The layers of the Point-to-Point Protocol are implemented in Linux as a combination of kernel drivers and a PPP daemon (pppd). The HDLC Data Link layer protocol is installed as a kernel module, as are the Physical layer protocols for the serial devices upon which PPP depends.
The serial device drivers are usually compiled into the Linux kernel. Therefore, an external modem can be attached to a serial port without installing any additional device drivers. An internal modem, however, may require a special device driver. The Linux hardware detection software should detect the internal modem during the initial operating system installation or the first time the system is rebooted after a new internal modem is installed. Figure 2.3 shows kudzu detecting a newly installed internal modem.
-igure 2.3: kudzu installing a modem driver
Selecting the Configure button installs the device driver module that provides the physical layer services for this modem. kudzu is a Red Hat tool, but all Linux distributions have some way to detect newly installed hardware.
Although the Physical layer and Data Link layer portions of PPP are provided by the kernel, the Link Control layer and the Network Control layer are provided by the PPP daemon. Thus, the lower layers of PPP are implemented as kernel modules, and the upper layers are implemented as a daemon process. In order for PPP to function, all of these components must be properly installed.
Was this article helpful?