Central to the establishment of a formal basis for providing time-constrained communication services are the DCTS model and its scheduling schemes. To better characterize real-time tasks with temporal constraints, we proposed in [han:92] the (temporal) distance-constrained task system model and designed an efficient scheduling scheme, called Scheduler Sr, for the model. The temporal distance constraint imposed in the DCTS model elegantly captures the need of delivering real-time messages subject to distance constraints (as illustrated in the transmission of continuous/isochronous media data). Also, Scheduler Sr devised for the DCTS model possesses a nice property: in addition to satisfying the distance constraints of all tasks, Sr will allocate at least C_i units of time to T_i during any time interval of length D_i for each task T_i with distance constraint D_i and computation time C_i. This suggests that Sr can be used as a candidate scheduler for scheduling the transmission of a set of message streams that satisfy certain traffic regulation and require deterministic delivery deadlines.

In the proposed research, we will extend our research results on the DCTS model to other application domains, lay a formal basis for transmitting messages with end-to-end delay bounds and delay jitter bounds, and design efficient and flexible connection establishment and scheduling schemes to achieve the above objectives in point-to-point packet(cell)-switched (e.g., ATM networks) and in wireless LANs.

We employ the (C,D)-smooth model to characterize traffic with timing requirements. The (C,D)-smooth message model specifies that the total message size of the messages in a message stream that can arrive during any time interval of length D is at most C. Note that the (C,D)-smooth message model is quite general, and includes the well-known real-time peak-rate message model and the linear bounded message model as special cases. Using the (C,D)-smooth model for traffic characterization, we will

• define the (C,D)-smooth message model and the timing constraints imposed by this model, and lay a formal basis for the connection establishment and message scheduling problems,
• devise an effective DCTS-based message scheduler to schedule messages from different streams at an intermediate node subject to maximum link delays and link delay jitters, and
• formally prove that as long as a connection conforms to the traffic characteristics specified during its establishment, the proposed message scheduler will enable every message in the stream to meet its end-to-end delay bound and delay jitter bound.

With the proposed point-to-point packet-switched network as the backbone network, we then address time-constrained communication services in wireless networks. The network under consideration consists of a number of wireless LANs connected to a wired backbone point-to-point network. Mobile units within a wireless LAN communicate with other (mobile or stationary) terminals through a base station (which is installed within the wireless LAN). The base station is connected to other base stations and/or stationary terminals through the backbone network. With this wireless network model, we will

• propose a media access control (MAC) protocol for the base station and the mobile clients to use the radio channel of a wireless LAN,
• devise an effective DCTS-based scheduler to coordinate the the access of the base station and mobile clients to the radio channel of a wireless LAN, and
• integrate the proposed scheduler devised for wireless LAN with the scheduler devised for point-to-point network to form a complete scheduling scheme for a wide area network which contains wireless LANs as subnetworks.

Return to Project Home Page
Date last modified -- July 30, 1996
Direct comments concerning this WWW site to: jhou@ece.osu.edu