Solstice PPP 3.0.1 Administration Guide

PPP Frames

PPP frames encapsulate packets of information that contain either configuration information or data. The PPP frames have the general format shown in Figure A-2:

Figure A-2 PPP Frame Format

Graphic

Address Field

The address field is one octet in length, and is part of the HDLC-like framing for PPP defined by RFC 1662. It is always set to 0xff, which is the All-Stations address. Frames that contain any other address value are discarded silently.

Control Field

The control field is one octet in length, and is part of the HDLC-like framing for PPP defined by RFC 1662. It is always set to 0x03, which is the Unnumbered Information (UI) command with the Poll/Final bit set to zero. Frames that contain any other control value are silently discarded.

Protocol Id

The protocol id is one or two octets in length, and its value identifies the type of information contained in the information field of the frame.

The following values are significant for Solstice PPP:

0x0001 Padding protocol

0x0021 Internet protocol

0x002d Van Jacobson Compressed TCP/IP

0x002f Van Jacobson Uncompressed TCP/IP

0x8021 Internet Protocol Control Protocol

0xc021 Link Control Protocol

0xc023 Password Authentication Protocol

0xc223 Challenge Handshake Authentication Protocol

Information Field

The Information field is zero or more octets. The maximum length of the information field is determined by the maximum receive unit (MRU), which is a negotiated parameter. It is set to 1500 (for Ethernet networks) by default.

The information field can contain configuration information or data. In the case of Solstice PPP, the data represents compressed or uncompressed IP datagrams.