SLC 5/05's on ethernet

Rigth here's the problem we have 2 5/05's conected to the own InTouch PC's via there own hubs on ethernet .The two hubs are conected to a central switch as are 10 pc's .
Now the one 5/05 can be seen with out problems on the network via RSLinx the second however ,as soon as we connect it's hub to the network we get a collision alert flashing and we can't see it on the network I've tried swaping the hub for a cheap D-Link switch and that has the same problem .However if I swap it for a big switch (Nicked from IT) it connects no problem.

Any Ideas as to how to get round this ,if we need a new switch what spec do I need ?

Thanks in advance

10 vs 100 speed mismatch

My first guess is that you are having a mismatch between 100 mb/s Ethernet circuits and 10 Mb/s Ethernet circuits.

The SLC-5/05 was originally a 10 Mb/s half-duplex device only, but newer ones (since early 2005) have 10/100 autoconfiguring ports.

Probably that big switch from the IT department can attach to both 10 Mb/s and 100 Mb/s networks on a port-by-port basis, but the cheap hubs and switches you've tried previously cannot.

Do the existing hubs and switches indicate what data rate the connected equipment is using ? Often it's just a bicolor LED that glows green for one speed and amber for another.

Yep both the cheap units just have the bicoloured leds the netwoek is only 10mb/s so there is no risk of a mismatch.All the stuff we have tried has been 10/100 mb/s and all if it hasa set its self to 10 mb/s.

Does SLC #1 communicate without SLC #2 connected?

Does SLC #2 communicate without SLC #1 connected?

If so, check that you don't have your IP address duplicated.

There are no duplications of IP adresses on the network one is 10.0.0.53 and the other is 10.0.0.56

Jezz said:

the second however ,as soon as we connect it's hub to the network we get a collision alert flashing and we can't see it on the network

Click to expand...

Just a very off the wall shot, are you sure you are plugging in the right port to the right port? For older hubs/switches, without auto-crossover capabilities, you need to plug in the UPLINK port from the hub to a regular port on the switch.

Some older hubs had two physical ports, that were labeled 'normal' and 'x' or 'crossover' or 'uplink'. If so, those two ports cannot be used at the same time. Others had a switch to switch the sense of one port from normal to uplink.

Yep sure we are on the right ports (even tried the other ports just to be sure)

Jezz said:

... However if I swap it for a big switch (Nicked from IT) it connects no problem.

... if we need a new switch what spec do I need ?

Click to expand...

Well, since I read all the way to the end before replying, I won't ask about IP addresses since you're getting too many collisions due to something not totally known.

I only use a hub when NOT connecting things to a network, as you have found out the main reason.

So get a switch, most likely any will do. They are cheap ! Heck, can you even buy a hub nowdays ?

I'll mention that once upon a time I set up an Ethernet network composed entirely of nice little Netgear FS108 Fastlink switches with the Auto-Uplink feature.

When we plugged in one particular patch cord, we found that the collision LED blinked like mad, and communications on the rest of the system slowed to an absolute crawl.

What I found out after carefully tracing cables was that while I had run one cable between two switches to act as an uplink, another technician had run another cable between the same two switches for the same reason.

I don't know precisely what sort of routing table madness that caused, but of course it went away as soon as we had just one uplink cable.

I don't know what's the case in your installation. It could be a duplex conflict or a bad cable or something else that the "big" switch handles gracefully and a hub or cheap switch does not.

With a hub you cannot go over 10mb/s. Personally, I'd trash the hubs and buy some cheap switches. Unmanaged full auto sensing switches that would cover your needs should run well under $100USD

Hubs are multi-port repeaters. They are not intelligent. They simply get a signal incoming and send it to every connected device and leave it up to each node to decide whether or not the message was intended for it. It uses ethernet's early form of shared media (google the term CSMA/CD for more info.)

A switch in contrast is a multi-port bridge. Each port is it's own collision domain. So in effect if you run a node directly to the switch port you will no longer have any collisions. Switches are also intelligent and only send out information on the port of the device intended to recieve the message so they are much more efficient especially when handling multiple nodes. They are also required for 100mb/s full-duplex connections.

An overloaded hub will have lot's of collisions where two devices are trying to transmit simeotaneously. Whenever a collision occurs, both of the colliding hosts stop, and then try to re-transmit at random intervals.

We have a process that has several SLC5/05's and a couple micrologix controllers. When it was installed it came with a hub to connect all the controllers. It was awful. The collision light was practically always flashing and we kept losing data between the different parts of the process and the 5/05's liked to drop of the network randomly. Putting in a cheap unmanaged switch solved all our problems.

Ken Roach said:

What I found out after carefully tracing cables was that while I had run one cable between two switches to act as an uplink, another technician had run another cable between the same two switches for the same reason.

I don't know precisely what sort of routing table madness that caused, but of course it went away as soon as we had just one uplink cable.

Click to expand...

This was a big problem with switches when they were still new to market. Most modern switches use something like Spanning Tree Protocol to eliminate this type of behaviour.But on older equipment it's something you need to watch out for.

Basically with the two uplink cables between the two switches, messages being passed between them were just ending up in an endless loop and overloading the network. Can't remember the exact details of how it goes down offhand. But I do remember STP would detect this and disable one of the ports until it was needed. This gave network designers a way to create redundant links between switches.