quality of spc services

Quality of SPC services

Claudio BortoneClaudio Bortone

IV seminar in

“ICT Service Oriented Network Architectures“

University of Rome La Sapienza

March 24th 2009

Table of contents

• part 1:

– overview on ICT QoS management• definition of a supply contract

• definition of an ICT service

• definitionsand toolsfor measuringQoS• definitionsand toolsfor measuringQoS

• part 2:

– SPC network transport QoS management:• elements for measuring network transport QoS

• a network transport service of SPC: always-on

• always-on network transport SLA

Rome, March 24th 2009 Quality of SPC services

ICT QoS management

Overview of quality management

of complex ICT services’ supply

Supply contract

Supply contract

• a supply contract is a costly deal:

– against the financial cost supported by the supplier to provide the supplied object, corresponds a patrimonial benefit for the same supplier due to the object delivery to the supplier due to the object delivery to the counterpart

• a supply contract defines:

– conditions

– subjects

– characteristics of supply’s object


Supply conditions

• Supply conditions regulates:

– economical aspects

– delivery time

– mutual responsabilies

– involved resources– involved resources

– …

– service levels

– …


Supply subjects

• three kinds of supply subjects:

– supplier:• the economical subject that provides the supply

– user:• the user or beneficiary of the object of the supply• the user or beneficiary of the object of the supply

– contractor:• in some context, it is the direct interlocutor of the

supplier instead of the user

• a contractor can be a user


Supply object

• the supply object can be: – a product

• shoes• food• pencils• personal computers• …• …

– a service:• professional training• catering• library (keeping)• web site hosting• …


The difference between product and service

• product istangible:– omogeneous– production and distribution differ from consumption– a thing, an object– customers don’t partecipate to the production process– it can be stored– property transfer

• service si untangible:– eterogeneous– production and consumption are not separable– an activity, a process– customers partecipate to the production process– it cannot be stored– there’s not property transfer


Products and services overlapping

• a product can include more than one service erogationsuch as:– for istance: mobile phone

• ...• power supply• software• battery• …

• often a service can be“realized” by supplying more than oneproduct– for istance: network data transport

• …• connection• switch• router• …


Information and Communication Technology (ICT) services

ICT services supply

• the contractor is generally the counterpart of an ICT services supplier

• some examples of ICT services supply:– connectivity– security– security– VoIP– system management– web site design– asset management– …


ICT service supply life cycle: phases

• ICT service supply’s life cycle consists in 2 phases:

– phase 1: realization• includes activities for implementing the new service

and delivery predispositionand delivery predisposition

– phase 2: operation• includes activities for service erogation, change

management, problem mangement


ICT service supply life cycle: transitions

• the passage between the 2 life cycle phases is guaranteed by two transitions:

– from phase 1 to phase 2: test• service must be realized under the conditions

specified in the supply contract (verified and tested)specified in the supply contract (verified and tested)

– from phase 2 to phase 1 : design review• information on some troubles resolution or on

changes managed in the operation phase, can be used as input for reiterating the realization phase


ICT service supply life cycle : diagram


Macro processes for ICT service supply

• the international standard ISO/IEC 20000 defines the macro processes necessary to a ICT service supply:

– for the realization phase:• Planning and Implementing New or Changed Services

• Service Delivery Processes

– for the operation phase:• Release Processes

• Resolution Processes

• Relationship Processes

• Control Processes (activate the Design Review)


Quality of Service (QoS) measure

General consideration on the quality of service

• the International Standardization Organization (ISO), definines quality as:

– “the level with which a set of charateristics (of product, of system, or process) satisfies the requirements”requirements”

• the satisfation level of a user/contractor can be evaluated in two ways:

– subjectively

– objectively


Subjective quality

• the subjective QoS can be defined as the deviation between perceived QoS and desired QoS:

– QoS desired:• it is the quality level determined by explicit or

implicit needs or by user desireimplicit needs or by user desire

– QoS perceived:• it is the quality level that the user can be evaluate by

using service and by comparing the (actual or potential) service performance with his desire


Objective quality

• the objective quality can be defined as deviation between designed QoS and erogated QoS:

– designed QoS:• it is the quality level taken as reference (project

requirement) during the realization; it regulates the requirement) during the realization; it regulates the organizational system, the service realization modalities, and the functioning conditions

– erogated QoS: • it is the quality level objectively measured in the

operational phase by adeguated measuring tools


Key Performance Indicators

• the Key Performance Indicators (KPIs) are tools usedto objectively measure QoS, during the life cycle ofthe supply:– one or more KPIs can be determined for each

supply sub-process– KPIs can be put together to built another KPI

• constant monitoring of KPIs is an important activity:– it allows the supplier to identify precisely the

processes that need to be fine tuned to increase the satisfaction level

– it allows the user/contractor to measure more objectively the erogated QoS


KPI determination

• the determination of a significant KPI often is a challenging activity:

– it is necessary to avoid that:• it consists in a statistic data that is not

rappresentativerappresentative

• it is defined in a vage and interpretable way

– the requirements for a good KPI designer are:• technical and managerial skills which must be

reliable and horizontal

• capability analysis and affective reporting for all the factors which affect the indicator evaluation


Service Level Agreement (SLA)

• in a service supply, the SLA is a condition that establishes:

– the thresholds within which the objective quality aspects (measured by KPI) are accettableaccettable

– the penalities agreed with the supplier in case of established thresholds are exeded


Minimal requirements for SLA

• Minimal requirements for SLA are:– service characterization– involved KPIs list– KPIs aggregation algorithm– SLA target– SLA target– the referencing time slot– modality of evaluation and penalty payment– reporting modalities


