214 APPENDIX B: P ATH BUILDER S330/S310 MODULE AND A PPLICATION O VERVIEWSerial Interface The serial interface is designed to interconnect frame-based devices/networks andcell-based ATM devices/networks. The PathBuilder S330/S310 provides a singleserial interface that can be configured as DTE or DCE and, with different cableadapters, can support V.35/RS-449/RS-530/X.21 interface to routers.The PathBuilder S330/S310 can perform cell-to-frame as well as frame-to-cellconversion. On the serial interface receive side, frames received from the HDLCserial interfaces are segmented to cells by the SAR and passed to the CTX chipwhere they can be switched. On the serial interface transmit side, cells receivedfrom the ATM interfaces are reassembled into frames and passed to the HDLCserial interfaces.The PathBuilder S330/S310 uses a RISC processor to perform the lookup andinterworking functions between frame and ATM services. It also performs the LMIfunctions and collects alarms and statistics.The PathBuilder S330/S310 provides for frame relay service and networkinterworking (FRF 5 and 8), as well as ATM DXI and transparent HDLC operation.You can use it for interworking between the ATM network and a variety ofdifferent frame-based networks or devices such as Frame Relay and ATM DXI.The interface can be clocked up to 6.2Mbps, and it supports the following modesof operation:Internal timing—DCE provides the clock for a router.External timing—DTE receives a clock from a DCE device such as a DSU (digitalservice unit).The mode of operation is selected automatically (by autosensing), based on thetype of cable connected to the unit—DCE or DTE.Serial Interface FrameProtocol ModesThe PathBuilder S330/S310 supports three modes of Frame-to-Cell transit services:ATM DXI Mode 1A—Supported by certain routers.HDLC/SDLC—Used mainly for transparent point-to-point operation.Frame Relay Forum Specification 5 and 8; modes 1 and 2—Used to terminatea frame relay router.Each service is designed to support a different type of user application; however,all the services share the same ATM backbone characteristics. The serial portmodules are mapped over ATM Permanent Virtual Circuits (PVCs).
