Point-to-Point Protocol (PPP) and driver
The Point-to-Point Protocol (PPP) is a method for
transmitting datagrams over point-to-point serial links.
This implementation of PPP is compliant with
RFC 1332 (Internet Protocol Control Protocol (IPCP)),
RFC 1333 (Link Quality Monitoring (LQM)),
RFC 1334, (PPP Authentication Protocols),
RFC 1548, (Point-to-Point Protocol (PPP)),
RFC 1618 (PPP over ISDN),
RFC 1962 (Compression Control Protocol (CCP)), and
RFC 1990 (Multilink Protocol (MP)).
PPP is not specific to IP
like SLIP, but the current
implementation only supports transmission of IP
datagrams over serial links.
This implementation permits the use
of an asynchronous driver that can perform the packetization and
framing required by PPP to send data over a smart
third-party serial port device. Such a driver
offloads this processing from PPP onto the hardware.
Third-party drivers and modules are specified by a push
option specified for a link (physical device) definition in
the PPP configuration (see
The PPP daemon configures the PPP
stack with the named drivers and modules by pushing them in the
specified order onto the STREAMS stack below the
PPP Control Driver (PCID).
The pop option may be used to remove drivers and modules.
If push or pop options are not specified for
a device, the PPP daemon configures the default
PPP stack for its type.
PPP stack architecture
The PPP daemon is responsible for building the PPP
stack, placing calls, negotiating protocols such as the Link Control Protocol
(LCP) and Network Control Protocols (NCP),
implementing bandwidth control, and communicating with administration
utilities such as
The daemon does not handle data communication between the Network Layer and
the PPP driver after PPP negotiations have completed
and a link has been established. Because the daemon is multithreaded, only one
process is needed to handle administration of all PPP interfaces.
The PPP Control Driver (PCID) acts as a communications
tunnel between the PPP daemon, the PPP driver and
the lower part of the PPP stack.
It is used to construct the PPP stack interface to the
DLPI modules for synchronous and asynchronous
ISDN connections, to the
STREAMS tty and serial drivers for asynchronous serial
connections, and to third-party framing drivers for asynchronous
serial connections over ``intelligent'' serial interfaces.
The PPP STREAMS driver consists of multiplexer,
multilink and compression modules. Many of the functions that the
PPP driver performed in previous releases, such as
authentication, and link and network control, are now performed
by the PPP daemon.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004