PPP PCI
2 - Point-to-Point Protocol
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PPP provides WAN links on point-to-point lines. PPP is the successor of SLIP which could only serve the Internet Protocol (IP); PPP is able so serve any kind of network protocol (IPX, AppleTalk, DECnet and others).
Main components:
1.
A method for encapsulating datagrams over serial links. PPP uses HDLC (ISO 3309-1979) as a basis for encapsulating datagrams over point-to-point links. At this time, PPP specifies the use of asynchronous or synchronous duplex circuits, either dedicated or circuit switched.
2.
An extensible Link Control Protocol (LCP) to establish, configure, and test the data-link connection.
3.
A family of Network Control Protocols (NCP) for establishing and configuring different network-layer protocols. PPP is designed to allow the simultaneous use of multiple network-layer protocols.
In order to establish communications over a point-to-point link, the originating PPP would first send LCP packets to configure and test the data link. After the link has been establish and optional facilities have been negotiated as needed by the LCP, the originating PPP would send NCP packets to choose and configure one or more network-layer protocols. Once each of the chosen network-layer protocols has been configured, datagrams from each network-layer protocol can be sent over the link.
The link will remain configured for communications until explicit LCP or NCP packets close the link down, or until some external event occurs (e.g., inactivity timer expires or user intervention).
Physical Layer Requirements:
The Point-to-Point Protocol is capable of operating across any DTE/DCE interface (e.g., EIA RS-232-C, EIA RS-422, EIA RS-423 and CCITT V.35). The only absolute requirement imposed by PPP is the provision of a duplex circuit, either dedicated or circuit switched, which can operate in either an asynchronous (start/stop) or synchronous bit-serial mode, transparent to PPP Data Link Layer frames. PPP does not impose any restrictions regarding transmission rate, other than those imposed by the particular DTE/DCE interface in use.
PPP does not require the use of modem control signals, such as Request To Send (RTS), Clear To Send (CTS), Data Carrier Detect (DCD), and Data Terminal ready (DTR). However, using such signals when available can allow greater functionality and performance.
Literature/Sources: