Miroslav Voz ňák VŠB - Technical University of Ostrava Department of Telecommunications

1. 454-319/1: Voice over IP Lecture No.13 Quality of Service Miroslav Vozňák VŠB - Technical University of Ostrava Department of Telecommunications Faculty of Electrical Engineering and Computer Science 17. listopadu 15, 708 33 Ostrava – Poruba mailto:miroslav.voznak@vsb.cz http://homel.vsb.cz/~voz29 Miroslav Voznak, Lecture No.13

2. QoS • Quality of Service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. • SLA (Service Level Agreement) • specifies guarantees for the ability of a network or protocol to give guaranteed parameters • Guaranteed Parameters • bandwith, latency, jitter, packet loss, availability Miroslav Voznak, Lecture No.13

3. IntServ • The Integrated Services (Intserv) architecture RFC1633 uses an explicit mechanism to signal QoS requirements to network elements (hosts, routers). • Network elements, depending on the available resources, implement one of the defined Intserv services (Guaranteed or Control Load service) based on which QoS will be delivered in the data transmission path. Miroslav Voznak, Lecture No.13

4. IntServ • IntServ architecture has three traffic classes • Best-effort class is basic class • Controlled-Load Class offers better service than best effort • Guaranteed Class guarantees the delay, bandwith, losses • traffic descriptors: • TSpec (Traffic Specification) describes traffic properties like burstiness of a flow, • RSpec (Requirements Specification) describes service quality requirements as end-to-end delay, jitter, packet loss Miroslav Voznak, Lecture No.13

5. Resource Reservation Protocol • RSVP is signaling protocol defined in RFC 2205 and complying with IntServ design Miroslav Voznak, Lecture No.13

6. Resource Reservation Protocol • main RSVP messages: • PATH is sent by a source that initiates the communication session, describes traffic properties and the capabilities of the source, • RESV is issued by the receiver of the communication session and it follows exactly the path that the PATH message, it may install QoS states at each hop, these states are associated with the specific QoS resource requirements of the destination, Miroslav Voznak, Lecture No.13

7. DiffServ (RFC 2474) • Contrasting to IntServ it does not require any end-to-end reservation or signalling • DiffServ provides QoS by aggregating traffic in different service classes, each corresponding to a specific per-hop forward behaviour (PHB) along thenodes in the network path Miroslav Voznak, Lecture No.13

8. traffic entering to service-capable network is marked by Differentiate Services Code Point (DSCP) in the IP header Differentiated Services Field (DS) of each data packet, DS exploits ToS field in IPv4 or Traffic Class field in IPv6 • DS is composed of six bits DSCP , leaving • two bits are unused • DiffServ node must select • PHB by matching DSCP field Miroslav Voznak, Lecture No.13

9. Traffic Conditioner Block • Classifier identifies packets for assignment to classes, • Meter checks compliance to traffic parameters • Marker writes or rewrites DSCP value • Sharper delays some packets to be compliant with the profile • Dropper drops packets that exceed the profile Miroslav Voznak, Lecture No.13

10. DiffServ Architecture • DiffServ Domain– the same service policies, • In a network we can have any number of different DiffServ Domains • At the edge of each of domains packets may be remarked to comply with new policies • Edge router (set DSCP) and Core routers (implement PHB) • Ingress node (incomming traffic • to DS domain) and Egress • node (outgoing traffic) Miroslav Voznak, Lecture No.13

11. Standard PHB’s • Expedited Forwarding (EF) RFC 2598 • premium service, no queues in path, low latency queuing • low latency, loss, jitter, assured BW • virtual pipe between ingress and egress routers • provides the highest QoS possible (VoIP, Video, ...) • Codepoint 101110is recommended Miroslav Voznak, Lecture No.13

12. Assured Forwarding (AF) RFC 2597 • better than Best-effort, low loss, higher BW share, no guarantee on latency • upon congestion – protect AF marked packet and drop BE first, codepoint for BE will be set to 000000 • AF groups packets into one of foure classes • each class has three drop precedence levels: low,medium,high Miroslav Voznak, Lecture No.13

13. Assured Forwarding (AF) • 12 PHBs , 4 classes ( 4 Queues) each with 3 drop preferences Miroslav Voznak, Lecture No.13

14. QoS Tools • Classification, packet classification features provide the capability to partition network traffic into multiple priority levels or classes of service. • Congestion Management, these features operate to control congestion once it occurs. • Congestion Avoidance, these techniques monitor network traffic loads in an effort to anticipate and avoid congestion before it becomes a problem. • Policing and Shaping, it includes traffic policing and shaping capabilities. • Link Efficiency Mechanisms Miroslav Voznak, Lecture No.13

