Overview

This paper describes a method to encode and transport individual IRIG 106 Ch 10 data channels over UDP packets. The purpose of this method is to allow multiple seperate data channels to transmit their data to 1) a single UDP receiver in the case of unicast, or 2) multiple receivers in the case of multicast, and reconstruct the multiple data sources as a valid IRIG 106 Ch 10 data stream.

Traditional instrumentation consists of a recorder box with all the necessary various types of hardware interfaces, and a recording medium. The traditional instrumentation approach has several drawbacks.

• The type and number of recorded data channels are limited to the specific capability of the recorder.
• Data signals must travel to the recorder interface.

This paper describes a distributed instrumentation architecture where each data channel is implemented as a node on a suitable network (like Ethernet) and uses connectionless datagrams (like UDP) to transport data. Typically data interfaces are implemented using a small dedicated network aware processor such as those offered by Rabbit Semiconductor and Netburner. In a lab environment data interfaces can be inexpensive personal computers with the appropriate hardware interface. These data channel network nodes transmit data to one or more receivers which can then record, decode and display, and/or resend the data. Benefits of this architecture include:

• It is easy to "mix and match" various data interface to meet instrumentation requirements simply by plugging them into the network hub.
• The type and number of data interface channels is only limited by the number of network ports available
• Small dedicated data channel interfaces can be placed near the data source and sampled data is then transmitted over the network to the receiver.
• Multiple data recorders and/or data displays can receive all data channels.
• Data can be transported over existing TCP/IP networks

Key goals of this propose architecture are:

• Permit scalability only limited by network throughput and topology constraints
• Provide a design that easily accomodates new data types and hardware interface types
• Takes advantage of existing protocols and hardware
• Non-proprietary

Proposed Method

The basic unit of information is an IRIG 106 Ch 10 data packet consisting of an IRIG 106 header and data payload sections. If a complete IRIG 106 data packet can fit into a UDP packet then it can be transmitted as-is with no additional header or other data overhead. In many cases, though, a complete Ch 10 data packets is too big to fit into one UDP network packet. In this cases method to fragment those large packets is proposed.

Each UDP packet has a header. An

• Multicast Type - IRIG Header, IRIG Data, etc.
• Sequence Num - Header Seq Num + Data Seq Num (+ Subdata Seq Num)
• Channel ID - Same as IRIG
• Data Type - Same as IRIG IRIG Header packet has: Multicast Header IRIG Header Channel Specific Data IRIG Data packet (maybe in multiple UDP packets) has: Interpacket Header Data packet

Unaddressed issues

• Distribution of time
• Remote configuration of data channel interfaces

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