5 Replies Latest reply: Nov 1, 2017 12:02 PM by Gus RSS

    Business applications QoS requirements

    Juan

      Enabling QoS in a network allows the convergence of different types of services with different and particular needs, such as voice, video and data, using the same infrastructure.

       

      Design phase previous to QoS real deployment requires a strategical definition of the objectives to achieve via QoS mechanisms:

       

      • Define the QoS objectives from an organizational point of view.
      • Select the appropriate number of traffic classes to be able to meet previously defined objectives.

       

      This dynamic process should be ahead of the business application needs, in way that should allow to use network services with the best possible Quality of Experience (QoE) for the end users.

       

       

      Traffic classes

       

      As defined in the DiffServ model, the network can provide a classification where each Traffic Class will receive a special treatment that minimizes the effects of the parameters to which each type of traffic is more sensitive. It’s key to define the Traffic Classes (TC) that the network will give a special treatment according to their particular needs.

       

       

      qos-parameters.png

       


      With this design objective in mind, the network can transport TCs with completely different characteristics maximizing the QoE of each application making use of the network.

       

       

      Traffic characteristics

       

      The basic traffic parameters used to characterize the traffic traversing the network can be defined in the next way:

       

      • Delay: the amount of time it takes a packet to travel from source to destination. Delay degradation effects are talkover and echo.
      • Jitter or delay variance: the measure of the variability over time of the latency across a network. Jitter causes abnormal speech rhythm and irregular video image.
      • Packet loss: the amount of packets that are unsuccessful in arriving at the destination. Packet loss causes missing sounds, syllables, words or phrases.

       

      QoS design must consider some major points for a successful deployment, like current network ability to accommodate Real-Time services and continuous monitoring of QoS parameters.

       

       

      Applications service level requirements

       

      Network designer should analyze the specific requirements of each Traffic Class and translate business applications needs to appropriate network policies. Each policy should minimize the effects of network quality parameters degradation on business critical applications.


      VoIP, Video, Data and Control Plane are traffic classes with specific network requirements. Next, we’ll take a short review of each class of traffic.

       

       

      VoIP

       

      VoIP traffic has real time needs and it’s affected by all the QoS quality parameters.


      An excessive delay causes voice quality degradation, while packets loss causes voice clipping and skips in the conversation. Jitter effects depend on the jitter buffer size. An excessively big buffer can cause an excessive delay and one too small can lead to packets loss.

       

       

      Video

       

      Interactive video has similar QoS requirements as VoIP because it is affected by the same factors, as voice is transported with video. On the contrary, traffic patterns of Interactive Video are very different than the ones of VoIP because video traffic has varying packet sizes and variable packet rates, while VoIP maintains a stable and predictable bandwidth usage per call.


      Streaming Video is less delay and jitter sensitive because these effects can be minimized by the use of buffering techniques. Streaming Video is unidirectional, so the LAN to WAN QoS specific policies are not needed in that direction.

       

       

      Data

       

      Let’s analyse data apps by dividing the all the applications as a whole into subclasses by relevance to the business and particular needs:

       

      • Critical to the enterprise
        • Bulk.
        • Transactional / Interactive.
        • Locally-Defined Mission-Critical Data.
      • NOT critical to the enterprise.
        • Best Effort.
        • Scavenger.

       

      Best Effort

       

      Best Effort is the default class for data applications without special needs. The app will be removed from this class (the default class) if it has some special treatment requirement. As there are a huge number of applications potentially classified into the default class, it’s recommended to provision a relevant minimal BW requirement for it.

       

      Scavenger

       

      Scavenger traffic is one level below BE. It’s designed to provide less than best effort service. Applications with little or not at all business related relevance should be assigned to this TC.

       

      Bulk

       

      Bulk class is reserved for non-interactive drop-insensitive applications that can span their operations over long periods of time or when the network is underutilized. Examples of that are backup background operations.

       

      From a design point of view, It’s better to reserve a reasonable amount of bandwidth to Bulk data instead of applying policing to it. By doing it this way, Bulk data traffic can take advantage of remaining bandwidth resources on periods of inactivity or low resources demand. The amount of Bulk data bandwidth is limited so this kind of traffic can’t affect other more business critical ones.

       

      Transactional

       

      Client-Server applications can be classified following the Response Time Requirement (RTR) parameter. RTR separates:

       

      • Generic client-server applications.
      • Transactional client-server applications.

       

      Transactional means that the user waits for the operation to complete before proceeding. That’s the reason why Transactional data traffic needs for a special QoS treatment. Transactional data is a combination of two similar types of applications: Transactional Data Client-Server Applications and Interactive Messaging Applications.

       

      Locally-Defined Mission-Critical

       

      This class is intended to provide an enterprise with a premium class as a subset of the transactional data class. It’s a subset of transactional data that is selected by its significant contribution to the overall business objectives. It’s recommended to include in this class as few apps as possible. The admission criteria for this class is not technical, it’s organizational (political).

       

      In this class would be included apps with a higher business priority for the organization and executive endorsement is recommended in advance to get the required business support for successful implementation in the network.

       

       

      Network Control

       

      Under network control category is included all IP Routing and Network Management traffic.


      IP Routing traffic includes all the control plane traffic generated by interior and exterior gateway protocols like OSPF, EIGRP and BGP. It’s critical for the network operation to reserve some portion of resources to ensure this kind of traffic don’t experiment problems due to network resources exhaustion.

       

      Network Management traffic includes all the traffic generated by network management applications to analyze, predict, observe and troubleshoot the network. An example of network management applications are SNMP, NTP and Syslog. These kind of applications help to act before failure by analyzing network performance and resource utilization.

       

       

      Summary

       

      Optimal deployment of QoS in the enterprise environment requires the analysis of service-level requirements of the different traffic classes. The next table categorizes the traffic classes into 4 big groups: Voice, Video, Data and Control Plane.

       


      Group

      Traffic Class

      IPP

      PHB

      DSCP

      L2 CoS

      Loss

      Latency

      Jitter

      BW

      VoIP

      VoIP telephony

      5

      EF

      46

      5

      < 1%

      < 150 ms

      < 30 ms

      21 - 320 kbps

      Call Signaling

      3

      AF31

      26

      3

      -

      -

      -

      150 bps

      Video

      Interactive Video

      4

      AF41

      34

      4

      < 1 %

      < 150 ms

      < 30 ms

      Overprovision +20% for bursts

      Streaming Video

      4

      CS4

      32

      4

      < 5 %

      < 5 s

      -

      Encoding dependant.

      Control Plane

      Network Control / IP Routing

      6

      CS6

      48

      6

      -

      -

      -

      Minimum guarantee.

      Network Management

      2

      CS2

      16

      2

      -

      -

      -

      Minimum guarantee.

      Data

      Scavenger

      1

      CS1

      8

      1

      -

      -

      -

      Lowest configurable.

      Best Effort

      0

      0

      0

      0

      -

      -

      -

      25 % as a minimum

      Bulk Data

      1

      AF11

      10

      1

      -

      -

      -

      Moderate guarantee

      Transactional / Interactive

      2

      AF21

      18

      2

      -

      -

      -

      Adequate guarantee

      Locally-Defined Mission-Critical

      3

      -

      25

      3

      -

      -

      -

      Adequate guarantee


       

      I hope you find it useful.