Intelligent Interworking Units, I/sup 2/Us a Proposal for the Lan/man/b-ISDN Environment

Abstract

The paper proposes a new interworking concept called Intelligent Interworking Units (I/sup 2/Us). This concept is applied to the interconnection of IEEE 802.x LANs, IEEE 802.6 (DQDB) Metropolitan Area Networks (MANs) and ATM based B-ISDN. Between all the above mentioned network types Interworking Units (IWUs) are necessary to provide flexible communication capabilities. Today IWUs use a fixed layering scheme and are thus classified in bridges, routers or brouters. The I/sup 2/U concept enhances conventional IWUs to allow for a more sophisticated operation in a high-speed environment. I/sup 2/Us dynamically select the layers for interworking according to the received data type. This avoids encapsulation at the source and makes use of Layer 3 network functions only when needed. The proposed concepts relies on the special features of the DQDB MAN protocol which supports the concurrent use of different address types (16-, 48 and 60-bit) and the allocation of a set of addresses of each type to one node. The paper gives a short overview of the provision of connectionless services in the three mentioned network types, pointing out the differences concerning PDU formats and addressing schemes. The I/sup 2/Us concept for the interconnection of LANs via MANs and of MANs via the B-ISDN is subsequently described. The rationale for using the address translation mechanism only at the receiving IWU is also addressed. The I/sup 2/Us concept is part of the ongoing Enhanced Network- System (ENS) project at the GMD Berlin.