Teldat REGESTA 1 Installation And Configuration Manual page 38

4 Configuration
4.4.2.9 Serial Line IP (SLIP)
The SLIP protocol (Serial Line Internet Protocol) is an IP datagram transmission standard for serial lines. It was de-
signed to work over serial ports and modem connections. The specification for this can be found in RFC 1055.
SLIP is the predecessor of the more commonly used and extended PPP (Point-to-Point Protocol). However, with mi-
cro-controllers, SLIP encapsulation for IP packets continues to be used as it has a very small overhead.
SLIP needs its IP address to be configured before being established.
So that SLIP runs correctly, its serial port configuration needs to be 8 data bits with no parity. One version of SLIP
with header compression is CSLIP (Compressed SLIP). This was developed through Van Jacobson and its role was
to reduce the typical 40 byte header to 3 or 5 bytes helped by the fact that many of the header fields do not vary dur-
ing a connection.
In the REGESTA 1 router, SLIP is configured so that the protocol knows the local IP address and the IP address of
its remote pair beforehand. I.e. there is no dynamic addressing so the two connected devices must know their re-
spective IP addresses. Both addresses must pertain to the same network.
You must also program the type of SLIP to use. It's very important that both devices are configured with the same
mode (slip, cslip, slip6, cslip6).
The mode that the REGESTA 1 router uses to route the IP datagrams, which come through the GPRS interface, is
based on the creation of visible ports. This routing mode DNAT (Destination-NAT) is valid to create the visible port.
When the device is configured in SLIP mode, all IP datagrams with source in the GPRS network that have the port
configured in visible port as destination TCP port, are sent through the SLIP serial port to the remote terminal. All the
IP datagrams with source in the remote terminal, which are sent through the SLIP serial port, are sent to the GPRS
network.
The following image shows a typical user scenario for the SLIP protocol in a SCADA environment:
Serial Line IP (SLIP)
Fig. 14:
For the SLIP protocol to be operative, you need to configure the SLIP mode through the AT*Z18=2 command. When
you change the configuration from IEC or TRANSPARENT to SLIP, you need to reset the device so the configuration
activates.
When the device starts up in SLIP mode, its behavior is different than in IEC or TRANSPARENT modes. In this
mode, the device immediately starts up in the AT commands and remains in command mode for 120 seconds or until
the ATO command is entered. Each time you enter a valid AT command (the device must return an OK) the counter
for 120 seconds restarts.
Teldat REGESTA 1 (c)2009
GSM/GPRS ROUTER Release 1.2
SCADA IEC-101/102 gateway
Enter in COMMAND mode.
Type ATO or wait 120 secons, to switch DATA mode .....
AT+CGMR
APP: 1.2 GSM: 07.03.940
OK
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Teldat S.A.
REGESTA 1