The IMS determines the conditions and requirements to be implemented by factories in order to ensure accuracy of measurement devices used in all stages of production. For certain product groups the certification is mandatory see here for details. If the certification is not mandatory, manufacturers can choose to implement the system as an option. There is no on-site audit necessary for the IMS certification. Figure 1 Horizontal and vertical telecommunication architectures 3.
The telecommunications industry is adopting the IP Multimedia Subsystem ims as the reference architecture for the development of all telecommunica tions services for ngns 4 that are able to support current telecommunica tions services and that will be useful in the future. One advantage of ims is that it integrates the concept of the convergence of services supported by heterogeneous networks, i.
However, ims does not standardize applications but facilitates access to multimedia applications and voice access to different types of terminals and access technologies. One of the most important aspects concerning the convergence of services is Quality of Service QoS because IP networks originally lacked QoS control mechanisms.
These networks were designed to provide service delivery without guaranteeing the reliability of the corresponding information, depending on the amount of bandwidth required, especially for services requiring real-time connections 5. Based on recommendation Y.
Globally, QoS is currently one of the most researched areas because of its interest to users, operators and regulators 7. Therefore, QoS policy control has become an important research topic 9 , The IP Multimedia Subsystem is a reference architecture for next-generation service provision standardized by the 3 rd Generation Partnership Project 3gpp and introduced into umts Releases 5 and 6 March This subsystem is important because it allows different types of access networks to be integrated regardless of technology or internet services combining fixed and mobile networks 13 ; however, for the 3gpp ims described from the point of view of mobile operators those that support new applications , a body of standardization telecommunication members of the European Standards Institute etsi called the Telecommunications and Internet Converged Services and Protocol for Advanced Networking tispan adds the necessary ims compatible with networks of fixed-operator convergence specifications.
The flexibility of this architecture allows for modifications and extensions in the subsystem 14 , and it also simplifies the application design by harmonizing the ability to obtain session control through the Session Initiation Protocol sip Figure 2 illustrates the ims architecture and its three main levels 16 , which are as follows: the multimedia services layer; the control session layer; and the ip transport layer, in which an ims-based network architecture enables the convergence of different technologies for access networks, such as a fixed network pstn, a broadband xdsl, a wireless lan, or 2G, 3G and 4G cellular mobile networks.
Figure 2 IMS architecture of layered and access networks A distinction must be made between "ims core" and "ims" because the ims architecture refers to a "core" or "ims core" defined by 3gpp in addition to a non-ims subsystem number defined by tispan , such as the Network Attachment Subsystem nass , a Resource Admission Control Subsystem racs or the pstn Emulation Subsystem pes The central components of the ims architecture are the Call Session or State Control Function cscf entities, which are actually sip servers.
These entities have specific functions for signaling and routing traffic 18 and are located at the core level of the Proxy-cscf p-cscf , the Interrogating-cscf i-cscf , the Serving-cscf s-cscf , the Home Subscriber Server hss and the Application Server as. Figure 3 IMS architecture of the layered components Figure 3 shows the different types of components used in the ims architecture 19 ; the main elements found in a basic solution are the CSCF entities.
Simi larly, various functional entities for managing fixed and mobile networks are defined, and some entities are responsible for contacting the transport network to ensure QoS and prevent misuse of the services provided. The specification of the functional architecture of an ims subsystem can be found in 3gpp One of the essential criteria for evaluating a system lies in the measurement of network performance from the points of view of deployment, operation and customer satisfaction.
Quality of Experience is related to the satisfaction levels centered on the user according to their expectations, perceptions and un derlying effect on QoS The overall effect of these factors has a subjective evaluation that can vary between low, medium or high percentages These parameters are focused on the user and are of great research interest Quality of Service provides a set of metrics focused on network performance 26 , which can be technically evaluated and are ne gotiated based on the possible factors that define QoE In IMS QoS, control plays an important role through a series of indicators that allow for evaluations according to service type, such as bandwidth, e2e delay delay , delay variation jitter , data rate and bit error rate Within the context of an IP network, a service refers to the overall traffic handling of a client through a particular domain; a service is useful only if it meets the requirements of the end user Corresponding to the ims services, these requirements also apply to the interconnection of networks that are IP-based ip-can access networks and ims.
These four classes are listed in table 1. Table 1 QoS classes for transport networks An e2e multimedia session can traverse a series of heterogeneous admin istrative domains in NGNs, in which the control system of policies must be able to guarantee the QoS resources in all domains involved Figure 4.
Each domain defines its own mechanisms and policies for the provision of QoS depending on the technologies that are accessible to the operator; however, in an e2e session, a mutual negotiation of Service Level Agreements slas between the domains involved is required. An sla is a formal contract 31 negotiated between two parties that defines the commitment levels associated with network performance and service responsiveness. The two parties can be a user and an operator or two operators, in which case one takes the role of customer to purchase services from another provider Figure 4 QoS management across domains DiffServ is based on the division of traffic into different classes and the prioritization of these aggregates with a code in the datagram when congestion occurs 9.
The nodes in the network must know and identify the code to prioritize packets IntServ implements a channel reservation and admission control packets through the nodes in the network using the rsvp Resource Reservation Protocol ; the implementation consists of three types of services, controlled, guaranteed and best effort load However, there are issues concerning scalability and complexity, which are overcome by implementing DiffServ 37 ; all cases of interoperability between operators are based on the use of SLAs, which is an integral part of DiffServ The ietf describes a policy framework through RFC 39 Figure 5 , which sets policy rules defined as models that become network configurations or devices in an administrative domain.
These rules are stored in repositories called Policy Decision Points pdps and Policy Decision Functions pdfs ; these repositories recover the rules of appropriate policies in response to requests for policies that are generated by the QoS requirements of services The Policy Enforcement Point pep refers to the point where a server enforces policy admission control and policy decisions in response to a transaction request from a user who wants to access a resource on a server network.
It is the main component that interacts with the access network and the core network that carries a service that can affect the priorities of the packets through the DiffServ protocol and book resources with RSVP For example, the entities of the access network and the entities of the home NGN network that belong to different operators must pass through the SEGFs.
Security domain 1 Security domain 2. It can be assumed that communications between the functional entities belonging to a same security domain are free of threats because it is a network under the administrative domain of the same operator or, optionally, the IPSec ESP Zb interface can be used to ensure communications between them.
The yellow-colored functional entities pertain to applications. The functional entities whose abbreviations have the letter A preceding them pertain to access network entities, those with the letter V preceding them pertain to the home network and those with the letter H preceding them pertain to the home network. Security domains in general are needed to: Protect the integrity, and optionally the confidentiality, of functional entities and their activities. Figure 4 — IPSec Tunnel between SEGFs It can be assumed that communications between the functional entities belonging to a same security domain are free of threats because it is a network under the administrative domain of the same operator or, optionally, the IPSec ESP Zb interface can be used to ensure communications between them.
CITEL offered 15 scholarships of the complete amount of the registration fee. The RACS layer is the TISPAN next-generation network subsystem that is responsible for elements of policing control, including resource reservation and admission control in the access and aggregation networks.
The RACS layer also includes support for NAT in the access, aggregation, and core networks required to support end-to-end application-initiated sessions. The RACS provides policy-based transport control services to applications.
These services enable applications to request and reserve transport resources from the transport networks within the scope of the RACS. These requests indicate IP QoS characteristics. The SPDF is a functional element that coordinates the resource reservation requests that it receives from the application function the application-level controller, such as a SIP server.
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