Bug 367

Summary: WiFi APs should generate beacons by default
Product: ns-3 Reporter: Gustavo J. A. M. Carneiro <gjcarneiro>
Component: wifiAssignee: Mathieu Lacage <mathieu.lacage>
Status: RESOLVED FIXED    
Severity: normal CC: ns-bugs
Priority: P3    
Version: ns-3-dev   
Hardware: All   
OS: All   
Attachments: patch to add logging and attempt to do some filtering

Description Gustavo J. A. M. Carneiro 2008-09-24 07:40:04 UTC 
I have been experiencing strange periodic ARP request/reply pairs, approximately once per second, from my Wifi stations.  It turns out that the link change callback is being called for wifi netdevices every second, causing ARP caches to be flushed.

Some logging I added shows this (the bug appears to come from below the NetDevice layer, from the WifiMac or below layer):

12.155s WifiNetDevice:LinkDown(0xe47f80)
12.155s WifiNetDevice:LinkDown(): link changed
12.1556s WifiNetDevice:LinkUp(0xe47f80)
12.1556s WifiNetDevice:LinkUp(): link changed
12.2009s WifiNetDevice:LinkDown(0xe453e0)
12.2009s WifiNetDevice:LinkDown(): link changed
12.2015s WifiNetDevice:LinkUp(0xe453e0)
12.2015s WifiNetDevice:LinkUp(): link changed
12.2656s WifiNetDevice:LinkDown(0xe42840)
12.2656s WifiNetDevice:LinkDown(): link changed
12.2662s WifiNetDevice:LinkUp(0xe42840)
12.2662s WifiNetDevice:LinkUp(): link changed
12.3641s WifiNetDevice:LinkDown(0xe3fce0)
12.3641s WifiNetDevice:LinkDown(): link changed
12.3647s WifiNetDevice:LinkUp(0xe3fce0)
12.3647s WifiNetDevice:LinkUp(): link changed
13.1484s WifiNetDevice:LinkDown(0xe47f80)
13.1484s WifiNetDevice:LinkDown(): link changed
13.149s WifiNetDevice:LinkUp(0xe47f80)
13.149s WifiNetDevice:LinkUp(): link changed
13.1944s WifiNetDevice:LinkDown(0xe453e0)
13.1944s WifiNetDevice:LinkDown(): link changed
13.1949s WifiNetDevice:LinkUp(0xe453e0)
13.1949s WifiNetDevice:LinkUp(): link changed
13.259s WifiNetDevice:LinkDown(0xe42840)
13.259s WifiNetDevice:LinkDown(): link changed
13.2596s WifiNetDevice:LinkUp(0xe42840)
13.2596s WifiNetDevice:LinkUp(): link changed
13.3576s WifiNetDevice:LinkDown(0xe3fce0)
13.3576s WifiNetDevice:LinkDown(): link changed
13.3581s WifiNetDevice:LinkUp(0xe3fce0)
13.3581s WifiNetDevice:LinkUp(): link changed
Comment 1 Gustavo J. A. M. Carneiro 2008-09-24 07:41:25 UTC 
Created attachment 261 [details]
patch to add logging and attempt to do some filtering
Comment 2 Gustavo J. A. M. Carneiro 2008-09-24 07:42:10 UTC 
Comment on attachment 261 [details]
patch to add logging and attempt to do some filtering

This patch doesn't solve anything, it's just what I used to add the logging.
Comment 3 Gustavo J. A. M. Carneiro 2008-09-24 08:48:03 UTC 
*sigh* it turns out this is due to APs not sending beacons by default.

I have to question the logic of this behaviour.  This means that, by default, wifi stations will once per second see their wifi links go down and up, and ARP caches flushed, all due to the fact that wifi beacons are not generated.  I think no one can question that lack of wifi beacons is a unrealistic scenario even if the standard allows it.  Just go buy any access point and turn it on; you will see it generates beacons every 100ms by default.  So I don't think NS 3 should have a different default behaviour.

And please don't just mask this ugly default value in the wifi helper, it should be fixed in the low level class, since not everyone uses helpers for everything.
Comment 4 Mathieu Lacage 2008-10-10 05:19:13 UTC 
changeset 0dd9486ceaf4