Specifications

Configuration Tasks
8
Cisco IOS Release 12.0(3)T
• Queueing
In general, backbone routers perform the following QoS functions:
• High-speed switching and transport
• Congestion management
• Queue management
Scalable QoS solutions require cooperative edge and backbone functions.
Note In a subsequent Cisco IOS release, we have implemented enhancements to improve QoS on
low speed, wide-area links, such as ISDN, MLPPP, and Frame Relay running on edge routers. For
more information about these enhancements, refer to the Cisco IOS Release 12.0(5)T “IP RTP”
feature module.
Although they are not mandatory, some QoS tools have been identified as being valuable in
fine-tuning your network to support real-time voice traffic. To configure your IP network for QoS
using these tools, perform one or more of the following tasks:
• Configure Multilink PPP with Interleaving
• Configure RTP Header Compression
• Configure Custom Queueing
• Configure Weighted Fair Queueing
Each of these components is discussed in the following sections.
Configure Multilink PPP with Interleaving
Multiclass Multilink PPP interleaving allows large packets to be multilink-encapsulated and
fragmented into smaller packets to satisfy the delay requirements of real-time voice traffic; small
real-time packets, which are not multilink-encapsulated, are transmitted between fragments of the
large packets. The interleaving feature also provides a special transmit queue for the smaller,
delay-sensitive packets, enabling them to be transmitted earlier than other flows. Interleaving
provides the delay bounds for delay-sensitive voice packets on a slow link that is used for other
best-effort traffic.
Note Interleaving applies only to interfaces that can configure a multilink bundle interface. These
interfaces include virtual templates, dialer interfaces, and Integrated Services Digital Network
(ISDN) Basic Rate Interface (BRI) or Primary Rate Interface (PRI) interfaces.
In general, Multilink PPP with interleaving is used in conjunction with weighted fair queueing and
RSVP or IP Precedence to ensure voice packet delivery. Use Multilink PPP with interleaving and
weighted fair queueing to define how data will be managed; use RSVP or IP Precedence to give
priority to voice packets.
You should configure Multilink PPP if the following conditions exist in your network:
• Point-to-point connection using PPP encapsulation
• Slow links