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Home > Archive > General Discussion > October 2001 > What does the speed on a cat5 cable mean?
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What does the speed on a cat5 cable mean?
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| Boulware5 2001-10-26, 3:09 pm |
| I'm about to buy some Cat5 cable to hook into my router. The place I am buying it from says the 100ft. cable is a 350 MHz cable. What does that mean? I know Cat5 has a maximum bandwith of 100 MBps but I never heard of a speed rating when talking about network cable. | |
| Nicole 2001-10-26, 4:59 pm |
| The 350 MHz refers to the attenuation frequency, not the speed. | |
| macaries 2001-10-26, 5:44 pm |
| So what is meant by attenuation frequency? Attenuation is loss of signal strength and is this frequency dependent? | |
| macaries 2001-10-26, 5:55 pm |
| Oh yes and does everyone know that Cat-5 cabling supports frequencies up to 100MHz and speeds up to 1000 Mbps. But for 1000 Mbps (1Gb/s) it's usually labled Cat-5e
I'm not aware of any cabling that's rated in MBps. | |
| Nicole 2001-10-26, 7:27 pm |
| As I understand it, by listing an attenuation frequency of 350 MHz, the cable is by definition Cat 5e. Cat 5 has an attenuation frequency of 100 MHz.
quote:
Originally posted by macaries
So what is meant by attenuation frequency? Attenuation is loss of signal strength and is this frequency dependent?
In a word: partially.
My cable knowledge comes from my audio engineer days, so someone please correct me if I've gotten the details wrong from a networking standpoint... it's all just electrical impulses, so I assume it's the same.
Simply put, a higher attenuation frequency provides for better performance by reducing the amount of crosstalk. Attenuation is affected by distance, frequency, and grade of cable. If the cable grade were the same, the shorter wavelength (350 MHz) would allow longer cable runs without a repeater or signal booster.
For example, you don't want to run Cat 5 more than about 325 feet since the signal strength (and therefore accuracy) will be diminished by the amount of background noise on the line. Running cable next to poorly shielded electrical cable (like zip cord) will make it even worse, by picking up the other's cable's electrical noise.
Presumably, the Cat 5e will not only carry a higher level of bandwidth, but is better shielded and capable of longer cable runs.
Is there an EE in the house??? | |
| Boulware5 2001-10-26, 7:55 pm |
| Ah, gotcha...Thanks. I just haven't seen a megahertz rating when talking about UTP cable before. | |
| Nicole 2001-10-26, 9:44 pm |
| It's kinda redundant to put one on it... the standard "Cat" ratings take care of that detail. Marketing, I guess, or somebody just dying to fill up more space on the label.
I'm still trying to figure out why I know this, but can't remember anyone's name  | |
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| I don't pretend to be an expert.
CAT 5 is UTP and most UTP, according to IEEE has a mas distance of 100 METERS <--- not feet. As a rule when networking you should not go beyond this with out a repeater of some sort(active hub, switch, routers all repeat the signal). Another rule is NEVER listen to salespeople, they're worried about their wallets not your network. In order to be rated CAT 5 a cable has to meet the specifications put out by IEEE and there should be some text on the cable stating this. | |
| depamo 2001-10-30, 8:45 am |
| 350Mhz - is really defining a speed at which you can send a frequency through the cable and still get the same signal out the other side and stay within the companies parameters for signal attenuation and distortation with a given distance. A Hz is just a cycle of a repetable signal over a period of 1 second or 1 over a signals period (time for one cycle in seconds). Better known as cycles a second. A 'bit' in 100Mb/s or 100BaseT represents a half a complete cycle of a repeatable signal. So, lets think about this for a second. The worst case you can have at 100Mb/s would be sending a 1 then a zero and to continue this pattern which will cause the signal to change at the fastest rate possible. One complete cycle would be a 1 changing to a 0 or one complete period of the signal. So the minimum requirement is to have acceptable signal loss and distortion over this period which is two bits. One bit takes 1/100Mb/s or 1.0E-8s or 10 micro seconds. The time it takes two bits to pass is 20 microseconds on this same network. Reverse the equation - 1/2.0E-8 and you get 50Mb/s or 50MHz(50 repeated complete signal changes per second). Usually in the computer world you want to go 2/3's over on your cable stats to insure you get a good singal under possibly high EM conditions (power cables, lights, monitors and such).
The big things missing here are the parameters that this number is measured against. Distance, amplitude, and acceptable degradation of signal within a certain external EM rating. These are the conditions that the cable must be exposed to when tested to acheiv this rating.
This is probably standardized for a specific purpose. From this though you can see that the cable will not support GigE as it is not rated at 500MHz with acceptable loss.
In simplest terms without the rest of the information on the rating, it is saying that under certain pre-defined conditions that are standard for this rating, a signal can change upto 350 million times a second and the signal comming out the other side will have acceptable loss or signal distortion.
This is mostly effected by the design of the cable, the radius of the copper core, the shielding on the internal and external wires, the number of twists per unit of length, the purity of the conductors elements and such. |
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