18 - QOS Flashcards
QOS Tools give you a means to manage what 4 characteristics ?
- Bandwidth
- Delay
- Jitter
- Loss
What is bandwidth as it relates to QOS?
Capacity of the link.
What is delay?
- 2 types of delay
- One-way Delay - the time between sending a packet and that same packet arriving at the destination host.
- Round-trip Delay - the time it takes to send a packet and receive one back
What is jitter?
A variation in one-way delay between consecutive packets sent by the same application.
What is loss?
The amount of lost packets usually as a percentage of the total packets sent.
What are the guidelines for Interactive Voice?
- Delay - 150 ms or less
- Jitter - 30 ms or less
- Loss - 1% or less
What are the guidelines for Video?
- Bandwidth - 384 kbps to 20+ Mbps
- Delay - 200 to 400 ms
- Jitter - 30 to 50 ms
- Loss - .1% to 1%
What is Classification and Marking?
Marking of packets and the definition of trust boundaries
What is another name for Congestion Management?
Queuing
What is Congestion Management?
The scheduling of packets to give one type of packet priority over another.
What is Congestion Avoidance?
Addresses how to manage the packet loss that occurs when network devices get too busy.
What is NBAR?
Network Based Application Recognition
What do IP Phones mark voice payload packets with?
EF
What do Cisco IP Phones mark call setup packets with?
CS3
In an X-Y chart which is on the horizontal axis?
X which is the Best Drop to Worst Drop priority
In an X-Y chart which is on the vertical axis?
Y which are the 4 separate queues with Best queue at the top and Worst queue at the bottom.
What was the TOS byte originally?
3 bit IP Precedence field
What is the TOS byte now?
Class Selector DSCP values
What are the names of the Class Selector values?
CS0 through CS7
What is Prioritization?
The process of giving one queue priority over another in some way.
What is Class Based Weighted Fair Queuing (CBWFQ)?
Uses a round robin scheduler letting the network engineer define the weightings as a percentage of bandwidth.
What is Low Latency Queuing?
- LLQ tells scheduler to treat one or more queues as Priority Queues.
- Priority Queues are always ‘next’.
- Policer is used to prevent queue starvation.
- Call Admission Control limits the number of calls the network will handle.
What is the Trust Boundary?
The point in the network where devices can trust the current QOS markings
Where is the Trust Boundary on a VOIP network?
The phone
What is the DSCP Value (text name and decimal value) suggested by the DIffServ RFC for Voice payloads?
Suggested DSCP text name and decimal value for Voice Payloads is EF 46
What DSCP Value does the DiffServ RFC recommend that Call Signaling packets be marked as?
CS3
What are the 3 sets of DSCP values used in DiffServ?
- Expedited Forwarding
- Assured Forwarding
- Class Selector
What is Assured Forwarding?
- Defines
- 12 DSPC AF values used in concert with each other
- Made up of 4 queues
- with 3 levels of drop priority for each queue.
In DiffServ Class Selector what are the decimal values?
Multiples of 8 starting with CSO = 0 up to CS7 = 56
CS1 = 8
CS2 = 16
CS3 = 24
CS4 = 32
CS5 = 40
CS6 = 48
CS7 = 56
What are the 5 names of Marking Fields?
- DSCP
- IPP
- CoS
- TID
- EXP
What are the 3 Sets of DSCP Values used in DiffServ architecture?
- Express Forwarding (EF) - One DSCP value
- Assured Forwarding (AF) - 12 DSCP Values
- Class Selector (CS) - 8 DSCP Values
