Definition

As an MPLS-based point-to-multipoint (P2MP) Layer 2 Virtual Private Network (L2VPN) service provided over a public network, the virtual private LAN service (VPLS) ensures that geographically isolated user sites can communicate over metropolitan area networks (MANs) and wide area networks (WANs) as if they were on the same local area network (LAN). VPLS is also called the transparent LAN service (TLS).

Figure 8-1 shows a typical VPLS scenario. Users located in different geographical regions communicate with each other over different provider edge (PE) devices. An MPLS network is a Layer 2 switched network that allows users to communicate with each other similarly to communication over a LAN.

Figure 8-1  Typical VPLS scenario

Purpose

With increased use of applications such as VoIP, instant messaging, and teleconferencing, VPLS becomes increasingly important for enterprises setting up branches in different regions. This imposes high requirements for end-to-end (E2E) dotcom technologies. P2MP services are necessary for data communications.

Other commonly used technologies, such as asynchronous transfer mode (ATM) and frame relay (FR) can provide only Layer 2 point-to-point (P2P) connections. Compared to VPLS, networks using these technologies are costly to construct, complex to deploy, and slow. The development of Internet Protocol (IP) has led to MPLS VPN technology that provides VPN services over an IP network and offers advantages such as easy configuration and flexible bandwidth control. MPLS VPNs are classified as follows:

• MPLS L2VPNs

  These include virtual leased lines (VLLs). Ordinary MPLS L2VPNs can provide P2P services but not P2MP services over a public network.

• MPLS L3VPNs

  These provide P2MP services on the precondition that PEs keep routes destined for end users. This requires PEs to have high routing performance.

VPLS is a specific MPLS-based Ethernet technology that uses L2VPNs.

• Because it uses Ethernet, VPLS supports P2MP communication.

• VPLS is a Layer 2 label switching technology. From a user perspective, the entire MPLS IP backbone network is a Layer 2 switching device. PEs do not need to keep routes destined for end users.

VPLS integrates the advantages of both Ethernet and MPLS to provide a comprehensive multipoint communication solution. By emulating traditional LAN functions, VPLS enables users on different LANs to communicate with each other over MPLS networks as if they were on the same LAN.

Benefits

• VPLS networks can be constructed based on carriers' existing IP networks, reducing construction costs.

• VPLS networks inherit the high-speed advantage of the Ethernet.

• VPLS networks allow users to communicate over Ethernet links, regardless of whether these links are on WANs or LANs. This allows services to be rapidly and flexibly deployed.

• Administrators do not need to configure and maintain routing policies, reducing operational expenditure.