HL7 Sending Facility/Logical Link relationship    ICR (5698)

The VistA Radiology/Nuclear Medicine application uses
HL7 messages to communicate with the teleradiologists associated with the
National Teleradiology Program. The interface between these two applications
requires the software on the NTP side to query the VistA radiology database
when an order is received by NTP for a new patient.

The first iteration of the NTP query/Radiology response software utilized v2.3
HL7 messages and the destination of those responses was defined by the data
stored in the following two fields: TCP/IP ADDRESS (#400.01) and the TCP/IP
PORT (OPTIMIZED) (#400.08). These two fields reside within the HL LOGICAL LINK
(#870) file.

RA*5.0*107 is the second iteration of the NTP query/Radiology response
interface. This iteration will upgrade the HL7 version of the message from
V2.3 to V2.4 and the query will identify the DNS Domain (MSH-4.2) where the
responses are to be broadcast.

DNS Domain information is passed as a component of the Sending Facility
(MSH-4) field associated with the query.

The DNS Domain is then used to 'look up' the logical link record required to
complete the HL7 information transfer.