ISO/IEC JTC1/SC21/Nxxxx (K11)
DATE: November, 1995
Open Systems Interconnection, data management and
Open Distributed Processing
Secretariat: USA (ANSI)
Title: Quality of Service Interim Meeting Report
Source: Collaborative ISO/IEC JTC1/SC21 & ITU-T SG7 Interim Meeting on QoS, Kobe, Nov. 1995
Project: JTC1.21.57/ITU-T Q19/7 & Q2/7
Status: Meeting output
Required Action: For information
Summary: The QoS Methods and Mechanisms text (K10) was developed to PDTR and is circulated for NBLO ballot in time for input to an Editing Meeting expected to be
held in late 1996.
Informal discussion during the Interim Meeting on the proposed New Question on
QoS in ODP (SC21/WG7/N1034) generated useful guidance information for NBLO
responses and this material is included here (Appendix D, also published as
Improvements to the Methods and Mechanisms document have (limited) editorial
impact on the QoS Framework CD. NBLOs are requested to consider proposals for
revising the QoS FW in their ballot comments, due 15 February 1996.
1. QoS PROJECT MEETING
1.1 1.1 General
A meeting of joint project JTC1.21.57 | ITU-T Q19/7 & Q2/7 on Quality of Service was held in Kobe, Japan between 95-11-06 and 95-11-10 to develop the QoS Methods and Mechanisms document to PDTR.
Participation was invited from the other Working Groups of SC21 and from experts from SC6, SC18, TC184, and other standards developers. The meeting was attended by representatives from Canada and the UK together with a representative from TCCA (ISO/TC184/SC5/WG2).
Input was received from one national body (UK: K3) and this was supported by late contributions at the meeting (K4, K5).
The list of attendees can be found in Appendix A.
1.2 Documents Considered
For the list of documents considered, see Appendix B. This list contains documents from the previous meeting carried forward for further work, together with input documents and meeting outputs.
2. QoS FRAMEWORK
The Final CD ballot is underway and therefore no technical discussion of this text was undertaken during this meeting. (For information: the ballot deadline on this Final CD 13236.2 [SC21 N9680] has been recently extended from 1995- 11-25 to 1996-02-15 in SC21 N9926.)
3. QoS METHODS & MECHANISMS
One national body developed an input text (UK: K3) supported by late contributions (K4, K5) provided at the start of the meeting. The major proposal of the contributions was that the scope of the Methods and Mechanisms (M&M) document should be extended to include references to standards and specifications dealing with QoS.
The meeting accepted the proposals made in K3 and as augmented by K4 and K5 and work proceeded on that basis. The meeting discussed the topic of the relationship between the QoS documents and other texts, e.g. OSI and ODP, and related on-going developments elsewhere, e.g. in OMG. It concluded that to extract mechanisms from on-going work and then express them in terms of the QoS Framework would take more resources than are available. As the QoS Framework begins to influence others to use these common concepts and terminology, as it has done with the TCCA community (ISO TC184/SC5/WG2), then the results from these diverse areas will converge in at least their underlying concepts and therefore the task of developing the M&M TR into a valuable reference text will become easier and less resource-hungry.
The present state of the TR as a list of references together with some results of analysis of existing standards, primarily from ITU-T, is thus a temporary state and the first in the evolution of this TR.
Invitations will be extended to ITU-T and OMG to provide candidate material on mechanisms for inclusion in clause 5.1 of the TR.
The meeting reaffirmed that an interval of probably 18-24 months between successive updates is both desirable, to keep the text up-to-date, and realistic, in terms of the effort required and the approval timescales.
The meeting agreed the following two instructions to the editor:
? update the Definitions and Abbreviations clauses
? create a table for Clause 5.2 covering an index of QoS characteristics
based on material in the document.
The meeting agreed unanimously that the text was sufficiently mature to go forward for ballot as PDTR, in accordance with the delegated authority from SC21 as per SC21 N9872, Resolution 2.2.
4. Discussion on the proposed New Question on 'QoS in ODP'
An informal meeting between the ODP and QoS groups was held in order to:
a. discuss and develop views into the currently active ballot on the proposed new question on 'QoS in ODP' (SC21 WG7 N1034)
b. discuss development of the application of QoS concepts to object-oriented specifications and systems, as evidenced by recent developments (e.g. Appendix D)
c. determine whether QoS mechanisms may be identified within the ODP work.
There was general consensus that the scope of the discussions was ?QoS in distributed systems? rather than ?QoS in ODP?, the title currently proposed in SC21/WG7/N1034.
As a input to the debate on (a) the UK offered an expert contribution (K8). The two main points from this paper and the related debate are that conformance is a key issue, and the complexity of the behaviour of several objects is important and should not be ignored in the consideration of individual objects. Document K8 was revised following this discussion, K8 (Rev) is included here at Appendix D.
The relationships between the QoS work and that on OSI, ODP etc. was seen as an area of importance, and that the process of ?influence? of OSI, ODP etc. to use the QoS Framework concepts and terminology is an ongoing task that will continue: an important potential benefit of this is the development, in ISO and elsewhere, of QoS Methods and Mechanisms (using the QoS Framework as their basis), which may then become candidates for inclusion in the M&M TR with minimal rework.
