Beginners guide to network switches

[T i m]

10Base5 / RG8?

And you still had to follow the 5-4-3 rule.

I never saw a 10Base5 repeater.

Sounds reasonable. ;-)

Or 'repeater'? ;-)

10Base2 and 185m [1] if I remember correctly and the 5-4-3 rules applies. I used made up (not crimp) BNC connectors and never had a problem with them.

Because of the shape of the building I had an 8 Port multiport repeater with one port going to my room and 10 'servers / gateways' and each of the other ports radiating around the building, typically to different business zones (like 'Sales' or 'Admin').

Not sure about that?

Again, I used proper taps, not the 'vampire' type. ;-)

'Network cards' are still in common use. ;-)

Yes, the transceiver / TAP and the AUI 'drop cables' (max 50m I think).

I started with a mixture of Token Ring and 'Omninet 1' via the Amstrad

3 user network starter kit that was a bit like the early Apple networking. That then became LAN Manager / basic NetBIOS network over thin Ethernet and because it was very simple was pretty fast (a lower overhead than TCP/IP etc). Then we brought Netware and TCP/IP into it etc.

They were the good days when you really had to know what you were doing to even 'network' a PC. ;-)

Cheers, T i m

[1] And a minimum cable length of .6m or something, a rule I was able to relay to a mate who ran a fairly big network and was having trouble with when I pointed out the 6" Ethernet cables between his multi-port repeaters were possibly the issue (and they were). ;-)

[T i m]

The thicker version of RG58 (still 50 ohm but lower loss). It's what I use between my A.R. kit and the triband antenna on the roof.

Yup, had a smart arse marketing manager do just that. *Luckily*, the multiport repeater just isolated that segment so he only affected his own department. ;-)

Quite.

Nope. If you were doing it fully you fitted TNC connectors to the ends of the RG8 and used Transceivers with TNC connectors. ;-)

Agreed.

It might be a 'better' card (Gb over 10/100), Wireless, multiport or higher performance for example. Or you might use one to simply replace a faulty Ethernet port (physically or logically).

In the case of the training centre I was working at, they ordered (from Dell) 120 *identical* PC to use thought the centre. They had to be identical because we (the instructors) built images of the machines that were then burnt to CD's and so each room could be re-imaged for whatever course was on in that room the next week by just sticking the right CD in the machine and rebooting it. [1]

However, whilst the first batch of PC's were identical, the second batch were different (from the first) and came with different networking built onto the Mobo. So, we had to disable the onboard LAN option and Dell supplied us with 20 PCI network cards that used the same chipset as the others so the OS images worked across all machines.

I had to cover 'Networking' on the Novell 'Service and Support' course so I had the delegates physically playing with Arcnet, Token Ring and (thin) Ethernet and we had 'Show and tell' and theory for a few more.

Cheers, T i m

[1] We did try downloading the images over the LAN using NetBoot but the load of 120 machines all streaming (different) images at once was just too slow. We also kept some rooms off the backbone because it made some courses more complicated and the lunchtime multiplayer FPS games got too big. ;-)

[Tim Streater]

You mean something like the Cabletron ST-500-02? OK, I see what you mean. I don't know whether we ever considered those, but either you have to design your segment and know where all the taps will be needed ahead of time, or you need to take the segment OOS to add one (hmm, I suppose that's true of all thinnet too).

I suspect we gave up on vampire taps altogether and just had 10base5 backbones with a few repeaters on them and thinnet for everything else.

10baseT hadn't really got going by the time I moved back to the UK.

But I still have my Cabletron mug!

[Bob Eager]

I have four! Sounds bad but...

I need > 24 ports to handle what I have in the house. I went for two 24 port switches rather than a 48 port one because:

- if one fails at lesat I have a fallback for important ports

- the 48 port one has a fan and will be noisier

Then I discovered I didn't have enough ports in the workshop...so I got an 8 port one. Used up all the ports. Got another 8 port one.

They are all HP 18{1,2}0 models - they were a good price at the time.

I have a little bit of that, and it's handy for security.

[Bob Eager]

When you want an extra one...!

[polygonum]

Just been dealing with two machines which simply do not work with one particular function. Different models of Dell. Different companies. Same failure.

Needed to add a different network card to sort it.

[Chris J Dixon]

We had an office network which kept having intermittent cable faults which brought everybody's work to a stop. The IT department gave us no support at all, and our most sophisticated piece of fault-finding equipment was a GBP5 multi-meter from somebody's car boot.

I badgered IT to get some proper kit, but no joy.

Eventually I wrote a proposal for our department to buy a GBP1000 hand-held tester, showing that it would pay back its cost in the first 15 minutes of network inactivity.

Money well spent, and fault easily found and cured.

Chris

[dennis]

Don't tie knots in your cable or you will find that bend radius matters especially at 1G.

[Tim Streater]

Luckily our lot had a TDR, so when it was easy to find the short caused when raccoons or something chewed the ethernet cable almost through. "Lift that slab", said our man and sure enough ...

[Tim Streater]

Not as badly as it mattered with original thick yellow ethernet cable.

[Johnny B Good]

Keep them in a large poly bag in the bottom drawer of a filing cabinet... for at least a decade? :-)

[The Natural Philosopher]

Chuck em for scrap. even the cable at 50 ohms is no good for TV/VHF radio.

[dennis]

In theory most ethernet chips had a TDR function built in, however finding software that could use it was hard.

[Johnny B Good]

Not a Netgear GS608 by any chance? :-)

That's certainly been my experience with that particular GBit switch over the years. The symptoms being rather oddball problems effecting wan rather than lan connections (i.e. internet connections).

My first attempts at resetting the 'Usual Suspect' failed to fix the issue due to my neglecting to include the GS608 in the "Reset Program". Once I realised that resetting the switch, rather than the router/cable modem was all that was needed in almost every subsequent case of 'networking issues', restarting or even power cycling the VM Superhub2 became the very last resort.

Prior to the speed upgrade that had precipitated the replacement of the Ambit cable modem with a Superhub2 cable modem router with Gbit lan ports, I'd been using my own seperate routers which were all in need of resetting from time to time (weeks to several months depending on the make and model used) whilst the fast ethernet switches (a maximum of two at my QTH) never ever needed a reset.

The change of "Usual Suspect" from router to Gbit switch was a novel experience for me at that time. I've just assumed it was simply something peculiar to my particular example of a GS608 Netgear switch. Has anyone else seen similar problems with other makes/models of ethernet switch?

[charles]

[Tim Streater]

Wrong impedance, needs to be 75ohm.

[The Natural Philosopher]

Well not for an antenna anyway.

Most RF work is done at 75ohms or 300 ohms for reasons to do with the permittivity of free space or summat. Mr Sayer might know more

50 ohms is very much the 'lab standard for RF/video kit that never gets to see an aerial'..

I.e. one tended to come into the first stage RF preamp via 75 ohm using belling lee or other suitable 75 ohm connector, terminate with 75 ohm, then amplify and spit it out to the next bit of kit at 50 ohms/BNC.

People doing clever RF in the lab might take some of them.

[charles]

a great many professional aerials (or should I say antennae?) are of 50ohm impedance.

[The Natural Philosopher]

Unlikely. Not at the raw antenna level. You HAVE to match using some kind of extra circuitry for any other impedance than 75 ohm (quarter wave) or 300 ohm (half wave).

[charles]

Ground plane antenna?