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Qualité de Service et Performances des Protocoles de Transport dans l'UTRAN

Abstract : The 3GPP (3rd Generation Partneship Project) has chosen, in the Release 99, the AAL2/ATM protocol as a transport protocol on the Iub et Iur interfaces of the UMTS access network called UTRAN (UMTS Terrestrial Radio Access Network). The AAL-2 (ATM Adaptation Layer - Type 2) is an adaptation layer above the ATM layer. It consists in aggregating several packets from different flows in the same ATM cell in order to decrease the packetization delay especially for low bit rate real time applications. There are few studies about the performance of the AAL2 protocol but there are no enough studies of the AAL2 in the special context of the UTRAN where the time constraints become stringent because of the synchronisation mechanisms of the radio channels. The link between a Node B and a RNC, where the AAL2 protocol is deployed, should not be the bottleneck of the network. The AAL2 protocol should be well studied to evaluate its performance and its capabilities for the transport of radio channels.
The AAL2 is a real transport protocol but in the specifications, there is no quality of service (QoS) definition at the AAL2 layer. We contributed to define some classes of service, QoS parameters, AAL2 transfer capabilities (AAL2-TC) and performance criterions. Then, we propose a mapping scheme on the one hand between the different classes of service of the UMTS and the classes of the AAL2 layer and on the other hand between AAL2 classes and ATM classes. We propose a bandwidth sharing scheme between different classes as well as a connection admission control scheme for AAL2 connections. In the case where several types of flows are aggregated in the same ATM VC, a scheduling mechanism is needed to differentiate between the different classes of service. Several scheduling algorithms are proposed at the AAL2 layer and a comparison between them is done in several contexts in order to evaluate the advantages and drawbacks of each algorithm. We propose also a new dynamic scheduling algorithm called DyWRR. Then, we studied an important parameter of the AAL2 protocol that is the Timer-CU (Timer-Combined Use). This parameter has an impact on the transfer delay and on the bandwidth efficiency. A detailed study of this parameter is achieved in order to obtain results about the optimal value of this parameter. The choice of the ATC (ATM Transfer Capability) for the transport of AAL2 connections represents a part of our study. The DBR and the SBR are two proposed solutions and a comparison between their performances is done. The AAL2 switching technology is an important aspect in the AAL2 networks. Small and variable size packets (mini-cells) are switched rather than ATM cells. The AAL2 switching technology is studied to evaluate its advantages and drawbacks and to compare it with the ATM switching technology.
The results of our study on the AAL2 were used in a contribution to the standardization works of the ITU-T (International Telecommunication Union Telecommunication standardization sector). These standardization efforts had leaded to a new standard called ITU-T I.378 which treats the problematic of the quality of service and traffic control at the AAL2 layer.
In the Release 5 of the 3GPP, the IP protocol was chosen to transport radio channels on Iub and Iur interfaces. The IP protocol cannot guarantee a quality of service without any special mechanisms like DiffServ or IntServ because in the present networks, only one class of service is used, the Best Effort class. Several architectures are presented for the use of the IP protocol on the Iub interface. These solutions introduce additional overhead because of the long size headers. The optimization of the bandwidth especially at the Last Mile Link is an important issue for the telecommunication operators. Then, we studied several solutions in order to evaluate their performance in the special context of the UTRAN.
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Submitted on : Monday, April 5, 2004 - 5:57:31 PM
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  • HAL Id : tel-00005734, version 1

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Rani Makké. Qualité de Service et Performances des Protocoles de Transport dans l'UTRAN. Réseaux et télécommunications [cs.NI]. Télécom ParisTech, 2003. Français. ⟨tel-00005734⟩

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