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Cisco AVVID Network Infrastructure Enterprise Quality of Service Design
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Chapter 6 QoS with MPLS in an AVVID-Enabled Network
Implementing MPLS VPN QoS
A Data Multicast Data Tree (MDT) is a dynamically generated group, created when a customer's stream
of multicast traffic exceeds a configured threshold on the PE. The purpose of the MDT is to allow only
those remote PEs who are interested in that stream to receive it. Currently, only one MVRF is permitted.
Effectively, there can be only a single Closed User Group such that you can not provide for
MVRF-MVRF connectivity within the MPLS network, as can be done for unicast VRFs through the use
of route targets.
When MDTs are created, the remote PEs are notified of the Data MDT via a UDP packet on port 3232.
This UDP packet is sent on the default MDT to all remote PEs. The UDP packet encapsulates a
224.0.0.13, all PIM routers message. The receiving PE router runs an RFP check and verifies that the
originating PE is correct for the connected CE router. Each customer must use a different group number
for the MDT within the provider network.
Note
Cisco's implementation of MVPN is currently scheduled to FCS in IOS version 12.2(12)T, which is
subject to change. Contact the your Cisco representative to verify the availability of MVPNs.
One other option for providing IP multicast capabilities, is to use a satellite network for the transmission
of the IP multicast data. Within IOS, there are tools to provide for this functionality without causing
reverse path-forwarding failures. This is not unique to the MPLS environment and can be used to
supplement any data network.
Implementing MPLS VPN QoS
In an MPLS VPN, QoS is applied at all levels of the MPLS architecture: CE routers, PE routers, and
P routers.
CE Routers
As mentioned earlier, the CE routers are not aware of the presence of the MPLS VPN network. As a
result, the QoS capabilities of each CE device are unaltered, that is, the use of all QoS mechanisms
available for that platform is retained. WAN edge routers within the AVVID architecture are required
to be able to provide the appropriate queuing mechanisms, such as LLQ. The router may also provide
packet (re)classification, link fragmentation and interleaving, and congestion avoidance.
Following the AVVID architecture, the PE-CE link typically uses LLQ, with voice bearer traffic and
H.323 video conferencing traffic assigned to the priority queue, each policed individually with a separate
threshold. Voice bearer traffic is given a IP Precedence of 5 (DSCP label of EF). H.323 video
conferencing traffic is given an IP Precedence of 4 (DSCP label of AF41). All voice signalling traffic,
as well as data traffic, uses CBWFQ.
The CE router is responsible for all classification and marking to ensure that traffic is treated
appropriately throughout the MPLS network, conforming to the agreement with the carrier. In addition,
the CE router is required to perform traffic shaping to ensure that no packets are marked discard eligible
by the carrier and to match the rate agreed to by the SP.
For sites with a single CE-to-PE link, with or without a backup link, the CE router can use a single
default route from the MPLS network, rather than full routing tables. For more complex topologies, CE
routers typically require that the MPLS network send full routes to the customer routing protocol
(EIGRP, OSPF, etc.).