Multimedia applications such as music or video streaming, video teleconferencing and IP telephony are flourishing in packet-switched networks. Applications that generate such real-time data can have very diverse quality-of-service (QoS) requirements. In order to guarantee diverse QoS requirements, the combined use of a packet scheduling algorithm based on Generalized Processor Sharing (GPS) and leaky bucket traffic regulator is the most successful QoS mechanism. GPS can provide a minimum guaranteed service rate for each session and tight delay bounds for leaky bucket constrained sessions. However, the delay bounds for leaky bucket constrained sessions under GPS are unnecessarily large because each session is served according to its associated constant weight until the session buffer is empty. In order to solve this problem, a scheduling policy called Output Rate-Controlled Generalized Processor Sharing (ORC-GPS) was proposed in [17]. ORC-GPS is a rate-based scheduling like GPS, and controls the service rate in order to lower the delay bounds for leaky bucket constrained sessions. In this paper, we propose a call admission control (CAC) algorithm for ORC-GPS, for leaky-bucket constrained sessions with deterministic delay requirements. This CAC algorithm for ORC-GPS determines the optimal values of parameters of ORC-GPS from the deterministic delay requirements of the sessions. In numerical experiments, we compare the CAC algorithm for ORC-GPS with one for GPS in terms of schedulable region and computational complexity.

Interference in ad hoc WLANs is a common occurrence as there is no centralized access point controlling device access to the wireless channel. IEEE 802.11 WLANs use carrier sense multiple access with collision avoidance (CSMA/CA) which initiates the Request to Send/Clear to Send (RTS/CTS) handshaking mechanism to solve the hidden node problem. While it solves the hidden node problem, RTS/CTS triggers the exposed node problem. In this paper, we present an evaluation of a method for reducing exposed nodes in 802.11 ad hoc WLANs. Using asymmetric transmission ranges for RTS and CTS frames, a cross-layer design is implemented between Layer 2 and 3 of the OSI model. Information obtained by the AODV routing protocol is utilized in adjusting the RTS transmission range at the MAC Layer. The proposed method is evaluated with the NS-2 simulator and we observe significant throughput improvement, and confirm the effectiveness of the proposed method. Especially when the mobile nodes are randomly distributed, the throughput gain of the Asymmetric RTS/CTS method is up to 30% over the Standard RTS/CTS method.