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Some applications, such as high-resolution video, require consistent, dedicated bandwidth to provide sufficient quality for viewers. IntServ was introduced to guarantee predictable network behavior for these applications.

Because IntServ reserves bandwidth throughout a network, no other traffic can use the reserved bandwidth. Bandwidth that is unused, but reserved, is wasted.

IntServ is similar to a concept known as "hard QoS ." With hard QoS, traffic characteristics such as bandwidth, delay, and packet-loss rates are guaranteed end to end. This guarantee ensures both predictable and guaranteed service levels for mission-critical applications. There will be no impact on traffic when guarantees are made, regardless of additional network traffic. Hard QoS is accomplished by negotiating specific QoS requirements upon establishment of a connection and by using Call Admission Controls (CACs) to ensure that no new traffic will violate the guarantee. Such guarantees require an end-to-end QoS approach with both complexity and scalability limitations. Large network environments that contain heavy traffic loads will be extremely challenged to track QoS guarantees for hundreds of thousands of signaled flows.

Using IntServ is like having a private courier airplane or truck dedicated to the delivery of your traffic. This model ensures quality and delivery, is expensive, and is not scalable.

Provides multiple service levels

Requests specific kind of service from the network before sending data

Uses RSVP to reserve network resources

Uses intelligent queuing mechanisms

End to end

IntServ is a multiple-service model that can accommodate multiple QoS requirements. IntServ inherits the connection-oriented approach from telephony network design. Every individual communication must explicitly specify its traffic descriptor and requested resources to the network. The edge router performs admission control to ensure that available resources are sufficient in the network. The IntServ standard assumes that routers along a path set and maintain the state for each individual communication.

The role of Resource Reservation Protocol (RSVP) in the Cisco QoS architecture is to provide resource admission control for VoIP networks. If resources are available, RSVP accepts a reservation and installs a traffic classifier in the QoS forwarding path. The traffic classifier tells the QoS forwarding path how to classify packets from a particular flow and what forwarding treatment to provide.

In the IntServ model, the application requests a specific kind of service from the network before sending data. The application informs the network of its traffic profile and requests a particular kind of service that can encompass its bandwidth and delay requirements. The application is expected to send data only after it gets a confirmation from the network. The application is also expected to send data that lies within its described traffic profile.

The network performs admission control based on information from the application and available network resources. The network commits to meeting the QoS requirements of the application as long as the traffic remains within the profile specifications. The network fulfills its commitment by maintaining the per-flow state, and then performing packet classification, policing, and intelligent queuing based on that state.

The QoS feature set in Cisco IOS software includes these features that provide controlled-load service:

■ RSVP can be used by applications to signal their QoS requirements to the router.

■ Intelligent queuing mechanisms can be used with RSVP to provide these QoS service levels:

— Guaranteed-rate: Guaranteed-rate service level allows applications to reserve bandwidth to meet their requirements. For example, a VoIP application can reserve 32 Mbps end to end using this type of service. Cisco IOS QoS uses low-latency queuing (LLQ) with RSVP to provide guaranteed-rate type of service.

— Controlled-load: Controlled-load service level allows applications to have low delay and high throughput, even during times of congestion. For example, adaptive realtime applications, such as the playback of a recorded conference, can use this service. Cisco IOS QoS uses RSVP with weighted random early detection (WRED) to provide controlled-load type of service.

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