The paper on QoS in an object environment (Appendix E) was noted by the QoS group as a potential starting point for the consideration of QoS in distributed systems. The ODP group agreed to consider this proposal during their Kobe meeting.
Existing QoS mechanisms within the ODP work were not identified, though the Trader was seen as an important focus for QoS developments in ODP.
See Appendix C for a list of the participants at the informal meeting on QoS in distributed systems held on 7 November.
5. OUTPUT DOCUMENTS
QoS - Methods and Mechanisms - PDTR K10
QoS Meeting Report (95-11) K11
Liaison statement to JTC1/SC6 on QoS K12
Liaison statement to TC184/SC5/WG2 on QoS K13
Relationships between documents concerned with QoS K14
6. FUTURE MEETINGS
The following are known key dates for the QoS work as a whole:
96-01 Issue of the M&M PDTR for ballot
96-02-15 Close of the FW Final CD ballot
96-05-06/10 FW Final CD editing meeting, at ANSI in NY, USA
96-05-13/24 SC21 WG meetings in Kansas, USA
96-11? M&M PDTR editing meeting
NB 1. ? indicates tentative date(s)
2. the dates for ballot on the proposed new question on 'QoS in ODP' (SC21 WG7 N1034) are not known at this time.
The scope of the discussions on QoS at the Kansas meetings is limited by the ongoing ballot cycles for both the Framework and the Methods & Mechanisms documents; the main topic will be QoS in distributed systems.
Appendix A Participants at Kobe QoS meeting
Appendix B Documents Considered at Kobe QoS meeting
Appendix C Participants at Informal Meeting on QoS in Distributed Systems (95-11-07)
Appendix D ?Issues for discussion on QoS and ODP? [K8(Rev)]
Appendix E ?Overview of Quality of Service for Distributed Objects? by Zinky et al
(only included in paper-distributed copies)
Participants at Kobe QoS Meeting
John Holmes UK Rapporteur for QoS
Donald Sheppard CA
Yasuhisa Shiobara J TC184/SC5/WG2 representative
Chris Sluman UK
Jeremy Tucker UK Editor for QoS Methods & Mechanisms
Documents considered at Kobe QoS Meeting
QoS - Methods and Mechanisms - WD #3 Editor QoS MM SC21 N9681 QoS Meeting Report, 95-07 QoS Rapporteur SC21 N9683 Liaison statement to JTC1/SC6 on QoS SC6 Liaison Rep SC21 N9684 Liaison statement to TC184/SC5/WG2 on QoS QoS Rapporteur SC21 N9685
Proposed Future Directions for the Methods and Mechanisms TR UK K3 Further proposed changes to SC21 N9681, QoS Methods and M. UK K4 Proposed Addition To The QoS M & M document (SC21
A note on issues for discussion on QoS and ODP UK K8
Issues for discussion on QoS and ODP UK K8 (Rev) QoS - Methods and Mechanisms - PDTR Editor QoS MM K10 QoS Interim Meeting Report QoS Rapporteur K11 Liaison statement to JTC1/SC6 on QoS Editor QoS MM K12 Liaison statement to TC184/SC5/WG2 on QoS TCCA Representative K13 Relationships between Documents concerned with QoS Editor QoS FW K14
Participants at Informal Meeting on QoS in Distributed Systems (95-11-07)
John Holmes UK Rapporteur for QoS
Horikazu Horiguchi J
Hidehito Kubo J
Peter Linington UK Chairperson
Kerry Raymond AUS
Don Sheppard CA
Chris Sluman UK Editor for QoS Framework
Akira Tanaka J
Jeremy Tucker UK Editor for QoS Methods & Mechanisms
Mitsukazu Uchiyama J
Bryan Wood UK
?Issues for discussion on QoS and ODP?
This note identifies a number of issues for consideration in progressing the proposed new question on QoS and ODP.
The QoS Framework (ISO/IEC CD 13236) is primarily concerned with defining a ?structured collection of concepts and
their relationships? that will provide a common means of description for use in the discussion of QoS in the context of
systems, services and resources of various kinds. The proposed new question is concerned with the application of those
concepts in the context of ODP systems - in other words, their application in the context of a system specification within
the framework defined by the Reference Model of Open Distributed Processing (RM-ODP) (ITU-T Rec. X.901-904 |
There are three areas for consideration:
? where are QoS statements applicable within an RM-ODP object model of a system?
? how do QoS concepts from the QoS Framework relate to the RM-ODP concept of quality of service and the closely related concept of environment contract?
? what kinds of QoS statement are applicable within each of the viewpoint descriptions of a system defined
in the RM-ODP?
