Basic Information About the XASDI Feed

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Basic Information About the XASDI Feed

• A Telcon with Vendors

ASDI Vendors and Users
FAA
18 May 2007
2
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

3
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.

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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

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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.

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What Is Different?

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

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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.

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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.

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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.

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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)
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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 vendors 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.

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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

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XML Schema

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

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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

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Support Provided by the FAA

• If you have questions about the MOA or the annual
  audits, contact Judy Morrill at
  judy.morrill_at_faa.gov
• If you have questions about VPN, XML, or
  operational issues, send an email to
  ASDI_Support_at_volpe.dot.gov
• Contact information revised 11/1/2007

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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.
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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.