Patton electronics 2701/I User Manual

Also see for NetLink 2701/I: Specification sheet Specification sheet User manual

Patton electronics 2701/I User Manual Manual pdf 9 page image

93.0 PPP OPERATIONAL BACKGROUNDPPP is a protocol used for multi-plexed transport over a point-to-pointlink. PPP operates on all full duplex media, and is a symmetric peer-to-peer protocol, which can be broken into three main components: 1. Astandard method to encapsulate datagrams over serial links; 2. A LinkControl Protocol (LCP) to establish, configure, and test the data-link con-nection; 3. A family of Network Control Protocols (NCPs) to establish andconfigure different network layer protocols.In order to establish communications over a point-to-point link, each endof the PPP link must first announce its capabilities and agree on theparameters of the link’s operation. This exchange is facilitated throughLCP Configure-Request packets.Once the link has been established and optional facilities have beennegotiated, PPP will attempt to establish a network protocol. PPP willuse Network Control Protocol (NCP) to choose and configure one ormore network layer protocols. Once each of the network layer protocolshave been configured, datagrams from the established network layerprotocol can be sent over the link. The link will remain configured forthese communications until explicit LCP or NCP packets close the linkdown, or until some external event occurs.The PPP Bridging Control Protocol (BCP), defined in RFC 1638, config-ures and enables/disables the bridge protocol on both ends of the point-to-point link. BCP uses the same packet exchange mechanism as theLink Control Protocol (LCP). BCP is a Network Control Protocol of PPP,bridge packets may not be exchanged until PPP has reached the net-work layer protocol phase.3.1 APPLICATIONSIn situations where a routed network requires connectivity to a remoteEthernet network, the interface on a router can be configured as a PPPIP Half Bridge. The serial line to the remote bridge functions as a VirtualEthernet interface, effectively extending the routers serial port connec-tion to the remote network. The bridge device sends bridge packets(BPDU's) to the router's serial interface. The router will receive the layerthree address information and will forward these packets based on its IPaddress.Figure 1 shows a typical Cisco router with a serial interface configuredas a PPP Half Bridge. The router serial interface uses a remote devicethat supports PPP bridging to function as a node on the remote Ethernetnetwork. The serial interface on the Cisco will have an IP address on thesame Ethernet subnet as the bridge.