MPLS VPN QoS 237
In Router NewYork, the second section of the BGP configuration shows that you use BGP
peering to learn the VRF green routes from New York site. Note that on Router
SanFrancisco discussed earlier, you configured the San Francisco site VRF green routes
statically.
MPLS VPN QoS
QoS is a key component of a VPN service. Similar to IP QoS discussed in Part I of the book,
the MPLS VPN QoS can be a differentiated service or a guaranteed service. You can use the
same IP QoS functionality discussed in Part I, “IP QoS,” to deliver MPLS VPN QoS. The
coarse-grained differentiated QoS is provided by use of the CAR, WFQ, and WRED
functions, whereas the fine-grained guaranteed service is provided by use of the RSVP
protocol.
Differentiated MPLS VPN QoS
This QoS model delivers capabilities that, in some ways, look similar to Committed
Information Rate (CIR) in a Frame Relay network.
Each VPN site is offered a CAR and a Committed Delivery Rate (CDR) for each port at
which they access the network. In a Frame Relay network, CIR applies to both the incoming
and the outgoing traffic from a device connected to the network. In a connectionless IP VPN
environment, however, two different rates exist for each port connected to the network
offering VPN service:
CAR for all incoming traffic from the site into the VPN service network’s access port
CDR for all outgoing traffic from the rest of the VPN network to the site connected
through the access port
The traffic on an MPLS VPN-enabled network’s access port is said to be committed if the
access port’s incoming and outgoing traffic falls below the contracted CAR and CDR,
respectively. Committed packets are delivered with a probability higher than that of
uncommitted traffic.
Because of the connectionless nature of an IP VPN service, you can send packets from any
site to any site within a VPN, but you must specify the committed traffic rate for a site’s
outgoing and incoming traffic separately. Because Frame Relay is connection-oriented, the
same traffic rate applies for both ends of the circuit.
To implement CAR and CDR service on an access port, a traffic policing function for both
incoming and outgoing traffic is applied. A policing function applies a higher IP precedence
value for committed traffic than uncommitted traffic. In the service provider VPN
backbone, the WFQ and WRED differentiated QoS functions are applied to deliver
committed traffic at a probability higher than uncommitted traffic. Table 9-5 illustrates the
QoS functions applied on traffic from one VPN site to the other through an MPLS VPN
provider network.

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