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QoS Part II (Advanced)


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Quality of Service (QoS) is back by popular demand! Part II of our Webcast series on QoS is a more technical, deeper dive into this technology. This webcast covers:

• A quick refresher on QoS
• Traffic shaping
• Scheduling and queuing algorithms
• Congestion avoidance

Cisco's Class-Based Quality of Service or CBQoS It’s hard to imagine a network in today’s world that doesn’t or couldn’t benefit from implementing some form of QoS. Watch this webcast and learn some of the things you need to know in order to successfully implement, manage, and monitor QoS on your network.

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QoS Part II (Advanced)

  1. 1. Introduction  A big “Howdy” from SolarWinds based in Austin, Texas » Josh Stephens - Head Geek, Monster Blogger, Constant Tweeter » Chris LaPoint – Senior Product Manager  Today’s Topic: Quality of Service (QoS) – Part II  Who is SolarWinds? » What we do… » Who are our customers? » The SolarWinds community…
  2. 2. Housekeeping  Can you hear me now?  If not, use the WebEx Q&A panel to contact the moderator  How do you win the free stuff?  How do you ask questions?  Will this thing be recorded?
  3. 3. Agenda  Quick refresher on what we learned about QoS in Part I  Traffic Shaping  Scheduling and Queuing Algorithms  T-shirt Giveaway  Congestion Avoidance  Cisco’s Class Based Quality of Service (CBQoS)  Using Orion to monitor QoS  Summary and Q&A
  4. 4. Refresher – QoS Part I  QoS is a resource reservation system  It is not a measure of achieved quality or a guarantee of quality.  It is a workaround for congestion.  It’s especially important with latency sensitive applications.  QoS may be referred to as:  DSCP  ToS  IntServ
  5. 5. Refresher – QoS Part I continued…  When to use QoS  Anytime you have worry of congestion  If you have latency sensitive and latency insensitive traffic on the same links  As an alternative to buying more bandwidth  Tips for implementing QoS  Don’t be afraid – it isn’t as hard as it sounds  Leverage templates provided by the hardware vendors (Cisco SBA for instance)  Monitor, monitor, monitor
  6. 6. Traffic Shaping Traffic Shaping (or packet shaping) is a way of optimizing network performance by inducing delay within specific traffic types or flows. There are many methods of traffic shaping, but they all involve adding delay.  Some common methods of traffic shaping are:  Bandwidth Throttling  Rate Limiting  GCRA (Generic Cell Rate Algorithm) * More complete definition at
  7. 7. Bandwidth Throttling  Bandwidth throttling is way of limiting the amount of traffic a device will send or receive within a set period of time.  Bandwidth throttling is typically done at the server or the device generating the traffic.
  8. 8. Rate Limiting Rate limiting is a way of controlling the rate of traffic being sent over the network. In rate limiting, traffic being sent at or below the rate limit will be sent whereas traffic being sent above the limit will be discarded or delayed. Rate limiting is usually performed by a router or another intermediary device.  Rate limiting is performed by:  Policing (discarding excess packets)  Queuing (delaying packets in transit)  Congestion control (manipulating the protocol’s congestion mechanism)
  9. 9. Scheduling and Queuing  Token bucket vs. leaky bucket  Scheduling algorithms  Weighted Fair Queuing  Class Based Weighted Fair Queuing  Weighted Round Robin  Deficit Weighted Round Robin  Hierarchal Fair Service Curve
  10. 10. Token bucket vs. leaky bucket  Leaky bucket  Traffic flows into the queue at variable rates  Traffic always flows out of the queue at the same rate  Doesn’t allow for bursting even when there’s available bandwidth  The automobile traffic analogy
  11. 11. Token bucket  This algorithm can be conceptually understood as follows:  A token is added to the bucket every 1 / r seconds.  The bucket can hold at the most b tokens. If a token arrives when the bucket is full, it is discarded.  When a packet (network layer PDU) of n bytes arrives, n tokens are removed from the bucket, and the packet is sent to the network.  If fewer than n tokens are available, no tokens are removed from the bucket, and the packet is considered to be non-conformant.
  12. 12. Token bucket continued…  The algorithm allows bursts of up to b bytes, but over the long run the output of conformant packets is limited to the constant rate, r. Non- conformant packets can be treated in various ways.  To calculate the time for which the Token Bucket Algorithm allows burst of maximum possible size, assume that the capacity of the Token Bucket is C bytes, the token arrival rate is R bytes/second and the maximum possible transmission rate is M bytes/second and S is the number of seconds for which it is possible to transmit at maximum rate.  Then, the following equality holds C + R * S = M * S which gives S = C / (M − R) seconds  Best Practice – use token bucket and leaky bucket methods together for better traffic management.
  13. 13. Scheduling Algorithms  Weighted Fair Queuing  Class Based Weighted Fair Queuing  Weighted Round Robin  Deficit Weighted Round Robin  Hierarchal Fair Service Curve
  14. 14. Congestion Avoidance  RED and WRED  Policing  Explicit Congestion Notification (ECN)
  15. 15. RED and WRED  RED - Random Early Detection  Active queue management algorithm (also a congestion avoidance algorithm)  Avoids global synchronization  Treats bursty traffic fairly – more fair than tail drop  Makes QoS differentiation impossible  WRED  Extension to RED  Each queue has different queue thresholds associated to different IP precedence  Makes QoS differentiation possible
  16. 16. Traffic Policing  Monitors network traffic for compliance with policies or contracts  Actively makes changes to enforce the contract  May apply traffic shaping  More common in ATM networks
  17. 17. ECN – Explicit Congestion Notification  An extension to IP as specified in RFC 3168  End-to-end notification of network congestion  Only used with both endpoints signal they want to use it  Can be used to avoid packet drops  Uses 2 bits in the differentiated services field of the IP header
  18. 18. Cisco’s Class Based Quality of Service (CBQoS)  Cisco CBQoS has two primary functions  Congestion avoidance  Congestion management  How it’s different from regular QoS methods  It’s dynamic  Automatically adjusts queue sizes  Automatically adjusts application responses  Best in class, modern QoS method
  19. 19. Monitoring CBQoS - Slide 20 -
  20. 20. Summary and Q&A Thank you for attending! To learn more or to download free 30-day trials of SolarWinds products visit: Contact information Josh Stephens, Head Geek twitter: sw_headgeek Blog: p.s. Remember to renew your maintenance!!!