# Presentation: 659307

## Basic Information About the XASDI Feed

**A Telcon with Vendors**** **

- ASDI Vendors and Users

- FAA

- 18 May 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](http://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

**To set up your VPN, contact Phyllis Hutchinson, (617) 494-3607, **_**[hutchinson@volpe.dot.gov](mailto:hutchinson@volpe.dot.gov)**__**.**_
**If you have questions about the feed contact Phyllis or Matt Maki, (617) 494-3948, **_**[maki@volpe.dot.gov](mailto:maki@volpe.dot.gov)**__**.**_
- Phyllis or Matt will if necessary refer you to someone else.

## Slide 16

## 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.**