quality of spc services
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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
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
Rome, March 24th 2009 Quality of SPC services
Supply conditions
• Supply conditions regulates:
– economical aspects
– delivery time
– mutual responsabilies
– involved resources– involved resources
– …
– service levels
– …
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
Supply object
• the supply object can be: – a product
• shoes• food• pencils• personal computers• …• …
– a service:• professional training• catering• library (keeping)• web site hosting• …
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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• …
Rome, March 24th 2009 Quality of SPC 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– …
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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)
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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– …
Rome, March 24th 2009 Quality of SPC services
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
– …
Rome, March 24th 2009 Quality of SPC services
SPC network transport QoS managementQoS management
QoS management of the network transport service included in the SPC supply
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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|
Rome, March 24th 2009 Quality of SPC services
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)
Rome, March 24th 2009 Quality of SPC services
Destination(Responder)
T2 T3 T6 T7
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”
Rome, March 24th 2009 Quality of SPC services
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)
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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
Rome, March 24th 2009 Quality of SPC services
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