I have a Centrino N 6200 AGN card in two Sony VAIO VPCZ12 laptops (Intel® Core™ i5-520M, 6GB RAM, Win7 Pro 64bit) with the latest Intel drivers installed (version 184.108.40.206 September 2010).
As soon as I connect to a 802.11n network I experience permanently oscillating download bandwidth no matter what kind of IP-service I use and how much bandwidth it requires (FTP, HTTP, Shoutcast, Slingbox), allthough I've a perfect signal and a bandwidth of up to 300 MBit/s.
~600 KBit/s Slingbox stream through a Conceptronics C300BRS4 router:
~600 KBit/s Slingbox stream through an AVM Fritz!Box 7270 router:
I've reproduced this even on other routers than the Conceptronics C300BRS4 and the AVM Fritz!Box 7270.
As soon as I switch off 802.11n on these routers and run the WiFi network on 802.11g, the throughput is absolutely stable and the graph shows a constant line instead of the zigzag with 802.11n.
Other laptops with other Intel WiFi adaptors (e.g. 5100N) or Atheros-powered adaptors run absolutely flawless on the same routers even in 802.11n mode.
As mentioned above the graph shows an extreme zigzag no matter if I perform a FTP transfer with 10 MBit/s or if I watch a stream with few hundred KBit/s.
Apparently the Centrino N 6200 AGN has some severe compatibility problem with 802.11n routers.
Is anyone else aware of this issue? Is there any workaround besides disabling 802.11n on the router?
Any help is appreciated.
I just solved the issue. The MTU was preset to 1300 bytes on the preinstalled Windows 7 by Sony. Lifting the MTU size to 1500 bytes in the registry solved it - now I have constant data rates. Interestingly the small MTU size apparently only makes impact when connected to 802.11n networks.