So basically the engineers who developed the protocols for the routing infrastructure most likely learned some things from learning how telephone switches like this utilized alternative routing capabilities and thus the base logic for internet data routing protocols like RIPv1, RIPv2, and OSPF were most likely based on the alternative routing functions of these telephone switching systems.

@@byebyedarren It probably is! It all evolved from this. BGP is really interesting, and a lot is said on the "honor system" of it. Hey, the world runs with it and not much issues arise .. well with BGP at least...

The most important principal that carried over is the "well, that's weird!" which I've said in front of internet routers doing BGP carrying gigabit/sec of traffic when they did something that i'm sure means they're broken.

It's not the sounds I did not know about. It was the alternate routing. And I don't have the outside phone number for the CM

Hey thats neat. Thanks!

Not long before it's all SIP

Yeah, it’s pretty sad that nobody thought to save more of them. There were plenty to go around!

Hi Bryan. I didn’t forget 4M. I just didn’t list it because I figured most people wouldn’t notice the distinction. You probably know this already, but for those who don’t, 4M was a modified version of the original No. 4 Toll Crossbar. “M” stood for “modified”. It was modified to match the configuration of the later 4A or 4 “Advanced”. The need for toll crossbar systems was very great, so the first ones were installed in a “beta” configuration. They were then modified later on and the “M” was added to the name.

@@ConnectionsMuseum Thank you for that information, do you guys have a 4A or any toll switch at the museum?

@@magesnz unfortunately we don’t. There probably just wasn’t enough room to store and display one.

Response times, and data from other routers (BGP at the edge, generally EIGRP/OSPF/IS-IS within a network) that may or may not include things like link bandwidth, a reliability index (observed packet loss), or, yes, RTT. This is all done transparently by routers, neither the sending side nor the receiving side really know nor care. One of them packages a stream of bytes (a file) into TCP segments, and packs that into an IP packet for routers to make their calculations. The other side just unwraps the packets and uses the TCP sequence number to ensure order. QUIC does the same thing, but is built upon UDP without some of the baggage that TCP has. Generally, one TCP connection tends to take the same path through the internet, it's not an intentional choice for large data transfers or long-running connections to have separate routes. The nice thing about routers is that they almost always have their path allocations laid out, it's called the Routing Information Base (RIB) for the higher-level logic, and the Forwarding Information Base (FIB) for what it actually does. The RIB may contain multiple routes to a destination (prefix), but only the most optimal route is installed into the FIB and actually utilized. Gateway protocols (BGP/OSPF/IS-IS/etc.) update the RIB as new data comes in about the state of links. Fun fact: every BGP enabled router on the internet (excluding iBGP, different purpose) more or less has a complete map of the internet, because they all synchronize eventually. BGP contains path data (what systems were in the path between the originator or a prefix and the router receiving it's information), which helps route selection. The "global internet routing table" is the theoretical RIB managed by internet BGP, and it's... Huge. But every BGP enabled router has an entire copy of it, to route traffic from wherever, to wherever.

Thank you!

The Audichron was usually shared between multiple offices in a city, but the crybaby tone generator was per-office. It was comparatively small (only 2 or 3 mounting plates high), and much less expensive than an Audichron, so there would be less need to share it. While you're connected to the crybaby tone, there are three major crosspoints that are being held up: the line link (for your line), the district link (for your district junctor), and the office link (for the trunk to the crybaby generator). The crybaby is just another destination...another trunk on the office link, just like the hundreds of other trunks that leave your office. Some go to other telephone switches. Others go to announcement machines. Still others go to the crybaby. Busy tone is different. The busy tone is a *function* of your district junctor or incoming trunk circuit, not a destination, like the other things. So you don't really "route" a call to a busy signal. You merely operate a relay, which cuts in the busy signal tone to the trunk you're already sitting on. Ringing tone is the same way. It is not a destination, but a function provided by relays in the trunk circuit you are using.

Where did the link to Kitty Carlisle come from? I found the bit you quote on (what I assume is) your website, but the April 1941 Bell Labs article merely notes "various combinations of existing tones were tried... [then] an entirely new sound was developed."

Good question! The route of last resort was used if all of the first and second choice trunks were busy. That would usually be an announcement or operator, depending on local practice. If all the announcement trunks were used up, then the route of last last last resort was to just leave you sitting there with no audio at all until you eventually hung up. That didn't happen often though, as it would need to be a major failure to use up all of the previous possible routes.

The easiest way to learn is to work on this equipment with your hands. I'm fortunate to live here in Seattle, and volunteer at the museum. I enjoy working on these old machines very much, so naturally, I spend a lot of time doing it. The switches need constant maintenance, and as we add more and more equipment, they need more and more circuits wired in. I'm (mostly) the one who does all of that!

@@ConnectionsMuseum all of our (now all retired) really good switch techs had worked with the vendor, installing the switch in the office they worked. No way the five day training that became standard could ever match that.

@@ConnectionsMuseum Your enthusiasm and dedication to preserving and demonstrating this equipment is a huge asset to us.

@@boballmendinger3799 Sarah here, responding personally: For my day job, I am an instructor at a large tech company. I am disappointed at the general trend of less training/faster training/computer-based training. I find that it produces less confident, less capable people, but it makes management happy by lowering costs, and giving the appearance that we're doing more with less money. The whole industry is going that way, and in my opinion, its a mistake.

@@ConnectionsMuseum I could not agree with you more. I find today most technical people know absolutely nothing about what they're supposed to be experts at, including the Geek Squad and things like that, I was with a friend of mine I said to him let me just go over to these people and ask a simple question and see how they respond. When I asked the question something very technical they had no idea even when I was talking about, but they try to give you a snow job well we'll have to take them and have our technicians look at it blah blah blah blah. Very disappointing I spent many many years in training with Western Electric AT&T, starting with, number one ESS, electronic switching system, tsps traffic service position systems, that's when we upgraded manual operators to electronic switching systems, ETS, electronic translator systems, number for ESS, First digital electronic switching system, number five ESS, Electronics switching digital fiber optic system. Many many years in school and I was an expert in my field at the time. Not bragging, just making a comment. Today is September 12th 2022. My employment started with Western Electric in February 1963, have a total of 36 years service.

Hi Robert, i’m not sure what you mean by “MTFs like link”. Did you mean to type something else?

Thanks. Will do!

Almost certainly this is what he was talking about. The "no such number" tone had the nickname "crybaby" because of its peculiar sound.

@@ConnectionsMuseum Awesome thanks for the fast reply. Keep up the great work you do and the videos as they are really interesting :)

I just came from Evan doorbell's KZfaq video, lol