3Com S330 manual Shows the applications for DXI

218APPENDIX B: PATHBUILDER S330/S310 MODULE AND APPLICATION OVERVIEW

DXI protocol frame is an HDLC LLC1 frame similar to PPP protocol. Mode 1A supports an AAL5 transit encapsulation. In terms of the Brouter, it is easier to implement DXI protocol, since it only requires the Brouter to encapsulate the SDU. DXI protocol supports up to 1023 connections and up to 9232 octets of payload. (See Figure 158 on the previous page.)

Figure 159 shows the applications for DXI.

Figure 159 DXI Applications

V.35/RS-449/RS-530/X.21/RS-366

PathBuilder S330/S310

PathBuilder S330/S310
	PVC
	ATM		DXI
			Mode
DXI		ATM
			1A
Mode
		Native

1A Host

When the PathBuilder S330/S310 receives a DXI Frame from the DXI DTE or an ATM CPCS protocol data unit (PDU) from the ATM network, it translates from frames into ATM CPCS PDUs or from ATM CPCS PDUs into frames by doing the following:

■Mapping the DFA in the DXI frame to the VPI/VCI in the ATM cell header

■Mapping the CLP in the DXI frame to the CLP in the ATM cell header

■Mapping the CN in the DXI Frame to the PTI in the ATM cell header

Mapping the DFA in the DXI Frame to the VPI/VCI in the ATM cell header

In the DXI frame header, the DFA occupies 6 bits (bit 3 to bit 8) in the first octet and 4 bits (bit 6 to bit 8) in the second octet. The ATM DXI Specification defines a method for mapping between DFA and VPI/VCI. You can configure the PathBuilder S330/S310 by assigning the mapping values in certain way. See “Configuring Virtual Circuits” in Chapter 4, for details.

Mapping the CLP in the DXI frame to the CLP in the ATM cell header

When data is moved from DXI to ATM, the CLP bit in the DXI header is copied into the CLP field in the ATM cell header without change. When data is moved in the reverse direction, the CLP bit in the DXI header is always set 0, no matter what value it is in the ATM cell header.

Mapping the CN in the DXI Frame to the PTI in the ATM cell header

When data is moved from DXI to ATM, the CN bit is always set to 0 by the DTE. When data is moved in the reverse direction, the CN bit is set to 1 if PTI is 01x in the last ATM cell of the AAL5 CPCS PDU; otherwise, it is set to 0.