Abstract — Although custodial transmission of multicast bundles would be a desirable capability to have in Delay-Tolerant Networks (DTNs), support for custodial multicast transmission was omitted from the Bundle Protocol Specification because of its complexity. This paper explains the difficulties that arise with respect to supporting custody transfer and retransmission of multicast bundles, and it describes some potential solutions for addressing these issues that the authors are currently exploring as work-in-progress. Keywords-Delay-Tolerant, Disruption-Tolerant, multicast, custody transfer, custody-based retransmission

Directional antennas are a promising technology for use in mobile ad hoc environments. By consuming smaller volumes than omni directional antennas, directional antennas enable significant increases in network capacity by allowing more simultaneous transmissions to occur within a multihop wireless network. In this paper, we present some of the challenges that face asynchronous directional channel access schemes and describe how these problems can be avoided by taking a synchronous approach. We describe a communications system architecture that enables modestly directional sectored antennas to be effectively exploited in a mobile ad hoc environment. A key part of this architecture is the directional synchronous unscheduled multiple access (DSUMA) protocol. By making intelligent decisions regarding the enabling/disabling of sector antennas, DSUMA provides an increased density of transmissions while insuring that collisions do not occur. Our results indicate how the number of sectors per node affects performance in terms of spatial reuse, the likelihood of collisions, and overall network capacity.

The space communication environment and mobile and wireless communication environments show many similarities when observed from the perspective of a transport protocol. Both types of environments exhibit loss caused by data corruption and link outage, in addition to congestion-related loss. The constraints imposed by the two environments are also similar --- power, weight, and physical volume of equipment are scarce resources. Finally, it is not uncommon for communication channel data rates to be severely limited and highly asymmetric. We are working on solutions to these types of problems for space communication environments, and we believe that these solutions may be applicable to the mobile and wireless community. As part of our work, we have defined and implemented the Space Communications Protocol Standards-Transport Protocol (SCPS-TP), a set of extensions to TCP that address the problems that we have identified. The results of our performance tests, both in the laboratory and on...