PEER protocol devices

Overview

The PEER connector implements the PEER protocol (ASTS USA, SM 9726), a peer-to-peer, session-based, vital serial signaling protocol used in railway and transit wayside applications. Unlike master/poll protocols, each pair of stations establishes a permanent communication session and exchanges the full operand interface of a station whenever a value changes; link integrity is maintained by periodic status/data messages paced by the heartbeat interval.

Compatible devices include the Ansaldo STS Microlok II. The protocol name is PEER; Microlok II is named only as a compatible device model.

Channel Configuration

Protocol Options

Not used in this driver.

Serial Settings

PEER is a point-to-point asynchronous serial protocol. The serial port settings default to values appropriate for a PEER link:

• Baud Rate: 19200 (supported range 300..38400)
• Data Bits: 8
• Stop Bits: 1
• Parity: None (message integrity is provided by the CRC-31 security field, so parity is not required)

Node Configuration

Station Configuration

A PEER station is identified by its own station address and the partner (peer) address. Vitality is a property of the station: a station defines vital or non-vital operands, never both. The configurable station parameters are:

• LocalAddress: this unit's PEER station address (source). Integer 0–65535.
• PeerAddress: partner peer station address (destination). Integer 0–65535.
• Vital: when checked, the station is vital and uses the Vital CRC-31 init value. Uncheck for a non-vital station.
• AckTimeout: acknowledge timeout in milliseconds. Default: 1000.
• HeartbeatInterval: heartbeat interval in milliseconds (≥100). Default: 4000.

The station string is semicolon-separated: LocalAddress;PeerAddress;Vital;AckTimeout;HeartbeatInterval (for example, 10;20;true;1000;4000 for a vital station with local address 10 and peer address 20).

Point Configuration

Address

The PEER driver uses a concatenated address format: <ClassCode><Index>[.<Bits>]

• ClassCode: the operand class — BO (Boolean Output), BI (Boolean Input), NO (Numeric Output), NI (Numeric Input).
• Index: ordinal position of the operand within its class (0-based, 0–255).
• .Bits: numeric size in bits — 8, 16, 24 or 32. Required for numeric operands (NO/NI), omitted for boolean operands (BO/BI).

Vitality is inherited from the station and is not encoded in the point address. Numeric values are transmitted big-endian on the wire.

Write Group

Output operands (BO/NO) are transmitted as a single data message carrying the whole operand interface of the station's class group. Output points are therefore configured within a WriteGroup AccessType so that all values of the group are sent together.

Notes and Limitations

The current release implements operand read/write over an established PEER link using Header Format 1 (sync $F4, 2-byte addressing). Message types supported: 01 (Initialization), 02 (Vital Data), 03 (Non-Vital Data), 04 (Status) and 06 (Service Signal / ACK-NAK). Message security uses CRC-31 (ATCS Specification 200, Appendix Y), with the Vital CRC-31 init value applied to vital messages.

The following are not included in this release: ATCS WAN addressing (Header Format 2, sync $F5), HMAC headers ($FE), diagnostic message types (05/07/08/09/0A) and OSS message types (0B/0C).

Driver Revision History

In this section...