PPP Operation PDF

CWE091 – 5 Industrial Networks II Point to Point Protocol (PPP) Slides taken from chapter 11 1.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  11-7 POINT...

CWE091 – 5 Industrial Networks II Point to Point Protocol (PPP) Slides taken from chapter 11 1.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  11-7 POINT-TO-POINT PROTOCOL Although HDLC is a general protocol that can be used for both point-to-point and multipoint configurations, one of the most common protocols for point-to-point access is the Point-to-Point Protocol (PPP). PPP is a byte-oriented protocol. Topics discussed in this section: Framing Transition Phases Multiplexing Multilink PPP 11.2 The Data Link Layer in the Internet A home personal computer acting as an internet host. Technology like Ethernet cannot provide “high-level” functionality like connection management and parameter negotiation  Figure 11.32 PPP frame format 11.4  Note PPP is a byte-oriented protocol using byte stuffing with the escape byte 01111101. 11.5  Figure 11.33 Transition phases 11.6  Figure 11.34 Multiplexing in PPP 11.7  Figure 11.35 LCP packet encapsulated in a frame 11.8  PPP assigned values for protocol type 11.9  Table 11.2 LCP packets 11.10  Table 11.3 Common options 11.11  Figure 11.36 PAP packets encapsulated in a PPP frame 11.12  Figure 11.37 CHAP packets encapsulated in a PPP frame 11.13  Figure 11.37 CHAP packets encapsulated in a PPP frame 11.14  Figure 11.38 IPCP packet encapsulated in PPP frame 11.15  Table 11.4 Code value for IPCP packets 11.16  Figure 11.39 IP datagram encapsulated in a PPP frame 11.17  Figure 11.40 Multilink PPP Below we have two serial links between R1 and R2, this gives us some redundancy and we can have load balancing at layer 3. (OSPF or RIP). We require two subnets to connect the routers 11.18  Figure 11.40 Multilink PPP If the metric is the same on both links, we will have Layer 3 load balancing OSPF neighbor adjacency OSPF neighbor adjacency 11.19  Figure 11.40 Multilink PPP Multilink PPP (MLPPP) allows an Admin to combine multiple physical serial links into a single logical link. Only a single subnet is required for the logical multilink interface and if you use OSPF only a single neighbor adjacency is required: 2 physical links – 1 logical link OSPF neighbor adjacency 11.20  Figure 11.40 Multilink PPP 11.21  Multilink PPP 11.22  Multilink PPP long sequence number 11.23  Multilink PPP short sequence number 11.24  Example 11.12 Let us go through the phases followed by a network layer packet as it is transmitted through a PPP connection. Figure 11.41 shows the steps. For simplicity, we assume unidirectional movement of data from the user site to the system site (such as sending an e-mail through an ISP). The first two frames show link establishment. We have chosen two options (not shown in the figure): using PAP for authentication and suppressing the address and control fields. Frames 3 and 4 are for authentication. Frames 5 and 6 establish the network layer connection using IPCP. 11.25  Example 11.12 (continued) The next several frames show that some IP packets are encapsulated in the PPP frame. The system (receiver) may have been running several network layer protocols, but it knows that the incoming data must be delivered to the IP protocol because the NCP protocol used before the data transfer was IPCP. After data transfer, the user then terminates the data link connection, which is acknowledged by the system. Of course the user or the system could have chosen to terminate the network layer IPCP and keep the data link layer running if it wanted to run another NCP protocol. 11.26  Figure 11.41 An example Code ID Length 11.27  Figure 11.41 An example (continued) 11.28