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Advanced QoS Techniques for VoIP Networks

Explore advanced Quality of Service techniques for Voice over IP networks, including Integrated Services (IntServ), DiffServ, cRTP, queuing methods, and traffic classification. Learn to configure and optimize QoS settings to ensure high voice quality and efficient traffic management in large network environments.

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Advanced QoS Techniques for VoIP Networks

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  1. CHAPTER 8 • Quality of Service Voice over IP Fundamentals

  2. Quality of Service • Integrated services (IntServ) • Ensure that a specific flow of traffic is going to receive the appropriate level of bandwidth across the entire network. • Resource ReSerVation Protocol (RSVP) • Differentiated Services (DiffServ) • Used in Large Networks • Classifies Traffic • Type of Service (ToS) • DiffServ Code Point (DSCP)

  3. Delay Budget

  4. Edge Functions • Classify traffic as close to the edge as possible! • Provider Edge • Customer Edge

  5. Header Compression: cRTP will compress traffic by recording header information and incrementally increasing it per each received packet

  6. cRTP Configuration: Leased line ! Interface serial 0/0/0 ip address 192.168.121.18 255.255.255.252 no ip mroute-cache ip rtp header-compression encapsulation ppp

  7. cRTP Configuration: Frame Relay ! Interface serial 0/0/0 ip address 192.168.120.10 255.255.255.0 encapsulation frame-relay no ip route-cache no ip mroute-cache frame-relay ip rtp header-compression

  8. Queuing: • Identify Traffic • First in First out (FIFO) (Single Que) • Weighted Fair Queuing • Custom Queuing • Priority Queuing • Class Based Weighted Fair Queuing • Low Latency Queuing

  9. Weighted Fair Queuing (WFQ): • Identifies Traffic Flows • Uses Source and Destination Addresses • Protocol Type • Port Number • Qos/Tos Values • Shares Traffic in a Fair Manner • Low-bandwidth get Priority • High-bandwidth shares remaining bandwidth • Enabled on an interface by the fair-queue command

  10. Weighted Fair Queuing (WFQ): • Affected by • IP Precedence (0-7) • Frame-Relay FECN • Frame-Relay BECN • Frame-Relay DE bits • Options to the fair-queue Command • congestive-discard-threshold (64) (16-4096) • dynamic-queues (256) (16,32,64,128,256,…4096) • reservable-queues (0) (0-1000) • Not meant for use on links with bandwidth greater than 2.048 Mbps

  11. Custom Queuing (CQ): • Specifies a percentage of available Bandwidth • Max 16 output queues • Serviced Sequentially • Dynamic allocation of unused bandwidth interface serial 0/0/0 ip address 20.0.0.1 255.0.0.0 custom-queue-list 1 ! queue-list 1 protocol ip 1 list 101 queue-list 1 default 2 queue-list 1 queue 1 byte-count 4000 queue-list 1 queue 2 byte-count 2000 ! access-list 101 permit udp any any range 16380 16480 precedence 5 access-list 101 permit tcp any any eq 1720

  12. Priority Queuing: • Four traffic queues (High, Normal, Medium, Low) • Each queue is serviced till empty • Can starve traffic flows interface serial 0/0/1 ip address 192.168.121.17 255.255.255.248 encapsulation ppp no ip mroute-cache priority-group 1 ! access-list 101 permit udp any any range 16384 16484 access-list 101 permit tcp any any eq 1720 priority-list 1 protocol ip high list 101

  13. Priority Queuing:

  14. CB-WFQ (Class Based Weighted Fair Queuing): • Can run on links up to T3 • Defines what constitutes a class • Specify the exact amount of bandwidth allocated • Specify the minimum amount of bandwidth allocated • 64 different classes • Each class is associated with a separate queue • Can be skewed to simulate PQ

  15. PQ within CB-WFQ (Low Latency Queuing): • Gives absolute priority to voice traffic

  16. Traffic Classification: • Three bits in the ToS field of the IP Header • in-band QoS

  17. DSCP, TOS, and COS:

  18. Traffic Classification: • Three bits in the ToS field of the IP Header • in-band QoS

  19. Traffic Classification: • Can be set by destination phone number dial-peer voice 650 voip destination-pattern 650 ip precedence 5 session target RAS

  20. Policy Routing: • Can reset IP Precedence bits • Can base policies on IP addresses, Port numbers, Protocols, or Packet size • Uses route-maps to filter • Can use any ACL interface FastEthernet0/0 ip address 192.168.15.18 255.255.255.0 ip policy route-map RESET-PRECEDENCE ! access-list 105 permit ip any any route-map RESET-PRECEDENCE permit 10 match ip address 105 set ip precedence routine

  21. RSVP: • Each interface must be explicitly configured for RSVP • The receiving station is the requester of the service • interface-kbps: reserved bandwidth per interface (1-10,000,000) • single-flow-kbps: amount of bandwidth allocated to a flow (1-10,000,000) • default: 75% of available bandwidth if not specified • show ip rsvp reservation • Scalability issues ip rsvp bandwidth [interface-kbps] [single-flow-kbps]

  22. Traffic Policing: • Define the bandwidth limit for an application • Rate limiting tools • Used at the edge • Traffic dropped based upon the bandwidth limit • Subscriber cannot exceed the bandwidth set by contract rate-limit {input | output} bps burst-normal burst-max conform-action action exceed-action action

  23. Traffic Shaping: • Control usage of available bandwidth • Establish traffic policies • Regulate traffic flow to avoid congestion traffic-shape ratebit-rate [burst-size [excess-burst-size]]

  24. Traffic Shaping: Interface serial0/0/0 encapsulation frame-relay traffic-shape rate 32000 4000 0 Interface serial0/0/0 traffic-shape group 101 64000 8000 0 ! access-list 101 permit tcp any eq ftp any

  25. Fragmentation: Packet size in bytes/sec x 8 = Packet size in bits/sec Packet size in bits/sec / Circuit size in bits/sec = Time required to transmit 1500 bytes/sec x 8 = 12000 bits/sec 12000 bits/sec / 56000 bits/sec = 0.214 sec = 214 msec

  26. Fragmentation MTU: interface serial 0/0/0 ip mtu 300 no ip address encapsulation frame-relay fair-queue 64 256 1000 ! interface serial0/0/0.1 point-to-point ip mtu 300 ip address 40.0.0.7 255.0.0.0 interface serial 0/0/0 mtu 300 no ip address encapsulation frame-relay fair-queue 64 256 1000 ! interface serial0/0/0.1 point-to-point mtu 300 ip address 40.0.0.7 255.0.0.0

  27. Congestion Avoidance: • WRED • Randomly drops packets when queue gets to a set % of capacity • Uses TCP window size to reduce flow

  28. Cisco Auto QoS: • On the interface to the phone Switch(config)#interface fa0/1 Switch(config-if)#auto qos voip ? cisco-phone Trust the QoS marking of the Cisco IP Phone cisco-softphone Trust the QoS marking of the Cisco IP Softphone trust Trust the DSCP/CoS marking Switch(config-if)#auto qos voip cisco-phone

  29. Cisco Auto QoS: • On the interface to the Router Switch(config)#interface fa0/1 Switch(config-if)#auto qos voip ? cisco-phone Trust the QoS marking of the Cisco IP Phone cisco-softphone Trust the QoS marking of the Cisco IP Softphone trust Trust the DSCP/CoS marking Switch(config-if)#auto qos voip trust CME(config)#interface fa0/1 CME(config-if)#auto ? discovery Configure auto Discovery qos Configure AutoQoS CME(config-if)#auto qos voip trust

  30. End of Chapter 8

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