Two SSIDs on one router
I wish to set up two networks using my router. If I create two SSIDs, can I assign them to two different channels, to keep them "physically" separate? If I cant do this, does this mean the two networks are treated the same as a single network?
EDIT: If both the SSIDs used the same encryption technique, would this affect whether they are viewed as one single network? Or is it just the channel which matters?
You can only have a different SSID on a different channel if you have multiple radios in the WAP.
Channels come under the responsibility of a physical transceiver which can only transmit on one channel at a time. Dual radio WAPs are not usually within the realm of consumer grade equipment, unless it's dual band A/B or G/N units.
Different routers have different functions. However, generally speaking, the following applies to all routers:
In order to work on two different channels at the same time, the router have to have two separate radios. I'm not aware of any consumer-grade equipment that have 2 same-technology radios (e.g. two 802.11g radios). However, many routers exist that have 2.4GHz Band radio for 802.11g and 5Ghz radio for 802.11n.
In order to have two SSIDs, the router's firmware has to support it. For example, D-Link DIR-825 has a "guest zone", which is essentially a separate SSID that you can use. You can choose whether you want the routing between zones enabled or not. This feature is created in order to give your house guests Internet access without letting them into your home's network, and without giving them your "main" SSID's password.
To sum up, getting a router that can work on two same-technology channels independently is not possible unless you're paying a premium to get an enterprise-level equipment, in which case buying 2 consumer-level routers will be cheaper. However, getting two SSIDs is possible, but depends on firmware a specific router has, you need to research a specific model you wish to buy to know for sure.
Some routers now give you the option of hosting two separate SSID's, though I am not aware of any that let you use separate channels for each SSID. (If there were, they'd probably be more expensive than just buying two cheap routers anyway!)
Routers that can host two different SSID's typically let you decide how you want these two "networks" to interact. They typically have web-based configuration panels that let you control the level of interaction between SSID's. You can completely firewall off the two networks from eachother, or let them fully interact.
I was able to setup completely different encryption schemes for each SSID on my Netgear N300 router (WNR2000v3), though I was -not- able to select different channels for each one - they share the same channel.
Wireless devices consider the SSID as the unique identifier for a network. If you have two different SSID's, your device assumes that each one is for a separate network. On the other hand, if you have one SSID at home, and find that same SSID somewhere else, your device will consider these two hotspots THE SAME, and can not differentiate between them.
You CAN NOT have different encryption settings for two different routers that use a common SSID, and connect to both of them with one device - unless you manually intervene. This might change as more and more devices come to contain GPS units - it is conceivable that SSID + location might eventually become a differentiator.