8228 MAU

Multistation Access Unit

8228 Overview (PDF, 2 pages)
8228 Sales Reference Sheet (PDF, 1 page)
8228 Official Web Page (archived)

MAU Inside (ccapitalia.net)

8228 Setup Aid

Overview
Oorts
MAU Intro
Oops! Pulling the plug...
Operational Sounds
8230 20-port LAM, not MAU


Overview (source)

The IBM 8228 Multistation Access Unit is a simple 8-lobe wiring concentrator that can be installed in a rack in a wiring closet. Each 8228 allows up to eight attaching devices to have access to a ring. The 8228 does not require an external power source for operation.


The IBM 8228 Multistation Access Unit together with the original Setup Aid.

The IBM 8228 is an unintelligent, unpowered Token-Ring multistation access unit. It can attach up to eight devices in a 4-Mbps or 16-Mbps TokenRing network. Using IBM Cabling System ICS Connectors, cables from the workstations or devices are simply plugged into the unit. The 8228 supports STP cabling as well as UTP cabling when used with appropriate connectors or filters.

8228s can be linked together to form rings that are larger than eight lobes by attaching the RO receptacle of one 8228 to the RI receptacle of another 8228. The 8228 uses IBM type 1 or type 2 STP cabling and connectors.


Oorts

The advantage of the passive MAU is its simplicity. It contains a relay for each workstation port, which is opened through a "phantom voltage" (DC-overlay on the data-wires) and has two special ports "Ring In (RI)" and "Ring Out (RO)", which are used to daisy-chain multiple MAU up to 240 user stations.

You don't need a "token server" for either IBM Token Ring or FDDI. Both of them have protocols built into the network interface cards that start the token and reconfigure the network when stations are added or removed.

Neither type goes down when a station is disconnected. The MAU closes the circuit when it detects loss of connection, unless of course there's something wrong with the MAU. When that happens the network cards reconfigure the ring in a few milliseconds and you never notice that it was down briefly.

With IBM Token Ring, if the network is large enough to require two MAUs, then if one of the connections from MAU to MAU is broken the MAUs can reconfigure to run on the remaining cable (MAUs are always connected to each other with two cables).

With FDDI, the ring can be configured as two rings with separate tokens, one going around the ring in one direction and the other in the other. If there is a break anywhere, the ring can reconfigure and keep running.

To connect Ethernet and Token Ring you need a router — the router extracts data from Token Ring frames and reencapsulates it into Ethernet frames. The type of network that can connect to Token Ring without a router is 100VG, which is designed for the purpose.


MAU Intro (from Peter)

The IBM passive MAU is the 8228 Model 001. It has 10 ports, 8 of them are for user-stations, 1 is called Ring In, 1 is called Ring Out. These 2 are for cascading multiple MAU up to 240 stations.

Front view of the IBM 8228 Multistation Access Unit (MAU):

+--------------------------------------------------------------------+
| H   RI     1     2     3     4     5     6     7     8    RO     H |
| H  +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+   H |
| H  | # | | # | | # | | # | | # | | # | | # | | # | | # | | # |   H |
| H  +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+   H |
| H                                                                H |
+--------------------------------------------------------------------+
       |     |__________________________________________|    |
                                   |                          
     From                                                    To
    another           8 connectors for stations            another
     8228                                                   8228
   (orange)                                                (blue)

The original 8228 has connectors of IBM Cabling System (ICS) and use a very unfamiliar plug, which is called 'Hermaphrodite Plug' and is plug and socket as well. There are however compatible MAU available from i.e. AMP, which use RJ-45 connectors. The typical IBM Token-Ring cable has a 9 pin Sub-D plug on the adapters end and an ICS plug on the MAU end. The cable can be extended very easy using another cable with ICS-plugs on both ends. The maximum cable length between MAU and station can be 300 feet at 4 MBit/s and 150 feet at 16 MBit/s.

One *can* create an own cable using shielded twisted pair cables like used on telephone lines, if the length between adapter and MAU does not exceed 60 feet. (That's what I often did!) - the ICS plugs are available separately and are very easy to install with only a larger plier to press
in the self-cutting cable connector. Takes about 2 minutes with some experience.

