KEEPALIVE's do not always work.

[louie at umd5.UUCP]

I would have to question the existance in TCP of a KEEPALIVE construct at 
all.  Suppose that I want to have a connection alive for many hours at a 
time; why should I force traffic to flow across it at periodic intervals?
This is a real issue if your link-level network is a PDN, and you get charged
by the packet.

I you want to verify the existance of the connection, why not have whatever
application that uses TCP make sure that the connection is "warm".  This can
easily be done in the case of a TELNET session by sending a timing-mark
TELNET option every so often.

-- 
Louis A. Mamakos WA3YMH   University of Maryland, Computer Science Center
 Internet: louie at umd5.arpa
 UUCP: {seismo!umcp-cs, ihnp4!rlgvax}!cvl!umd5!louie