3Com S330 manual Serial Interface Frame, Protocol Modes

214APPENDIX B: PATHBUILDER S330/S310 MODULE AND APPLICATION OVERVIEW

Serial Interface	The serial interface is designed to interconnect frame-based devices/networks and
	cell-based ATM devices/networks. The PathBuilder S330/S310 provides a single
	serial interface that can be configured as DTE or DCE and, with different cable
	adapters, 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-cell
	conversion. On the serial interface receive side, frames received from the HDLC
	serial interfaces are segmented to cells by the SAR and passed to the CTX chip
	where they can be switched. On the serial interface transmit side, cells received
	from the ATM interfaces are reassembled into frames and passed to the HDLC
	serial interfaces.
	The PathBuilder S330/S310 uses a RISC processor to perform the lookup and
	interworking functions between frame and ATM services. It also performs the LMI
	functions and collects alarms and statistics.
	The PathBuilder S330/S310 provides for frame relay service and network
	interworking (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 of
	different 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 modes
	of operation:
	Internal timing—DCE provides the clock for a router.
	External timing—DTE receives a clock from a DCE device such as a DSU (digital
	service unit).
	The mode of operation is selected automatically (by autosensing), based on the
	type of cable connected to the unit—DCE or DTE.
Serial Interface Frame	The PathBuilder S330/S310 supports three modes of Frame-to-Cell transit services:
Protocol Modes	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 terminate
	a 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 port
	modules are mapped over ATM Permanent Virtual Circuits (PVCs).