Reliable Transport of TLPs Across Each Link
The function of the Data Link Layer (shown in Figure 5-1 on page 210) is two fold:
'Reliable' transport of TLPs from one device to another device across the Link.
The receiver's Transaction Layer should receive TLPs in the same order that the transmitter sent them. The Data Link Layer must preserve this order despite any occurrence of errors that require TLPs to be replayed (retried).
Figure 5-1. Data Link Layer
The ACK/NAK protocol associated with the Data Link Layer is described with the aid of Figure 5-2 on page 211 which shows sub-blocks with greater detail. For every TLP that is sent from one ...
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