EtherPath User’s Guide
80
Locking Avoidance Mechanism
When two EtherPaths are used to emulate a direct serial connection
over the network as described previously, the ‘Server Mode’
EtherPath could be locked if its connecting ‘Client Mode’ EtherPath
disconnects abnormally. If this situation happens, no connection to
the ‘Server Mode’ EtherPath is possible, and it should be reset. To
solve this problem, the following system is used.
When in Telnet Server mode:
a telnet NOP command is used
as a heatbeat keep-alive signal. A fixed keep-alive time of 60
seconds is used.
When in Raw Server mode:
1.
A "Keep-Alive" message is defined as a 21-byte string:
sErIaLsErVeRkEePaLiVe
2.
This string “sErIaLsErVeRkEePaLiVe” is sent out by the
‘
Client
Mode’ EtherPath if the time since the previous
transmission exceeds
the configured keep-alive time.
It tells
the ‘Server Mode’ EtherPath that ‘I am still alive and do not
close the connection’. It keeps sending out this string every
keep-alive time seconds if there is no data to send.
3.
The ‘
Server
Mode’ EtherPath will disconnect the link if it does
not receive any packet from the ‘Client Mode’ EtherPath within
a period of three times the keep-alive time.
4.
The ‘Server Mode’ EtherPath will then initialize and accept a
new connection. The ‘Client Mode’ EtherPath will attempt to
reconnect as soon as a network path becomes available.
5.
User-written programs can avoid this operation by setting the
keep-alive time to zero. If a user-written program uses the
EtherPath keep-alive, the program must handle the keep-alive
packet properly.
