Serial Interface; Serial Interface Frame Protocol Modes - 3Com SuperStack II PathBuilder S330 Reference Manual

214 A B: P B S330/S310 M A O
PPENDIX ATH UILDER ODULE AND PPLICATION VERVIEW

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).