106 CHAPTER 4: WAN INTERFACE CONFIGURATION■ Verify the type of the interface provided by your telecom service provider,whether it is ISDN BRI U or ISDN BRI S/T. Despite that ITU-T I.411 has providedan ISDN user-network interface reference model, there are some arguments inthe position of the user-network dividing point. For this reason, some nationsadopt the U interface while some others adopt the S/T interface depending ontheir needs. Therefore, you must make sure the interface type provided by yourservice provider before making a router purchase decision.■ Request for digital service. As ISDN can provide integrated services includingboth digital and voice, you must request for an ISDN line allowing digital callservice so that your router can make digital communications.■ Select connection type, which can be a point-to-point connection or apoint-to-multipoint connection (optional). As ISDN supports semipermanentconnection, you can adopt the ISDN leased line in the event that you adoptISDN only for connecting two fixed points. Otherwise, you must select apoint-to-multipoint connection.■ Request for the delivery of Calling Line Identification (CLI) function (optional).With it, you can implement calling ID filtering on your ISDN line to reject someusers from accessing the local router and hence enhance the network security.Configuring ISDN BRIInterfaceFollow these steps to configure an ISDN BRI interface:ISDN BRI interfaces are used for dialup purpose. For details on ISBN BRI interfaceconfiguration, refer to “DCC for Dialup ISDN BRI Line and Leased Line Connection”on page 192.CE1/PRI InterfaceOverview In 1960s, the time division multiplexing (TDM) technology gained increasinglywide application in the data communications system along with the introductionof pulse code modulation (PCM) technology. So far, there exist two TDM systemsin the data communications system. One is the ITU-T recommended E1 systemthat is widely adopted in Europe and P.R. China. The other is the ANSIrecommended T1 system that is widely used in North American and Japan. (Thesystem that Japan adopts is actually called J1. It is regarded as a T1 system due tohigh similarity between them.)A CE1/PRI interface can work in either E1 mode (also called non-channelizedmode) and CE1/PRI mode (that is, channelized mode).A CE1/PRI interface in E1 mode equals an interface of 2 Mbps data bandwidth, onwhich, no timeslots are divided. Its logic features are the same like those of asynchronous serial interface. It supports the link layer protocols such as PPP, FR,LAPB and X.25 and the network protocols such as IP and IPX.To do... Use the command... RemarksEnter system view system-view --Enter ISDN BRI interface view interface bri number RequiredEnable external loopback on theISDN BRI interfaceloopback { b1 | b2 | both } Disabled by default
