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Configuring Multilink PPP with Interleaving

Configuring Voice over IP for Cisco MC3810 Series Concentrators 5

in your network do not necessarily perform the same operations; the QoS tasks they perform might

differ as well. To conﬁgure your IP network for real-time voice trafﬁc, you need to take into

consideration the functions of both edge and backbone routers in your network, then select the

appropriate QoS tool or tools.

In general, edge routers perform the following QoS functions:

• Packet classiﬁcation

• Admission control

• Bandwidth management

• Queuing

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.

Although 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:

• Conﬁguring Multilink PPP with Interleaving

• Conﬁguring RTP Header Compression

• Conﬁguring IP RTP Priority

Each of these components is discussed in the following sections.

Conﬁguring 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

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 queuing or IP

Precedence to ensure voice packet delivery. Use Multilink PPP with interleaving and weighted fair

queuing to deﬁne how data will be managed; use 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

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