TIME AND CAN'T FIND A REASON/SOLUTION TO MY PROBLEM. MAYBE IT COULD BE A BUG.
Please check.
Thanks,
Mahesh

[Mahesh]

Hi Peter,

Thanks for your kind reply. The thing is, I have been waiting since 2-3 weeks for someone to reply but no one has.

Can you please let me know where exactly I am going wrong with static routes? The simulation is working fine if all flows are on same channel, but when each flow is on a different channel, then I run into problems.

Honestly, I'm unable to get around the issue. Please help. You're an ns-3 expert, so please help me out.

Thanks,

Mahesh

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[Rediet]

Hello,

Absolutely in line with Peter, something's not right with the routing part. Why don't you use different subnetworks per channel? You could thus avoid using static routing.

Rediet

P.S: There is no use in logging OnOffApplication outputs in this case, it's much better to have SpectrumWifiPhy and/or RegularWifiMac/AdHocWifiMac and/or WifiNetDevice logs for debugging.

[Mahesh]

Hi Rediet,

I have to use static routing only. Where am I going wrong? I have checked the static routes but I can't find any error.

Kindly let me know a workaround if I want to use static routing only.

[Mahesh]

I'm interested in understanding why static routing does not work in this case. 

Any insights into why it doesn't work as expected when each flow is on a separate channel?

[Rediet]

I haven't executed the code but from what can be read in it, your routes are quite complex (btw, have you considered the internal bridging that has to be done?). Try generating Wireshark traces (don't forget that there are different channels, thus the appropriate NetDevices should be monitored) and check if your ARP requests have replies. It might lead you the wrongly configured route.

[Mahesh]

I haven't done any bridging. I read in the ns-3 docs that bridging doesn't work in adhoc wifi mode. Is bridging required for my case? I will generate the wireshark traces, analyse them and get back to you.

[Mahesh]

Hi Rediet,

So I enabled pcap tracing and found that there is no ARP reply for the flow having 0 throughput. However, when all the interfaces on the node (which is connected to P2P/CSMA network) are listening on the same channel, all 3 flows have ARP requests followed by replies and generate throughput. 

This kind of proves that the issue is not with my static routes, right? Does it mean that there has to be some bridging between the different interfaces (on different channels) on the node?

If yes, then how do I proceed given that bridging does not work in adhoc mode of Wi-Fi? What reason prevents it from working in adhoc mode?

I look forward to your kind reply.

Thanks,

Mahesh

[Mahesh]

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