RFC 1549 (rfc1549) - Page 3 of 18
PPP in HDLC Framing
Alternative Format: Original Text Document
RFC 1549 HDLC Framing Decvember 1993
1.2 Terminology
This document frequently uses the following terms:
datagram
The unit of transmission in the network layer (such as IP). A
datagram may be encapsulated in one or more packets passed to the
data link layer.
frame
The unit of transmission at the data link layer. A frame may
include a header and/or a trailer, along with some number of units
of data.
packet
The basic unit of encapsulation, which is passed across the
interface between the network layer and the data link layer. A
packet is usually mapped to a frame; the exceptions are when data
link layer fragmentation is being performed, or when multiple
packets are incorporated into a single frame.
peer
The other end of the point-to-point link.
silently discard
This means the implementation discards the packet without further
processing. The implementation SHOULD provide the capability of
logging the error, including the contents of the silently
discarded packet, and SHOULD record the event in a statistics
counter.
2. Physical Layer Requirements
PPP is capable of operating across most DTE/DCE interfaces (such as,
EIA RS-232-C, EIA RS-422, EIA RS-423 and CCITT V.35). The only
absolute requirement imposed by PPP is the provision of a full-duplex
circuit, either dedicated or circuit-switched, which can operate in
either an asynchronous (start/stop), bit-synchronous, or octet-
synchronous mode, transparent to PPP Data Link Layer frames.
Interface Format
PPP presents an octet interface to the physical layer. There is
Simpson