Data Link Layer Network Components

3.3 Serial Line IP Support

The VxWorks target can support IP communication with the host operating system over serial connections using the following protocols:

Serial Line IP (SLIP)

Compressed Serial Line IP (CSLIP)

SLIP and CSLIP (SLIP with compressed headers) provide a simple form of encapsulation for IP datagrams on serial lines. Using SLIP or CSLIP as a network interface driver is a straightforward way to use TCP/IP software with point-to-point configurations such as long-distance telephone lines or RS-232 serial connections between machines.

PPP also provides a simple form of encapsulation for IP datagrams on serial lines. However, unlike SLIP or CSLIP, PPP provides support for multiple protocols on a single serial line, dynamic negotiation of the IP addresses at each end, and much more. Of course, it comes at the cost of additional overhead with each frame, and extra frames when the link is first created.

CAUTION: The VxWorks implementation of PPP supports only IP. For more information on PPP, see 3.4 PPP, the Point-to-Point Protocol for Serial Line IP.

3.3.1 Serial Line Driver Configuration

Configuring your system for SLIP requires configuring both target and host systems. See your host system's manual for information on configuring your host.

CAUTION: If you choose to use CSLIP, remember to make sure your host is also using CSLIP. If your host is configured for SLIP, the VxWorks target receives packets from the host, but the host cannot correctly decode the CSLIP packets from the target. Eventually TCP resends the packets as SLIP packets, at which time the host receives and acknowledge them. However, the whole process is slow. To avoid this, configure the host and target to use the same serial protocol.

To use SLIP with your VxWorks target, make the following configuration changes (for more information on configuring VxWorks, see the Tornado User's Guide: Projects):

Reconfigure VxWorks to include SLIP support. The relevant configuration macro is INCLUDE_SLIP.

Specify the device to be used for the SLIP connection, the SLIP Channel Identifier. The relevant configuration macro is SLIP_TTY. By default this is set to 1, which sets the serial device to /tyCo/1.

Specify the baud rate or SLIP Channel Speed (optional). The relevant configuration macro is SLIP_BAUDRATE. If this is not defined, SLIP uses the baud rate defined by your serial driver.

Specify the SLIP Channel Capacity (optional). The relevant configuration macro is SLIP_MTU. If you do not set this, the default value (576) will be used.

You can force the use of CSLIP when communicating with the host by setting the Transmit Header Compression Flag. The relevant configuration macro is CSLIP_ENABLE.

Otherwise, you can allow the use of plain SLIP unless the VxWorks target receives a CSLIP packet (in which case the target also uses CSLIP) by setting the Receive Header Compression Flag. The relevant configuration macro is CSLIP_ALLOW.

CAUTION: If you want to use VxSim for Solaris with PPP as the backend, you must reconfigure VxWorks to remove BSD 4.3 compatability. (The relevant configuration macro is BSD43_COMPATIBLE). Otherwise, you get an exception in the WDB task when the target server tries to connect to the WDB agent.