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From: darrell@sdcsvax.UUCP
Newsgroups: comp.os.research
Subject: Re: How do you tell if a remote site is alive?
Message-ID: <3295@sdcsvax.UCSD.EDU>
Date: Tue, 9-Jun-87 21:58:37 EDT
Article-I.D.: sdcsvax.3295
Posted: Tue Jun  9 21:58:37 1987
Date-Received: Sat, 13-Jun-87 03:39:45 EDT
Lines: 28
Approved: mod-os@sdcsvax.uucp

> ... In a distributed system, how do you tell if a remote
> site is alive or not?  A time-out could be used, but it's not reliable and its
> also very slow.  I can think of many approximate solutions, but reliability is
> important.
> 
> 
> How do the folks in industry do it?  Performance is critical there, unlike a
> university prototype.

Many systems [Ah La STARLAN {AT&T}] use a conection mode service with a keep
alive signal.  The absence of the signal within a long time frame kills the
connection.  When a node dies, or is dead, it's LOGICAL name is removed from
the network.  Any attempt to establish a new connection responds with
"NO SUCH DEVICE ON NETWORK" (-: the electronic version thereof as app. :-)

When you can't afford the wait, and must know "NOW" you send a message
through the "connection" or attempt to establish a new "connection" and
the lack of an ACK packet, or addressable logical name provides you with
the information in question.

[ Doesn't this still imply a time-out? --DL ]

Robert.
-- 
Darrell Long
Department of Computer Science & Engineering, UC San Diego, La Jolla CA 92093
ARPA: Darrell@Beowulf.UCSD.EDU  UUCP: darrell@sdcsvax.uucp
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