Telecommunications operators and research institutions pay close attention to the issue of quality of service. The paper deals with methods of admission control in IP networks, which is only one of the subsets of quality of service. There are two large groups of AC methods: parameter-based admission control and measurement-based admission control. The core of the paper is simulation of AC methods and algorithms for topology model in MATLAB. Our simulations are mainly focused on required bandwidth and loss rates. At the end of the paper there are compared results of simulations. 1. Introduction Nowadays we face the unstoppable development of information technology, which penetrate into various spheres of users activities and services. Technology make available to end users more and more information. One of the technological advances to which the term information technology is related is a computer network. It is used in many ways, but especially for the transmission of voice, video, and data (i.e., communication). Network provides conditions for Quality of Service (QoS), which lead to the satisfaction of the end user. The process, which significantly affects the QoS, is admission control methods [1, 2]. The present and future networks are a precondition for the satisfaction of user availability of needed bandwidth. In places where the replacement of infrastructure would be costly it is necessary to develop means for more efficient use of available bandwidth. One of the tools used in IP Multimedia Subsystem (IMS) technology is an element of Resource Admission Control Subsystem (RACS). RACS is an important logical network element that is used to communicate between the control layer and transmission management functions resource reservation, admission control, support for border gateway services, network address translation, networks aggregation, and QoS support. Between RACF (Resource Admission Control Function) element and RACS element there are some differences consisting in bandwidth reservation, sharing service addresses across the network. It could be said that RACS is in some way specification of RACF. It was designed by TISPAN organization. A network element is responsible for the implementation of procedures and mechanisms handling policy-based resource reservation and admission control for both unicast and multicast traffics in access networks, core networks, and customer premises networks [3]. RACS reserves appropriate resources and allow the requirement assuming policies, and required resources in the transport network are available. RACS
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