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AIX Version 4.3 Communications Programming Concepts

DLC FDDI Programming Interfaces

The data link control (DLC) fiber distributed data interface (FDDI) conforms to generic data link control (GDLC) guidelines except where noted below. Additional structures and definitions for DLC FDDI are found in the /usr/include/sys/fdlextcb.h file.

The following entry points are supported by DLC FDDI:

Note: The dlc prefix is replaced with the fdl prefix for the DLC FDDI device manager.
fdlclose Fully compatible with the dlcclose GDLC interface.
fdlconfig Fully compatible with the dlcconfig GDLC interface. No initialization parameters are required.
fdlmpx Fully compatible with the dlcmpx GDLC interface.
fdlopen Fully compatible with the dlcopen GDLC interface.
fdlread Compatible with the dlcread GDLC interface with the following conditions:
  • The readx subroutines may have DLC FDDI data link header information prefixed to the information field (I-field) being passed to the application. This is optional based on the readx subroutine data link header length extension parameter in the gdl_io_ext structure.
  • If this field is nonzero, DLC FDDI copies the data link header and the I-field to user space, and sets the actual length of the data link header into the length field.
  • If the field is 0, no data link header information is copied to user space. See the DLC FDDI Frame Encapsulation figure for more details.

Kernel receive packet function handlers always have the DLC FDDI data link header information within the communications memory buffer (mbuf), and can locate it by subtracting the length passed (in the gdl_io_ext structure) from the data offset field of the mbuf structure.

fdlselect Fully compatible with the dlcselect GDLC interface.
fdlwrite Compatible with the dlcwrite GDLC interface, with the exception that network data can only be written as an unnumbered information (UI) packet and must have the complete data link header prefixed to the data. DLC FDDI verifies that the local (source) service access point (SAP) is enabled and that the control byte is UI (0x03). See the DLC FDDI Frame Encapsulation figure for more details.
fdlioctl Compatible with the dlcioctl GDLC interface. The following ioctl operations contain FDDI-specific conditions on GDLC operations:

The following sections describe these conditions.


The ioctl subroutine argument structure for enabling a SAP, dlc_esap_arg, has the following specifics:


The ioctl subroutine argument structure for starting a link station, dlc_sls_arg, has the following specifics:


The ioctl subroutine argument structure for altering a link station, dlc_alter_arg, has the following specifics:


The enter_short_hold option is not supported.


The exit_short_hold option is not supported.


The add_group, or multicast address, option is supported by DLC FDDI as a six-byte value as described above in DLC_ENABLE_SAP (group address).

The grp_addr (group address) field for FDDI contains the full six-byte group address with the individual/group and universal/local control bits located in the most significant bit positions of the first (leftmost) byte.


The add_functional_address option is not supported.


The delete_functional_address option is not supported.


The delete group or multicast option is supported by the DLC FDDI device manager. The address being removed must match an address that was added with a DLC_ENABLE_SAP or DLC_ADD_GRP ioctl operation.


The device driver-dependent data returned from DLC FDDI for this ioctl operation is the fddi_ndd_stats_t structure defined in the /usr/include/sys/cdli_fddiuser.h file.


There is no protocol-specific data area supported by DLC FDDI for this ioctl operation.


The ioctype variable returned is defined as a DD_DLC definition and the subtype returned is DS_DLCFDDI.

Asynchronous Function Calls

DLC FDDI is fully compatible with the GDLC interface concerning asynchronous function calls to the kernel mode user.

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