Layer 2 Leased Lines with HDLC
A leased line provides a Layer 1 service. In other words, it promises to deliver bits between the devices connected to the leased line. However, the leased line itself does not define a data link layer protocol to be used on the leased line. HDLC provides one option for a data link protocol for a leased line.
HDLC has only a few big functions to perform with the simple point-to-point topology of a point-to-point leased line. First, the frame header lets the receiving router know that a new frame is coming. Plus, like all the other data link protocols, the HDLC trailer has a Frame Check Sequence (FCS) field that the receiving router can use to decide whether the frame had errors in transit, and if so, discard the ...
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