3Com MSR 50 Series Configuration Manual page 1317

MPLS Overview 1317
Nonetheless, MPLS can easily implement the seamless integration between IP
networks and Layer 2 networks of ATM, frame relay, and the like, and offer better
solutions to quality of service (QoS), traffic engineering (TE), and virtual private
network (VPN) applications thanks to the following advantages.
MPLS-based VPN
Traditional VPN depends on tunneling protocols such as GRE, L2TP, and PPTP to
transport data between private networks across public networks, while an LSP
itself is a tunnel over public networks. Therefore, implementation of VPN using
MPLS is of natural advantages.
MPLS-based VPN connects geographically different branches of a private network
to form a united network by using LSPs. MPLS-based VPN also supports the
interconnection between VPNs.
Figure 382 MPLS-based VPN
VPN 3
CE 3
PE 3
MPLS backbone
VPN 1 VPN 2
CE 1 PE 1 PE 2 CE 2
Figure 382 shows the basic structure of an MPLS-based VPN. Two of the
fundamental components are customer edge device (CE) and service provider
edge router (PE). A CE can be a router, switch, or host. All PEs are on the backbone
network.
PE is responsible for managing VPN users, establishing LSP connections between
PEs, and allocating routes among different branches of the same VPN. Route
allocation among PEs is usually implemented by LDP or extended BGP.
MPLS-based VPN supports IP address multiplexing between branches and
interconnection between VPNs. Compared with a traditional route, a VPN route
requires the branch and VPN identification information. Therefore, it is necessary
to extend BGP to carry VPN routing information.
MPLS-based TE
MPLS-based TE and the Diff-Serv feature allow not only high network utilization,
but different levels of services based on traffic precedence, providing voice and
video streams with services of low delay, low packet loss, and stable bandwidth
guarantee.
Since TE is more difficult to be implemented on an entire network, the Diff-Serv
model is often adopted in practical networking schemes.