The Group Allocation Multihop Multiple Access (GAMMA) protocol is presented; this protocol schedules data traffic over a multihop, multi-channel, wireless network. GAMMA provides excellent performance and remains stable under all network load levels by dividing the channel into cycles; each cycle is composed of a combination of contention and data slots. Every station in the network has a unique channel for receiving data. Each station maintains a set of stations called the "transmission group", only members of this group are allowed to transmit data collision-free to the station maintaining the group.

The group allocation multiple access with collision detection (GAMA/CD) protocol for scheduling variable-length packet transmissions in a local area network is specified and analyzed. The GAMA/CD provides the advantages of both TDMA and CSMA/CD by maintaining a dynamically-sized cycle that varies in length depending on the network load; each cycle is composed of a contention period and a group-transmission period. During the contention period, a station with one or more packets to send competes for membership in the transmission group. Once a member of the transmission group, a station is able to send data without collision during each cycle; as long as a station has data to send, it maintains its position in the group. This can be viewed as either allowing stations to "share the floor" in an organized manner, or as establishing frames that are not synchronized on a slot-basis and vary their length dynamically based on demand. Both the throughput and the delay of GAMA/CD are presented and analyzed. To validate our analysis, the results of both models are compared to the throughput and delay produced by a simulation of GAMA/CD.

Two protocols for scheduling variable-length packet transmissions in an optical passive star network using wavelength division multiplexing (WDM) are specified and analyzed. These protocols require: a separate channel for transmission of control packets, a fixed transmitter and receiver and a tunable transmitter and receiver. The distinction between these protocols and other WDM protocols is that message transmissions are initiated by the receipt of a control message; other schemes schedule packet transmission for some fixed point in the future. This flexibility allows these protocols to avoid "head-of-line" blocking which is a problem encountered in some other protocols. The protocols presented place no constraints on the size of a message, the size of a packet or on the number of available data channels; maintain a distributed queue for each of the output nodes; and guarantee that there are no receiver or data channel collisions. The delay characteristics of these protocols are analyzed and compared to those of the TTAS algorithm.

An accurate estimate of host reliability is important for correct analysis of many fault-tolerance and replication mechanisms. In a previous study, we estimated host system reliability by querying a large number of hosts to find how long they had been functioning, estimating the mean time-to-failure (MTTF) and availability from those measures, and in turn deriving an estimate of the mean time-to-repair (MTTR). However, this approach had a bias towards more reliable hosts that could result in overestimating MTTR and underestimating availability. To address this bias we have conducted a second experiment using a fault-tolerant replicated monitoring tool. This tool directly measures TTF, TTR, and availability by polling many sites frequently from several locations. We find that these more accurate results generally confirm and improve our earlier estimates, particularly for TTR. We also find that failure and repair are unlikely to follow Poisson processes.