The DSC segment is used in the continuation protocol.
(Definition from DSC.1 in Ch. 2)
Definition: This field contains the continuation pointer. In an initial query, this field is not present. If the responder returns a value of delete indicator or not present, then there is no more data to fulfill any future continuation requests. For use with continuations of unsolicited messages, see chapter 5 and section 2.10.2, "Continuation messages and segments." Note that continuation protocols work with both display- and record-oriented messages.
(Definition from MSH.14 in Ch. 2)
Definition: This field is used to define continuations in application-specific ways.
Only the sender of a fragmented message values this field.
Definition: Indicates whether this is a fragmented message (see Section 2.10.2, "Continuation messages and segments"), or if it is part of an interactive continuation message (see Section 5.6.3, "Interactive continuation of response messages").
Refer to HL7 Table 0398 – Continuation Style Code in Chapter 2C, Code Tables, for valid values.