It’s just a serial cable. The 9-pin goes at the PC end. The RJ45 plug goes into the switch/router/firewall/access point and is simply a serial port presented as RJ45. They don’t connect to ethernet ports at all.

There were Cisco devices out there that allowed you to connect multiple network devices (say 8 routers) to a single PC with one serial cable, but not the reverse (multiple end user devices into one network device).

yes, just a serial cable as per type of cable used to connect a computer's serial port to a Cisco router's console port

RJ-11 was used for networking (230 KBit/s). On Mac. PhoneNet. :)

https://en.wikipedia.org/wiki/PhoneNET
https://lowendmac.com/2014/appletalk-localtalk-and-phonenet/

https://www.youtube.com/watch?v=gRfJ8MtX5a0

pbagain wrote on 2022-07-15, 20:06:

Going through my collection of computer cables to find a way to make a typewriter/terminal talk to a modern PC , I found a numbe […]
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Going through my collection of computer cables to find a way to make a typewriter/terminal talk to a modern PC , I found a number of these SUB-D serial to "RJ45" cables (image from Wikipedia).
CiscoConsoleCable.jpg
Curious as to what these cables are normally used for, I googled and most hits refer to connecting to serial consoles of networking equipment (switches and such).

Later I also asked a friend about it who has been working in IT since the eighties. He seems to remember that such cables were also used in the early days of local networks to connect multiple computers via a low-speed ethernet hub (not switch). Apparently the advantage was that not all computers were equipped with expensive NICs, but they all had a serial COM port or two. Disadvantage would be the low speed.

Does anyone else remember this method of networking? I can't seem to find anything about it online, but maybe I'm using wrong keywords. Any suggestions?

Also: how could this method actually work? I can kind of see how you could broadcast a serial signal from a COM-port over the hub which would then repeat it to other connected clients. But how would the receivers know who was the intended target? How would synchronization work? Was there a special protocol and driver stack?

It's a bit of a mystery to me, so hoping for some pointers. Thanks!

I've got some self made cables like that given to me by a chap when he worked on telephone equipment and used a 8-bit NEc computer to do interacting with the phone systems via it's serial port on that computer in the '80s/90s.

Separate issue but it was also common (and sometimes even still see it today) to see little DB-25 serial to RJ-45 converters on the overhead terminals in a restaurant showing the cooks what to make, and on the receipt printers. So it's still RS-232, point-to-point with a multi-port serial card or terminal server, but just routed over CAT3 or CAT5.

jakethompson1 wrote on 2022-07-16, 01:42:

Separate issue but it was also common (and sometimes even still see it today) to see little DB-25 serial to RJ-45 converters on the overhead terminals in a restaurant showing the cooks what to make, and on the receipt printers. So it's still RS-232, point-to-point with a multi-port serial card or terminal server, but just routed over CAT3 or CAT5.

Thanks everyone for providing some context and Jake for the "terminal server" lead!

I didn't know about terminal servers and they're visually quite similar to hubs/switches. Additionally, a Console server seems to make the console ports of the devices you want to control available over regular network. So maybe that's what my friend was trying to explain or maybe he misremembered them as regular hubs, I'll check back later.

I briefly considered getting a terminal/console server for a bit of fun experimentation. But checking my usual places for getting second hand hardware come up really expensive ..