lesson 6 Flashcards
traditional nonconverged network characteristics
- bursty data flow
- fifo access
- not overly time sensitive
- brief outages are survivable
converged network realities
- constant small packet voice flow competes with bursty data flow
- critical traffic must have priority
- voice and video are time sensitive
- outages are not acceptable
converged network quality issues
- lack of bandwidth
- end to end delay
- variation of delay
- packet loss
advanced queuing techniques
- weighted fair queue (wfq)
- priority queuing (pq)
- custom queuing (cq)
- modified deficit round robin (mdrr)
- class-based weighted fair queue (cb-wfq)
types of delay
- processing delay, router examining packet
- queuing delay, packet waiting in output queue
- serialization delay, time it takes to put the bits on the wire
- propagation delay, time it takes for packet to cross the link
types of packet drops
- tail drops, full output queue
- input drop, router congestion
- ignore, router congestion
- overrun, router congestion
- frame error, router congestion
voip performance requirements
- latency, 150 ms one way
- jitter, less than 100 ms
- packet loss, less than 1%
qos metrics
- delay
- jitter
- packet loss
live voice and video qos sensitivities
- delay
- jitter
- packet loss
streaming video and audio qos sensitivities
- jitter
- packet loss
transactional/interactive application qos sensitivities
-delay
bulk data, email, file transfer qos sensitivities
-none
qos tools
- congestion management
- queue management
- traffic shaping and policing
fifo
- first in first out queuing
- stores packets when the network is congested and forwards them in order of arrival when congestion is relieved
pq
- priority queuing
- puts data into four queue levels (high, medium, normal (*default), low)
cq
- custom queuing
- assigns specified amount of queue space to each class of packet
- performs round robin to service up to 17 queues
wfq
- weighted fair queuing
- makes transfer rates of high volume conversations more predictable
- made up of per flow fifo queues
- uses hash algorithm to produce the index queue
wred
- weighted random early detection
- stochastically discards packets if congestion begins to increase
steps to implement qos
- identify traffic and its requirements
- group traffic into classes
- define qos policies for each class
qos traffic classification
- voice, low latency
- mission critical, guaranteed delivery
- transactional, guaranteed delivery
- best-effort, no delivery guarantee
- scavenger class, less than best effort
qos models
- best effort, no qos
- integrated services, applications communicate their qos requirements
- differentiated services, network implements qos based on recognized classes
differentiated services model steps
- classification of packets
2. marking of packets
dscp
- differentiated services code points
- layer 3 precedence mechanism
cisco qos service class baseline models
- 4/5 class model
- 8 class model
- 11 class model
4/5 class model
- realtime
- call signaling, critical data
- best effort
- scavenger
8 class model
- routing protocols
- interactive voice
- video
- call signaling
- critical data
- bulk data
- best effort
- scavenger
11 class model
- routing protocols
- interactive voice
- streaming video
- call signaling
- network management
- mission critical data
- transactional data
- bulk data
- best effort
- scavenger
router physical interface queues
- hardware queue
- software queue, used when hardware queue is congested
- if hardware queue is not congested the software queue is bypassed
- hardware queue is always fifo
- software queue can be selected and configured
default cisco queuing algorithm
-wfq
wfq classification parameters
- source ip
- destination ip
- source tcp or udp
- destination tcp or udp
- transport protocol
- tos field
benefits of wfq
- simple configuration
- guarantees some throughput to all flows
- drops packets of most aggressive flows
drawbacks of wfq
- possibility of multiple flows ending up in one queue
- lack of control over classification
- doesnt provide fixed bandwidth guarantees
