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Voice over IP Fundamentals

CHAPTER 8 Quality of Service. Voice over IP Fundamentals. 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)

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Voice over IP Fundamentals

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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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