- CONFIG_PPP：使系统支持PPP协议。
- CONFIG_PPP_ASYNC：使系统支持PPP协议的异步串行端口模式（关于异步和同步模式有什么不同我就不是很清楚了）。
config PPP_ASYNC
tristate "PPP support for async serial ports"
depends on PPP
select CRC_CCITT
help
Say Y (or M) here if you want to be able to use PPP over standard
asynchronous serial ports, such as COM1 or COM2 on a PC. If you use
a modem (not a synchronous or ISDN modem) to contact your ISP, you
need this option.
To compile this driver as a module, choose M here.
If unsure, say Y.
- CONFIG_PPP_SYNC_TTY：使系统支持PPP协议的同步模式。
Say Y (or M) here if you want to be able to use PPP over synchronous
(HDLC) tty devices, such as the SyncLink adapter. These devices
are often used for high-speed leased lines like T1/E1.
- CONFIG_PPP_DEFLATE：使系统支持PPP协议的Deflate压缩算法（和gzip一样的压缩算法）。
config PPP_DEFLATE
tristate "PPP Deflate compression"
depends on PPP
select ZLIB_INFLATE
select ZLIB_DEFLATE
help
Support for the Deflate compression method for PPP, which uses the
Deflate algorithm (the same algorithm that gzip uses) to compress
each PPP packet before it is sent over the wire. The machine at the
other end of the PPP link (usually your ISP) has to support the
Deflate compression method as well for this to be useful. Even if
they don't support it, it is safe to say Y here.
To compile this driver as a module, choose M here.
- CONFIG_PPP_BSDCOMP：使系统支持PPP协议的BSD-Compress压缩算法。
config PPP_BSDCOMP
tristate "PPP BSD-Compress compression"
depends on PPP
help
Support for the BSD-Compress compression method for PPP, which uses
the LZW compression method to compress each PPP packet before it is
sent over the wire. The machine at the other end of the PPP link
(usually your ISP) has to support the BSD-Compress compression
method as well for this to be useful. Even if they don't support it,
it is safe to say Y here.
The PPP Deflate compression method ("PPP Deflate compression",
above) is preferable to BSD-Compress, because it compresses better
and is patent-free.
Note that the BSD compression code will always be compiled as a
module; it is called bsd_comp and will show up in the directory
modules once you have said "make modules". If unsure, say N.
- CONFIG_PPPOE：使系统支持PPPOE协议。
config PPPOE
tristate "PPP over Ethernet"
depends on PPP
help
Support for PPP over Ethernet.
This driver requires the latest version of pppd from the CVS
repository at cvs.samba.org. Alternatively, see the
RoaringPenguin package (<http://www.roaringpenguin.com/pppoe>)
which contains instruction on how to use this driver (under
the heading "Kernel mode PPPoE").
config PPTP
tristate "PPP over IPv4 (PPTP)"
depends on PPP && NET_IPGRE_DEMUX
help
Support for PPP over IPv4.(Point-to-Point Tunneling Protocol)
This driver requires pppd plugin to work in client mode or
modified pptpd (poptop) to work in server mode.
See http://accel-pptp.sourceforge.net/ for information how to
utilize this module.
config PPPOL2TP
tristate "PPP over L2TP"
depends on L2TP && PPP
help
Support for PPP-over-L2TP socket family. L2TP is a protocol
used by ISPs and enterprises to tunnel PPP traffic over UDP
tunnels. L2TP is replacing PPTP for VPN uses.
- CONFIG_SERIAL_NONSTANDARD：使系统支持多个串行口来允许多个终端的拨号连接。
- CONFIG_N_HDLC：使用系统支持同步HDLC通信。
