The ATN (Air Traffic Network) Directory is defined
by ICAO (International Civil Aviation Authority) as a part of the
overall ATN specifications. A major goal of the ATN Directory is to
support AMHS, which is described in Isode's AMHS
Solutions Page. Isode uses directory services as a core part of
its AMHS solution, and to enable the Extended ATS Message Service,
that requires support of the ATN Directory.
The ATN Directory has broader scope than AMHS, and is
appropriate for holding general information and in particular PKI
and security related information. The general purpose benefits of
a directory are discussed in more detail as a part of Isode's Government
Directory Solutions.
ATN Directory Architecture

The ATN Directory holds data in a hierarchy containing
information about CAAs (Civil Aviation Authorities) and other ATN
users. The above screen shot, using example data in Isode’s
directory administration tool (Sodium), shows how this data could
look. Data in the ATN Directory is available to users worldwide.

The diagram above shows how the ATN Directory is provided
by multiple directory servers, and can support AMHS and non-AMHS applications
utilizing data in the ATN Directory. Directory data will be stored
in a server operated by the data owner. This model allows a CAA to
start with a single directory server containing the CAA's own data
for local use. This isolated server can then be connected to other
servers using one or both of two mechanisms:
-
Chaining, where one server knows about data held
in another, and can connect to that server in order to retrieve
data for an end user or application.
-
Replication, where selected data is copied to another
server, thus making it available locally to users of that server.
This interconnection will allow incremental building of a distributed
global service.
What Isode Provides
Isode provides everything needed to build, operate and use an ATN directory:
- Directory Server. Isode's M-Vault
X.500 directory sever is the core component of an ATN Directory.
It has full compliance to the ICAO specifications for ATN Directory
products, and supports chaining, replication and security features.
- Secure Administration. Isode's Sodium
(Secure Open Data, Identity & User Manager) provides secure GUI
management of data.
- Operational Management. Isode provides tools for operating directory
services, and integration with standard network management systems.
- The Isode ATN Directory
API is use to connect AMHS applications to M-Vault X.500 using
X.500 DAP (Directory Access Protocol). This allows lookup of information
such as Certificates and AMHS parameters, and supports mappings between
AFTN addresses and X.400 O/R Addresses.
How AMHS Uses the ATN Directory
AMHS, as described in Isode's AMHS Solution Page, requires use of the
ATN Directory in order to provide the Extended ATS Message Service.
This provides the following benefits to the user:
- Recipient validation prior to and after message submission.
- Access to the end user X.509 certificate.
- Access to information about (potential) message recipients.
- Determining AMHS capabilities (e.g., maximum message size supported),
and in particular determining if the Extended ATS Service is supported
by the message recipient. This allows an originator to determine the
service level a recipient supports, and to only send messages with
Extended ATS Service capabilities to recipients that can correctly
handle this.
An additional benefit of using the ATN Directory is to manage address
mapping between X.400 OR Addresses and AFTN addresses. The following
diagram illustrates the information held in the directory to enable
this mapping:
Click Image for larger view
This mapping can be used by AFTN/AMHS Gateways, and also to enable
users to enter AFTN addresses and have them automatically converted.
Holding this mapping in the directory enables the same mapping information
to be easily used by all users and servers that need it, and to be conveniently
managed in a machine oriented format. Isode's ATN
Directory API provides simple calls to enable applications to easily
use this mapping.
Conformance
The ATN Directory is specified in "The ATN SARPS,
sub-volume 7, ATN Directory Services". This specification is
based on X.500 directory, as illustrated above. It is expected that
an operational ATN directory will be accessed by LDAP clients, as
well as clients using X.500 DAP (Directory Access Protocol).
Managing Data in an ATN Directory
The ATN Directory holds data that needs to be managed.
The tool to do this is often referred to as an ADUA (Administrative
Directory User Agent). Sodium (Secure Open Directory, User and Identity
Manager) is Isode's ADUA. Sodium provides a flexible GUI for data
administration with features that include:
-
Use of Strong Authentication and Signed Operations
may be chosen for all operations.
-
Support for the full ATN Directory Schema, that
may be extended as needed.
-
Display of data based on XML templates that may
be adapted for local requirements.
-
Templates for convenient entry and display of structured
attributes.
-
Integrated management of PKI (X.509) data and associated
identity management.

Operational Management
The ATN Directory is critical infrastructure that is important
in itself and as support for other applications. It is important to
monitor servers for availability and correct operation. Isode provides
two approaches to achieve this.
This first approach is use of SNMP (Simple Network Management
Protocol) for this. Isode's M-Vault X.500 can be monitored with standard
SNMP Management tools, such as HP OpenView or Solstice Enterprise Manager.
The big advantage of SNMP is that it enables operational management
to be integrated with management of networks and other components with
a single operator interface.
The second approach is Isode's DConsole tool (shown below),
which provides GUI monitoring of one or more M-Vault directory servers.
DConsole also has knowledge of directory replication and can monitor
replication agreements from both ends. This is important to ensure that
all servers are up to date with the most recent information.

DConsole: Click for larger image
Further Information
Isode has written a number of whitepapers that give more
information on the ATN Directory, and its use by AMHS:
- How AMHS users
benefit from directory
This paper looks at how an AMHS end application, such as an AMHS Terminal
sending and receiving flight plans, will utilize and benefit from
the directory. This paper assumes a very basic understanding of AMHS
and ATN Directory. For those unfamiliar with AMHS and ATN directory,
a simple introduction is given in the Isode introduction
to the Aviation industry.
- Deploying ATN Directory
with AMHS: What you can do now
Much discussion on ATN Directory has set out a big vision as to how
directories can interconnect globally and solve a wide range of problems.
This paper gives a much more pragmatic and short term view and looks
the nature of the ATN Directory and its deployment in support of AMHS
together with what products and systems can be deployed today.
- Addressing in AMHS:
Building a solution that works for the end-user
AMHS provides a complex addressing scheme, which is used in conjunction
with the ATN Directory. Users need to address messages, and the complexity
of the AMHS addressing has potential to make this difficult. This
whitepaper explains how AMHS and the ATN Directory can be used together
to provide a simple and effective user experience
- ATN Directory Vision:
An Infrastructure for Supporting AMHS and Ground to Ground Communication
This paper sets out the benefits of using an ATN Directory in support
of AMHS (Air Traffic Services (ATS) Message Handling Services) and
ground to ground messaging communication, and explains how this directory
could be deployed in conjunction with AMHS.
In conclusion: Why Isode?
Isode provides a complete solution for building an ATN Directoy.
Important characteristics of the Isode solution:
-
Close integration with Isode’s widely used
AMHS Servers.
-
Full ICAO ATN Directory Compliance, including full
replication support.
-
Excellent security features, including strong authentication
for all directory protocols and signed operations.
-
Comprehensive management and operational tools.
-
Mature and robust products deployed for many years
in demanding operational environments.