Cisco 1760 - VPN Bundle Router, Quick Start Manual

33

Multilink PPP with Link Fragmentation Interleave

Multilink PPP with link fragmentation interleave (MLPPP with LFI) allows large packets to be multilink-encapsulated and 
fragmented into smaller packets, thus ensuring that voice packets are transmitted without delay; 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.

You should configure MLPPP with LFI if you have a dialer, an ISDN PRI or BRI interface, or a virtual template, and either of 
the following:

•

Point-to-point connections using PPP encapsulation

•

Links slower than 2 Mbps

Note

Do not use MLPPP with LFI on links faster than 2 Mbps.

Configuring MLPPP with LFI

To configure MLPPP with LFI on a dialer, ISDN PRI or ISDN BRI interface, or a virtual template, you must first configure 
MLPPP with LFI on the interface or template by entering the following commands while in interface configuration mode:

Router(config-if)# 

encapsulation

ppp

Router(config-if)# 

ppp multilink

Router(config-if)# 

ppp multilink interleave

Optionally, configure a maximum fragment delay:

Router(config-if)# 

ppp multilink fragment-delay 

milliseconds

You can also 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. You need the following command only if you have not 
configured RSVP: 

Router(config-if)# 

ip rtp reserve

lowest-UDP-port range-of-ports

For virtual templates only, apply the virtual template to the multilink bundle:

Router(config-if)# 

multilink virtual-template 1

To create a virtual template interface, enter the following 

interface virtual-template

 global configuration command: 

Router(config)# 

interface

virtual-template 1

Real-Time Transport Protocol Header Compression

Real-Time Transport Protocol (RTP) header compression on a PPP, HDLC, or similar serial interface compresses the packet 
header to reduce network overhead. 

You should configure RTP header compression on a serial interface if you have either of the following:

•

Links slower than 2 Mbps

•

A need to conserve bandwidth

Note

Do not use RTP header compression on links faster than 2 Mbps.

Configuring RTP Header Compression

Enable RTP header compression at both ends of the serial link by entering the 

ip rtp header-compression

interface configuration 

command:

Router(config-if)# 

ip rtp header-compression