How NetWare Link/PPP Works

NetWare Link/PPP corresponds to the Data-Link layer of the Open Systems Interconnection (OSI) model, with additional services provided on behalf of the Network layer. It defines the automatic establishment and configuration of serial links, or connections, within router- and bridge-based network topologies.

NetWare Link/PPP comprises three main components:

• A method for encapsulating datagrams over serial links
• A Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection
• A group of Network Control Protocols (NCPs) for establishing and configuring logical connections on behalf of various Network-layer protocols

NetWare Link/PPP defines encapsulation methods supporting bit-synchronous and character-asynchronous serial communication links. NetWare Link/PPP supports the use of both types of links and operates across many standard models of modems and data terminal equipment/data circuit-terminating equipment (DTE/DCE) interfaces (for example, EIA RS-232, EIA RS-422, EIA RS-423, X.21, and International Telecommunication Union [ITU] V.35). The links must be full-duplex and can be either dedicated or switched.

NetWare Link/PPP uses a variant of HDLC that provides basic data-link delivery services over point-to-point serial connections. Typically, PPP uses HDLC unnumbered information frames providing low overhead and high throughput exchange of control and data packets. In this case, error detection is based on the CRC-16 frame check sequence (FCS). Data delivery is considered best effort , with error recovery left to higher-level Network- and Transport-layer protocols.

When NetWare Link/PPP data compression is enabled, HDLC sequenced information frames provide reliable delivery of control and data packets. In this case, both error detection and retransmission error recovery is provided by the data link.

A mechanism allows control data to be transmitted transparently, and removes spurious control data that can be injected into the link by intervening hardware and software. Recovery is left to higher-layer protocols.

PPP is a point-to-point service, but is capable of supporting multiple Network-layer protocols simultaneously over the same link. Because PPP provides for multiplexing of multiple Network-layer protocols (such as the Internetwork Packet Exchange^TM [IPX^TM] protocol, IP, AppleTalk, and source route bridging) simultaneously over one link, NetWare Link/PPP provides a means of easy connection at the Data-Link layer for a variety of hosts, bridges, and routers.

For more information about how NetWare Link/PPP works, refer to:

• Communications Medium
• NetWare Link/PPP Features