2    Data Link Provider Interface

Digital UNIX provides the dlb STREAMS pseudodriver, which is a partial implementation of the Data Link Provider Interface (DLPI).

This chapter describes the dlb STREAMS pseudodriver and the basics of DLPI. A PostScript copy of the DLPI specification ( dlpi.ps) is located in the /usr/share/doclib/dlpi directory.

Note

You must have the OSFPGMK200 subset installed to access the DLPI specification online.

Figure 2-1 highlights the data link interfaces and shows their relationship to the rest of the network programming environment.

Figure 2-1: DLPI Interface

Note

The dlb STREAMS pseudodriver supports a subset of DLPI primitives. See Section 2.4 for a list of the supported primitives.

The data link interface is the boundary between the network and data link layers of the OSI reference model. A network application, or data link service user (DLS user), uses the services of the data link interface. A driver, pseudodriver, or data link service provider (DLS provider), provides the services to the data link layer.

DLPI specifies a STREAMS kernel-level service interface that maps to the OSI reference model. It defines an interface to the services of the data link layer and provides a definition of service primitives that make up the interface.

Figure 2-2 shows the components of DLPI. The DLS user communicates with the DLS provider using request/response primitives; the DLS provider communicates with the DLS user with indication/confirmation primitives.

Figure 2-2: DLPI Service Interface

The primitives that Digital UNIX supports are listed in Section 2.4.

2.1    Modes of Communication

DLPI supports three modes of communication:

2.2    Types of Service

This section describes the types of service, or phases of communication, supported by DLPI. Note that the types of service available depend on the mode of communication (connection, connectionless, acknowledged connectionless) between the DLS provider and the DLS user.

DLPI supports the following types of service:

2.2.1    Local Managment Services

The local management services apply to all three modes of communication supported by DLPI. They enable a DLS user to initialize a Stream that is connected to a DLS provider and to establish an identity with that provider. The local management services support the following:

2.2.2    Connection-Mode Services

The connection-mode services allow two DLS users to establish a data link connection between them to exchange data, and to reset the link and release the connection when the conversation is through. The connection-mode services support the following:

2.2.3    Connectionless-Mode Services

The connectionless-mode services allow DLS users to exchange data without incurring the overhead of establishing and releasing a connection. The connectionless-mode services support the following:

2.2.4    Acknowledged Connectionless-Mode Data Transfer

The acknowledged connectionless-mode data transfer services are designed for general use for the reliable transfer of data between peer DLS users. These services are intended for applications that require acknowledgment of data transfer between local area networks, but wish to avoid using the connection mode services. In-sequence delivery is guaranteed for data sent by the initiating station. The following services are supported:

2.3     DLPI Addressing

Each DLPI user must establish an identity to communicate with other data link users. This identity consists of the following pieces of information:

The format of the DLSAP address is an unsigned character array containing the Medium Access Control (MAC) addresses followed by the bound Service Access Point (SAP). The SAP is usually two bytes in the case of Ethernet, or one byte in the case of ISO 8802-2 (IEEE 802.2). The one exception is when a HIERACHICAL DL_SUBS_BIND_REQ is processed. In that case, the DLSAP address consists of the MAC address, the SNAP SAP (0xAA), and a five-byte SNAP.

Figure 2-3 illustrates the components of this identification approach.

Figure 2-3: Identifying Components of a DLPI Address

The PPA is the point at which a system attaches itself to a physical communications medium. All communication on that physical medium funnels through the PPA. On systems where a DLS provider supports more than one physical medium, the DLS user must identify the medium through which it will communicate. A PPA is identified by a unique PPA identifier.

DLPI defines the following two styles of DLS provider, which are distinguished by the way they enable a DLS user to choose a particular PPA:

2.4     DLPI Primitives

Table 2-1 lists and describes the DLPI primitives that Digital UNIX supports in the dlb STREAMS pseudodriver. For a complete list of DLPI primitives see the DLPI specification in the /usr/share/doclib/dlpi/dlpi.ps file.

