Poll: Help! Signal Attenuation Difference Between Hubs and Switches?!?!?

[mud]

What is the cat5 cable length limitation for 100Mb switches (NOT hubs)?

I am aware that the limit for fast ethernet is 100 meters, or about 300 feet. So, here's my problem...

I have a 250 foot cat5 rj45 Belkin cable that will work properly when connected to a 10Mb hub from my computer. But, when I connect the same cable to my switches (Linksys 5 port and Dlink DSS-24 port), the link light goes off and I have no connection.

Is there a difference in signal attenuation between switches and hubs? I do not have any 100Mb hubs to test on though.

So far my guess is that the 10Mb hub I used acts like a repeater. However, switches on the other hand don't seem to be able act like a repeater. My reasoning is based on another similar problem.

I have 2 switches that are about 200 feet apart in my warehouse. When I connect them directly, the link lights don't come on. But only when I put 2 leftover 10Mb hubs in between them, then they link up! although not at 100mbs 🙁 like so

100MbSwitch<--->10MbHub<--->10MbHub<--->100MbSwitch

anyone got any insight? You guys have come through for me on some esoteric stuff before, so I hope you guys can do it again! Thanks! 🙂

 

[BoNeZ]

Well the 100M (318 Ft) limit is the limit of the CAT5 cabling, it has nothing to do with the hubs or switches themselves, but rather the ethernet cabling, which is an international standerd for CAT5, and CAT3 is even less than that.

Now with that being said. Both switches and hubs &quot;amplify&quot; and repeat the signal on down the line. The difference lies in the way a hub and a switch handle the available bandwidth. On say a 100Mb network with a hub and 20 PC's, your 100Mb/s is shared between the 20 PC's effectively giving each only 5Mb/s of available bandwidth, whereas a switch does not share bandwidth, but rather dedicates 100Mb/s to each PC, and if the switch is able to perforom full duplexing, you have 100Mb/s up and down at the same time, giving an effective 200Mb/s.

Now with the technical stuff out of the way. Basically what I could see happening is since you do get a link light with your 10Mb hub, I would bet if you had a 10Mb switch you would also get a link light. But since you're going from a 10Mb hub to a 100Mb switch (if I understand you correctly) then it's possible that your signal loss over that length of cable is too great for the 100Mb signal to come across without corruption.

While this cable is good enough for 10Mb it's likely that tha attenuation is to great for 100Mb. So how do you solve it? Well you can either put in a 100Mb hub/repeater halfway down the line, or run a new cable, which probably isn't your first choice, or simply communicate at 10Mb/s.

Also have you considered that possibly that twhat you think is a 250 Ft run could be longer? Have you taken into consideration any routing up one side of a wall and down the other? I mean you really only have 68 Ft of leeway.

I hope this helps, or at least gives you a little insight and a starting point.

BoNeZ

 

[shadow]

he could also be running by a source of EMI which is weak enough not to affect the 10mb/s link but will trip up the 100mb/s one. You can look at it as having the effective distance of your cable reduced due to the EMI.

-shadow

 

[Supergax]

I thought that switches only acted as repeaters, and that hubs don't strenghten the signal.

 

[mud]

Hey, thanks everyone for all the info! HOwever, I borked up my post and it showed up in the forum twice. Here's the link the to the other thread, and I discuss what I discovered and pose a few more questions.

http://forums.anandtech.com/messageview.cfm?catid=36&amp;threadid=273148

in short, the cable is definitely 250ft, I bought it precut. I was testing the cable from the switch to my 10/100 linksys *PCMCIA* card. link light went on and off slowly. no connection.

then I connected the line to my desktop linksys PCI card, and the connection seems fine. Go figure. I guess my linksys PCMCIA card has a lower cable length limit.