A publisher sends a SUBSCRIBE_OK control message for successful subscriptions.
SUBSCRIBE_OK Message {
Type (i) = 0x4,
Length (16),
Request ID (i),
Track Alias (i),
Expires (i),
Group Order (8),
Content Exists (8),
[Largest Location (Location)],
Number of Parameters (i),
Subscribe Parameters (..) ...
}
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Request ID: The Request ID of the SUBSCRIBE this message is replying to Section 8.7.
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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 SUBSCRIBE_OK that uses the same Track Alias as a different track with an active subscription, it MUST close the session with error 'Duplicate Track Alias'.
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Expires: Time in milliseconds after which the subscription is no longer valid. A value of 0 indicates that the subscription does not expire or expires at an unknown time. Expires is advisory and a subscription can end prior to the expiry time or last longer.
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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.
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Content Exists: 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).
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Largest Location: The location of the largest object available for this track. This field is only present if Content Exists has a value of 1.
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Subscribe Parameters: The parameters are defined in Section 8.2.1.