Metropolitan area network architecture and services

An MAN (metropolitan area network) architecture is described which is a hybrid two-level switching-hierarchy using distributed switching at the lower level and centralized switching at the upper. The architecture thus merges centralized and distributed switching into a single integrated architecture, preserving the advantages of both and offering a graceful evolution toward the anticipated broadband ISDN (integrated services digital network) network. The central switch provides fast interconnectivity between networks, removes the bandwidth limitations of shared medium architectures, and ensures security. The shared-medium approach efficiently utilizes the available bandwidth, provides mechanisms for congestion control, supports broadcast/multicast services, and reduces the load offered to the central switch