Cisco QoS Part I Part, QoS, Cisco

Quality of Service

Introduction

A communications network forms the backbone of any successful organization. These networks transport a multitude of applications and data, including high-quality video and delay-sensitive data such as real-time voice. The bandwidth-intensive applications stretch network capabilities and resources, but also complement, add value, and enhance every business process. Networks must provide secure, predictable, measurable, and sometimes guaranteed services. Achieving the required Quality of Service (QoS) by managing the delay, delay variation (jitter), bandwidth, and packet loss parameters on a network becomes the secret to a successful end-to-end business solution. Thus, QoS is the set of techniques to manage network resources.

Differentiated Services

Cisco IOS Software supports two fundamental Quality of Service architectures: Differentiated Services (DiffServ) and Integrated Services (IntServ). In the DiffServ model a packet's "class" can be marked directly in the packet, which contrasts with the IntServ model where a signaling protocol is required to tell the routers which flows of packets requires special QoS treatment. DiffServ achieves better QoS scalability, while IntServ provides a tighter QoS mechanism for real-time traffic. These approaches can be complimentary and are not mutually exclusive.

The DiffServ architecture model (RFC 2475, December 1998) divides traffic into a small number of classes, and allocates resources on a per-class basis. Because DiffServ has only a few classes of traffic, a packet's "class" can be marked directly in the packet.

In the DiffServ model, packets are classified and marked to receive a particular forwarding treatment (per-hop behavior or PHB) on nodes along their path. Sophisticated classification, marking, policing, and shaping operations need only be implemented at network boundaries or hosts, enabling greater scalability than other models of service differentiation.

Integrated Services

Cisco IOS Software supports two fundamental Quality of Service architectures: Differentiated Services (DiffServ) and Integrated Services (IntServ). In the DiffServ model a packet's "class" can be marked directly in the packet, which contrasts with the IntServ model where a signaling protocol is required to tell the routers which flows of packets requires special QoS treatment. DiffServ achieves better QoS scalability, while IntServ provides a tighter QoS mechanism for real-time traffic. These approaches can be complimentary and are not mutually exclusive.

The IntServ architecture model (RFC 1633, June 1994) was motivated by the needs of real-time applications such as remote video, multimedia conferencing, visualization, and virtual reality. It provides a way to deliver the end-to-end Quality of Service (QoS) that real-time applications require by explicitly managing network resources to provide QoS to specific user packet streams (flows). It uses "resource reservation" and "admission control" mechanisms as key building blocks to establish and maintain QoS.

IntServ uses Resource Reservation Protocol (RSVP) to explicitly signal the QoS needs of an application's traffic along the devices in the end-to-end path through the network. If every network device along the path can reserve the necessary bandwidth, the originating application can begin transmitting.

Besides end-to-end signaling, IntServ requires several functions on routers and switches along the path:

• Admission Control: determine whether a new flow can be granted the requested QoS without impacting existing reservations
• Classification: recognize packets that need particular levels of QoS
• Policing: take action, including possibly dropping packets, when traffic does not conform to its specified characteristics
• Queuing and Scheduling: forward packets according to those QoS requests that have been granted

Network Based Application Recognition (NBAR)

Applications in today's enterprise networks require different levels of service based upon business requirements. These requirements can be translated into network policies. The resources provided here assist you in configuring your network to provide the appropriate level of service to these applications.

Mission critical applications including ERP and workforce optimization applications can be intelligently identified and classified using Network Based Application Recognition ( NBAR ). Once these mission critical applications are classified they can be guaranteed a minimum amount of bandwidth, policy routed, and marked for preferential treatment. Non-critical applications including Internet gaming applications and MP3 file sharing applications can also be classified using NBAR and marked for best effort service, policed, or blocked as required.


Provisioning, Monitoring, and Management

Cisco IOS Software provides multiple tools for provisioning, monitoring, and measurement of Quality of Service (QoS) Mechanisms.

• Cisco AutoQoS simplifies the provisioning of Cisco IOS QoS features in enterprise and small business environments by automatically identifying traffic types. It can optionally configure the QoS policies appropriate to that traffic.
• CiscoWorks QoS Policy Manager provides centralized management of QoS policy creation, deployment, and monitoring
• Cisco Intelligent Service Gateway dynamically provisions broadband on demand and hierarchical bandwidth shaping in the Service Provider broadband aggregation environment.
• Cisco IP Solution Center supports QoS provisioning in the IP and MPLS service environments.
• Modular QoS CLI defines detailed QoS policies by providing ,common QoS behaviors across product lines and Cisco IOS Software releases.
• Cisco IOS MIB and Trap support provides fine-grained traffic statistics, per-interface/PVC and application statistics, as well as path statistics. Multiple third party applications integrate with the Cisco Class-Based Quality of Service (CBQoSMIB) and Netflow MIBs.
• Cisco IOS IP Service Level Agreements (SLAs) provide jitter, latency and delay measurements. The estimated bandwidth required to meet QoS criteria for drop probability and delay can now be identified through the Corvil Bandwidth technology.

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29-8-2009 21:16