The 51R is classed as a medium size remote controller for 317x and similar terminals. It is connected to the mainframe through either a serial link or a token ring network, with the link level protocol for serial being either Bisynchronous Serial Communications (BSC) or Synchronous Data Link Control (SDLC). SDLC requires the IBM telecommunications software VTAM, while several older bits of software including user written code can communicate with BSC.
The serial link was connected to a modem, with speeds ranging from 9.6K to 56K baud, going over dedicated or switched (telco) lines to the mainframe side. Various physical link protocols are used to the modems, such as EIA, X.21 or V.35.
On the mainframe a modem connects the serial traffic to a communications controller such as the IBM 3705, which in turn would generally be cabled by mainframe channel to the processor. SDLC or BSC travels out to the 3705, over the serial link through the modems and into the Type 1 Communications Adapter built into my 3174.
REPLACING THE CHAIN OF HARDWARE TO USE THE 3174 WITH HERCULES
Herein my problem. I don't have a 3705 or similar controller. I could wire up modem eliminator cables to connect my 3174 to the missing controller using the desired physical and link level protocols. The missing 3705 needs missing channel cables to the missing physical mainframe.
There have been SDLC cards to put into PCs, but that is not an easy process especially trying to connect that to the Hercules mainframe emulator. My P390 system could also mount a Wide Area Communications card to talk SDLC, but I don't have the driver software to update OS/2 to use such a card, nor do I have the card.
MATT BURK'S WORK TO USE CISCO DLSw THROUGH ROUTER
Matt Burk of 9track.net fame discovered a CISCO/IBM protocol, DLSw, that would allow routing SDLC packets over TCP/IP between routers. He worked out a way to use a router with a proper serial interface to connect the 3174 on one side.
He then made modifications to the 3705 device emulation capability of Hercules to understand DLSw. This means that a PC running Hercules can have a TCP/IP link to the CISCO router and pass SDLC packets through the router to the IBM 3174.
See Matt Burk's description of the process for more details.
BOUGHT 2811 ROUTER AND WIC-2T SERIAL INTERFACE MODULE
I jumped on eBay, bought a used 2811 router with appropriate equipment as well a used WIC-2T serial interface module. When it arrives I will program the link to run DLSw and set up the IP address for my PC where I can run Hercules.
CABLING IS THE OPEN ISSUE
The 'last mile' problem here is the cabling between the 2811 router and my 3174. Cisco uses a 26 pin connector they call "smart serial" while my 3174 has a DB-25 male connector. I need to sort out the
connections necessary or find the proper Cisco cable part number and buy it on ebay.
I used to have the cables you need but they all went when our old data centre was demolished a few years ago. We also did some interesting things using a product called "SunLink-SNA" which ran on a Sun Microsystems machine and talked to our IBM main frame over a SNA link, the SUN appeared to the main frame to be a terminal controler.
ReplyDeleteHi Stephen
DeleteInteresting alternative - I also know that DEC had something similar.
Once I figure out either the wiring or the proper cable name I should get this working.
Actually, I believe it’s DLSw for “Data Link Switching”, not DSLw.
ReplyDeleteThanks for catching my dyslexic rendering. I will go back and update this post to fix the name.
Delete