Abstract-Routing is one of the most challenging development issues in delay-tolerant networks (DTNs) because of lack of continuous connection. Existing routing schemes for DTNs provide best effort service, but are unable to optimize QoS and support message priority. In this paper, we present a Look-Ahead Routing and Message Scheduling approach (ALARMS) which exploits more accurate knowledge about various parameters regarding routing to achieve better QoS in the DTN. We assume a variation of the well-known ferry model, in which there are ferry nodes moving along pre-defined routes to exchange messages with the gateway node of each region on the route and also pass to the gateway nodes look-ahead routing information about when it will arrive at each gateway node on the route in the next two rounds and how long it will stay. The gateway nodes use this information to estimate the delivery delay of each message when being delivered by different ferries, and schedule the message to be delivered by the ferry which arrives earliest at the destination. Simulation results show that ALARMS outperforms three existing routing protocols: epidemic routing, spray-and-wait, and spray-and-focus, in terms of delay time, delivery ratio, and overhead. We also discuss three enhancement strategies on ALARMS and how ALARMS can support message priority. Index Terms-Delay-Tolerant Networks, Quality of Service, Look-Ahead Routing, Message Scheduling. Delay Tolerant Networks (DTN) is one emerging type of networks whose distinguishing characteristic is that communications between two nodes in a DTN take prolonged period of time because of lack of continuous connection. DTNs were initially designed to operate over extreme distances encountered in space communications where the long latency in communications inevitably causes TCP connections in the network to break down. As the TCP communication breaks down in a DTN, a Bundle Protocol [15] can be used to handle the underlying communication with the remote party using node-to-node custody transfers. This protocol also allows the DTN to span multiple heterogeneous networks and allows the DTN protocols to be separated from the naming and addressing schemes used in the underlying networks. However, the discontinuous connection problem due to the cosmic distances can also occur over shorter terrestrial distances due to lack of infrastructure. For example, many people living in remote rural areas and in developing countries do not have access to the Internet [8] . To realize data communication in such cases, it requires hardware to store large amounts of data, and also requires special media to transfer data between the nodes. Therefore, in a terrestrial context, a DTN can be appropriately regarded as a group of highly disconnected networks/regions where the communication environment is characterized by high error rates, long delays and sporadic connectivity with the outside world. An approach to transfer the data between the disconnected network regions is by making use of message ferry [20, 21] which travels on arbitrary paths between the regions and has a data storage buffer which can be used to keep messages. Each region has a fixed gateway node which handles the communication needs of incoming and outgoing traffic for the hosts within the region. When a ferry arrives at a region, it contacts the gateway node, and during the contact time it will unload to the gateway the messages that are destined to this region, and load from the gateway the messages that this region wants to send to other regions. To reduce the latency, multiple ferries can be deployed in the network. Figure 1 illustrates the use of multiple message ferries. However, this message ferry approach has two main constraints. First, there is no guarantee of the performance of the network if the disconnected regions have no information of the ferry route, schedule and capacity. Second, this straightforward approach does not support message prioritization [5] , which is characterized by different importance levels of messages and is usually handled with differentiated scheduling and delivery of messages. Although the communication quality of DTNs is far from ideal, QoS and message prioritization are still desirable in many cases, especially when the DTN is used in critical missions such as rescue tasks after natural disasters and emergency response in face of terrorist attacks. In this paper, we propose to use a Look-Ahead Routing and Message Scheduling (ALARMS) approach to optimize the performance in a DTN. The main motivation of our work is to improve the DTN performance via smart forwarding of routing information to the disconnected regions and informed scheduling of data packets by the gateway nodes in the network. In our model we assume that the DTN has multiple ferries operating on predefined routes within the network. Each time when a ferry arrives at a gateway node on its route, the ferry will pass to the gateway node the look-ahead routing information about when it is estimated to arrive at each gateway
In REF , the author has proposed look-ahead routing and message scheduling (ALARMS) scheme in which the ferry nodes inform the gateway nodes about their travel schedule so that the gateway nodes can decide which ferry to use for each message in advance and schedule the message in the queue accordingly.
Look-ahead routing and Message Scheduling in delay-tolerant networks
IEEE Local Computer Network Conference
IEEE Local Computer Network Conference
Computer Science