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I bought a D-LINK Dir-855 ,, works great.

But it is not clear to me if, when I switch on both the 2.4Ghz wifi network and the 5 Ghz network, how I should use it on my laptop?

I can only use one wifi network at the same time? Do I need some special kind of wifi network card? (I have an old ibm t-60 notebook).

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up vote 1 down vote accepted

I'm a little confused here, if the user bought a nice dual band 802.11n router with a lot of bells and whistles, why wouldnt he want to get the most out of it, rather than staying on the built in G/N capabilities of his old Toshiba.

Yes, the router uses 2.4 and 5ghz simultaneous bands,
Yes, that creates two simultaneous streams, but
No, not all N cards or adapters can run off of and take advantage of both the 2.4 and 5ghz dual band routers out there.

You will need to get a new dual band adapter or PCI slot card to connect to both bands, and you decide which channel, channel width, and wireless mode from your router configuration.

IPCONFIG/ALL from your CMD prompt and then open up a browser and type in your Default gateway to access your router. Usually or something like that. Understand that your distance goes down with 5ghz, but you get a cleaner band to play on.

Ask yourself, is it worth the money to get all of these components or is N at 2.4ghz good enough?

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This is not technically an answer to the question asked, but a clarification to counter some of the misinformation here. The frequency of the signal (2.4 vs 5 GHZ) and the wifi standard (802.11 B vs G vs N) are two different things. While you are more likely to find 5 GHZ and 802.11N together because both are more recent capabilities of later model routers, those same routers are generally capable also of broadcasting 802.11 B/G, and 802.11N can run at either 2.4 or 5 GHZ (or both on a dual-band router).

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But it is not clear to me if, when I switch on both the 2.4Ghz wifi network and the 5 Ghz network, how I should use it on my laptop?

The router you have mentioned is a dual band 2.4%ghz & 5GHz router & supports 802.11n. It's highly unlikely that it supports 802.11n ( this review suggests the same). Now depending on how you've setup the router, it's possible that the older 802.11 b/g protocols will use the 2.4GHz band & 802.11 will use the 5GHz - in this case your laptop will not need any extra cards

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I have now only switched on the 2.4 Ghz network. When I switch on the 5 Ghz network how should I configure my laptop to use them both? – edelwater Dec 19 '10 at 10:34
You'll need a 802.11n WiFi card like this – Sathya Dec 19 '10 at 14:54
Ah... so I DO NEED a "dual band" adapter"? So I need to e.g. buy a usb wifi stick that has DUAL BAND support. Yes. probably. – edelwater Dec 19 '10 at 17:09
@EdwardDe Leau You don't need it, unless you want your laptop to make use of the 802.11n protocol. – Sathya Dec 19 '10 at 18:47

If you go to your adapter properties your will have an option to set it to 2.4 Ghz (802.11b.g) or 5 GHz (802.11a). 802.11b is slower and older technology. I wouldn't use it. 802.11g is faster but has only 11 channels. You can only use 1,6 and 11 which the same proximity. Most Wifi uses this so you have to check to interference from other Wifi devices. It however spreads a little bit further than 802.11a. 802.11a has 15 channels.

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Um, 802.11n uses 5GHz as well. – Sathya Dec 18 '10 at 14:06

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