Token Ring for Beginners

This text is largely based on Peter Wendt's posts.

1st Rule you learn: Station ports are for stations only, Ring In / Ring Out 
for RI/RO only. Especially when it comes to the "dumb" (but rock-solid) 8228. 

>They had me use the setup aid in the bad port with the network live at 
that time, hence why I thought that doing this was OK.  However using the setup aid did not fix the port and we had to move the plug to a free port ( the last one free) on one of the other MAUs.

Aha. The self-acclaimed "experts" weren't any better. It's some sort of a miracle that the entire net didn't go down. Usually "breaking the ring" with a setup tool causes the other ports to shut down and drop the relays.
   In either case you cannot test a bad port / relay whatever with the network on. Simply not possible due to the "double-ring" structure of TR. What morons !

>I pulled the plug labeled receiving in the LAN closet and inserted the setup aid.  Once the setup aid finished (red light blinked) the 2 lanmanager servers that run the POS system (plugged in on the POS closet) started beeping and reporting beaconing.

Awww. Great. You *may* try to disconnect a station for about one - two 
seconds e.g. while changing to a different port by what reason - or to a 
different MAU on the same ring - but once you hold it off the ring for more 
than 3 or 4 seconds it will surely collapse. In most cases the TR interface 
does not open again. It will maintain the pulse (phanto voltage) for 2 
seconds probably, which forces the "new" port open - but after that it is 
ordered to shut the port from the card hardware. Uh-oh.

>I was told that the 2 closets were on separate loops by the staff at work 
that was supposed to know how to maintain the POS system.  It must not be, otherwise the POS system would not have went down with the LAN loop.  All could have been avoided if someone had actually documented something correctly, all I had to work with was a 4 year old diagram of the POS loop which must have changed since they put in the second closet ( and never bothered to document the changes ).

Sigh. What more to say ? It's the usual stuff. Everywhere - all the time.

>Is it possible to connect loops through one of the 1-8 ports on a 8228, or would it have to run through either the RI/RO ports?

No. You cannot. Not that easy. There were "station splitters" available from e.g. Olicom that allowed to abuse a "station port" for another "stub 8228", which holds "another subset" of stations.

Basically and directly you cannot a) connect 2 station ports of  two 
different 8228s to make "one net from formerly two nets" nor b) connect a RI or RO port from an 8228 to a data station port. It lacks the phantom voltage for the relays on these ports. Only 4 data wires are present there, which are 2 by 2 shortened by default and automatic (ICS connectors).

For a) you need to RI/RO daisy-chain them. Usually no problem - even in 
online mode. For b) you need an intelligent MAU like the 8238 where port # 16 can be configured to act as RI/RO chain for 8228s (but the stations attached on the 8228s show up as attached to port #16 in "the inventory list" on the 8238).

>Do you think that the troubleshooting I went through the first time could
have changed, caused or contributed to the problems that I had noticed
recently ( workstations randomly dropping from the net )?  I think there  was, if not still is some problems with the setup that is currently running as the MAUs in the LAN closet tend to cick-clack too much for workstations that are always on and not turned off ( also something the people who maintain the POS system say is normal when I asked about it "oh they always make that noise allot" ).

Ugh ... not true normally. You *sure* hear the relays click on / off when a 
station enters / leaves the ring - but for some period of time there should 
be "deafening silence" in a MAU room full of 8228s with no additional 
components, routers, switches etc.

>Lastly to note is that once I had unplugged all the nodes from the LAN 
closet ( I left the RI/RO ports in on all the MAUs though) and reset each port all the workstations came back up including the one in receiving that prompted the whole thing. 

That's the consequent method to get it done. Usually all alone in the 
building, during the night and with some spare 9V battery blocks at hand ... 
Been there - did that. Drove to a 24h filling station at 3 in the morning 
after my 3 or 4 MAU tools exhausted their batteries.

>I didn't test the dead port that I had found the first time though, it makes me wonder if I happened to fix that as well this time around.

Well - "Why not ?" You do them all - or none. If there is one really defective port there you have the potential danger of running into the same scenario once again later. There are *rare* incidents where an 8228 is really defective - but I *had* that. And you can only find out with testing *all* ports ... best with the RI/RO cables detached too and a second Tester in the RI or RO port. When the lamp on the station port stays out the RI (or RO) port *must* come on. That's the indication that the 8228-internal data path is working. You can rely however on the "click-...-clack" noise fo the station relay only and hope everything internally is well-fabricated. Most are - working fine for decades. Some are not. We had a number of Brazil-made 8228s, which had an internal fault and did not pass the signal to either RI or RO (or both on one). All station ports clicked fine ....

