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Solstice X.25 9.2 Developer's Guide

6.4.10 N_PVC_ATTACH--PVC Attach

Synopsis
#include <stream.h>
 #include <netx25/x25_proto.h >

 struct strbuf ctlb;

 struct pvcattf attach;
 .
 .
 .
 ctlb.len = sizeof(struct pvcattf);
 ctlb.buf = (char *)attach;

 putmsg(x25_fd, &ctlb, NULL, 0);
Description

N_PVC_ATTCH is used when an application wants to attach to a PVC.The control part of the PVC Attach is defined by the pvcattf structure. The example shows a putmsg. Example 6-1 shows how a getmsg can be constructed.

The pvcattf structure is shown below: 

struct pvcattf {
        unsigned char     xl_type;      /* Always XL_CTL */
        unsigned char     xl_command;   /* Always N_PVC_ATTACH */
        unsigned short    lci;          /* Logical channel */
        uint32_t     link_id;      /* Link # */
        /* 0 for next 3 parameters implies use of default */
        unsigned char     reqackservice;
        unsigned char     reqnsdulimit;
        int               nsdulimit;
        int               result_code;     /* Non-zero - error */
};

The members used by pvcattf are:

Table 6-13 PVC Attach Parameters

Member 

Description 

lci

Contains the logical channel identifier of the required PVC. 

link_id

Denotes the particular link identifier for the PVC. 

reqackservice

If non-zero, denotes that the receipt acknowledgement service is requested by use of the D-bit. Setting reqackservice to 1 signifies receipt confirmation by the remote DTE. Setting reqackservice to 2 signifies receipt confirmation by the remote application.

In the case of receipt confirmation by the remote DTE, no acknowledgements are expected or given over the X.25 interface. In the case of receipt confirmation by the remote application, there is a one-to-one correspondence between D-bit data and acknowledgements with one data acknowledgement being received/sent for each D-bit data packet sent/received over the X.25 interface. 

reqnsdulimit

If this is non-zero, use value in nsdulimit.

nsdulimit

Specifies the packet concatenation limit for NSDUs. If you want to use this parameter, reqnsdulimit must be non-zero. (The X.25 driver does not look at reqnsdulimit if nsdulimit is zero.)

result_code

In the attach message sent to the user as acknowledgment, this member denotes whether the attach was successful. The possible values are defined in the netx25/x25_proto.h file.