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Cisco 1751 Voice-over-IP Quick Start Guide
78-11259-05
Configuring Voice-over-IP
RSVP
Resource Reservation Protocol (RSVP) enables routers to reserve enough bandwidth on an interface for
reliable and quality performance. RSVP works well on PPP, HDLC, and similar serial line interfaces. It
does not work well on multi-access LANs.
You should configure RSVP if you have a serial interface and any of the following:
•
Links slower than 2 Mbps
•
Links with high utilization
•
Need for the best possible voice quality
Note
If you configure multilink PPP interleaving, you can use the
ip rtp reserve
command instead of
configuring RSVP. Refer to the next section on “
Multilink PPP Interleaving
.”
Configuring RSVP
By default, RSVP is disabled so that it is backwards compatible with routers that do not implement it.
To enable RSVP on an IP network, enter the
ip rsvp bandwidth
command from interface configuration
mode. The following example enables RSVP on serial interface 0/0 and sets the maximum bandwidth to
96 kbps and the maximum bandwidth per single request to 24 kbps:
Router(config)#
interface serial 0/0
Router(config-if)#
ip rsvp bandwidth 96 24
The default maximum bandwidth is 75 percent of the bandwidth available on each interface.
RSVP must be enabled at each LAN or WAN interface that voice packets will travel across. 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)#
req-qos controlled-load
For further information about this command, refer to the
Cisco 1751 Router Software Configuration
Guide
.
Multilink PPP Interleaving
Multilink PPP interleaving allows large packets to be multilink-encapsulated and fragmented into
smaller packets to make sure 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 multilink PPP interleaving if you have a dialer, 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 multilink PPP on links faster than 2 Mbps.
