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Chapter 9 The VPN Transport Screens
User’s Guide
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interface is simply a set of information that takes frames from a VLAN and put
them on an Ethernet pseudowire, and vice versa.
In this example, the WiMAX Device takes frames tagged with two different VLAN
IDs (10 and 20) and using the customer interfaces, assigns them to specific
pseudowires (PW1 and PW2).
Figure 49 Pseudowire Mapping
The WiMAX Device has a default customer interface configured for frames that
arrive at the WiMAX Device without VLAN tags.
9.3.1 Multi-Protocol Label Switching
The WiMAX Device uses MPLS VPNs to create virtual private LANs. MPLS stands for
Multi-Protocol Label Switching, and is a packet-switching technology that allows
packets with different VLAN tags to be transported on different paths (known as
LSPs, or Label Switched Paths). Each packet is identified by its VLAN tag and sent
to a specific LSP for transport over the WiMAX network.
Each LSP has a defined start-point and end-point. Since MPLS creates mono-
directional paths (traffic flows in only one direction), each Ethernet pseudowire
uses two LSPs so that traffic can flow both ways. One LSP carries upstream traffic,
and the other carries downstream traffic.
9.3.2 Generic Routing Encapsulation
In order to transport the VPLS traffic over the WiMAX network, the WiMAX Device
uses the Generic Routing Encapsulation (GRE) protocol. Like MPLS, GRE is a
tunneling protocol that has specified endpoints. The GRE tunnel is bi-directional,
and transports both LSPs. The GRE tunnel runs across the WiMAX network
between the WiMAX Device and your service provider’s router.
VLAN 10 PW1
VLAN 20 PW2
10
20
PW1
PW2
1
2
WiMAX
R