Abstract
This Special Issue originates from the international conference 2021 Joint EuCNC & 6G Summit (Joint European Conference on Networks and Communications and 6G Summit), which was held in June 2021 in virtual format. The Technical Programme Chairs of the conference selected the best papers and invited authors to submit an extended version of their paper by at least one-third of their length. Only the top ranked papers were invited to this Special Issue, in order to fulfil its purpose. The main target was to collect and present quality research contributions in the most recent activities related to technologies, systems and networks beyond 5G. Through this Special Issue, the state-of-the-art is presented and the new challenges highlighted, regarding the latest advances on systems and network perspectives that are already being positioned beyond 5G, bridging as well with the evolution of 5G, including applications and trials. Therefore, the motivation for this Special Issue is to present the latest and finest results on the evolution of research of mobile and wireless communications, coming, but not exclusively (since Joint EuCNC & 6G Summit is a conference open to the whole research community), from projects co-financed by the European Commission within its R&D programmes.

Abstract
In the networking research and development field, one recurring problem faced is the duplication of effort to write first simulation and then implementation code. We posit an alternative development process that takes advantage of the built in network emulation features of Network Simulator 3 (ns-3) and allows developers to share most code between simulation and implementation of a protocol. Tests show that ns-3 can handle a data plane processing large packets, but has difficulties with small packets. When using ns-3 for implementing the control plane of a protocol, we found that ns-3 can even outperform a dedicated implementation.

Abstract
The users of telecommunications services are demanding access to their subscribed services in mobile contexts. This demand leads to the development of mechanisms that enable the transference of service sessions between networks, seamlessly to the user. These mechanisms allow the operator to jointly manage its networks resources, providing a better service to its customers and, simultaneously, increasing its revenue. Starting from the UMTS and WLAN interconnection architecture defined by 3GPP, this paper presents a new strategy for joint radio resource management, suitable for contexts where these networks are interconnected. This strategy bases its decisions on criteria related to user mobility characteristics. The algorithm also introduces the possibility of renegotiating new calls and reallocating running calls from one access network to another. The new radio resource management strategy is compared with two well-known strategies, the former based on coverage area and the later based on load balancing. The comparison studies show the proposed strategy outperforms the other strategies in what concerns call blocking probability and applications QoS support. Besides, the proposed strategy tends to reduce the handoffs between networks.

Abstract
ATM networks will support new multimedia services that will require new protocols. Those services and protocols will need different test strategies and tools. In this paper, the concepts of functional and non-functional testers of ATM networks are discussed, a multimedia service and its requirements are presented and, finally, a summary description of an ATM network and of the test tool that will be used to validate it are presented.

Abstract
This paper presents a Multimedia Art Directory, that has been developed for an ATM network, by describing its main characteristics and the creation environment and the network facilities used.

Abstract
Factors such as the growing number of multimedia terminals, the constant increase of bandwidth available per user, and the large number of existing data sharing applications, are compelling users to generate and distribute their own content to restricted groups of other users. Inorder to support such scenario, we present an IMS-based solution that enables content distribution, in multicast, to groups of users, where the source of the content is also an end-user The proposed solution allows the source of content to configure the service, indicating a list of authorized receivers and both the transmission date and duration. Moreover, the proposed solution also allows the operator to manage the registered user profiles, to impose access control and to validate the configurations submitted by the users.