What are the advantages of a "dual" band wireless router?

Hi Everyone;

        I am wondering what are the advantages of having a dual-band wireless router which transmits at both, 2.4GHz and 4GHz.  Are there more channels?  For instance, I have up to 11 different channels with my current 2.4GHz wireless router.  Perhaps the dual-band has more unique frequencies to choose from at 4GHz.  Does the dual-band router transmit at further distances and less vulnerable to outside interferences?  Of course, these are just "example" questions I have regarding the possible advantages of a dual-band wireless router.  

          In closing, any information regarding the pros of having a dual-band router will be appreciated.

          Thank you.

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I may be wrong, but i believe it lets you have two Wi-Fi networks, like the D-Link DIR-655 that i have. One is secured and where all the cross-network talk can happen, the other can only connect to the internet and not any local machines. Useful if you like sharing your WiFi with your nighbors, but are concerned with your network security.
P.S.- The fact that it's Dual-band means that there's no interference between the two.
The 2.4GHz range is very corwded (ie. lots of devices use this range) and there are only a maximum of 3 channels (1, 6, 11) that can be used without overlapping and causing interference with each other.
I haven't seen any 4Ghz devices but 5GHz is commonly used. This is much less crowded and has more channels that do not overlap (8). Some routers/access points will allow you to use both simultainiously.
Your client devices will need to support 5GHz to use that frequency.

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OK, there are 4 standards of WiFI (technically 3, 'n' is not yet standard)

Starting with the earliest:

  802.11b - the first standardized WiFi
    operates in the 2.4GHz frequency range
    uses cck modulation
    up to 11Mbps
  802.11a - higher bandwidth, shorter range
    operates in the 5GHz frequency range
    uses odfm modulation
    up to 54Mbps
    shorter range than b, g, or n

  802.11g - high bandwidth and good range
    operates in the 2.4GHz frequency range
    uses odfm modulation
    up to 54Mbps

  802.11n-draft - high bandwidth and increased range
    operates in the 2.4GHz frequency range
    uses odfm modulation
    up to 54Mbps

Any wireless device capable of n is also compatible with b and g
Any wireless device capable of g is also compatible with b

A dual-band wireless device can operate in both the 2.4 and 5 GHz frequencies (some devices at the same time).

The number is channels is only significant when it comes to interference. A channel is selected based on the least interference. A wireless device can only tune to one channel at a time.
>  802.11n-draft - high bandwidth and increased range
>    operates in the 2.4GHz frequency range
>    uses odfm modulation
>    up to 54Mbps

There is nothing in the draft-n specs limiting 11n to the 2.4GHz band, and it causes far less interference with legacy devices in the 5GHz band. The 2.4GHz-only draft-n routers are cheaper because they require only 1 radio, but with 40MHz-wide channels (for the fastest speeds) take up 2 of the 3 non-overlapping channels in the 2.4GHz b/g band.

besides offering more channels (12 in the Americas; 19 in Europe), the 5GHz UNII band (see attached - to clarify, Europe has 11 more channels in UNII-2, but none in UNII-3), the main advantage is many dual-band infrastructure devices are able to bridge between the 2 bands, so they can e.g. talk to each other on the 5GHz band and then talk to clients on the 2.4GHz band. That's how many 'mesh' networks function.
2.4GHz devices far-outnumber 5GHz in clients, but dual-band cards are *still* quite common... most people that have them don't even realize it because 2.4GHz is so common in public hotspots they've never used the 11a part. If you're bothered by interference in the 2.4GHz band from high-density deployment (either a plethora of other 11g networks or 2.4GHz draft-n routers using 40MHz-wide channels nearby), 11a is a very-viable option. Used WRT55AG (et al) routers typically go for $20-$45 on auction sites, with brand new a/b/g cards even cheaper... the only drawback might be adding a 5GHz antenna to the client device, as not all came with them... an antenna tuned for the 2.4GHz band won't be efficient for the 5GHz band.
GMartinAuthor Commented:
Hi Everyone;

       Thanks so much for the information along with the links.  I have a clearer understanding now of the 2.4GHz - 5GHz frequency bands of routers now.

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