Possible Duplicate:
Combining two ethernet ports
I have two available wireless networks in my area, and currently I'm connected to one of them. I want to get a USB wireless adapter and connect to the second network and thus improving my bandwidth, mainly for P2P purposes. Will windows (XP Pro. SP3) know how to handle such configuration? Will my bandwidth be widened?
TL;DR Will simultaneous connection to two different networks improve my P2P bandwidth?
TL;DR Probably not.
You will have a different IP address on each network. Outgoing traffic will be determined by your routing table, and it is (theoretically at least) fairly easy to send half the packets out each connection, because the decision is under your control. However, you could run into reverse-path checking that thinks those are spoofed packets and drops them.
Incoming is a different story. Packets will come in one connection or the other depending on the IP address. You can use multiple addresses simultaneously, but your P2P software would have to do that explicitly, and incoming packets won't automatically split up optimally, instead whichever peers are given address A will use connection A, and peers given address B will use connection B to send you data. Estimating the bandwidth to each peer in order to set up the P2P link using the right address for optimal balancing is decidedly non-trivial.
And none of this is going to "just happen" in any OS, neither to the best of my knowledge does Windows XP SP3 provide the tools necessary to make it happen. On linux, with weighted multipath routing, you'd at least be able to load balance outgoing traffic. On Windows you'll need additional drivers which bypass the TCP/IP stack and kernel routing decision in order to get multipath routing, or you can have deterministic routing tables that use one connection for half the internet and the other connection for the other half (but half the addresses likely doesn't represent half the traffic). This is far from optimal. And the P2P app needs to be rewritten to use multiple sockets with explicitly bound IP addresses in order to split incoming traffic.
There are ways to do that using loadbalancing techniques. And while this could be fairly easily configured using UNIX/Linux or one of the Windows Servers, I'm not so sure about the windows client variants. Basically, it works by loadbalancing not simple packets (which wouldn't work in your case) but whole TCP connections. So new TCP connection would be dispatched to one the available network connections (normally alternating, but could be configurable)
According to some posts on the net [1], [2], it appears as if Windows 7 does automatic round-robin loadbalancing over all available networks. But there seems to be little actual information. You should better just try it yourself.
With wired ethernet you have Link aggregation but, so far as I know, there is no equivalent for Wireless.
Wireless LANS have a limited number of frequencies to operate on, a greater number of wireless devices (including wireless routers or access points) increases the chances of a conflict and can actually reduce throughput for some devices.
