IBM 3174 C 6.4 Microcode Disks?

Grant Taylor cctalk at
Wed Feb 20 22:31:21 CST 2019

On 2/20/19 12:23 PM, Paul Koning via cctalk wrote:
> Please note that among LANs, there is Token Ring (802.5) and there is 
> everything else.

I think it really depends on how you look at them.

 From a frame formatting point of view, Ethernet is the odd ball when 
looking at how TCP/IP is carried.

Everything other than Ethernet (802.3) uses 802.2 or a medium specific 
varient of 802.2.  Then there's Ethernet which predominantly uses either 
Ethernet II for TCP/IP or 802.3 (a.k.a. "Raw") Ethernet frames for IPX.

> FDDI is like Ethernet and like 802.4.  Token Ring is the oddball because 
> (a) it doesn't have proper multicast addresses, and (b) for some reason 
> IBM invented source-routed bridging and tied that to Token Ring.

Does it actually need a broadcast address like Ethernet when the ring 
passes through all the stations?  Or is that functionally comparable to 
a multicast?

> FDDI is in no way at all like Token Ring.  The only thing the two have 
> in common is "token" and "ring".  The MAC protocol is utterly different; 
> the closest relative is 802.4 Token Bus.  And as far as addressing is 
> concerned, FDDI is like 802.4 and Ethernet, with real multicast and 
> general use of normal transparent bridges.
> The only complication with FDDI (and 802.4, if you could find it) 
> is that it only has 802.2 frames, not classic-Ethernet (with 16 bit 
> protocol types).  So an FDDI to Ethernet bridge has to translate Ethernet 
> frames to an 802.2 based encapsulation.  That is done by converting them 
> to SNAP frames, as described in RFC 1042.



> Bridges like the DECbridge 500 and DECbridge 900 will do that; I assume 
> Cisco does likewise.
> FDDI didn't live all that long because 100 Mb Ethernet replaced it, but 
> while it was out there it made a fine backbone for Ethernet-based LANs.


Grant. . . .
unix || die

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