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Configure Multilink PPP with Interleaving
Configuring Voice over IP for the Cisco 3600 Series VC-19
Configure Multilink PPP with Interleaving
Multi-class 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 and
RSVP 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 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
Note Multilink PPP should not be used on links greater than 2 Mbps.
Multilink PPP support for interleaving can be configured on virtual templates, dialer interfaces, and
ISDN BRI or PRI interfaces. To configure interleaving, you need to complete the following tasks:
• Configure the dialer interface or virtual template, as defined in the relevant chapters of the
Dial Solutions Configuration Guide.
• Configure Multilink PPP and interleaving on the interface or template.
To configure Multilink PPP and interleaving on a configured and operational interface or virtual
interface template, use the following commands in interface mode:
Note The ip rtp reserve command can be used instead of configuring RSVP. If you configure
RSVP, this command is not required.
Step Command Purpose
1 ppp multilink Enable Multilink PPP.
2 ppp multilink interleave Enable real-time packet interleaving.
3 ppp multilink fragment-delay milliseconds Optionally, configure a maximum fragment delay.
4 ip rtp reserve lowest-UDP-port
range-of-ports [maximum-bandwidth]
Reserve a special queue for real-time packet flows
to specified destination User Datagram Protocol
(UDP) ports, allowing real-time traffic to have
higher priority than other flows. This is only
applicable if you have not configured RSVP.