presented to: by: date: federal aviation administration basic information about the xasdi feed a...

Presented to:

By:

Date:

Federal AviationAdministrationBasic Information

About the XASDI Feed

A Telcon with Vendors

ASDI Vendors and Users

FAA

18 May 2007

XASDI Telcon with Vendors2Federal Aviation

AdministrationMay 18, 2007

Agenda

• Introduction• What is changed and unchanged?• VPN Over the Internet• Batching of messages• Packet header• Compression• XML schema• Support provided by the FAA• Schedule



Introduction

• The ASDI feed provides near-real time flight data.

• Since 1992 this data has been in plain, ASCII text.

• The FAA is now redesigning the feed so that the data is in XML.

• This redesign is causing various aspects of the feed to change.

• This telcon covers the basics and allows vendor to ask questions.



ASDI Web Page

• For the latest version of all XASDI documentation as well as sample data files, go to

www.fly.faa.gov/ASDI/asdi.html



What is the Same?• The application level method of connecting

is the same.– The client must provide a vendor name and

password.– Note: New vendor names and passwords will be

used for the XASDI feed.

• The method of transmission is still a TCP/IP socket.– Note: New IP addresses and port numbers are used.

• The content of the data is the same.– It is in a different format.– Minor exceptions: Dates are given more fully, and

flight index in RT message is no longer provided.



What Is Different?

• VPN Over the Internet• Batching of messages• Packet header• Compression• XML Schema



VPN Over the Internet

• With the old feed, each vendor was required to install a dedicated line.

• With the new feed, vendors will use a VPN over the Internet.– Dedicated lines are not allowed (except for vendors

that carry CDM data).

• See “XML ASDI Over the Internet: VPN End User Requirements and Guidelines” on the web site.



Batching of Messages

• In the old feed, messages were sent individually.

• Since XML uses more bandwidth, messages are batched and compressed to make more efficient use of bandwidth.

• The current thinking is that at most 64 messages will be batched together into a packet, though this is a configurable number that might be changed.

• At a busy time, the feed contains perhaps 110 messages/second.



Packet Header• The length of the header is always 32 bytes.• The header is not compressed.• The header is in network format and must

be converted to host format before processing it.

• Five fields are in the header.– The date/timestamp is 14 characters in

yyyymmddhhmmss format.– The other four fields in the header are 4-byte

integers.

• The header is followed immediately by the compressed data for, say, 64 messages.



Structure of the Packet

Timestamp (16 bytes)

Data Type (4 bytes)

Sequence Number (4 bytes)

Compressed Size (4 bytes)

Decompressed Size (4 bytes)

Data (as given by the Compressed Size field)



Compression

• If the XML were uncompressed, it would use an unacceptably large amount of bandwidth.

• To deal with this problem, messages are batched and then compressed.

• The vendor’s client software will need to unzip the compressed payload of each packet.

• The last field in the packet header gives the size of the buffer needed for the uncompressed data.



XML Schema

• The ASDI data is fully formed using XML– Lowest level of data items are described by XML

elements and attributes

• The ASDI XML documents are validated using XML Schema Definitions (XSD)– XSDs ensure that only valid data is sent to each

client– Definitions are based on NAS and ETMS standards



XML Schema

• There are five schemas used to describe and validate ASDI data– TFMS_XIS.xsd– ASDI.xsd– MessageMetaData.xsd– NasXCommonMessages.xsd– NasXCoreElements.xsd



XML Schema

• The ASDI XSD uses inheritance of common message and data types

• XSD namespaces are used to access inherited schema definitions

• Each ASDI XML document contains a preamble followed by multiple ASDI messages– The preamble is included at the beginning of each

ASDI XML document and lists the namespaces used to describe and validate the ASDI data



Support Provided by the FAA

• If you have questions about the MOA or the annual audits, contact Judy Morrill at [email protected]

• If you have questions about VPN, XML, or operational issues, send an email to [email protected]

Contact information revised 11/1/2007



Schedule

Already accomplished XASDI Server made available for vendor testing.

Summer 2007 XASDI Server is deployed operationally. (Legacy ASDI Server runs in parallel.)

January 2008 Legacy ASDI Server is decommissioned.



Summary

• The XML version of the ASDI server is coming. Get ready for it.

• Changing over to XML will be a significant programming task.

• Once everyone is switched to XML, it will be easier to introduce enhancements into the feed.

presented to: by: date: federal aviation administration basic information about the xasdi feed a...

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