Alcatel-Lucent 7750 SR-OS, Configuration Manual

Page: 26 / 674

Configuring IP Router Parameters
Page 26 7750 SR OS Router Configuration Guide
achieved by advertising the source prefix with a BGP community, as discussed above. However, in
this case other approaches are equally valid, such as marking the DSCP or other CoS fields based
on source IP address so that downstream domains can take action based on a common
understanding of the QoS treatment implied by different DSCP values.
In the above examples, coordination of QoS policies using QPPB could be between a business
customer and its IP VPN service provider, or between one service provider and another.
Traffic Differentiation Based on Route Characteristics
There may be times when a network operator wants to provide differentiated service to certain
traffic flows within its network, and these traffic flows can be identified with known routes. For
example, the operator of an ISP network may want to give priority to traffic originating in a
particular ASN (the ASN of a content provider offering over-the-top services to the ISP’s
customers), following a certain AS_PATH, or destined for a particular next-hop (remaining on-net
vs. off-net).
Figure 1 shows an example of an ISP that has an agreement with the content provider managing
AS300 to provide traffic sourced and terminating within AS300 with differentiated service
appropriate to the content being transported. In this example we presume that ASBR1 and ASBR2
mark the DSCP of packets terminating and sourced, respectively, in AS300 so that other nodes
within the ISP’s network do not need to rely on QPPB to determine the correct forwarding-class to
use for the traffic. Note however, that the DSCP or other COS markings could be left unchanged in
the ISP’s network and QPPB used on every node.