20-19
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 20 Configuring Quality of Service for MPLS Traffic
MPLS Traffic Engineering—DiffServ Aware
MPLS traffic engineering allows constraint-based routing of IP traffic. One of the constraints satisfied
by constraint-based routing is the availability of required bandwidth over a selected path. DS-TE extends
MPLS TE so that constraint-based routing and admission control of special TE tunnels (referred to as
guaranteed bandwidth TE tunnels) are performed over a more restrictive bandwidth constraint than
regular TE tunnels. A more restrictive bandwidth constraint enables you to achieve higher QoS
performance (in terms of delay, jitter, or loss) for the guaranteed traffic.
The more restrictive bandwidth is referred to as a
sub-pool
, while the regular TE tunnel bandwidth is
called the
global pool
. The sub-pool is a portion of the global pool and applies to tunnels that carry traffic
requiring strict bandwidth guarantees or delay guarantees. The global pool applies to tunnels that carry
traffic requiring only differentiated service.
Having a separate pool for traffic requiring strict guarantees allows you to limit the amount of such
traffic admitted on any given link. Often, it is possible to achieve strict QoS guarantees only if the
amount of guaranteed traffic is limited to a portion of the total link bandwidth.
Having a separate pool for other traffic (best-effort or DiffServ traffic) allows you to have a separate limit
for the amount of such traffic admitted on any given link. This is useful because it allows you to fill up
links with best-effort and DiffServ traffic, thereby achieving a greater utilization of those links.
The DS-TE feature also extends the Open Shortest Path First (OSPF) routing protocol so that the
available sub-pool bandwidth at each preemption level is advertised in addition to the available global
pool bandwidth at each preemption level. The DS-TE feature also modifies constraint-based routing to
take this more complex advertised information into account during path computation.
For more information, see the
MPLS Traffic Engineering—DiffServ Aware, Release 12.2(14)S
feature
module.
Feature History for MPLS TE—DS
Sub-pool Tunnels
A sub-pool tunnel carries traffic that requires strict bandwidth guarantees or delay guarantees, such as
real-time voice, virtual IP leased line, and bandwidth trading traffic. As traffic enters the sub-pool tunnel,
DS-TE marks the traffic with a unique value in the MPLS EXP field. The router places traffic with this
unique value in the guaranteed bandwidth queue at the outbound interface of every tunnel hop. The strict
guaranteed traffic has exclusive use of the guaranteed bandwidth queue; no other traffic can use this
queue.
DS-TE ensures that the guaranteed bandwidth queue is never oversubscribed and limits the amount of
traffic that enters the queue to a percentage
of the total bandwidth of the corresponding outbound link.
Therefore, the amount of traffic sent into the sub-pool is never more than the amount the guaranteed
bandwidth queue can handle.
Cisco IOS Release
Description
Required PRE
Release 12.3(7)XI
The MPLS Traffic Engineering—DiffServ Aware (DS-TE)
feature was introduced on the PRE2.
PRE2
Release 12.2(28)SB
This feature was integrated in Cisco IOS
Release 12.2(28)SB for the PRE2.
PRE2
