Quality of Service(Queuing Methods)
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The document discusses various queuing methods used in routers to manage network traffic effectively, emphasizing the differences between softqueues and hard queues. It outlines various queuing strategies such as FIFO, priority queuing, and weighted fair queuing, detailing their configurations and guarantees for delay and bandwidth. Additionally, it highlights the features and scenarios for applying class-based weighted fair queuing and low-latency queuing, underscoring their significance in ensuring Quality of Service (QoS) for different types of network traffic.
Quality of Service(Queuing Methods)
- 1. Quality of Service(QoS)-Part 2 By : Reza Farahani
- 2. Queuing The goal of queuing method? routers can be configured to perform queuing for packets that are waiting to exit an interface. For example, if a router receives 5 Mbps of traffic every second for the next several seconds, and all that traffic needs to exit a T1 serial link, the router can’t forward all the traffic.
- 3. Types of Queue There are two types of Queue: SoftQueue : The queues created on an interface by the queuing tools are called software queues , as these queues are implemented in software. However, when the queuing scheduler picks the next packet to take from the software queues, the packet does not move directly out the interface.
- 4. Types of Queue Hard Queue : Instead, the router moves the packet from the interface software queue to a small hardware FIFO queue on each interface. Cisco calls this separate, final queue either the transmit queue (Tx queue) or transmit ring (Tx ring)
- 5. Queuing Transmit Ring (TX Ring) OR Transmit Queue (TX Queue)
- 6. HW Queue Hardware queues provide the following features:
- 7. Length of HW Queue
- 8. Queuing The size of the output queue affects delay, jitter, and loss. Because the queue has a finite size, it may fill Length Of The Queue Tail Drop Delay Jitter Queue Scheduling
- 10. Queuing Tools FIFO Priority queuing (PQ) Custom queuing (CQ) Weighted fair queuing (WFQ) Class-based weighted fair queuing (CBWFQ) Low-latency queuing (LLQ)
- 11. Queuing Methods-FIFO Fist-In-First-Out Number Of Queue = 1 Method = FIFO Delay Guarantee = No Bandwidth Guarantee = No Recommended For Voice = No Pointer to Memory
- 12. FIFO R3(config)#int s 0/0 R3(config-if)#no fair-queue R3#sh int s 0/0 . . Queuing strategy : fifo Output queue :0/40 (size/max) . . R3(config)#int s 0/0 R3(config-if)#hold-queue 50 out
- 13. Queuing Methods-PQ Number Of Queue = 4 (High, Medium, Normal, and Low) Method = Strict Priority Delay Guarantee = Yes (Only for High Priority) Bandwidth Guarantee = No Recommended For Voice = Somewhat
- 14. PQ WORKFLOW
- 15. Queuing Methods-CQ Number Of Queue = 16 Method = Round Robin Delay Guarantee = No Bandwidth Guarantee = Yes Recommended For Voice = No
- 16. CQ WORKFLOW Queue 1 5000 Byte 10% Queue 2 5000 Byte 10% Queue 3 10000 Byte 20% Queue 4 10000 Byte 20% Queue 5 20000 Byte 40% Example:
- 17. Queuing Methods-WFQ Number Of Queue = Per Flow(Max=4096) Method = Weighted Fair Delay Guarantee = No Bandwidth Guarantee = No Recommended For Voice = No Small Packets service First! Telnet HTTP FTP
- 18. WFQ Scheduler 32384 (IP_Precedence + 1) SN= Previous_SN in Queue + (weight * new_packet_length)
- 19. WFQ Sequence Number Assignment Example
- 20. WFQ Sequence Number Assignment Example 2 Order of Packets : 13, 14, 15, 16, 9, 5, 10, 1, 11, 6, 12, 2, 7, 8, 3, 4
- 21. WFQ Modified Tail Drop The hold-queue size limits the total number of packets in all of the flow or conversation queues. CDT limits the number of packets in each individual queue
- 22. Weighted Fair Queuing Points WFQ does not allow classification options to be configured! WFQ Classification Flow-Based WFQ, or just WFQ, classifies traffic into flows. Flows are identified by at least five items in an IP packet: ■ Source IP address ■ Destination IP address ■ Transport layer protocol (TCP or UDP) as defined by the IP Protocol header field ■ TCP or UDP source port ■ TCP or UDP destination port ■ IP Precedence WFQ scheduler is to provide more bandwidth to flows with higher IP precedence values and small length In a network where most of the delay-sensitive traffic is lower-volume traffic, WFQ is a great solution WFQ can be configured for a maximum of 4096 queues, but interestingly, the actual value can only be a power of 2 between 16 and 4096 because WFQ performs a hash algorithm to classify traffic, and the hash algorithm only works when the number of queues is one of these valid values
- 23. WFQ Configuration R3(config)#int s 0/0 R3(config-if)#fair-queue R3#show queueing fair R3# show queue s 0/0 . . Queuing strategy: weighted fair . . R3#configure terminal R3(config)#int s 0/0 R3(config-if)#fair-queue 100 64 10 R3(config-if)#hold-queue 500 out
- 24. CB WFQ Queuing Number Of Queue = 64 Method = N/A Delay Guarantee = No Bandwidth Guarantee = Yes Recommended For Voice = No CBWFQ=ECQ+ WFQ
- 25. CBWFQ
- 26. CBWFQ Functions and Features
- 27. CBWFQ
- 28. Class Based Weighted Fair Queuing Points CBWFQ supports two types of drop policy, namely tail drop and WRED. You can enable WRED on any of the 64 queues available with CBWFQ. CBWFQ supports 64 queues, with a maximum and default queue length varying depending on the model of router and the amount of memory installed. CBWFQ provides a great advantage by allowing WFQ to be used in the class-default queue. If some queues do not need their bandwidth for a short period, the bandwidth is spread across the other classes
- 29. CBWFQ Example Scenario • R3 uses CBWFQ on its S0/0 interface • All VoIP payload traffic is placed in a queue. • All other traffic is placed in another queue. • Give the VoIP traffic 50 percent of the bandwidth. • WFQ and WRED should be used on the non-VoIP traffic.
- 30. CBWFQ Example Scenario R3#show running-config Building configuration... ip cef class-map match-all voip-rtp match ip rtp 16384 16383 policy-map queue-voip class voip-rtp bandwidth percent 50 class class-default fair-queue interface Serial0/0 description connected to FRS port S0. Single PVC to R1. no ip address encapsulation frame-relay load-interval 30 bandwidth 128 service-policy output queue-voip clockrate 128000
- 31. Low Latency Queuing (LLQ) Number Of Queue = 1 PQ + CBFWQ Method = N/A Delay Guarantee = Yes (For PQ Traffic) Bandwidth Guarantee = Yes Recommended For Voice = Yes LLQ= PQ+ CBWFQ
- 32. Low Latency Queuing (LLQ)
- 33. Cisco LLQ Bandwidth Allocation Recommendation
- 34. Comparisons of WFQ, CBWFQ, and LLQ