Network slowdown when 4+ systems plugged into the HUB

[Freddie_P]

Hi all,
This is a strange one. I have a Surecom 508T hub 10Tbase hub which has 8 ports. Until recently, I had only 4 computers hooked up to the hub at any one time. These included 1 Linux box acting as a DHCP server (an eventually a router for high speed access) plus 3 W98SE machines. I then got a laptop (W2K PRO installed) and plugged it into the Network. Normally not all machines are on all at once however they remained plugged into the hub. I then noticed that file copies between the machines slow down dramatically.
I am used to a transfer rate of about 1M per second. This is not a scientific measurement just a rough guess. If I copy a 5M file between machines its takes roughly 5 seconds. With 5 machines plugged into the hub the same transfer takes 2+ minutes!
At first I though it was a NIC problem so I swapped some around etc but no difference. I then found if I unplugged any one of jacks file transfers would resume the normal speed. The machine did not even have to be booted as long as the cable was unplugged file transfers were normal.
I have a range of NIC's installed. 1 3com 905B, 2 SMC1211TX's, one Intel in the laptop and one Realtek 8139 in the Linux box. Right now I simply umplug the laptop from the network as a bypass but I am at a loss to figure out whether it is a NIC or a HUB problem and why is 5 the magic number. Any thoughts would be appreciated...FP

 

[spidey07]

????????

Let me get this straight - your 5 MB file takes 5 seconds with only four computers attach but 2+ minutes when five are attach? And it doesn't matter which machine you unplug or the OS you're copying files to/from?

If those are correct statements then swap the hub. Generally network troubleshooting can be reduced to a single common denominator and since unplugging any one of the PCs solves it, then the only point left would be the hub (nics/cables/OS/drivers have been taken out of the equation)

Very, very strange. I could see this if you had a bad nic or cable or serious jabber going on but if you can't isolate it to a partciular maching/nic/cable then it HAS to be a problem with the hub.

BTW - how do your collisions look when you are copying the file with 4 machines? How about when 5 machines?

<edit> reread your post - can you only fix it when you remove the 2K laptop or can you unplug another device? That will be a very important question and shift focus from the hub to the laptop.

 

[Freddie_P]

Hi Spidey07,
Thanks for the reply. Yes your first statements are correct. I'll give you a bot more background that I didn't include at first because I felt it would make the post too long.
Until about 2 weeks ago my setup was this: linux box (realtek nic), w98se (smc), w95 (intel) and w98 (3com) and everything was fine. Then I replaced the w95 desktop with a laptop (this was my work machine) and then added another W98SE machine (initially with a realtek NIC installed same make as the linux box). So I went from 4 to 5 machines. The W98 machine took a h/d hit so I had to start from scratch and installed W98Se on that one. The laptop and the newest desktop share screen keyboard and moue so they are seldom on at the same time (once I'm done work I can turn it over to the kids). The W98SE with the 3com nic is the least used.
Now when I look at the hub all the link indicators are ON and remain on when the associated boxes are shutdown except for the W98SE with the 3com nic. When it shuts down its link light goes off so I would be back down to 4 active links. So when it is powered up and the W98SE machine I share with the laptop is not UP its link indicator is still on.
Now if I try to file transfer in this situation my 5 meg file takes 2+ minutes. Looking at the hub the collision lite is certainly not solid but it does blip. The link lites blink synchronously for the two machines doing the transfer. Now if I unplug the LINUX cable or the shared W98SE cable or the laptop cable then transfer rates return to normal and there is no collision indicators and the link lites for the two transfering machines blink much faster (this is true even if I unplug it while the transfer is going on, it immediately speeds up).
To correct the problem I had swapped out of the older cables. I replaced the realtek nic with the smc one. I tried moving the plugs around in the hub. Installed latest drivers etc. I was reluctant to blame the hub simply because it looks so darn simple. I know collisions are bad but I do not really know what they mean and if it is the hubs fault or a NIC's fault.
Anyway, I do not have much choice but to replace the hub at this point. My wife has a laptop of her own which occasionally gets connected to the LAN, I may try and play with that some and see if I can isolate a NIC that way. However if your experience tells you that it is the hub then I will feel better (time for that 100tbase anyways).
Thanks, FP

 

[spidey07]

<< all the link indicators are ON and remain on when the associated boxes are shutdown >>



That singular statement says the hub is bad. Go out and buy you an 8 port hub or switch. switches are cheap so i'd get one of those...year 2001 ya know.

if it doesn't solve your problem then return the hub/switch and post again. then you can take the hub out of the troubleshooting process.

you've reset the hub haven't you?

 

[L3Guy]

One quick thought.

If you have an uplink port (MDI) on the hub, there usually is a normal port (MDIX) pared
with it. If you are using both, it would be bad. Otherwise, I agree with Spidy,
get another box. If one works and the other doesn't, either you are misusing it or its dead.

HTH

Doug

 

[Freddie_P]

reset the hub? Well its been powered off and on. I don't see any reset button just switch that says NORMAL/CASCADE which I suppose you switch it to if the last port is used to plug into another hub/switch. Well, I guess I'll have to scrape up the money for the 8 port switch...thanks

 

[Xanathar]

Is it possible your duplexing is mis-matched (all should be half). A box (or boxes, or the Hub itself) may not be properly handling collisions. This would then cause packet loss instead of a collision. Packet loss in TCP transfer reduces thoroput signifigantly comparativly to a normal collision due to the timing involved.

 

[Freddie_P]

Well they are all set to auto as far as I can tell on the various boxes. Also I should be using IPX for file sharing and not TCP/IP although they are both bound to file sharing. My understanding is IPX should be used if I did not make TCP the default protocol. FP