I house that currently has 3 computers. Almost getting a fourth one. One runs on a wired connection. And the other 2 (almost 3) run on Wi-Fi. I would like to know if I get a Ethernet cable will my MW3 gameplay stop lagging even if someone else is using the internet? And I would like to know if two Ethernet cables can run on 1 modem or router.
Welcome to the PlayStation Community.
In relation to the "lag issue", this can only be answered by knowing how good or not your current internet connection is & also how fast it is, if you have a very fast service then you should experience little to no lag, a bad connection or slow speeds could hinder it.
Most routers these days have at least 4 ports for Ethernet cables.
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theres a few things you can do, first off check your internet speed with the broadban dsl reports website, I forgot the url but a search engine find it or similar sites. But generally your ps3 will do better on an ethernet cable than wifi, true for most game systems or computers. PS3 specifically can do gigabit (yes 1000 megs / second) on ethernet if your router supports it and your using cat 5e or cat 6 cables. Otherwise it'll step down to 100 megs / second which is still better than the wifi G onboard the PS3 which is 54 megs and will have slower throughput from increased overhead (security and such). My general rule is use ethernet whenever possible and have a decent router, mines a Linksys E3000 and theres some other good units out there too.