VPWS is an L2VPN technology that transmits Layer 2 services by simulating the basic behaviors and features of services, such as ATM, FR, Ethernet, low-speed time division multiplexing (TDM) circuits, and synchronous optical network (SONET)/synchronous digital hierarchy (SDH) on a packet switched network (PSN). VPWS emulates the traditional leased line on an IP network and provides asymmetric and low-cost digital data network (DDN) services. For users at both ends of a VPWS connection, the connection is similar to the traditional leased line. VPWS functions as a point-to-point virtual private wire technology that can support almost all the link layer protocols.
As IP networks develop, the expansibility, upgradability, and compatibility of IP networks have been greatly enhanced. Nevertheless, the expansibility, upgradability, and interworking capability of traditional communications networks are relatively poor. Confined by transmission modes and service types, resource sharing among newly constructed communications networks is also poor, complicating interworking management. In the process of upgrading and expanding a traditional communications network, you must determine whether to achieve your goal by constructing more traditional communications networks, or by utilizing existing network resources at your disposal, or by utilizing public network resources. VPWS is a solution that enables traditional communications networks to interwork with existing PSNs.
VPWS offers the following benefits:
Carriers can provide MPLS L2VPN services by using only one network. In addition, carriers can use enhanced MPLS-related technologies, such as traffic engineering (TE) and quality of service (QoS), to provide users with different classes of services to meet their requirements.
On an ATM network where MPLS is not enabled, virtual circuits (VCs) are used to provide the L2VPN service. For each VC, both the PE and provider (P) devices on the network need to maintain complete VC information. That means that when the PEs of a carrier connect to multiple CEs, multiple VCs are required, and information about multiple VCs must be maintained on both PEs and Ps. VPWS uses label stacking to multiplex multiple VCs on a label switched path (LSP). As a result, Ps only need to maintain information about one LSP. This improves the scalability of a system.
On a VPWS network, a carrier provides only Layer 2 connectivity and users are responsible for Layer 3 connectivity, such as routing. This implementation prevents route flapping caused by incorrect configurations from affecting the stability of the carrier's network.
Carriers provide only Layer 2 connections, whereas users can use any Layer 3 protocol, such as IPv4 and IPv6.
The VPWS network is transparent to users. When a carrier upgrades the network from a traditional L2VPN, such as an ATM network, to a VPWS network, users do not need to perform any configuration. The network upgrade does not affect user services, except for data loss for a short period during the network cutover.