User`s manual

Appendix
276 AX3000 - User's Manual
The TCP port assignment can be either random or fixed. The default value
depends on the current network service.
The random method means the AX3000 TCP ports are different after every re-
boot. On booting the AX3000 generates a new base value. This value (x) is
between 1024 and 3072. For each session a range of 8 TCP ports is given:
session 1 = (x...x+7), session 2 = (x+8…x+15)... When a connection is
established the next port of the associated range is used. After 8 connections,
the same TCP port of a range is re-used.
The main benefit of this method is that if the AX3000 is suddenly powered off
(power cut for example), at the next boot time, the connections are immediately
accepted by the server. (i.e. the sessions are hooked on different sockets
because the TCP ports are different). However this does create ‘phantom’
sessions, as the initial sessions are still active from the server’s perspective,
and must be killed by the server.
This can be done with the ‘keepalive’ process, manually killing or rebooting.
In some situations it may be beneficial to have always the same TCP port for an
AX3000 resource (to avoid phantom sessions or to identify connections). This is
the fixed port assignment. With this method the AX3000 resources are always:
- session 1 = 1024, ..., session 8 = 1031,
- aux1 port = 1032, aux2 port = 1033, parallel port 1034.
- net1 = 1035, net2 = 1036,
- usb1 = 1037, ... ,usb4 = 1040
f) The 'Nagle's Algorithm' Parameter
The Nagle's Algorithm controls behaviour of the output network dataflow of a
TCP/IP device. This algorithm allows the number of datagrams sent by the
AX3000 to decrease. However a certain latency may be noticeable due to the
caching of data before transmission.
This algorithm is disabled to prioritise performance. However some operating
systems require this function to be enabled.
g) The 'Keepalive' Parameter
The keepalive is a mechanism that allows the AX3000 to regularly check its
TCP/IP connection status.