PPP Architecture


Upper-Layer Protocols {such as IP, IPX, AppteTalk}





Protocol (NCP)



(specific to each

network-layer protocol)

© 2004 Cisco Systems, Inc. All rights reserved. BCRAN v2.1—3-3

PPP is a nonproprietary protocol that is defined by a series of open Internet standards called RFC standards. For this reason, PPP is referred to as a standards-based protocol.

PPP also describes mechanisms for the following features:

■ Network-protocol multiplexing

■ Link configuration

■ Link-quality testing Authentication Header compression Error detection Link-option negotiation

PPP also includes these functional components:

Method for encapsulating datagrams over serial links, based on the International Organization for Standardization (ISO) HDLC protocol (not Cisco HDLC)

Link control protocol (LCP) for establishing, configuring, and testing the data-link connection

PPP IP Control Protocol (IPCP), for managing TCP header compression and IP address negotiation


Network Control Protocols (NCPs) for establishing and configuring various network-layer protocols such as IP, IPX, and AppleTalk (for example, IPCP is the NCP for IP)

Note Authentication level for access control is optional.

The following is a partial list of RFCs of interest for access products: 1220: "Point-to-Point Protocol Extensions for Bridging" 1332: "PPP IP Control Protocol (IPCP)" 1378: "PPP AppleTalk Control Protocol (ATCP)" 1492: "Access Control Protocol or TACACS+" 1549: "PPP in HDLC Framing"

1552: "The PPP Internetwork Packet Exchange Control Protocol (IPXCP)" 1570: "PPP LCP Extensions" 1661: "The Point-to-Point Protocol (PPP)" 1990: (Replaces RFC 1717): "The PPP Multilink Protocol (MP)"

HDLC and PPP Frames

This topic describes the similarities and differences between HDLC and PPP frames.

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