CAT reporting includes a requirement to distinguish orders routed internally (between two desks within the same market participant) from orders routed between different market participants. From section 3.2 of the document distributed with EP253, there is a comment which states:
DeskType(1033) to distinguish external and internal routes
However, no additional values appear to be added to DeskTypeCodeSet as part of this extension pack.
I am hoping to solicit guidance on how DeskType can be used to make this distinction between external and internal routes.
The CAT technical specs state “An Order Internal Route Accepted event is required to be reported from the perspective of the recipient desk, and indicates that an order was received by an internal destination.”
According to the FIX mapping rules that were defined for phase 2A (see https://www.fixtrading.org/packages/recommended-mapping-cat-phase-2a-errata-equities - tab “FIX RegulatoryReportType”), it is the presence of DeskType(1033) that distinguishes an Internal Route Accepted event (MEIR) from, say, an (external) Order Accepted (MEOA) event.
Note EP135 gives some examples of how to set the DeskType.
The CAT attribute receivingDeskType is only relevant (present) for internal route events. Hence, as @martinat pointed out, the presence of the FIX field DeskType(1033) in the TrdRegTimestamps component indicates that a FIX message going to CAT represents an internal route event as defined by CAT.