PUBLISH

The publisher sends the PUBLISH control message to initiate a subscription to a track. The receiver verifies the publisher is authorized to publish this track.

PUBLISH Message {
  Type (i) = 0x1D,
  Length (i),
  Request ID (i),
  Track Namespace (tuple),
  Track Name Length (i),
  Track Name (..),
  Track Alias (i),
  Group Order (8),
  ContentExists (8),
  [Largest (Location),]
  Forward (8),
  Number of Parameters (i),
  Parameters (..) ...,
}

• Request ID: See Section 8.1.

• Track Namespace: Identifies a track's namespace as defined in (Section 2.4.1)

• Track Name: Identifies the track name as defined in (Section 2.4.1).

• Track Alias: The identifer used for this track in Subgroups or Datagrams (see Section 9.1). The same Track Alias MUST NOT be used to refer to two different Tracks simultaneously. If a subscriber receives a PUBLISH that uses the same Track Alias as a different track with an active subscription, it MUST close the session with error 'Duplicate Track Alias'.

• Group Order: Indicates the subscription will be delivered in Ascending (0x1) or Descending (0x2) order by group. See Section 6. Values of 0x0 and those larger than 0x2 are a protocol error.

• ContentExists: 1 if an object has been published on this track, 0 if not. If 0, then the Largest Group ID and Largest Object ID fields will not be present. Any other value is a protocol error and MUST terminate the session with a Protocol Violation (Section 3.4).

• Largest: The location of the largest object available for this track.

• Forward: The forward mode for this subscription. Any value other than 0 or 1 is a Protocol Violation. 0 indicates the publisher will not transmit any objects until the subscriber sets the Forward State to 1. 1 indicates the publisher will start transmitting objects immediately, even before PUBLISH_OK.

• Parameters: The parameters are defined in Section 8.2.1.