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In article <1992Oct12.021503.7597@nuscc.nus.sg> eletanjm@nuscc.nus.sg (Tan Jin Meng) writes:
=>I know almost nothing about ARCNET except that it is a token passing
=>architecture. 
=>
=>Question : 
=>What are the similarities and differences between ARCNET and Token
=>Ring? (this is really a question about what is ARCNET).
=>
   I know nothing of Token Ring, so I can't make comparisons, but I
have done some work with ARCNet. ARCNet is a 2.5Mbps token passing
network.  The node address is only 8 bits, so there is a fixed limit of
255 nodes on a single ARCNet (zero being reserved for broadcast
addressing). I have seen is running on coax and unshielded twisted
pair, and I have heard rumors of it running on fiber. I have also heard
rumors of 10 and 100Mbps versions under development. I have used ARCNet
in a mixed star/bus topology over UTP with a fair amount of success.
The max cable stretch is longer than 10BaseT as well, at 400 feet for
UTP (from an active hub).  Stability is good, especially if you use
intelligent hubs with one node per hub port. Node addressing can be a
bit of a pain since you have to keep track of them to assure that no
two nodes have the same address.  Otherwise, ARCNet seems to be a good,
if not terribly speedy, network.

=>Question :
=>I know that Token Rings are almost real time capable due to more predictable
=>response/delay times, allowance for priority etc (simplistically
=>speaking). How would an ARCNET implementation serve in this regard.
=>
   I would think that ARCNet would be a reasonable medium for real-time
systems (assuming that everyone else's idea of real-time matches mine. :-)
The only hitch I see is the additional reconfiguration delay incurred
when new nodes are connected to the network (or other, more melicious
things happen, like duplicate node addresses.) Bounded delay is always
going to be a difficult thing to achieve, I think.

                                        Gary Duzan
                                        Time  Lord
                                    Third Regeneration
                                      Two-Bit Hacker



-- 
                             duzan@cis.udel.edu
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