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From: pom@under.s1.gov (Peter)
Newsgroups: comp.os.research
Subject: Ethernet: modsim article
Message-ID: <3819@sdcsvax.UCSD.EDU>
Date: Fri, 11-Sep-87 12:29:58 EDT
Article-I.D.: sdcsvax.3819
Posted: Fri Sep 11 12:29:58 1987
Date-Received: Sat, 12-Sep-87 18:35:56 EDT
Sender: darrell@sdcsvax.UCSD.EDU
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Approved: mod-os@sdcsvax.uucp

Well, well This is really the right discussion group for me.  One does not
get smothered long tracts.

I recall somewhat irritated reaction to my sweeping question on merits of
Synchronous vs Asynchronous Protocols  ( SP vs AP ).

As  I do not want to be left  Holding the Token for ever, I will respond to
that comment:

The answer that Ethernet is both SP and AP is not correct.  Ethernet does
'exponetial backing' after collision - which means that PROBABILITY of
sending a packet is determined by a formula.  Neverthless, such protocol
remains fully asynchronous.

Better example of protocol, which has both ( AP and SP) is Hyperchannel --
which was described in a very imaginative way in Mitre book on LANs .
Hyperchannel  enters "Free for all" mode after  (fixed) period of silence. In
that mode, any station can send - without waiting(=AP).  In case of
collision, nodes enter into 'slotted mode' in which each each station is
assigned a 'fixed time interval' or 'slot' in which it can send a packet
(SP).

My question attempted to draw  attention to that universal parameter, ( which
Tanenbaum calls 'a'  and )  which is a (dimesionless) ratio of two
time-intervals 1) rate of transmition * length of packet 2) Speed of
propagation * length of the bus

General dependence of throughput on a T[a] says that in 'heavy traffic' you
prefer SP and in 'light traffic' you prefer AP. This universal tendency is
seen even on (very simple example of a ) traffic lights:

In low traffic, the light should revert to 4-way stop ( red blinking) and
only AFTER FIRST COLLISION, they should revert to  usual slots ...

Did I missed something? It looked so logical, when I started..

Anyway, all those with first name in [a...k] should now post a statement of
their interest [ LANs, VANs, ...???  ??? ]

Yours  Peter || pom    alias   pom@under.s1.gov ||  pom@s1-under.UUCP