QOS

Question 1

QOS

Answer 1

To end user applications are performing properly (no drop calls, videos are smooth)

To network managers: Maximize utilization of the network bandwidth while meeting performance expectation

Question 2

Jitter

Answer 2

Change in the amount of time it takes a packet to move from A to B

Question 3

What is QoS mechanism for IP network

Answer 3

QoS is a mean to distinguish the packets and treat them differently

Question 4

There are two QoS mechanisms for IP networks

Answer 4

IntServ (Integrated services)

DiffServ (Differentiated Services)

Question 5

IntServ - Integrated Services

Answer 5

Individual flows are distinguished on end-to-end basis

Question 6

DiffServ

Answer 6

Individual flows are aggregated into smaller number of classes given differential treatment on a per hop basis

Question 7

In integrated Services (IntServ) each device in the network will reserve bandwidth for the flow

Answer 7

True

Question 8

In Differentiated Services (Diff Serv) the flow is assigned to a class and each device garauntee bandwidth for the class

Answer 8

True

Question 9

RSVP is a protocol that requests …………. …………. from every …………. in the path of the flow

Answer 9

bandwiidth reservation node

Question 10

RSVP T or F

It is not a protocol to signal QoS information for bandwidth reservation

Answer 10

F , It is a protocol

Question 11

RSVP T or F

It can make resource reservation for only unicast application

Answer 11

F , it can make resorce reservation for unicast and multicast applications

Question 12

RSVP T or F

It is sender oriented ( the sender of data flow initiates and maintains resource reservation )

Answer 12

F

It is receiver oriented (meaning receiver of data flow initiates and maintains the resource reservation used for that flow)

Question 13

RSVP T or F

RSVP does not maintain states in router and hosts

Answer 13

F RSVP do maintain states in router and hosts

Question 14

RSVP T or F

RSVP is routing protocol

Answer 14

F

RSVP is not a routing protocol but it depends on routing protocols to determine path of the flow

Question 15

RSVP T or F

RSVP supports only IPv4

Answer 15

RSVP supports both IPv4 and IPv6

Question 16

QoS applicable when we have transient congestion

Answer 16

True

Question 17

QoS has three operations

Answer 17

1-Classification and marking
2-Policing
3-Scheduling (queuing and dropping)

Question 18

Classification and marking

Answer 18

Classify thhe traffic that should be treated differently

Question 19

Policing

Answer 19

Check if packets ar confronting to administrively defined traffic rates and take actions (marking, remarking and dropping)

Question 20

Scheduling

Answer 20

How packets exists and queued
Post queueing mechanisms
Network tool to optimize link utlization

Question 21

T or F

Classification of packets can happen without marking

Answer 21

True

Question 22

How the classification of packet is done

Answer 22

Classification of packets is done at each node of the network but not required to be done everywhere where packets are sorted into different types which different policies can be applied

Question 23

Marking is the process of setting of the Differential Setting field (DS value field) so that traffic can be easily identified later

Answer 23

True

Question 24

There are different types of classification, we may consider for example Etherenet classification according to

Answer 24

• Physical interface (layer 1)
• MAC address (layer 2)
• Source/destination IP (layer 3)
• Transport protocol (layer 4)
• Application signeture (layer 5)

Question 25

Many ways of marking field

Answer 25

Layer 2 marking (add 32 bit field betrween source MAC address and the type of field in the original frame

Question 26

Layer 3 marking field

Answer 26

Type of Service (TOS Byte)

Question 27

Policies are not applied directly

Answer 27

True, 1- Packets are identified according to their classification 2- Packets are marketed according to rules 3- A decision is taken according to available rules

Question 28

Policing - Leaky bucket

Answer 28

Smooth out traffic by passing out traffic at a specific rate If the bucket is full - packets are discarded Used to enforce very strict policy on the traffic

Question 29

Token bucket

Answer 29

Allow burst but in a controlled way , it smoothes traffic too but permits burstiness quivilant to the number of tokens accumulated in the bucket Duration of Burst= Duration of empty bucket

Question 30

Duration of a burst = (bucket capacity in bytes)/ (Maximuum transmision rate in bytes/s - token arrival rate in bytes/s)

Answer 30

True

Question 31

CIR : Commited information rate

Answer 31

Long term average rate that the network provider is committed to honor by an agreement with thecustomer

Question 32

CIR is measured in bytes per second

Answer 32

True

Question 33

Only the IP layer is considerd in countin the CIR

Answer 33

True

Question 34

In general packet transmission is a series of bursts intervened by quiet intervals

Answer 34

True

Question 35

PIR Peak information Rate

Answer 35

Maximum rate the traffic is allowed

Question 36

Max transmission is limited by PIR

Answer 36

TRUE

Question 37

Excess burst are permitted above CIR ( committed information rate) but only until PIR is reached

Answer 37

TRUE

Question 38

Long term average should remain below CIR , Traffic above PIR is not permitted

Answer 38

true

Question 39

There are three types of trafic metering and coloring mechanisms:

Answer 39

Simple one tate two color marker Single rate three color marker two rate three color marker

Question 40

Buffer

Answer 40

Physical memory to store packets

Question 41

Queue

Answer 41

Holding an ordered identifiers to packets

Question 42

One queue means no scheduler implies no QoS

Answer 42

True

Question 43

Multiple queues needs a scheduler

Answer 43

True, the scheduler determine which queue to serve nxt

Question 44

Schedluer: FIFO First input first output

Answer 44

True

Question 45

Priority scheduling: If prioiruy queue is active it is served after any non-priority queue currently ebing served Head packet in prioiruty queue waits at most the serving time of non prioirity packet

Answer 45

true

Question 46

``` Weighted bandwidth schedluing It contains many algorithms: 1-WRR weighted Round Robin 2-WFQ weighted fair queuing 3-Deficit Round Robin ```

Answer 46

TRUE

Question 47

Weighted Round Robin Scheduler In a round of scheduler , the scheduler visits each queue and serves an amount of traffic from that queue determinde by the queue weights

Answer 47

TRUE

Question 48

Weighted Fair queuing : Each Flow i is given a weight wi

Answer 48

True

Question 49

Queue cannot drom to an infinite length because memory space is not infininte

Answer 49

True

Question 50

Dropping algorithms used to drop packets are as queues grom in length

Answer 50

true

Question 51

Two types of dropping algoritms

Answer 51

1- Tail drop (default behavior) | 2-RED (random early detection)

Question 52

Tail drop

Answer 52

If queue depth > = queue limit drop packet else addd packet to queue

Question 53

Weighted tail drop we have different thresholds

Answer 53

true

Question 54

Random early detection RED is a congestion avoidance technique • RED distributes drops over various sessions to desynchronize TCP sessions

Answer 54

``` Average queue depth < qmin → enqueue packet Average queue depth > qmax → drop packet Average queue depth between min and max → drop packet with a random → but increasing probability ```