Ok...
I will start with I am a network engineer so it is my job to understand how this stuff works. And the guys and I at work have been having a huge laugh about this thread since I found it yesterday.
The answer to the original question of running 4 computers and an xbox and what is adequate for you given you have a 30mbps cable connections.... depends if you want gigabit or not. If you do then cat5e is the minimum you should use. If you want 100mbps it doesn't matter anything from cat5 up will do 100mbps.
When I say if you want 1gbps or 100mbps this means internally to your network only. It does not matter what you do inside your house you will never get more than 30mbps out to the internet if you have a 30mbps cable connection.
Now for all the comments on this thread OMG seriously? I dont even know where to start with explaining how so much of what has been said is totally wrong and honestly I couldnt follow most of it because it jumped from topic to topic all of which are completely unrelated. So I am just going to go through each post and explain whats wrong with what you said hoping that you learn something from me. This is not meant in anyway to be derogatory but more so to assist in you learning how things actually work.
There was one person that posted who actually knew what he was talking about and not one of you bothered to listen to anything he had to say and continued to follow your path of absolute hilarity.
1. (Hawkeye22) You are correct if you only have 10/100mbps then cat5e is just fine. You can also use cat5 for this but no one uses cat 5 because there is no point 5e is cheaper, better and easier to find. There are 2 pairs used on 10/100mbps and you can use the additional 2 pairs either for POE, A secondary analogue phone connection or you can use a splitter to split the wiring up on both sides and use the additional 2 pairs to get a second 10/100 mbps over the one cable. (http://www.jaycar.com.au/productView.asp?ID=YT6090). 1000mbps (1gbps) does indeed use all 4 pairs but you can still run POE over gbps networks but you cannot split them to get a second phone service or a second network link over the cable as there are no spare pairs.
2. (pazsion)
This is where the hilarity starts. You are implying that the frequency range on the cable somehow ties to and represents the speed of data the cable is capable of. This is so far from correct its not funny.
the 100/250/600mhz specifications mearly represents the frequency rating of the signal being sent down the cable and what the cable is capable of accepting while staying within the attenuation and signal degridation of the specifications of the cable.
This has absolutely nothing I repeat NOTHING to do with the PCI bus, USB, FSB, or CPU frequencies or speeds in your PC What so ever. They are used for totally different measurements and have no correlation at all between them. Trying to compare these measurements into speed on the cable is like attempting to find out the fuel economy of your car car by riding your horse.
But if you want to compare speeds here what you can do is say well my PCI bus has a maximum rate of 133MB/s (based on a 33Mhz bus speed and a 32bit card.) And a 10/100 network card will acheive a maximum rate of 100Mb/s which works out to be approx (not exact) 10MB/s so you have around 120MB/s of capacity still on your pci bus after a 10/100mbps nic is used at full capacity. If you move to gigabit you are looking at 1000Mb/s which is around 100MB/s and you will almost be using your PCI bus to capacity.
The correlation between how the ethernet nic produces a 100-250mhz signal on the wire compared to the 33mhz pci bus speed does not exist. The 33mhz bus speed is the speed at which the PCI card can communicate with the PC. (33mhz x 4bytes (32bit) = 133MB/s) Where as the 100-250 (600mhz for cat7) is mearly a rating that the cable is able to accept a frequency range to be transmitted at over the wire. Similar to a radio station in the way that they transmit sound at a set frequency. You dont get your music faster from a radio station that has a higher frequency that one that has a lower frequency... Almost exactly the same thing.
So as you can see they are two entirely different measurements for different things. Please dont get them confused because it makes a big difference when you are looking at things and makes my day funny as hell when I read stuff like that when I should be working.
The router and ethernet devices do not detect what wire is used. They go through a negotiation with the device that they are connected to at the other end to detect what the other device is able to communicate at. They then select that speed and duplex setting and set themselves accordingly. This is the reason why you see CRC errors on your network interfaces. CRC errors are caused when the cable is not the correct type for the speed selected OR it is a faulty cable. And you will find 9/10 times that replacing the cable fixes the issue.
When you say that some routers network balance I have no idea what you are talking about there but if you set 100mbps on one side of the link ie at the PC you should be manually setting 100mbps on the router port aswell. The reason why you are seeing the 10mbps connection on the router is because speed and duplex negotiation failed because you set one side to a specific setting and not the other. And the default speed and duplex setting that all ethernet devices revert to if the speed/duplex negotiation fails is 10mbps half duplex because this is the lowest setting that all devices must support to be able to comply with ethernet standards.
You are correct in saying you wouldnt see any gains past cat6. Infact if you are only ever going to run 10/100 or even 1000mbps you will not see any benifet in going past cat5e.
3. (Kewlx25)
Cat 5 does not support gigabit period. You may be able to get 1gbps speeds on cat 5 if you try depending on the cable but it was never designed for it.
