Specifications

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Cisco 1751 Router Software Configuration Guide
OL-1070-01
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 can be valuable in fine-tuning your network to support
real-time voice traffic. To configure your IP network for QoS, perform one or more of the following
tasks:
• Configure RSVP for Voice
• Configure Multilink PPP with Interleaving
• Configure RTP Header Compression
• Configure Custom Queuing
• Configure Weighted Fair Queuing
Each of these tasks is discussed in the following sections.
Configure RSVP for Voice
Resource Reservation Protocol (RSVP) enables routers to reserve enough bandwidth on an interface for
reliability and quality performance. RSVP allows end systems to request a particular QoS from the
network. Real-time voice traffic requires network consistency. Without consistent QoS, real-time traffic
can experience jitter, insufficient bandwidth, delay variations, or information loss. RSVP works in
conjunction with current queuing mechanisms. It is up to the interface queuing mechanism (such as
weighted fair queuing or WRED) to implement the reservation.
RSVP works well on PPP, HDLC, and similar serial line interfaces. It does not work well on
multi-access LANs. RSVP can be equated to a dynamic access list for packet flows.
You should configure RSVP to ensure QoS if the following conditions describe your network:
• Small scale voice network implementation
• Links slower than 2 Mbps
• Links with high utilization
• Need for the best possible voice quality
Enable RSVP
To minimally configure RSVP for voice traffic, you must enable RSVP on each interface where priority
needs to be set.
By default, RSVP is disabled so that it is backwards compatible with systems that do not implement
RSVP. To enable RSVP for IP on an interface, use the following interface configuration command: