## 3 Related Works  
In this section, we delve into an exploration of recent advancements in VPLS and highlight their distinct characteristics. When VPLS was initially proposed, it was described as possessing a flat topology that was well-suited for small to medium-sized networks [10; 41]. However, these flat topologies encountered significant scaling challenges in both the data and control planes as larger networks necessitated a complete mesh of PWs. To mitigate this issue, the H-VPLS design was introduced as a viable solution by reducing the number of PWs and effectively addressing the scalability concerns [15]. In response to the early obstacles pertaining to  
Figure 5: VPLS Partial mesh scenario configuration in MPLS environment. Figure 6: H-VPLS with MPLS access network configuration in MPLS environment. Figure 7: H-VPLS with QinQ access network configuration in MPLS environment. scalability, security, and neighbor discovery, MPLS (Multiprotocol Label Switching) was employed instead of VPLS. Subsequently, the Border Gateway Protocol (BGP) and the Label Distribution Protocol (LDP) were suggested as two standard implementations for signaling and automatic neighbor detection [16]. Consequently, multiple architectural designs were proposed to enhance the operational capabilities of these frameworks. The authors of reference [41] provide an in-depth analysis of VPLS and its design, elucidating its capabilities, such as MAC addressing, packet encapsulation, loop avoidance, auto-discovery, and signaling. They also briefly touch upon the advantages of H-VPLS over flat topologies. However, with the increase in users, scalability and security have emerged as critical concerns in VPLS. In reference [42], the architecture and applications of SDN are explained, while the authors of reference [43] explore novel approaches to enhance VPLS security and scalability, leveraging the potential of SDN. According to reference [42], SDN has the potential to address the scalability issues in VPLS. The communication path between the control plane and the data plane is referred to as the control channel, which is established using SDN control protocols. Network control functionalities and services are implemented as software applications in the application plane [17]. The controller sends flow entries to the data plane devices to govern their forwarding behavior, which is stored in local flow tables. If there is no matching entry, the packet is forwarded to the controller for further processing. In reference [17], an SD-VPLS architecture is described where each LAN is represented as an island, with the Island Controller responsible for controlling the OpenFlow switch, packet acceptance, and forwarding to the provider's network. The majority of VPLS topologies utilize MPLS as the underlying network infrastructure. MPLS acts as a virtual bridge within the network core, connecting various attachment circuits on each PE device and creating a unified broadcast domain [44]. BGP is a fundamental component of VPLS networks. BGP consists of speakers, peers, connections, and border routers. A BGP speaker is a host responsible for implementing the BGP protocol within the network. BGP peers are pairs of BGP speakers that establish connections and communicate with each other. An external BGP peer is located in a different autonomous system than the reference BGP speaker, while an internal BGP peer is within the same autonomous system [45]. Reliable BGP links are established using TCP. Signaling plays a crucial role in VPLS and involves the exchange of demultiplexers to establish and tear down PWs. Specific PW characteristics are transmitted during signaling, allowing a PE to establish a particular VPLS. Signaling occurs after the auto-discovery process is completed. The exchange of demultiplexers among PEs enables the transmission of update messages to other PEs in the same VPLS instance, thereby increasing the load on both the PE and the control plane [10].