University of Utah

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University of Utah

• Quality of Services Overview

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QOS Terminology

• Packet Loss is a measurement of packets
  received compared to the total number of packets
  transmitted and is usually express as a percent.
• Latency The total amount of time it takes to
  reach the receiving endpoint.
• Jitter Is the delay variation between packets

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What is QoS?

• QoS is the measure of transmission quality and
  service availability of a network
• Quality of Services Toolset - is the ability to
  provide different priority including dedicated
  bandwidth, controlled jitter and latency to
  different applications, users, or data flow.

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Why Enable QoS?

• QoS is needed as a safety belt
• High Availability
• Quality and Performance of an application
• Voice - Phones
• Video Conferencing Remote Classrooms
• Requirement for VoIP Certification
• Security
• Help maintain availability in the event of DoS or
  worm attacks
• Gigabit link can be saturated in less then one
  minute

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How does QoS Work?

• Three fundamental pieces for QoS implementation.
• Classification and Marking traffic so that
  network devices can differentiate traffic flows
• Queuing and selectively dropping packets based on
  the QoS tags
• Traffic Shaping and Policing

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Classification and Marking

• Layer 2 Markings
• CoS (802.1p)
• 3 most significant bits of the Tag Field

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Classification and Marking

• Layer 3 Markings
• IP Precedence ( 3 most significant bits)
• DSCP ( 6 most significant bits )
• PHB
• Class Selector (CSx)
• Assured Forwarding (Afxy)
• Expedited Forwarding (EF)

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Classification and Marking

• QoS Baseline Markings

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What Application Require QoS?

• Voice
• Interactive-Video (Video Conferencing)
• Streaming Video
• Mission-Critical Applications
• Really all traffic even the bad traffic

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Voice QoS Requirements

• Traffic Characteristics
• Small fixed-size packets
• Constant rate
• Drop sensitive
• Delay sensitive
• Performance Requirements
• Latency lt 150ms (one-way)
• Jitter lt 30ms (one-way)
• Loss lt 1 (one-way)
• Bandwidth lt 21 320 Kbps per call (one-way)

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Video Conferencing QoS Requirements

• Traffic Characteristics
• Variable size packets
• Adaptive rate
• Drop sensitive
• Delay sensitive
• Performance Requirements
• Latency lt 150ms (one-way)
• Jitter lt 30ms (one-way)
• Loss lt 1 (one-way)
• Bandwidth
• Standard Resolution 1 Mbps per call (one-way)
• HD Resolution 2 to 3 Mbps per call (one-way)

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Scavenger-ClassWhat is the Scavenger Class?

• The Scavenger class is an Internet 2 Draft
  Specification for a less-than best effort
  service
• Scavenger class markings distinguish
  out-of-profile and abnormal traffic flows from
  in-profile and normal flows.
• Scavenger class is a marking and does not mean
  the traffic will be dropped.
• Scavenger class marking has a PHB of CS1 DSCP 8

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Queuing

• FIFO First In First Out (Default Method)
• Weighted Round Robin (WRR)
• Priority Queuing
• LLQ
• Weight Random Early Detection

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QoS Related Tools

• DHCP Snooping, BPDU Guard, IP Source Guard,
  Control Plane Policing
• Spanning Tree
• Rapid Spanning Tree (802.1w)
• Multiple Spanning Tree (802.1s)
• VRRP Virtual Router Redundancy Protocol
• HSRP Hot Standby Routing Protocol
• VSS Virtual Switching System
• Single logical entity
• Eliminated layer 2 and layer 3 redundancy
  protocol
• Simplifies Configuration

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Questions?

• Thanks
• Tim Urban, CCIE,CISSP
• tim.urban_at_utah.edu
• 585-2662

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References

• Expedited Forwarding - RFC3246
• Class Selector - RFC2474
• Assured Forwarding - RFC2597
• Cisco QoS Documentation
• http//www.cisco.com/en/US/products/ps6558/product
  s_ios_technology_home.html