HP Intelligent Management Center Licenses - Manual (Page 10)

Basic VLL concepts
VLL(Virtual Leased Line): VLL provides point-to-point L2VPN services over the public network. With
VLL, two sites can communicate as if they were directly connected. VLL is a form of MPLS L2VPN.
It uses inner labels to identify virtual lines (Layer 2 tunnels), hereinafter referred to as virtual circuits
(VCs), and uses outer labels to identify public tunnels. The network devices of the service provider
do not need to maintain any Layer 2 information but perform MPLS forwarding on the public
neworks based on MPLS labels. In VLL, a Forwarding Equivalence Class (FEC) is about the VC
indentifier and some Layer 2 information.
The above figure shows a typical VLL networking scenario. With the existing technologies, VLL can
be implemented mainly in two methods, which use different signaling protocols to exchange VC
information. One method is called Martini (the L2VPN Manager only support this method). The
Martini method uses a standard two-layer label stack. The inner labels (VC labels) are exchanged
through the extended LDP. The Martini draft extends the standard LDP, adding a new FEC type,
the VC FEC, for exchanging VC labels. A VC FEC identifies a VC by VC Type and VC ID. VC Type
indicates the link layer encapsulation type and VC ID uniquely indentifies a VC of the same type
on a PE. The PEs that connect two CEs switch VC labels through LDP and bind the corresponding
CEs by the VC ID. A VC between the two CEs are then established and the two CEs can transport
Layer 2 data over the VC. The Martini method does not provide the local switching function. Outer
labels will be used to transport VCs' data over the service provider network. Because PEs can
identify data of different VCs by inner label, multiple VCs can share the public tunnel.
PBB overview
PBB Overview PBB is proposed to satisfy the Metro Ethernet Network (MEN) requirements. In the
MEN service hierarchy model, PBB is at the carrier level, used to establish MAC tunnels to separate
services of different customers on the backbone. A network employs 802.1ah is called a Provider
Backbone Bridge Network (PBBN).
Basic concepts of PBB
10 L2VPN Manager