Diplomat jr Model jrN-ASV User Guide Issue No. 2 (03/01)
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Operation
UDP Client/Server
When configured as a UDP Server the
Diplomat jrN will wait until a UDP
packet is received from a remote host which is addressed to the local IP
address and Server Port held in the jrN. The
Diplomat jrN cannot send
any data over the network until it has received a packet containing a
Source Port address for it to use as a return address.
If a UDP packet arrives from another host before the
Diplomat jrN has
sent a reply to the previous host, the new packet will be ignored unless
switch BSEXY of Configuration Byte B is set to 1. If BSEXY is set to 1
the new packet's Source IP and Port addresses become the new Des-
tination addresses for any Diplomat jrN reply.
When the
Diplomat jrN is configured as a UDP Client it will transmit a
UDP packet over the network as soon as it has some qualified data to
send. It will use the Remote Host address and Server Port address held
in its tables to address the packet and will use its own Client Port ad-
dress for the Source Port address field in the transmitted packet.
The UDP service is a connectionless service with no guarantee of deliv-
ery. Only data contained in UDP packets whose header checksums are
correct are passed on transparently to Port A.
TCP Client/Server
When configured as a TCP Server the
Diplomat jrN will wait until a remote
host attempts to establish a TCP Session with it. This requires a proper
three way handshake and matching Destination IP and Port Addresses
to those held within the jrN. The Source Port address and IP address of
the remote host are stored locally for use as a return address. The status
of the connection can be monitored through Port A.(see later) Should a
new attempt to initiate a TCP session be detected from the same IP
address then the existing session is considered broken and the
Diplomat
jrN returns to its initial waiting state after first issuing a Reset to the old
session. Similarly if the remote host sends a Reset or Close command
then the
Diplomat jrN terminates the current session and returns to the
waiting state.
These rules are relaxed if switch BSEXY in Configuration Byte B is set
to 1. If BSEXY is set to 1 any new host attempting to initiate a TCP
session will cause the current session to issue a Reset to the old ses-
sion and close down. The second attempt by the new host will be suc-
cessful. In addition if BSEXY is set to 1 any Reset packet received will
be actioned if it comes from the current host IP address but need not be
from the same port.
The switch BSEXY has no effect if the Firewall feature is enabled as this
alone will determine who is able to talk to the Diplomat jrN. New session
requests or Reset commands from any Firewall qualified host/ports will
be accepted and actioned as described above. The
Diplomat jrN can-
not initiate a TCP session when in Server mode.
When configured as a TCP Client the
Diplomat jrN will attempt to initiate
a TCP session with the Remote Server on the declared Server Port as
soon as the first character is received on Port A. The very first character
is consumed in the process. Only packets from the Remote Server IP
address and Port address will be processed.
