Compare line discipline methods ENQ/ACK and Poll/ Select?

Compare line discipline methods ENQ/ACK and Poll/ Select?

• ENQ/ACK coordinates which device may start a transmission and whether or not the intended recipient is ready and enabled. 
• Using ENQ/ACK, a session can be initiated by either station on a link as long as both are of equal rank. 
• In both half-duplex and full-duplex transmission, the initiating device establishes the session. 
• In half duplex, the initiator then sends its data while the responder waits. The responder may take over the link when the initiator is finished or has requested a response. 
• In full duplex, both devices can transmit simultaneously once the session has been established.

POLL/SELECT: 

• The poll/select method of line discipline works with topologies where one device is designated as a primary station and the other devices are secondary stations.
• Multipoint systems must coordinate several nodes, not just two. 
• The primary device controls the link and the secondary device follow sits instruction It is up to the primary to determine which device is allowed to use the channel data given time