C Class Messages

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C-Class train describer messages provide updates relating to the stepping of train descriptions between TD berths.

There are four types of C-Class message:

Type Name Details
CA Berth Step The CA message is a 'step' message.

This moves the description from the 'from' berth, in to the 'to' berth, cancelling the description in the 'from' berth and overwriting any description in the 'to' berth.

CB Berth Cancel The CB message is a 'cancel' message.

This cancels the description in the 'from' berth.

CC Berth Interpose The CC message is an 'interpose' message.

This inserts the description in to the 'to' berth, overwriting any description in the 'to' berth.

CT Heartbeat The CT message is a 'heartbeat' message, periodically sent from a train describer.

Message Format

Messages are sent in JSON format:

{"CA_MSG":{"time":"1349696911000", "area_id":"SK", "msg_type":"CA", "from":"3647", "to":"3649", "descr":"1F42"}}
{"CB_MSG":{"time":"1349696911000", "area_id":"G1", "msg_type":"CB", "from":"G669", "descr":"2J01"}}
{"CC_MSG":{"time":"1349696911000", "area_id":"G1", "msg_type":"CC", "descr":"2J01", "to":"G669"}}
{"CT_MSG":{"time":"1349696911000", "area_id":"SA", "msg_type":"CT", "report_time":"1249"}}

Message Fields

Field CA CB CC CT Details
time Message time

UNIX timestamp in milliseconds since the UNIX epoch

area_id Alphanumeric code representing the TD area that the message originates from (see list of train describers)
msg_type Type of message

Can be CA_MSG, CB_MSG, CC_MSG or CT_MSG

from From berth (see TD berths page)
to To berth (see TD berths page)
descr Train description

Four-letter alphanumeric code representing the headcode or description of the train

report_time Reporting time


Working with C-Class data

In order help working with this data Network Rail have agreed to release a number of technical documents for each TD which will provide the information you require. While this process has begun it will take some time to complete - you should check the list of train describers for any information that may already have been released or user contributions.

  • Block Schematics - These are a visual representation of all the berths in a TD area. They show the stepping flow for every berth. It should be noted that not all berths shown are sent to the NROD platform.
  • Stepping Tables - These are the set of conditions which must be met in order for a description to step from one berth to another. (such as routes set, track circuits occupied etc.)


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