Test Equipment Anonymous

As most of you lot are aware, I work in television with network engineering. Last week, I got an email from one of the project managers (who used to be an on-site technical operations manager, TOM, for TV work. The TOM is the engineering department responsible for a TV production; and has large powers. They are also expected to fix anything that breaks, while catering for the creative department whims on technology. A good TOM fetches coffee and looks about as stressed as a bowl of yoghurt. )

Now, with him coming from that side, he's a bit prone to overestimating his systems understanding. So, when he was assigned to a project to make a new space for weather presenters in our renovated newsroom, he of course thought up the entire solution in his head and ordered stuff before talking to network engineering. The specific part he needed help with was transmitting a relay closure to the machine room. The presenter has a small handheld radio remote, and it will pull relays in a receiver box. The closure will then advance the chroma-key weather map to the next picture, so it needs to be fed to the computer generating the map picture..



The radio of course is more or less line of sight; it needs to be in the same room. The machine room is reachable from the wiring room adjacent to the presenter room, but only via optical fibre. So, he'd concluded that he needed a way to push a relay closure over singlemode fibre.

Here's where he got in touch with me, because I have stock of SFPs (small optical plug-in module) and the thing he'd bought uses those for line interface. -- "I want two SFP's" he said. And dumped a PDF containing the thing's manual in the email too. -- "No", I said, having read the manual. "You are not getting a 9/125µm pair from A to B for that. You are getting a network port in the wiring closet, and one in the machine room. Fibres are relatively scarce; network ports in switches are abundant."

This being the first time I work with those Things, I decided to verify the solution properly. Also, I -- regardless of verification -- needed to check that everything actually worked, and learn how to program it. Lab time! I brought my toolcase and my latest counter acquisition, the 5316A, to work and started to wire things up. Now, the initial setup was, with the test points in ():

radio clicker -> receiver giving relay closure (5316A A in)-> Thing A having optocoupler input biased to 5V -> network to local switch -> Thing B -> relay output > (5316A B in)

After an ungodly amount of trial and error in triggering the 5316A A>B mode properly and actually understanding what the fuck I was doing, I had to find the control software for the Thing, (and here, about, is where the idea the PM had would break, because there was no way to control the Things in his solution.) be allowed to install it on a Windows machine, and finding the Things and when I'd found and controlled them, I actually could send a closure over the wire and I could see that the receiver trigged properly.



The yellow box is the radio receiver, the green ones are the Things. The plushies are Guardians of the TE.

There is some delay variation, but I could reliably get the signal over in about 3ms. Sometimes as low as 2,1ms, sometimes up to 3,5, but never above about 4. Now, here comes the funny part.

As I pulled a long cable to another wiring closet, and thus forced the signal through not only one, but 6 consecutive switching or routing hops, the latency through the system did not change. In my testing, the latency is entirely down to the whims of relays and optocoupler debouncing. Electro-mechanickal things are slow. Ask Konrad Zuse, the man who built a Turing-complete mechanical computer with a clock frequency of 1Hz.

Of course, were I to run this along some wide area path, the speed of light in silica glass (about 0,667 c) would interfere, but for runs of 1 km (common length of cable in our facility, if you have go to the computing centre and back out to another room) the additional latency is perhaps 5 x 10^-6 seconds.

TE saves the day! From meetings and boredom, that is. That was fun.

Some diversion on broadcast network engineering is needed here. Finding things on a network can be hard. The network world has invented ways for things to say "hi" and telling where they are. In the wide area network provider market, especially so the IP telephony industry and the enterprise Wi-Fi market, they have "detecting Things" down to an art form; a DHCP Option or a well-known DNS name is set up, and all the Things will call in to the Keeper thus announced and be Known (in the biblical sense, too, because being found means the Thing might get new firmware too.). This reliably works over big networks and long distances. It's known under names like "Zero touch provisioning" and such.

