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
• definitions and tools for measuring QoS• definitions and tools for measuring QoS
• 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
• 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 thesupplier 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 is tangible:
– 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 erogation such as:
– for istance: mobile phone
• ...
• power supply
• software
• battery
• …
• often a service can be “realized” by supplying more than one
product
– 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 therequirement) 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 used
to objectively measure QoS, during the life cycle of
the 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 SLA
definition 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 be reduced increasing resources• it can be reduced increasing resources
• propagation delay
– time needed for the signal to cover the distance from source to
destination
• it depends on the light speed
• it cannot be decreased
• ritrasmission delay
– time needed to ritransmit a lost packet
• only for links that provide ritrasmission feature

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 transport
requirements:
– 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
– KPIs aggregation algorithm– KPIs aggregation algorithm
– 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 of
transport 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 bytes
dimension 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 “survey
intervals” 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 Bortone
e-mail: claudio@bortone.it
web-site: http://www.linkedin.com/in/claudiobortone

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