SLA target

• the SLA target represents the acceptable threshold value within which the objective quality aspects are measured by one or more KPIs

• the supplier uses the SLA targets as quality level • the supplier uses the SLA targets as quality level reference (project requirements) during the relization phase


SLA target rappresenting desired QoS

• it is crucial that the contractor defines SLA targets in line with desired QoS:

– strict SLA targets imply an increase of referring desired quality levels while designing

– strict project requirements imply a non – strict project requirements imply a non proportional increase of performance price


SLA refining

• other useful information that can enrich the SLAdefinition are:– the erogation time slot (time during which the

service are erogated)– SLA updating modalities– …


SLA classification

• the classification of a SLA in accordance with the process that are involved in KPI is a best practice

• some example of classification are:

– delivery– delivery

– assurance

– performance

– …


SPC network transport QoS managementQoS management

QoS management of the network transport service included in the SPC supply

Elements for measuring quality of network service

Tipical metrics

• Packet Loss

– percentage of packets that do not reach their destination

• Delay

– One-Way-Delay• the time elapsing between the packet departure and arrival

– Round-Trip-Delay• the time elapsing between the packet departures and its

acknowledgement

• Jitter

– delay variation between two subsequent packets


Packet loss contributes

• network malfunctions– link error

• significant bit error probability

• congestion

– network equipement that does not have enough resources to manage incoming packetsresources to manage incoming packets

– memory resource shortage of interface output queue• transients

– transient and incoherent network configurations due to routing protocol convergence

• packets dropped for TTL zero value


Delay contributes

• sending delay– time between packet receiving and queuing on output interface

• queuing delay– time elapsed while packets remain in queue

• line delay– time needed to write a packet on the line

• it depends on the packet dimension and from the bit rate (technological facility)

• it can bereducedincreasingresources• it can bereducedincreasingresources• propagation delay

– time needed for the signal to cover the distance from source todestination

• it depends on the light speed• it cannot be decreased

• ritrasmission delay– time needed to ritransmit a lost packet

• only for links that provideritrasmissionfeature


Jitter

• mathematical jitter

– standard deviation of one-way-delay• it is the square root of variance (average of squares

of average deviation)

• inter-packet delay variation• inter-packet delay variation

– defined in RFC 3393

– average of interarrival times difference• let ti the time necessary to a packet i to reach

destination, it will be calculated the average of |ti+1 – ti|


Inter-packet delay variation

Source(Querier)

T1

P1 R1

T4 T5

P2 R2

T8

• Jitter SD = (T2 – T1) – (T6 – T5)

• Jitter DS = (T2 – T1) – (T6 – T5)


Destination(Responder)

T2 T3 T6 T7

Charatteristics of SPC transport service always-on

Always-on service

• technical specifications definition:

– “transport services allow linking to the supplier’s network by a technology that provides permanent access (link xDSL, SDH, etc.)”etc.)”

• technical specifications also define the service access point “Punto di Accesso al Servizio”(PAS) such as:

– “every service will be erogated by one or more phisical user interface called PAS”


Transfer component

• different applications need different data transportrequirements:– for each application and for each PAS the

supplier can provide one or more transfer components“Componente di Trasferimento “ (CdT)(CdT)

– every CdT is characterized by:• a scope• guaranteed amount of access bandwidth“Banda

Massima in Accesso”(BMA)• a service class “Classe di Servizio”(CdS)


Service class (CdS)

• 4 desired quality of transport requirement for a CdT can be associated to 4 CdS:

– real time (RT)• low delay and low jitter

– mission critical (MC)– mission critical (MC)• low delay and low packet loss

– streaming (ST)• low jitter

– best effort (BE)• no specific requirements


Always-on network transport SLA

Minimal requirements of SLA

• minimal requirements of SLA are:– service characterization– involved KPIs list– KPIsaggregationalgorithm– KPIsaggregationalgorithm– SLA target– the referencing time slot– modality of evaluation and penalty payment– reporting modalities


Service characterization

• one always-on service characterization:

– supply: • Public Connectivity System

– service: • always-on (AON)• always-on (AON)

– service characteristic: • one transport component with a real time service

class


Involved KPIs

• three tipical KPIs used for measuring quality oftransport services from source to destination:– one way delay (OWD)– packet loss – jitter

• KPIs measuring modalities:– each equipement that realizes the PAS will measure

constantly sending 10 packets with a 40 bytesdimension toward the QXN border router

– this measure will be done for each minute of the day, and for each CdT with a RT CdS


Aggregation algorithm and SLA target

• the measures must be aggregated in “surveyintervals” with 24 hours duration (for CdT BGA)

• SLA target for each KPI in each“survey interval” is:– for OWD:

• < 40 ms for 99% of packets

– for Packet Loss: • < 0,15% of packets

– for Jitter:• average value < 15 ms


Reference time slot and penalties

• for each four-month period:

– SLA considers survey intervals out of SLA target for each KPI

• the penalty for each four-month period under • the penalty for each four-month period under check will be:

– 1% of monthly charge of each survey interval out of SLA target in four months


Reporting modalities

• for each four-month period will be produced a report that represents:– the four-month period under check– the identificative of service – the measure of each KPI (PL, OWD, Jitter)– the number of intervals out of SLA target– the number of intervals out of SLA target– monthly charge– percentage of monthly charge used for calculating

penalty– economical value of penalty


Thanks

Claudio Bortonee-mail: [email protected]: http://www.linkedin.com/in/claudiobortone

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