Abstract-To bring TCP-based services to the mobile devices in a cellular network, it is necessary that TCP be extended over the wireless link. However, the performance of TCP severely degrades in a wireless medium. Hence, radio link protocols (RLPs) are used as an interface between TCP and the physical medium. RLPs fragment TCP segments into frames and use robust error correcting codes and fast retransmission schemes to shield the channel related losses from TCP, thus preventing TCP throughput degradation. In this paper, we show the limitations of the existing RLPs, which do not differentiate the frames generated from the same TCP segment. We claim that if selective frames are made more robust to transmission failures, then the performance of RLP and, hence, TCP can be improved. We identify such decisive frames and categorize them as crucial and noncrucial. Our claim is based on the fact that initial frames can afford a few trials of retransmissions, whereas the later ones cannot. We treat the frames differentially with respect to forward error correcting (FEC) coding and automatic repeat request (ARQ) schemes. We consider specific cases of FEC and ARQ strategies and show the qualitative difference in the performance of the RLP through analysis and simulations. The gain in the performance is more prominent when both FEC and ARQ (hybrid-ARQ) are used. The increase in TCP throughput with the proposed RLP is also demonstrated.

In this paper, we propose enhancements to radio link protocols by identifying decisive frames and categorizing them as crucial and non-crucial. The fact that initial frames from the same upper layer segment can afford a few trials of retransmissions and the later frames cannot, motivates our work. We treat the frames differentially with respect to FEC coding and ARQ schemes. We consider specific cases of FEC and ARQ strategies and qualitatively show how the differential treatment of frames can improve the performance of the RLP.

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Secure communication in ad hoc networks is an inherent problem because of the distributiveness of the nodes and the reliance on cooperation between the nodes. All the nodes in such networks rely and trust other nodes for forwarding packets because of their limitation in the range of transmission. Due to the absence of any central administrative node, verification of authenticity of nodes is very difficult. In this paper, we propose a clusterhead-based distributed security mechanism for securing the routes and communication in ad hoc networks. The clusterheads act as certificate agencies and distribute certificates to the communicating nodes, thereby making the communication secure. The clusterheads execute administrative functions and hold shares of network keys that are used for communication by the nodes in respective clusters. Due to the process of authentication, there are signalling and message overheads. Through simulation studies, we show how the presence of clusterheads can substantially reduce these overheads and still maintain secure communication.