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QoS Implementation

QoS Implementation. Robert Morrison University of Wyoming Westnet – January 2013. What is QoS ?. QoS (Quality of Service) refers to the ability to send different packets though the network with different priorities.  For example, VoIP traffic can take precedence over FTP or web traffic.

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QoS Implementation

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  1. QoS Implementation Robert Morrison University of Wyoming Westnet – January 2013

  2. What is QoS? QoS (Quality of Service) refers to the ability to send different packets though the network with different priorities.  For example, VoIP traffic can take precedence over FTP or web traffic.

  3. Is QoS really needed? • Perhaps not on fast links that aren't congested • However, it is essential for slow or congested links • Note: It is not possible/feasible to build all Internet links large enough to prevent packet loss, for example: • WiMAXlinks using public wireless spectrum • Wired Ethernet links limited to 10 mbps half duplex due to old Cat 3 wiring

  4. Two general approaches to QoS: IntServ or DiffServ • IntServ (Integrated Services) builds virtual circuits using RSVP • Based on flows • Does not scale - applications and each router in network path must participate • Not widely supported • DiffServ (Differentiated Services) prioritizes traffic based on traffic classification (RFC 2474) • Individual packets are marked • Individual packets prioritized on a per-hop basis • No advance setup or reservation required - Best efforts basis • Generally accepted method for implementing QoS

  5. How DiffServ works • Individual packets get marked (by various means - see below) with a priority marking  • Nodes along network path observe DiffServ markings and respond accordingly  • Individual nodes (switches and routers) are configured to use whatever 'per-hop behavior' queuing and prioritization mechanisms that may exist in the node

  6. DiffServ choices and considerations • How do packets get marked? • By end device • Efficient, but if not administratively enforced, may require monitoring and enforcement by network devices, which increases complexity and reduces efficiency • Simpler network device configuration • Assumes end devices assign correct DSCP values • Possibility for malicious misconfiguration (e.g. TCP80 assigned DSCP 46) • Administration & Implementation refocused in Server/Host Admin group • By network classification policy such as: • Source or destination address • VLAN • traffic type (protocol, port address, etc.) • Does network trust packets marked by end devices? • If not, does network re-mark, police, shape or otherwise rate limit? • Implement packet fragmentation? • important for slow links, and links with high-MTU traffic (FTP) • Implement congestion management & avoidance? • For example, Weighted Random Early Detection - Weighted-RED

  7. Commonly used “Per-Hop Behaviors”(PHB) • Default PHB - best-effort traffic [DSCP 0] • Expedited Forwarding (EF) PHB -  voice and video (low loss, jitter & delay) [DSCP 46, 44] • Assured Forwarding (AF) PHB - up to twelve classes with varying assurance of delivery [DSCP 38, 36, 34, 30, 28, 26, 22, 20, 18, 14, 12, 10] • Class Selector PHBs - for backward compatibility with the 3-bit TOS IP Precedence field [DSCP 48, 32, 24, 16, 8] • Note: there is no standardized DiffServ policies; therefore, there can be no guarantees about QoS across DiffServ domains

  8. What to prioritize? • VoIP packets • Think not only VoIP calls - but also call setup (Skinny) and phone booting • Example, VoIP on WiMAX 10 mbps links • Video packets • Mission critical application packets • Network management packets

  9. Cisco DSCP chartCampus QoS Design At-A Glance)

  10. Lessons learned at U of Wyoming • It is possible to inadvertently affect traffic • Example: Aruba packets marked with DSCP 8 may be unintentionally discarded • Need to document baseline of protocols and ports for predominant traffic types (top 30-40%) • Everything may work fine under light (summer) loads • Need network management tool to help analyze results • UWyoselected ActionPacked Networks “LiveAction” product • QoStools, capabilities & terminology vary greatly between vendors, platforms, and generations • All network staff should be trained and knowledgeable about QoS • It is possible to overwhelm even high end devices (Cisco 6509) with software-processed QoS features • QoS tools using ACLs, Class Maps, or Policy Maps are software-processed

  11. UWyocurrent QoS strategy • Expect endpoints to classify (i.e. mark) packets and generally trust them • Use hardware (ASIC) to priority queue packets wherever possible • Focus on slow or congested links first • Maintain packet markings end-to end • Use policing, re-marking, etc. only for untrusted subnets • Residence Halls • Computer Science department

  12. LiveAction Display Example (Overview)

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