No abstract

No abstract

Session Initiation Protocol (SIP) h as been widely applied to telephony service. SIP is also adopted as the signal communication protocol of VoIP and 3GPP, so the development of SIP receiving much concern. Currently the research of SIP can be divided into four issues, including terminal mobility, session mobility, personal mobility, and service mobility. In this paper, we address the issue of session mobility. We want to solve the problem allowing a user to transfer, split, and retrieve a session over multiple devices by using SIP. In order to provide the service, three new agents have been introduced based on the definition of user agent proposed in RFC 3261. There are session manager, session user, and free node. Based on these agents, we propose a complete mechanism, to transfer and retrieve a session over multiple devices. According to our mechanism, the user will facility transfers, splits, and retrieves a session over multiple devices. Finally, we implement the mechanism by modifying the open source project of "Sip-Communicator".

No abstract

For achieving high utilization and efficient code management of the OVSF code tree in 3G WCDMA networks, several researches have extensively studied. Based on combining both the code assignment and the reassignment mechanisms, it increases obviously high utilization and reduces completely the code blocking. Nevertheless, the required rate of traffic should be powers of two of the basic rate, i.e. 1R, 2R, 4R, . . ., etc., which is impractical and results in wasting the system bandwidth while the required rate is not powers of two of the basic rate. Several multi-code assignment mechanisms have proposed to reduce the waste rate. Nevertheless, these methods bring two inevitable drawbacks including, high complexity of handling multiple codes, and increasing the cost of using more rake combiners at both the base stations and mobile nodes. Therefore, we propose an adaptive grouping code assignment herein to provide a single channelization code for any possible rate of traffic, even though the required rate is not powers of two of the basic rate. Based on the dynamic programming algorithm, the adaptive grouping approach forms several calls into a group. Then it allocates a subtree to the group and adaptively shares the subtree codes for these calls in the concept of time-sharing of slots during a group cycle time. Therefore, the waste rate and code blocking are thus reduced obviously while using a single rake combiner. Since the delay problem may be occurred in such a time-sharing approach, we propose two schemes of cycle interleaving methods to reduce delay. Numerical results indicate that the proposed adaptive grouping approach reduces significantly the waste rate and thus increases the system utilization. Moreover, the proposed cycle interleaving scheme reduces data delay significantly.