Cat 5e is designed for 1gbps links and will do 1gbps over 100 meters. Cat 6 is not required for 1gbps over 100 meters.
4. (pazsion)
Incorrect. The adaptive link speed just means it auto detects speed and duplex settings and initiates the initial connection based on what each device on the network is capable of connecting at. See above the speed duplex settings and how it works.
Half duplex means only one device can send OR receive data at a time. So your PC sends its data to the router then says ok ive sent everything. Then the router can reply.
Full duplex means that both devices and send AND receive at the same time. So your PC can be sending data to your router at the same time that your router is sending data to your PC.
The speed of the electical pulse that carries data on the copper cable. Well that is very fast on unsheilded copper the speed of the electrical impulses on the cable would be around 97% of the speed of light in a vacuum. Considering the speed of light is around 300,000 kilometers per second lets just say its very fast.
The frequency on the cable which is what you are refering to is simply just the frequency used to communicate between the two devices just like a radio station uses a specific frequency to send music to your radio. It doesnt make the music any faster by being on a higher frequency than a lower one.
The quality of the music could be affected by the frequency for instance if you take a look at AM radio vs FM radio. But the differences between AM and FM are huge we are talking an AM station transmitting at a frew thousand cycles per second (Khz) compared to an FM station transmitting from between 87 and 108 million cycles per second (Mhz).
But this has no effect on a network cable and the frequency it uses I was mearly using that as an example of how its a different measurement to what you are thinking.
As for wifi running at 2.4ghz per second... Well again this is exactly the same thing. 2.4ghz is simply the frequency that the wireless device uses to connect to other devices. It has no bearing on the speed that data can travel over the frequency at all. You also have wifi devices that run in the 5.8ghz band aswell. Also some that run down in the 900mhz band also.
Infact with Wireless devices the higher the frequency the slower they usually are and also the less distance they travel. With RF propogation the lower the frequency the further the signal can travel without losing strength, The deeper it can penetrate a solid substance such as a building or mountain. Because the length of the radio wave that is produced is longer and is harder to stop. The higher the frequency the shorter the wave and the easier to stop.
As for why you only get 30mbps. Well that is because you are using a cable internet connection. It has nothing to do with the NIC in your computer or router. It has to do with A) the DOCSIS Standard that your cable provider is running on its WAN (http://en.wikipedia.org/wiki/DOCSIS) AND B) The service you are paying for is 30mbps so thats what you get given.
The reason why you dont get 100mbps or 1gbps services in WAN environments at the moment is because of the inherit limitations of copper mediums in transmitting data over long distances. The longer the copper path the more attenuation and noise is introduced onto the signal along the way which lowers the data throughput of the cable.
Also you seem to think that the copper going to your cable or ADSL provider happens to be a cat5/6 or 7 cable it is not. The cable that you use with CABLE internet is a coaxial cable. Which is not designed anywhere near the same as your standard internal house cabling. I mentioned earlier how on a cat 5/6/7 cable the speed of the electrical impulse is 97% speed of light. Well on a coax cable this drops to around 66% of the speed of light. This doesnt specifically have anything to do with the speed of data you will get on your internet connection its just a simple way of pointing out that the cable for the internet is very very different to your cat 5/6/7 cable to get 1gbps to your PC from your router.
A reasonable post to read might be this one
http://whirlpool.net.au/wiki/adsl_theory_attenuation that describes attenuation on ADSL lines which again uses another completely different type of cable to your cat 5/6/7. This uses standard phone lines which are just a single pair of copper lines going back to the exchange from your house. No sheilding other than a few twists every meter. But with ADSL give up to 24mbps connections and with VDSL can give up to 300mbps connections.
I have no idea what you were talking about with the voltage of the nic and the PCI bus but please just ignore everything you mentioned there it makes no sense.
4. RepoDraghon
Please do not ask your brother-in-law for advice.
While he is correct in that 5e and 6 cables are rated for 100mbps he has no idea about anything else by the sound of that post.
If you have a 30mbps connection and 5 network devices. They will not each get 6mbps. Ethernet is based on a first come first served basis. If one computer jumps in first and uses 28mbps of your 30 mbps. Then the second computer will only be able to use 2mbps untill the first computer has finished using its 28mbps. It is just the way it works UNLESS you have a better router that has the capacity for QoS (Quality of Service) and will actually put priority on certain types of traffic eg voice traffic gets transmitted before torrent traffic.
Also just for your reference a T1 connection is 1.544mbps syncronous meaning 1.544mbps upload and 1.544mbps download. It is no where near 1000mbps. (http://en.wikipedia.org/wiki/T-carrier)
And I agree with the last poster Awake33....
The level of misunderstanding and misinformation here is mind boggling. You gotta love all the internet "experts" out there