An IBM Token-Ring cabling consist out of 2 pairs of wires, which create a system of 2 'rings' - one main data ring and an additional backup ring. The topology is a star (the MAU in the center and the stations connecting with a single cable to it), the logical architecture is of course a ring. Each station inserts into this ring without disturbing data-traffic to the other stations over the MAU. Token-Ring is -other than Ethernet- a collision-free transmission and a failure in a single station or cable will not course larger segments to crash.

There are 2 different TR-systems out: the 4 MBit/s and the 16 MBit/s Token-Ring. If the cards have a round green decal at the rear bracket with 16/4 printed on it then these are the adapters which support both speeds. But you will have to decide which speed you use - either 4 or 16. An adapter supporting only 4 MBit/s or set to 4 MBit/s cannot work in a 16 MBit/s net and other way round.

It is very easy to setup a small network under WfW 3.11, using the drivers coming with WfW on the older standard MCA TR-adapters. You may have a dedicated server but must not have one necessarily. If you share only resources like disks or printers the Peer-To-Peer services will do. It will of course work with Win95 as well, but I would not recommend Win95 for the old Mod. 70s. A coexistence between WfW-3.11 and Win95 stations is possible. My personal Token-Ring network in my home-office consists out of an IBM 8228, an 8595 Server running under Win95, 2 Win95 workstations (Compaq LTE-5380 and IBM 9556-0BA) and 2 WfW-3.11 workstations (PS/VP and Mod. 80-A31). Copying of data among these machines works fine with no problems at 16 MBit/s.


Oops! Pulling the plug...

Hi Greg!
>Peter, if you have a smart MAU you are probably right but we have crashed a lot of grocery stores by pulling the wrong plug using an 8228! I always told my techs to never pull the PC end before they pulled the "IBM plug" and we stayed out of trouble.

My home network bases on an 8228 and occasionally I ripped out the D-Sub plug at the adapter card of a running machine. The station relay in the 8228 makes "clack" (closing - opposed to the "click" it switches on) - and nothing else happened. I was just backing up another machine over the net to a tape on a third active machine ... the machine I disrupted from the net however spit out a network error (logically). The rest of the net stayed stable.

You might come into troubled water if you only yank out the D-Sub *partially* and the +5V phantom voltage is still present - which keeps the station relay up... in this case the transmitter / receiver lines might be interrupted and the Token gets lost... and if this machine accidentally was your "active token monitor" (the first station that sets the initial Token) it might cause the other stations going into idle (that "tick - tick - tick" under DOS-LAN) or cause a beakoning condition while other active ring monitors try to substitute the lost Token. This happens occasionally in my network when I pull the PCMCIA TR-card from my Laptop in an absent-minded state before powering the machine down :-)


Operational Sounds

The 8228 is silent as a grave usually. No PSU, no fan, no harddisk, no speaker. It "Clicks" once a station inserts in the ring at power up and starting the adapter. It "Clacks" once a station adapter is shut down. It click-clack-click-clack-clicks" when Auto-speed adapters try figuring out what's the ring speed and -finally- enter the ring. It "click-clacks" multiple if a station tries entering the ring at fixed set a false speed, which could cause more "clacks" when the other station adapters are shut due to a "beaconing condition" on the ring (token got lost / adapter shut down and try to re-insert) which then may cause some speaker noise ("BIPP!") on the workstation(s) under DOS LAN Manager to notify the user / admin of that beaconing condition.

However, all these noises are of a pretty low level but still easily audible when you are sitting close to the unit. With other equipment running in the background, you will have trouble hearing the clicks and clacks.


8230 20-port LAM, not MAU

Image from Symmetry Computers.

Part Number: 53F5501. Has 20 Token Ring ports. Also has 9-pin and 25-pin ports in back of unit.

Peter fires back:
   This isn't a MAU, it's a LAM - Lobe Access Module and 1/4th of a 8230 MAU installation. You need the 8230 base (controller) unit to use the LAMs. The LAMs come either in 20 x ICS or 20 x RJ-45. They can be used in mixed configurations.

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