Figure 11.29 shows how U-frames can be used for connection establishment and connection release. Node A
asks for a connection with a set asynchronous balanced mode (SABM) frame; node B gives a positive response
with an unnumbered acknowledgment (UA) frame. After these two exchanges, data can be transferred between the
two nodes (not shown in the figure). After data transfer, node A sends a DISC (disconnect) frame to release the
connection; it is confirmed by node B responding with a UA (unnumbered acknowledgment).