Point-to-Point Protocol
The two most popular Layer 2 protocols used on point-to-point links are High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP). The ISO standard for the much older HDLC does not include a Type field, so the Cisco HDLC implementation adds a Cisco-proprietary 2-byte
Type field to support multiple protocols over an HDLC link. PPP includes an architected Protocol field, plus a long list of rich features. Table 17-5 points out some of the key comparison points of these two protocols.
Padding field to the original HDLC framing. (The Padding field allows PPP to ensure that the frame has an even number of bytes.)
Type field to support multiple protocols over an HDLC link. PPP includes an architected Protocol field, plus a long list of rich features. Table 17-5 points out some of the key comparison points of these two protocols.
Table 17-5 HDLC and PPP Comparisons
Padding field to the original HDLC framing. (The Padding field allows PPP to ensure that the frame has an even number of bytes.)
Figure 17-2 HDLC and PPP Framing Compared
