ZyXEL Communications MAX-200HW2, User Manual

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Chapter 11 VPN Transport
MAX-200HW2 Series User ’ s Guide
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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.
11.8.2 Generic Routing Encapsulation
In order to transport the VPLS traffic over the WiMAX network, the ZyXEL 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 ZyXEL Device and your service
provider ’ s router.
It is necessary to encapsulate the Ethernet pseudowire since the WiMAX connection is IP-
only. MPLS information is carried in a packet ’ s Ethernet header and, without encapsulation,
would be stripped from the packet prior to the packet ’ s transmission over the WiMAX link.
The following figure shows the VPLS connection between your ZyXEL Device ( A ) and your
service provider ’ s router ( B ), consisting of GRE-encapsulated Ethernet pseudowire traffic.
Figure 98 VPLS Tunneling
ETHERNET PSEUDOWIRES
GRE
TUNNEL
WiMAX CONNECTION