Chapter 9 - QoS Concepts Flashcards
how does congestion of packets occur?
- multiple communicate lines aggregate onto a single device and data is placed on few/slow outbound interfaces
- when large data packets prevent smaller packets from being transmitted in a timely manner
a technique for QoS
classifying data into multiple queues (high, medium, low priority)
code delay
- source of delay
- fixed amount of time it takes to compress data at the source before transmitting to the first internetworking device, usually a switch
packetization delay
- source of delay
- fixed time it takes to encapsulate a packet with all the necessary header info
queuing delay
- source of delay
- variable amount of time a frame or packet waits to be transmitted on the link
serialization delay
- source of delay
- fixed amount of time it takes to transmit a frame onto the wire
propagation delay
- source of delay
- variable amount of time it takes for the frame to travel btwn src and dst
de-jitter delay
- source of delay
- fixed amount of time it takes to buffer a flow of packets and then send them out in evenly spaced intervals
jitter
variance in time delays btwn packets
what is playout delay buffer
helps compensate for jitter by buffering packets and then plays them out in a steady stream on the outbound interface
voice traffic characteristics
smooth
benign
drop and delay sensitive
UDP priority
voice traffic minimum requirements
latency ≤ 150ms
jitter ≤ 30 ms
loss ≤ 1% bandwidth (30-128 Kbps)
video traffic characteristics
bursty greedy drop and delay sensitive UDP priority (unpredictable, inconsistent and bursty)
video minimum requirements
latency ≤ 200-400 ms
jitter ≤ 30-50 ms
loss ≤ 0.1-1% bandwidth (384 Kbps - >20Mbps)
what port does Real-Time Streaming Protocol use?
UDP 554
what ports does Cisco products use for voice traffic
UDP 16384-32767
data traffic characteristics
smooth/bursty
benign/greedy
drop and delay insensitive
TCP retransmits
what is FIFO
First-In, First-Out Queuing Algorithm buffers and forwards packets in the order of their arrival all packets are treated equally fastest method of queuing
what type of queuing algorithm is used by default by all interfaces except serial interfaces at E1 and below
FIFO
what is WFQ
Weighted Fair Queuing
Queuing Algorithm
applies priority to identified traffic and classifies it into flows then determines how much bandwidth each flow is allowed relative to other flows
- low bandwidth traffic flows receive preferential service while high-volume traffic flows share remaining capacity equally among themselves
what does WFQ use in the packet header to classify traffic
- source and dst IP add
- MAC add
- port number
- protocol
- ToS
limitations of WFQ
- not supported with tunneling and encryption
- no precise control over bandwidth allocation
what is CBWFQ
Class-Based Weighted Fair Queuing
- allows users to define traffic classes based on match criteria like protocols, ACLs and input interfaces
characteristics you can assign after defining a class to its match criteria
- bandwidth
- weight
- maximum packet limit
