Voice over IP Fundamentals

• CHAPTER 8• Quality of Service

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)

Delay Budget

Edge Functions

•Classify traffic as close to the edge as possible!

•Provider Edge

•Customer Edge

Header Compression:

cRTP will compress traffic by recording header information and incrementally increasing it per each received packet

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

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

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

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

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

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 101queue-list 1 default 2queue-list 1 queue 1 byte-count 4000queue-list 1 queue 2 byte-count 2000!access-list 101 permit udp any any range 16380 16480 precedence 5access-list 101 permit tcp any any eq 1720

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 16484access-list 101 permit tcp any any eq 1720priority-list 1 protocol ip high list 101

Priority Queuing:

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

PQ within CB-WFQ (Low Latency Queuing):

• Gives absolute priority to voice traffic

Traffic Classification:

• Three bits in the ToS field of the IP Header• in-band QoS

DSCP, TOS, and COS:

Traffic Classification:

• Three bits in the ToS field of the IP Header• in-band QoS

Traffic Classification:

• Can be set by destination phone number

dial-peer voice 650 voip destination-pattern 650 ip precedence 5 session target RAS

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 anyroute-map RESET-PRECEDENCE permit 10 match ip address 105 set ip precedence routine

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]

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 contractrate-limit {input | output} bps burst-normal burst-max conform-action action exceed-action action

Traffic Shaping:

• Control usage of available bandwidth• Establish traffic policies• Regulate traffic flow to avoid congestion

traffic-shape rate bit-rate [burst-size [excess-burst-size]]

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

Fragmentation:

Packet size in bytes/sec x 8 = Packet size in bits/secPacket size in bits/sec / Circuit size in bits/sec = Time required to transmit

1500 bytes/sec x 8 = 12000 bits/sec12000 bits/sec / 56000 bits/sec = 0.214 sec = 214 msec

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

Congestion Avoidance:

•WRED Randomly drops packets when queue

gets to a set % of capacity Uses TCP window size to reduce flow

Cisco Auto QoS:

•On the interface to the phone

Switch(config)#interface fa0/1Switch(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 markingSwitch(config-if)#auto qos voip cisco-phone

Cisco Auto QoS:

•On the interface to the Router

Switch(config)#interface fa0/1Switch(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 markingSwitch(config-if)#auto qos voip trust

CME(config)#interface fa0/1CME(config-if)#auto ? discovery Configure auto Discovery qos Configure AutoQoSCME(config-if)#auto qos voip trust

End of Chapter 8