Some other detection technologies are very much focussed on SOHO market. Apple Bonjour is probably the best known example in this area. It suffers from a number of very annoying limitations designed to make it "easy" to use. Bonjour Multicast packets used to signal the presence of Things are sent with a TTL of 255. And may only be processed if they're received with that 255 TTL intact. This implies that multicast routing, or for that part, any routing, is out. L2 networks it is. VXLAN or EOMPLS need not apply, because those TTL decrement as they label-switch packets.

Now a bit corporate sociology. As various TV series have thought us, the IT department is The Enemy. The inspiration for this is most likely the TV companies themselves. Creative people with a bit of technical understanding being firewalled by BOFHen and blocked from Doing Stuff with Things.

With the stage thus set, guess what the broadcast equipment industry has done to Make Things Easier.

Yes, Bonjour. Because with that, you can take that Netgear switch mnem pointed to LTT comparing with the Audio-Phool variant and build something that looks like it's working and is just like the Ethernet at home which works soo reliably with Netflix. And this sells Things, and the Vendor is happy, the Creative Person is happy, and the IT department shall stay the fuck out of Art.

Yeah. Now, do this on an enterprise scale, with 24/7 operations, over the entire country, without creating broadcast storms and L2 loops because The Creative People Thought They Knew And Just Plugged A Cable In.

My primary function at trade fairs is to be the Angry Network Person Who Speaks About Discovery Of Things Done Right.

Great read. Thanks for taking the time to write it up.

It's nice to see into a completely different world occasionally.

mansaxel wrote: ↑Thu Nov 03, 2022 9:08 am
The Creative People Thought They Knew And Just Plugged A Cable In.

My primary function at trade fairs is to be the Angry Network Person Who Speaks About Discovery Of Things Done Right.

Even back in dear old analog days beyond recall, "creative" people were the bane of our existence.

The news studio had just been refurbed, with Remote control cameras running on a track on the floor.
As part of this rejig, we had several big Sony floor monitors which were normally fed with separate 75 ohm sources.
Unfortunately, the floor manager had a habit of, because of some perceived need, piggy backing them on the same source.
The Sonys were reasonably tolerant of this.

The Newsreaders thought it would be nice if they had a couple of small monitors up close, so they could see themselves without having to "crane their necks" to see the proper ones.
To this end, a couple of small domestic Samsung TVs with video inputs were obtained, & stood up on a couple of wooden stands in front of the newsdesk. They, of course, were further piggybacked off the long suffering 75 ohm source.

As before, the Sonys "hung in there-----just, but the Samsungs were a mess, with noisy video & loss of syncs.
I took one look at the mess, shuddered, then remembered that somewhere, there was a small portable VDA.
Digging it out of the store, I powered it up & fed it from one 75 ohm source, connecting the monitors to its outputs.

All was well for a while, then one of the floor crew dropped one of the Samsungs in for repair.
It looked like it had been stomped!

It turns out that it had been "Karated" by the remote camera, & knocked off the stand!
After we fixed it, we tied both down to the stands with Gaffer tape----agricultural, but effective!

vk6zgo wrote: ↑Thu Nov 03, 2022 3:37 pm
Unfortunately, the floor manager had a habit of, because of some perceived need, piggy backing them on the same source.
The Sonys were reasonably tolerant of this.

Thanks to SDI and even more so 3G-SDI, this is so universally impossible today that even the densest analogue floor manager understands to avoid it.

mansaxel wrote: ↑Thu Nov 03, 2022 4:39 pm

vk6zgo wrote: ↑Thu Nov 03, 2022 3:37 pm
Unfortunately, the floor manager had a habit of, because of some perceived need, piggy backing them on the same source.
The Sonys were reasonably tolerant of this.

Thanks to SDI and even more so 3G-SDI, this is so universally impossible today that even the densest analogue floor manager understands to avoid it.

I'm sure they will still find some ingenious method of stuffing things up!

An aside to W10 --In what alternate universe does "sure" look like "some", & "things" somehow morph into "thind"?

Guardians of the TE! That should be a topic.

vk6zgo wrote: ↑Fri Nov 04, 2022 12:46 am I'm sure they will still find some ingenious method of stuffing things up!

Oh, indeed. Mostly it centers around sync and even more so its absence. And too long cables.