ATM (asynchronous transfer mode) is an international telecommunications standard designed for broadband integrated services; it is also well-suited for use within local-area networks. ATM LANs can provide the networking support needed for multimedia communication at rates of 100 Mbits/sec and higher. The authors first analyze the protocol processing required to handle ATM communication. Based on this analysis, they then discuss the architectural issues in the design of host interfaces for ATM local-area networks. In particular, they conclude that a simple host interface, which leaves most of the ATM protocol processing to be done by the host computer, supports good performance for data communication (around 100 Mbits/sec). However, to support real-time video and audio communication, the ATM interface should include an embedded processor.>

Multicomputersbuiltaround a general network are now a viable alternative to multicomputersbased on a system-speci~c interconnect because of architectural improvements in two areas.First, the host-network interface overhead can be minimized by reducing copy operations and host interrupts.Second, the network can provide high bandwidth and low latency by using high-speed crossbar switches and efficient protocol implementations.While still enjoying thejexibility of general networks, the resulting network-based multicomputers achieve high performance for typical multicomputer applications that use system-specijic interconnects.We have developed a network-based mtdticomputer called Nectar that supports these claims.

We have built a high-speed local-area network called Nectar that uses programmable communication processors as host interfaces. In contrast to most protocol engines, our communication processors have a flexible runtime system that supports multiple transport protocols as well as application-specific activities. In particular, we have implemented the TCP/IP protocol suite and Nectar-specific communication protocols on the communication processor. The Nectar network currently has 25 hosts and has been in use for over a year.

Nectar is a “network backplane” for use in heterogeneous multicomputers. The initial system consists of a star-shaped fiber-optic network with an aggregate bandwidth of 1.6 gigabits/second and a switching latency of 700 nanoseconds. The system can be scaled up by connecting hundreds of these networks together.

The Mach operating system supports secure local communication within one node of a distributed system by providing protected communication abstraction can be extended over a network by Network Server tasks. The network servers effectively act as local representatives for remote tasks by implementing an abstraction of Network Ports. To extend the security of the port-based communication abstraction into the network environment, the network servers must protect both the messages sent over the network to network ports and the access rights to network ports. This paper describes in detail the protocols used by the network servers to support security.