Specifications

Cisco 1751 Router Software Configuration Guide

OL-1070-01

Router(config-if)# ip rsvp bandwidth [interface-kbps] [single-flow-kbps]

This command starts RSVP and sets the bandwidth and single-flow limits. The default maximum

bandwidth is up to 75 percent of the bandwidth available on the interface. By default, the amount

reservable by a flow can be up to the entire reservable bandwidth.

On subinterfaces, RSVP applies to the more restrictive of the available bandwidths of the physical

interface and the subinterface.

Reservations on individual circuits that do not exceed the single flow limit normally succeed. However,

if reservations have been made on other circuits adding up to the line speed, and a reservation is made

on a subinterface that itself has enough remaining bandwidth, it will still be refused because the

physical interface lacks supporting bandwidth.

A Cisco 1751 router running VoIP and configured for RSVP requests allocations using the following

formula:

bps=packet_size+ip/udp/rtp header size * 50 per second

For G.729, the allocation works out to be 24,000 bps. For G.711, the allocation is 80,000 bps.

For more information about configuring RSVP, refer to the “Configuring RSVP” chapter of the Network

Protocols Configuration Guide, Part 1 for Cisco IOS Release 12.1T.

RSVP Configuration Example

The following example enables RSVP and sets the maximum bandwidth to 100 kbps and the maximum

bandwidth per single request to 32 kbps (the example presumes that both VoIP dial peers have been

configured):

Router(config)# interface serial 0/0

Router(config-if)# ip rsvp bandwidth 100 32

Router(config-if)# fair-queue

Router(config-if)# end

After enabling RSVP, you must also use the req-qos dial-peer configuration command to request an

RSVP session on each VoIP dial peer. Otherwise, no bandwidth is reserved for voice traffic.

Router(config)# dial-peer voice 211 voip

Router(config-dial-peer)# req-qos controlled-load

Router(config)# dial-peer voice 212 voip

Router(config-dial-peer)# req-qos controlled-load

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.

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 is managed; use RSVP or IP precedence to give priority to voice packets.

You should configure multilink PPP if the following conditions describe your network:

• Point-to-point connection using PPP encapsulation