Technical Standard: Networking Services (XNS), Issue 5.2 Draft 2.0
Copyright © 1999 The Open Group
XTI and TLI
XTI is based on the
System V Interface Definitions (SVID) Issue 2, Volume III,
Networking Services Extensions (see Referenced Documents).
XTI provides refinement of the Transport Level Interface (TLI)
where such refinement is considered necessary.
This refinement takes the form of:
additional commentary or explanatory text, in
cases where the TLI text is
either ambiguous or not sufficiently detailed
modifications to the interface, to cater for service and protocol problems
which have been fully considered.
In this case, it must be emphasised that such modifications are kept to an
absolute minimum, and are intended to avoid any fundamental changes to the
interface defined by TLI
the removal of dependencies on specific UNIX versions and specific
Restrictions Concerning the Use of XTI
It is important to bear in mind the following points
when considering the use of XTI:
It was stated that XTI "recommends" a
subset of the total set of functions and
facilities defined in TLI, and
also that XTI introduces modifications to some
of these functions and/or facilities where this is considered essential.
For these reasons, an application which is
written in conformance to XTI may
not be immediately portable to work over a provider which has been written in
conformance to TLI.
XTI does not address management aspects of the
interface, that is:
how addressing may be done in such a way that an application is truly
no selection and/or negotiation of service and protocol characteristics.
For addressing, the same is also true for TLI. In this case, it
is envisaged that addresses will be managed
by a higher-level directory function.
For options selection and/or negotiation,
XTI attempts to define a basic mechanism by
which such information may be passed across the
transport service interface, although
again, this selection/negotiation may be done by a higher-level management
function (rather than directly by the user).
Since address structure is not currently defined, the user protocol address
Relationship between XTI and TLI
The following features can be considered
as XTI extensions to the System V Release 3 version of TLI:
Some functions may return more error types.
The use of the [TOUTSTATE] error is generalised to almost all protocol
The transport provider identifier has been generalised to remove the dependence
on a device driver implementation.
Additional events have been defined to help applications make full use of the
asynchronous features of the interface.
Additional features have been introduced to
to allow fuller use of TCP transport providers.
Usage of options for certain types of transport service has been defined
to increase application portability.
Because most XTI functions require read/write access to the transport
provider, the usage of flags O_RDONLY and O_WRONLY
has been withdrawn from the XTI.
XTI checks the value of
and prevents an application from waiting forever when issuing
XTI allows an application to call
which is not bound to a local address.
XTI provides the additional utility functions