It is an integral part of PPP, and is defined in the same standard specification. LCP initiates and terminates connections gracefully, allowing hosts to negotiate connection options. There is one NCP for each higher-layer protocol supported by PPP. One or more Network Control Protocols (NCP) used to negotiate optional configuration parameters and facilities for the network layer.A Link Control Protocol (LCP) to establish, configure, and test the link as well as negotiate settings, options and the use of features.An encapsulation component that is used to transmit datagrams over the specified physical layer.PPP is a layered protocol that has three components: PPP, PPPoE and PPPoA are widely used in WAN lines. RFC 2364 describes Point-to-Point Protocol over ATM (PPPoA) as a method for transmitting PPP over ATM Adaptation Layer 5 ( AAL5), which is also a common alternative to PPPoE used with DSL.
RFC 2516 describes Point-to-Point Protocol over Ethernet (PPPoE) as a method for transmitting PPP over Ethernet that is sometimes used with DSL. The designers of PPP included many additional features that had been seen only in proprietary data-link protocols up to that time. PPP was designed somewhat after the original HDLC specifications. It is more reliable than SLIP because it double checks to make sure that Internet packets arrive intact. Like SLIP, this is a full Internet connection over telephone lines via modem. PPP was designed to work with numerous network layer protocols, including Internet Protocol (IP), TRILL, Novell's Internetwork Packet Exchange (IPX), NBF, DECnet and AppleTalk. The only requirement for PPP is that the circuit provided be duplex. PPP is commonly used as a data link layer protocol for connection over synchronous and asynchronous circuits, where it has largely superseded the older Serial Line Internet Protocol (SLIP) and telephone company mandated standards (such as Link Access Protocol, Balanced (LAPB) in the X.25 protocol suite).
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