ABSTRACT
The communicat ing entities defined i n a pro tocol specification assume various modes based on the nature o f the communicat ion. The specification defines w h i c h messages are sent by the communicat ing entities and i n wh ich mode the messages are va l id . Mas te r - slave communicat ion, as i n IBM's Synchronous Data L i n k Con t ro l (SDLC) pro tocol uses t w o modes for the protocol-master and slave. Telecom and W A N equipment often have a user mode and network mode. I n a pro tocol l ike Frame Relay L M I (Local M a n agement Interface), equipment located at a customer premise (termed Customer Premise Equipment or CPE) plays the role o f the user, whi le the Frame Relay switch interfacing to i t operates i n the ne twork mode. Here, the user node queries the ne twork equipment for the status o f the ne twork connections on the l ink th rough a Status Enquiry message. The ne twork equipment responds w i t h a Status message w i t h this in format ion .
