Chapter 2 About NLI

The Solstice X.25 Network Layer Interface (NLI) provides acces to the X.25 Packet Layer Protocol (PLP). The NLI defines the format that STREAMS messages must take when interfacing to the network layer. This allows for the easy construction of user level library software, and means that applications map conveniently onto the STREAMS format.

2.1 NLI Overview

The Solstice X.25 Network Layer Interface provides access to the X.25 Packet Layer Protocol (PLP). The NLI defines the format that STREAMS messages must take when interfacing to the network layer. This allows for the easy construction of user level library software, and means that applications map conveniently onto the STREAMS format.

Solstice X.25 applications use the putmsg and getmsg system calls to interact with the PLP driver.

Figure 2-1 NLI and STREAMS

Messages passed using NLI have both a control and a data part. Primitives and associated parameters are passed to the X.25 driver using the control part of the message. Data, if there is any, is contained in the data part of the message.

Figure 2-2 NLI Message Format

Solstice X.25 NLI provides the following:

• NLI messages

  These determine the format of the control parts of putmsg and getmsg, and are used to communicate with the network.

• A series of ioctls

  These communicate with the Solstice X.25 code, rather than with the network.

• A series of library functions

  These are not part of the NLI, but can be used along with it.

2.2 NLI Commands

Solstice X.25 NLI provides a series of NLI commands contained within C structures. These determine the format of the control parts of putmsg and getmsg. The NLI commands correspond to X.25 packet types, and are used to communicate with the network. For example, when an application passes down the NLI command N_CI to a stream using putmsg, this is translated into an X.25 Call Connect by the PLP module. When the PLP module receives a Connect Indication, it translates it into an N_CI command which is passed up to the application using a getmsg system call.

Table 2-1 summarizes the structures and their corresponding Packet Types and NLI Commands. Refer to the sections indicated for detailed information.

Table 2-1 NLI Commands and Structures

NLI Command	X.25 Packet	NLI Structure	See section
N_Abort	Abort Indication	xabortf	"6.4.1 N_Abort--Abort Indication"
N_CC	Call Response/ Confirmation	xccnff	"6.4.2 N_CC--Call Response/Confirmation"
N_CI	Call Request/ Indication	xcallf	"6.4.3 N_CI--Call Request/Indication"
N_DAck	Data Acknowledgment Request/Indication	xdatacf	"6.4.4 N_DAck--Data Ack Request/Indication"
N_Data	Data	xdataf	"6.4.5 N_Data--Data"
N_DC	Clear Confirm	xdcnff	"6.4.6 N_DC--Clear Confirm"
N_DI	Clear Request/Indication	xdiscf	"6.4.7 N_DI--Clear Request/Indication ""6.4.13 N_RI--Reset Request/Indication"
N_EAck	Expedited Data Acknowledgment	xedatacf	"6.4.8 N_EAck--Expedited Data Acknowledgement"
N_EData	Expedited Data	xedataf	"6.4.9 N_EData--Expedited Data"
N_RC	Reset Response/Confirm	xrscf	"6.4.12 N_RC--Reset Response/Confirm"
N_RI	Reset Request/Indication	xrstf	"6.4.13 N_RI--Reset Request/Indication"

The following commands and structures are also provided. They do not correspond to X.25 packet types:

Table 2-2 PVC and Listening Commands and Structures

NLI Command	NLI Structure	Description	See section
N_PVC_ATTACH	pvcattf	Specify X.25 service to use with PVC	"6.4.10 N_PVC_ATTACH--PVC Attach "
N_PVC_DETACH	pvcdetf	Specify X.25 service to stop using with PVC	"6.4.11 N_PVC_DETACH--PVC Detach "
N_Xcanlis	xcanlisf	Cancel listening	"6.4.14 N_Xcanlis--Listen Cancel Command/Response"
N_Xlisten	xlistenf	Listen for incoming calls	"6.4.15 N_Xlisten--Listen Command/Response"

2.3 NLI ioctls

Solstice X.25 NLI provides a series of ioctls. These are used to communicate with the Solstice X.25 code itself, rather than with the network. For example, ioctls are used to gather statistics about a link, or to set the parameters to be used on a link. This distinguishes them from the NLI Commands given in Table 2-1. To use them together, you might use an ioctl to set the parameters to be used on a link and then use an NLI command to initiate a call over the link. The NLI ioctls can be used for the following purposes:

• Operating on the Network User Identifiers mapping table

• Reading and resetting statistics

• Getting status information

• Operating on the X.25 Routing Table

• Overriding settings made using x25tool

2.4 Support Functions

Solstice X.25 also includes a library of Sun-specific support functions that you can use when writing applications. These are not part of the NLI, but can be used in NLI applications.

2.5 Support for OSI Connection-Mode Network Service (OSI CONS)

The Solstice X.25 NLI can support applications which use the OSI Connection-Mode Network Service, as defined in X.223 and ISO 8878. To be consistent with these documents, this service is referred to as OSI CONS in this guide. This service provides the mapping between the OSI CONS primitives and the elements of the X.25 Packet Layer Protocol.

2.6 Addressing

When making straightforward X.25 calls, you need to work with DTE and LSAP addresses. When making OSI CONS calls, you use NSAP and LSAP addresses. See "6.3.1 xaddrf--Define Addressing" for more information.

2.7 Facilities and QOS Parameters

The X.25 Recommendations allow service providers to offer a number of optional facilities, that affect the way that calls are made and handled.

• Non-OSI extended addressing

• X.25 fast select request/indication with no restriction on response

• X.25 fast select request/indication with restriction on response

• X.25 reverse charging

• X.25 packet size negotiation

• X.25 window size negotiation

• X.25 network user identification

• X.25 Recognized Private Operating Agency selection

• X.25 Closed User Groups

• X.25 programmable facilities

• X.25 call deflection.

The following Quality of Service (QOS) parameters are available when writing OSI CONS applications:

• Throughput Class

• Minimum Throughput Class

• Target Transit Delay

• Maximum Acceptable Transit Delay

• Use of Expedited Data

• Protection

• Priority

• Receipt Acknowledgment

2.8 Operating System Support

Solstice X.25 9.2 will run on Solaris 7 or Solaris 8. It is not compatible with earlier versions of the Solaris operating system.