Causes For Permanent "relay static" in a group of MAUs 

1.    Worn out plugs, improperly seated, partially seated and lacking the 
retainer. Largest group.
2.    Worn out cables. People walk over them, run over them with office chairs or place furniture on them. Second largest group.
3.    Cable lenght exceeded between two MAU (over 400 / 200 meters or 1200 / 600 feet at 16 / 4 Mbit/s or longer than 200 / 100 meters or 600 / 300 feet between MAU and station. Improper (to tight) bended with less than 5x the cable diameter. Happens. Fairly often. Often detected after components had been replaced or an existing net is switched from 4 to 16Mbit.
4.    Defective adapters. The capacitor building up / holding the relay phantom voltage is dryed out. Defective connectors, improperly affixed cables at the adapter end (see 1.).
5.    Devices usually *not* in the net with adapters installed and the LAN 
software still active try to insert in ring .... either with false speed or 
get disabled by LAN program timeouts periodically. No joke - happens at a customer. They had left-over machines with a 4Mbit adapter and had them yet attached to the MAU. They have been used to copy diskettes, virus-check files and suchlike. They come on, run 5 minutes - are turned down. Network interface opens several times ... closes ... causes beaconing ... goes away ...etc. Took me two days to locate the station with a LanAlyzer and fetch an address - which was then pointed to an "old machine no longer in use".
6.    Defective MAU. Happens, but is unlikely. Once you'd "prime set" an 8228 it is good for a few more years. The step should be repeated after 3 - 4 years in use.

So that's *my* experience of over 13 years with 8228 units ... :-)
Peter in Germany

What Are the Differences between Bridges, Routers, and Gateways?
   A bridge is a device that interconnects two subnets using the MAC address of stations. Bridges operate at layer 2 of the OSI protocol stack. Because MAC addresses are protocol independent, a bridge is very useful for physical network extension, speed matching, and wiring optimization. However, since a bridge is essentially transparent to the attaching stations, dependencies upon such protocol variables as timers, flow control and error recovery are not supported. Thus, problems may arise if too many workstations are bridged. These include issues such as broadcast storms, time-outs and congestion-caused delays in response times.
   A router is a device that interconnects two or more network segments on the basis of OSI layer 3 addresses. Because such addresses have protocol
dependencies, a router must either participate in the protocols for purposes of routing, flow control, and error recovery, or must encapsulate protocol dependent information in frames supported by the routers. Even with encapsulation however, a router must understand the network topology and where to send data frames. Routers maintain topology information as a result of an exchange of topology information with other routers in the network. Communication of topology information between the routers may use open standards for exchange such as OSPF or EGP or vendor-specific protocols. They do not assume responsibility for the integrity of the address information used within the network.
   A gateway is a device that handles interconnection and transfer of information between entities in layers 4 through 7 of the OSI Reference Model. Thus a gateway is required when an entity using one protocol needs to communicate with an entity using another protocol (protocol conversion), when the addressing structure of two entities is inconsistent, or when connection is required between independent networks.

Direct Cable Connection?

Unlike connecting two BNC net cards, you can't connect two TR cards together without a hub (apocryphal tales of a magic cable and software are unfortunately just that AT THIS TIME). The main problem is two-fold: 1.) the adapter detects the opening of the ring-insertion relay and 2.) on the "open adapter command" the communication (insertation) into the ring must be finished within a certain period of time.
   A direct cable connection does not supply the required change of current flow in the DC-phantom voltage line and to manage simultaneously starting the ring communication on two different PCs *within* the time-limit is more than unlikely.

Tales of Direct Connection
From Terry King:
   Peter, back when I was at IBM in Vermont there was some internal software you could use to make two token-ring cards talk to each other without a MAU. Somebody must have done this outside IBM??? 

Peter's Response:
As I wrote earlier in this relation (but not in this thread): there were rumors about such a tool - and corresponding to a team-mate "We had that back in 1990 or so ... required a particular cable with 2 resistors ..." but disk and cable have (of course !) gone.
   Funny fact: we once had this software in the company (back in 1990 or so). Someone brought it there and we had a "magic cable" with a little black box in the middle, which might have contained some resistors and caps - but no relay. 

On demand I got told that it works this way:
- connect the two computer with that "magical" cable
- start computer #1 ... will come up and "start the ring"
- start computer #2 ... will complain about not being able to insert in the ring
- start the "magical" software, which will *force* the TR-adapter to open and insert in the ring 

The normal opening requires to receive the "relay opened" sense signal (change of current flow in the two wires for the +5V phantom voltage when the relay opens), then trying to read the passing token (if ring-speed matches ! - or Autosense the ring speed before), then open the adapter and copy the token informations and pass the token to the next station (or copy the data from it ..). This procedure must have finished within a "time-out" limit. If the opening / inserting fails an error-code is displayed.
   The problem is to detect the "ring opened" flow-change with the MAU missing ... while this cannot be detected the follow-up inserting will not be started. The software only opens the adapter without waiting for the "ring opened" signal.
   I'm still trying to get more informations about that. In case I find something ... I will tell.

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Louis F. Ohland, Peter H. Wendt, David L. Beem, William R. Walsh, Tatsuo Sunagawa, Tomáš Slavotínek, Jim Shorney, Tim N. Clarke, Kevin Bowling, and many others.

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