SLIP and PPP protocols

The content of the PPP protocol is seldom described here. Here we will mainly discuss the relationship between the SLIP protocol and the PPP protocol. Both SLIP and PPP protocols are data link layer protocols. First, let's take a look at the content of the SLIP protocol.

SLIP Protocol

SLIP Protocol: Serial Line Internet protocol Serial Line Interenet Prococol ).

The SLIP protocol is one of the first and only two serial IP protocols. It implements the functions of running TCP/IP protocol and its application services on the serial communication line, and provides the dial-up IP Mode for thousands of households to access the Internet, in addition, the leased line IP address mode is provided for industrial users to transmit IP address datasync through serial media.

The Serial Line Internet Protocol SLIP (Serial Line Internet Protocol) is a Point-to-Point link layer communication Protocol that supports TCP/IP on a Serial communication Line, it not only sends and receives IP address dataphin, but also provides various network application services (such as rlogin, telnet, ftp, and rtp) for TCP/IP ). Individual users can use the SLIP protocol to dial up the Internet, while industry users can use the SLIP leased line to remotely transmit business data.

Currently, ADSL uses PPP for user identity authentication.

PPP: Point-to-Point Protocol PPP: Point to Point Protocol)

You need to use the PPPoe protocol to access the Internet using ADSL.

PPPoE is a PPP protocol over Ethernet.

PPoE: PPP over Ethernet

Point-to-Point Protocol (PPP)

It provides a standard method for transmitting multi-protocol data packets over point-to-point connections. PPP was initially designed to provide an encapsulation protocol for IP traffic transmission between two peer nodes. In the TCP-IP protocol set, it is a second layer in the OSI Mode of the data link layer protocol used for synchronous modulation connection), replacing the original non-standard second layer protocol, that is, SLIP. In addition to IP addresses, PPP can also carry other protocols, including DECnet and Novell Internet packet switching IPX ).

PPP consists of the following parts:

Encapsulation: a method for encapsulating multi-protocol datagram. PPP encapsulation provides multiplexing technology for simultaneous transmission over the same link using different network-layer protocols. The PPP encapsulation is well designed to maintain compatibility with most commonly used hardware.

Link Control Protocol: PPP provides comprehensive LCP functions and is suitable for most environments. LCP is used to automatically reach an agreement on Encapsulation Format options, handle packet size restrictions, detect loop links and other common configuration errors, and terminate links. Other optional functions provided by LCP are: Identity of the Peer unit in the authentication link, which determines whether the link function is normal or the link fails.

Network Control Protocol: an extended link control protocol used to establish, configure, test, and manage data link connections.

Configuration: the simple and self-made mechanism of the Link Control protocol is used. This mechanism is also applied to other control protocols, such as network control protocol (NCP ).

To establish point-to-point Link communication, each end of the PPP link must first send an LCP packet to set and test the data link. After a link is established and the optional functions required by LCP are selected, PPP must send an NCP package to select and set one or more network layer protocols. Once each selected network layer protocol is set, the datagram from each network layer protocol can be sent on the link.

The link will keep the communication settings unchanged until the LCP and NCP packets close the link, or when some external events occur, such as timer expiration or network administrator interference ).

Application: Assume that Windows 98 is also used and a "dial-up connection" has been created ". You can set the PPP protocol using the following method: First, open the "dial-up connection" attribute and select the "server type" tab. Then, select the default "PPP: Internet, windows NT Server, Windows 98, you can set other options for this Protocol in advanced options. Finally, click OK.

PPPOE allows a computer on a network to connect to a remote access device through simple bridging. In this model, each user host uses its own ppp stack and uses a familiar interface. Access control, billing, and service types can be implemented for each user, rather than for each site.

To provide point-to-point connections over Ethernet, each PPP session must know the ethernet address of the Remote Communication peer and create a unique session identifier. PPPoE contains an ethernet address.

The PPPoE process is divided into two different stages: the Discovery address Discovery phase and the PPP session phase. When a host wants to initiate a PPPoE session, it must first execute Discovery to determine the peer's Ethernet MAC address and establish a PPPoE session identifier SESSION_ID ). Although PPP defines an end-to-end peer relationship, Discovery is a client-server relationship. During the Discovery process, the host acts as the client) discovers an Access Concentrator as the server). According to the network topology, the host may discover Multiple Access Concentrator. The Discovery stage allows the host to discover all Access Concentrator and select one from it. After the Discovery stage is completed, both the host and the selected Access Concentrator have all the information required to establish a point-to-point connection over Ethernet.

Discovery stage maintains stateless) until a PPP session is established. Once a PPP session is established, both the host and the Access Concentrator must allocate resources to a PPP Virtual Interface.