I amend my statement as far as "all 8 messages at once" since most messages only go one way. Like so:

• Response message - RECEIVE to SEND task on both sides (ILS and EMS will handle this message - contains code notifying that message was accepted or rejected by socket)
• Ping message - SEND to RECEIVE task (this acts as the "keep alive" mechanism) Pings are sent from both sides at 40-second intervals.
• Add message - ILS to EMS only
• Delete message - ILS to EMS only
• Return message - ILS to EMS only
• Request message - ILS to EMS only
• Status Check message - ILS to EMS only
• Status message - EMS to ILS only

As a visual representation, a typical transaction would follow this order:

ILS            EMS
---            ---
Request   -->  
          <--  Response (request accepted/rejected)
          <--  Status (requested item in available/unavailable)
Response  -->
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