Table 2-1: DLPI Primitives Supported in Digital UNIX

Primitive Description
DL_ATTACH_REQ Requests that the DLS provider associate a physical point of attachment (PPA) with a Stream. Used on style 2 providers only.
DL_BIND_REQ Requests that the DLS provider bind a DLSAP to the Stream. The DLS user must identify the address of the DLSAP to be bound to the Stream.
DL_BIND_ACK Reports the successful bind of a DLSAP to a Stream, and returns the bound DLSAP address to the DLS user. Generated in response to a DL_BIND_REQ.
DL_UNBIND_REQ Requests that the DLS provider unbind the DLSAP that was bound by a previous DL_BIND_REQ from this Stream.
DL_DETTACH_REQ Requests the DLS provider disassociate a physical point of attachment (PPA) with a stream.
DL_DISABMULTI_REQ Request the DLS provider disable the multicast address.
DL_ENABMULTI_REQ Request the DLS provider enable a specific multicast address. (The current implementation of the DLB driver requires the state to be DL_IDLE.)
DL_ERROR_ACK Informs DLS user of a previously issued request which was invalid.
DL_INFO_ACK Response to DL_INFO_REQ primitive; conveys information about the DLPI stream.
DL_INFO_REQ Requests the DLS provider return information about the DLPI stream.
DL_OK_ACK Acknowledges to the DLS user that a previously issued request primitive was successfully received.
DL_PHYS_ADDR_REQ Requests that the DLS provider return either the default (factory) or current value of the physical address associated with the Stream, depending upon the value of the address type selected in the request.
DL_PHYS_ADDR_ACK Returns the value for the physical address to the link user in response to a DL_PHYS_ADDR_REQ.
DL_SUBS_BIND_ACK Is the positive response to a DL_SUBS_BIND_REQ from the DLS provider.
DL_SUBS_BIND_REQ Requests the DLS provider bind a subsequent DLSAP to stream. There are two classes of subsequent bind requests: HIERACHICAL and PEER.

HIERACHICAL requests are only valid for SNAPs (see the IEEE 802.1 specification) and you must have bound to the SNAP sap (0xAA) with a DL_BINDS_REQ before issuing the DL_SUBS_BIND_REQ for the SNAP.

The PEER request binds to additional saps but does not change the DLSAP address of the stream.

DL_SUBS_UNBIND_REQ Requests the DLS provider to unbind a sap which was previously bound by a DL_SUBS_BIND_REQ.
DL_TEST_CON Conveys that a DLSDU TEST response was received in response to a DL_TEST_REQ.
DL_TEST_IND Conveys to the DLS user that a TEST cmd DLSDU was received.
DL_TEST_REQ Requests the DLS provider to transmit a TEST cmd DLSDU on behalf of the DLS user.
DL_TEST_RES Requests the DLS provider to send a TEST response command on behalf of the DLS user.
DL_UDERROR_IND Informs DLS user that a previously sent DL_UNITDATA_REQ failed.
DL_UNITDATA_REQ Conveys one DLSDU from the DLS user to the DLS provider for transmission to a peer DLS user.
DL_UNITDATA_IND Conveys one DLSDU from the DLS provider to the DLS user.
DL_XID_CON Conveys that a XID DLSDU was received in response to a DL_XID_REQ.
DL_XID_IND Conveys to the DLS user that a XID DLSDU was received.
DL_XID_REQ Requests the DLS provider to transmit a XID DLSDU on behalf of the DLS user.
DL_XID_RES Requests the DLS provider to send a XID DLSDU on behalf of the DLS user. This is in repsonse to a DL_XID_RES.

2.5    Identifying Available PPAs

When compiled and run as root on a Digital UNIX system, the following program opens the STREAMS device /dev/streams/dlb and prints to the screen the PPAs available on the system. The PPA number should be passed in using the dl_ppa field of the DL_ATTACH_REQ DLPI primitive. 

#include <sys/ioctl.h>
#include <stropts.h>
#include <errno.h>
#include <fcntl.h>

 

#define ND_GET ('N' << 8 + 0)
#define BUFSIZE 256

 

main()
{
        int i;
        int fd;
        char buf [BUFSIZE];
        struct strioctl stri;

 

        fd = open("/dev/streams/dlb", O_RDWR, 0);
        if (fd < 0) {
                perror("open");
                exit(1);
        }

 

        sprintf(buf, "dl_ifnames");
        stri.ic_cmd = ND_GET;
        stri.ic_timout = -1;
        stri.ic_len = BUFSIZE;
        stri.ic_dp = buf;

 

        if (ioctl(fd, I_STR, &stri) < 0) {
                perror("ioctl");
                exit(1);
        }

 

        printf("Valid PPA names on this system are:\n");
        for (i=0; i<stri.ic_len; i++)  {
                if (buf[i] == 0)
                        printf(" ");
                else
                        printf("%c",buf[i]);
        }
        printf("\n");
}
#  a.out
Valid PPA names on this system are: 
sscc0 (PPA 1) ln0 (PPA 2) dsy0 (PPA 3) dsy1 (PPA 4) \
sl0 (PPA 5) sl1 (PPA 6) lo0
#