QoS

Question 1

QoS

Answer 1

Provide pridictable management of network resources during times of congestion

Assista in maximizing the end user experience of critical sessions

Provides differentiated services to packets based upon pre defined user criteria

Question 2

QoS Models

Answer 2

Best Effort : QoS is not enabled, it is used for traffic that does not require any special treatment

Integrated Services (IntServ) : Applications signal the network to make a bandwidth reservation and to indicate that they require a special QoS treatment

Differentiated Services (DiffServ) : The network identifies classes that require special QoS treatment

Question 3

IntServ

Answer 3

The IntServ Model was created for real time applications such as voice and video that require bandwidth, delay and packet loss gurrantess to ensure both prdictable and guranted service levels.

Int Serv uses Resource Reservation Protocol (RSVP) throughout a network for specific application and to provide call admission control to gurrantee that no other IP traffic can sue the reserved bandwidth

Question 4

QoS Characteristics

Answer 4

Banwidth

Delay

Question 5

DiffServ

Answer 5

Diffserv divides traffic into classes and marks it based on business requirements so that each of the classes can be assisnged a different level of service.

As IP traffic traverses a network, each of the network devises identifies the packet class by its marking and services the packets according to this class

Question 6

Classification

Answer 6

Packet Classification is a QoS mechanism responsible for distinguishing between different traffic streams. It uses traffic descriptors to categorize an ip packet within a specific class.

Packet classification should take place at the network edge as close to the source of the traffic as possible.

Once an IP packet is classifid, packets can then be market/remarked, queued, policed, shaped or any combination of these and other actions.

Question 7

Traffic Descriptors

Answer 7

Internal > QoS groups (Logically significant to a router)

Layer 1 > Physical Interface, subinterface or port

Layer 2 > MAC Address and 802.1Q/p class of service CoS bits

Layer 2.5 > MPLS Experimental EXP bits

Layer 3 > Differentiated services code points, IP precedence and source/destination IP address

Layer 4 > TCP or UDP ports

Layer 7 > Next Generation Network based application recognition (NBAR2)

Question 8

Layer 7 Classification

Answer 8

NBAR2 is a deep packet inspection engine that can classify and identify a wide variety of protocols and application using layer 3 to layer 7 data including difficult to classify application that dynamically assign TCP or UDP port numbers

NBAR can recognize more then 1000 applications and monthly protocol packs are provided for recognition of new and emerging application without requiring an IOS upgrade or router reload.

Question 9

NBAR2 Modes

Answer 9

Protocol discovery
Protocol Discovery enables NBAR2 to discover and get real time statistics on applications currently running in the network . These statistics from the protocol discovery mode can be used to define QoS classes and policies using MQC configration

Modular QoS CLI 
Using MQC, network traffic matching a specific network protocol such as webex can be placed into one traffic class while traffic that matches  a differnt network protocol such as youtube can be palced into another traffic class. After traffic has be classified in this way, different QoS policies can be applied to the different classes of traffic