15. Classification • IP Precedence allows to specify the class of service of a packet using the three precedence bits in the ToS field of the IPv4 header, IP Precedence is not a queueing method, other queueing methods can use the IP Precedence setting • Policy Based Routing, allows you to classify traffic based on extended access list criteria, to set IP Precedence bits and to route specific traffic to engineered paths • Commited Access Rate (packet classification), CAR is the main feature supporting packet classification, CAR uses ToS bits in the IP header to classify packets Miroslav Voznak, Lecture No.13

16. Congestion Management • FIFO Queuing is the default queueing algorithm • PQ (Priority Queuing) is designed to give strict priority to important traffic, PQ ensures that important traffic gets the fastest handling at each point where PQ is used • CQ(Custom Queuing)reserves a percentage of the available bandwidth of an interface for each selected traffic type, if a particular type of traffic is not using the bandwidth reserved for it, then other traffic types may use the remaining reserved bandw. • WFQ(Weighted Fair Queueing) applies priority (or weights) to identified traffic to classify traffic into conversations and determine how much bandwidth each conversation is allowed relative to other conversations. Miroslav Voznak, Lecture No.13

17. CBWFQ(Class-based WFQ) extends the standard WFQ functionality to provide support for user-defined traffic classes. It allows you to specify the exact amount of bandwidth to be allocated for a specific class of traffic. Taking into account available bandwidth on the interface, you can configure up to 64 classes and control distribution among them. • IP RTP Priority provides a strict priority queueing scheme that allows delay-sensitive data such as voice to be dequeued and sent first—that is, before packets in other queues are dequeued. • LLQ (Low Latency Queuing) provides strict priority queueing, allows to configure the priority status for a class within CBWFQ. Miroslav Voznak, Lecture No.13

18. Congestion Avoidance • WRED (Weighted Random Early Detection)combines the capabilities of the RED algorithm with IP Precedence to provide preferential traffic handling for higher priority packets. It can selectively discard lower priority traffic when the interface begins to get congested. • DWRED(Distributed WRED)is the high-speed version of WRED. The DWRED algorithm allows to define minimum and maximum queue depth thresholds and drop capabilities for each class of service. • Flow-Based WRED is a feature that forces WRED to afford greater fairness to all flows on an interface in regard to how packets are dropped. Miroslav Voznak, Lecture No.13

19. Policing and Shaping • CAR Rate Limiting (Commited Access Rate)provides the network operator with the means to define Layer 3 aggregate or granular access, or egress bandwidth rate limits, and to specify traffic handling policies when the traffic either conforms to or exceeds the specified rate limits. Aggregate access or egress matches all packets on an interface or subinterface. Granular access or egress matches a particular type of traffic based on precedence. CAR policies are based on physical port, packet classification, IP address, MAC address, application flow, and other criteria specifiable by access lists or extended access lists. An example of the use of the rate-limiting capability of CAR is application-based rates limiting HTTP World Wide Web traffic to 50 percent of link bandwidth, which ensures capacity for non-Web traffic including mission-critical applications. • Shaping(GTSGeneric Traffic Shaping) provides a mechanism to control the flow of outbound traffic on a particular interface. It reduces outbound traffic flow to avoid congestion by constraining specified traffic to a particular bit rate. Miroslav Voznak, Lecture No.13

20. Link Efficiency Mechanisms Compressed Real-Time Protocol(40Bytes RTP header to 2-3 Bytes cRTP), To avoid the unnecessary consumption of available bandwidth, the RTP header compression feature, referred to as CRTP, is used on a link-by-link basis. Link Fragmentation and Interleaving,Interactive traffic, such as Telnet and Voice over IP, is susceptible to increased latency and jitter when the network processes large packets, such as FTP transfers. This susceptibility increases as the traffic is queued on slower links. Cisco IOS QoS LFI reduces delay and jitter on slower speed links by breaking up large datagrams and interleaving low-delay traffic packets with the resulting smaller packets. Miroslav Voznak, Lecture No.13

21. CBWFQClass-based WFQ extends the standard WFQ functionality to provide support for user-defined traffic classes. It allows you to specify the exact amount of bandwidth to be allocated for a specific class of traffic. Taking into account available bandwidth on the interface, you can configure up to 64 classes and control distribution among them. • IP RTP Priority provides a strict priority queueing scheme that allows delay-sensitive data such as voice to be dequeued and sent first—that is, before packets in other queues are dequeued. • LLQ provides strict priority queueing, allows to configure the priority status for a class within CBWFQ. Miroslav Voznak, Lecture No.13

22. Thank you for your attentionmiroslav.voznak@vsb.cz Miroslav Voznak, Lecture No.13