If a peer requests authentication, a request must be issued during the link establishment process where configuration options are negotiated. Before proceeding to the NLP, a peer may request authentication or validation by the other peer. 4.4.3 Authentication phase This is an optional phase. The end of this phase indicates the LCP open state. When the link is in the network layer protocol (NLP) phase, receiving a Configure-Request packet causes the link to move back to the Link Establishment phase. Any non-LCP packets received during this phase should be discarded and logged.
Sync to start of ppp frame software#
These options are negotiated between the peers based on the hardware and software abilities at both the ends. These options are independent of the network layer protocol being implemented. įigure 4.2: Different phases of PPP Configuration options have defined default values, which can be modified during this phase. After the link configuration has been consented upon, Configure-Ack packets are sent and received. In this phase, the LCP establishes a healthy connection by exchanging configuration packets. 4.4.2 Link Establishment phase Once the presence of the peer is detected, the link proceeds to this phase.
Disconnecting from the modem line should bring the link back to this phase. The detection of a carrier signal at the peer triggers the link to proceed to the next phase. The link remains open for communications until special LCP/NCP packets are sent to close down the link or other events trigger a shutdown (time out, human intervention, etc.).Ĥ.4 PPP phases 4.4.1 Link Dead phase The link starts and stops in this phase. It is at this layer, that messages can be sent to select IP addresses. These protocols are similar to the LCP in message format, with varying details. Some of the available Network Layer Protocols (NLP) are ATCP (AppleTalk Control Protocol), IPCP (Internet Protocol Control Protocol), Novell IPX Control Protocol, etc. In this stage a Network Control Protocol (NCP) is first selected and then the link can proceed to obey the rules of sending/receiving NCP packets. The end of the link establishment phase (or the authentication phase as the case may be) triggers the next phase - the network phase. Figure 4.2 shows the phase diagram that the link passes through in order to support PPP. This phase is optional when there is no such request made. Any peer may request validation after link configuration. However, both peers should be able to recognize the padding bytes from the true data.Ĥ.3 Block diagram To establish communication between two peers, LCP packets must first be sent both ways to configure the link. The information field may be padded with as many bytes as needed to reach the MRU. Negotiations are possible between peers as to the MRU values. The default field length is also 1500 bytes. This limit is termed as the Maximum Receive Unit (MRU) at the receiving end and Maximum Transmit Unit (MTU) at the transmitting end. It has a maximum length (including padding and excluding the protocol field) of 1500 bytes.
Sync to start of ppp frame password#
Some examples of protocol field values are: 0xC021 for Link control protocol 0xC023 for Password Authentication Protocol 0x8021 for Internet Protocol Control ProtocolĤ.2.2 Information field This field is zero or more bytes long. Frames that violate these rules are treated as unrecognized protocols. The least significant bit of the lower byte is always set to "1" and that of the most significant bit is always set to "0". Protocol 8 - 16 bitsįigure 4.1: Encapsulation of PPP packets 4.2.1 Protocol field This field is one or two bytes and it identifies the data being sent in the information field. Data is transmitted from the left to right. Data is sent in frames whose general structure is shown in Figure 4.1. Network Control Protocol (NCP)Ĥ.2 Encapsulation Encapsulation is provided by PPP so that different protocols at the network layer can be supported simultaneously. PPP can be fragmented into three parts: 1.
The point-to-point links that utilize this protocol should be able to support full-duplex communication. Information is exchanged in the form of structured data packets. PPP is a protocol that can be used to establish communication between any two communicating devices that need to exchange information.
Ĥ.1 Introduction to PPP Much help was acquired from Internet Request-For-Comments (RFC) documents on the details of the point-to-point protocol. Chapter 4 The Point to Point Protocol (PPP) This chapter gives an overview of the PPP, explains the various stages, some packet formats, implementation details and options, and discusses the PPP implementation on the WMI™.
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