Interworking of B-ISDN and DQDB —A Simulation Study

Abstract

In this paper, we present an analysis of two interworking modes for interconnection of Metropolitan Area Networks (MANs) and ATM-based Broadband-ISDN (B-ISDN). We present simulation results of a DQDB network receiving traffic from B-ISDN. This connection is modelled by an Interworking Unit (IWU) within a DQDB network getting aggregated traffic from B-ISDN. The aggregated traffic is a mixture of various constant bitrate (CBR) and variable bitrate (VBR) traffic sources. To meet the bandwidth requirements of connection oriented (CO) traffic in MANs, an enhancement of the DQDB protocol for MANs has been studied: the Guaranteed Bandwidth (GBW) proposal, currently studied by IEEE 802.6 under the Project Authorization Request for Connection Oriented Data Service in the DQDB standard. The two interworking modes considered are the “cell-to-slot interworking” and the “frame interworking”. The cell-to-slot mode modifies ATM cells to DQDB slots and vice versa. In contrast to this, the frame mode reassembles cellslslots and modifies B-ISDN frames to DQDB frames and vice versa.

It turns out that the cell-to-slot mode is much better for meeting delay requirements than the frame mode, which causes additional delays due to the reassembly of cells.