The following three sections discuss each of these areas in more detail. For each area there is a statement of the issue followed by a brief discussion indicating the kinds of concern that need to be addressed
2. QoS in an RM-ODP object model
QoS statements can be made about the services offered by an object at an interface. However, in general a system will be described in terms of a configuration of objects and QoS statements about the individual objects in the system in isolation will be of no value in indicating describing the behaviour of the configuration as a whole. Thus, there is a need to consider
? what are the appropriate kinds of QoS statement to make about the behaviour of a configuration of objects;
? what principles should govern the choice of statement to be made.
QoS statements are potentially applicable to interactions between objects. Thus, they are potentially applicable at a binding between interfaces of objects (e.g. response time for the invocation of a service) or between two points at which bindings can be observed (e.g. transit delay between service invocations). Note that, in either case, there may be a sequence of interactions involving a number of objects between an invocation and a response at a single binding, or between the interactions at the pair of bindings to which the QoS statement applies.
The specification of a QoS characteristic implies the possibility of making observations of the system being modelled in order to make QoS estimates. Thus, while QoS statements may be potentially applicable at any binding between interfaces within a configuration of objects, actual statements of QoS characteristics can only be made for bindings for which observations can be made. What this constraint means in practice depends on the nature of the QoS characteristic. Thus, throughput for a binding may be observable at any point on the communication channel that is used. For transit delay, on the other hand, it is necessary to specify the locations in space and time at which the observations are made: this means that they can only be made in relation to bindings that are related to interaction points.
Thus, within the representation of a system as a configuration of objects, actual or potential bindings between interfaces of objects represent potential points at which QoS statements may apply. It may be the case, however, that the full object model exists only to express a potential functional decomposition and that, for any given system, there is interest only in the service seen at certain points within the object configuration: the behaviour at other points is an implementation choice subject to the specified requirements being met.
It follows that QoS statements about an object model involve the nomination of the bindings to which the such statements are to apply and the association of those bindings with interaction points.
The choice of bindings to which QoS statements apply will depend upon the nature of the system concerned. Examples are:
? where the system offers a service to some external user;
? where the binding or set of bindings concerned represents a partitioning of the system from the point of view of the separate supply of parts of the system.
3. Relationship of QoS Framework concepts and RM-ODP concepts
The RM-ODP defines the term quality of service (this definition is referenced from the QoS Framework) and applies
the term in the concept of environment contract. There is a need to consider the significance of the refinements of the
concept of QoS in relation to the concept of environment contract and the application of that concept in the object and
interface templates and viewpoint descriptions.
Although the RM-ODP defines and uses the term quality of service, the definition is generic and there is no specification of how QoS is to be expressed, assessed etc. The QoS Framework both refines the concept of QoS (distinguishing, for example, between the abstract definition of a QoS characteristic and the ways in which it may be represented and measured), and defines a specific set of QoS characteristics that are generally applicable to systems, services and resources of various kinds.
The QoS framework concepts should be applied in any refinement of the concept of environment contract. In particular, such refinement should address:
? the distinction between QoS statements in an object or interface template and QoS statements about instantiations of the template;
? information flows involved in establishing environment contracts (e.g. in negotiations to establish a binding to an interface)
? the implications for mechanisms and structures to establish bindings (e.g. the need to establish a partial binding or use a separate binding to allow negotiation to take place.
? the specification of QoS characteristics in service properties for the Trader;
4. QoS characteristics in RM-ODP viewpoint descriptions
A full ODP system specification comprises five separate but related specifications, one for each of the viewpoints
defined in the RM-ODP. Since each viewpoint specification is expressed in object terms using common concepts
defined in ITU-T X.902 | ISO/IEC 10746-2 with viewpoint specific refinements, the general considerations (discussed in
2 above) on QoS statements in object models apply. However, it is also necessary to consider what QoS statements are
appropriate for each viewpoint, and how statements in different viewpoints are related.
In the enterprise specification statements will be in a forms appropriate to the expression of the requirements of business e.g. permissible elapsed time for the delivery of a service and permissible restrictions on service availability. In the information specification statements will relate to timing constraints on state changes of information objects, on requirements of consistency between information objects (defined by the invariant schema etc.). In the computational specification statements will relate to the QoS characteristics of normal computational objects and of bindings between interfaces of objects (expressed as general characteristics of the supporting environment or as specific characteristics of binding objects). In some cases these QoS characteristics may imply QoS characteristics to be associated with the provision of transparencies (e.g. for failure transparency).
In the engineering specification the QoS requirements from the computational specification will be translated into a configuration of engineering objects capable of meeting the requirements, for example:
? use of replication of engineering objects for processing reliability or throughput;
? configurations of engineering objects to provide specific transparencies, with appropriate QoS;
? channels corresponding to binding objects, with appropriate QoS.
The technology specification will define a configuration of objects representing hardware and software components which will identify points of observation for QoS and specify the QoS characteristics to be observed at those points. Where relevant, the points of observation specified in the technology specification must be related to interaction points in the other viewpoint specifications, and the QoS characteristics specified in the technology specification must be related to, and consistent with QoS characteristics in the other viewpoint specifications.
'Overview of Quality of Service for Distributed Objects'
John A Zinky, David E Bakken and Richard Schantz