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unnumbered acknowledgement (UA)

The Unnumbered Acknowledgement (UA), the acknowledgement without sequence number, is used in the HDLC protocol to confirm that a connection has been established on the link layer and that the transmission is in spontaneous mode

. The UA message is used to acknowledge and accept U commands, such as Set Asynchronous Balanced Mode (SABM) and Disconnect (DISC). These commands basically execute a change to a different state than the previous one, from Asynchronous Balanced Mode (ABM) to Asynchronous Disconnect Mode (ADM) or vice versa.

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Englisch: unnumbered acknowledgement - UA
Updated at: 17.11.2012
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