Network QoS - University of Utah

							   University of Utah

Quality of Services Overview
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
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.
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
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
Classification and Marking
• Layer 2 Markings
  – CoS (802.1p)
  – 3 most significant bits of the Tag Field
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)
Classification and Marking
• QoS Baseline Markings
                           Layer 3 Classification     Layer 2
 Application
                         Iperf     PHB         DSCP    COS
 Routing                   6        CS6         48       6
 Voice                     5        EF          46       5
 Video Conferencing        4       AF41         34       4
 Streaming Video           4        CS4         32       4
 Mission-Critical Data     3       AF31         26       3
 Call-Signaling            3        CS3         24       3
 Transactional Data        2       AF21         18       2
 Network Managemnet        2        CS2         16       2
 Bulk Data                 1       AF11         10       1
 Scavenger                 1        CS1         8        1
 Best Effor                0         0          0        0
What Application Require QoS?
•   Voice
•   Interactive-Video (Video Conferencing)
•   Streaming Video
•   Mission-Critical Applications
•   Really all traffic even the bad traffic
Voice QoS Requirements
• Traffic Characteristics
   –   Small fixed-size packets
   –   Constant rate
   –   Drop sensitive
   –   Delay sensitive
• Performance Requirements
   –   Latency          <= 150ms      (one-way)
   –   Jitter           <= 30ms       (one-way)
   –   Loss             <= 1%         (one-way)
   –   Bandwidth        <= 21 – 320 Kbps per call   (one-way)
Video Conferencing QoS Requirements

• Traffic Characteristics
   –   Variable size packets
   –   Adaptive rate
   –   Drop sensitive
   –   Delay sensitive
• Performance Requirements
   –   Latency             <= 150ms          (one-way)
   –   Jitter              <= 30ms           (one-way)
   –   Loss                <= 1%             (one-way)
   –   Bandwidth
        • Standard Resolution 1 Mbps per call (one-way)
        • HD Resolution 2 to 3 Mbps per call (one-way)
Scavenger-Class
What 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
Queuing
•   FIFO – First In First Out (Default Method)
•   Weighted Round Robin (WRR)
•   Priority Queuing
•   LLQ
•   Weight Random Early Detection
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
             Questions?



• Thanks

Tim Urban, CCIE,CISSP
tim.urban@utah.edu
585-2662
References
•   Expedited Forwarding      - RFC3246
•   Class Selector            - RFC2474
•   Assured Forwarding        - RFC2597
•   Cisco QoS Documentation –
    –   http://www.cisco.com/en/US/products/ps6558/products_ios_technology_home.html