Question 19/II - Call oriented models for the serveability performance
in
networks (revised Question 35/II of the 19851988 period)

The CCITT,

considering

(a) that Recommendation E.800 contains definitions of QOS concepts
and terms;

(b) that Recommendation E.810 presents a call oriented model and
serveability performance for the telephone service;

(c) that measures for service accessibility, retainability and integrity
have already been defined in Recommendations E.845, E.850 and E.855;

(d) that Recommendations I.350, X.134, X.135 and X.136 describe a
matrix to identify network performance measures,

1. What models should be added to the model in Recommendation E.810
for the various telecommunication services;

2. What mathematical models can be recommended taking into account
already defined measures for service accessibility, service
retainability
and service integrity;

3. In which way can the phases of a call in various telecommunication
services and the most important characterizations of these services be
uniformly expressed e.g., in the form of a matrix?

Note - Dedicated data networks are not included.

Annex: Call oriented models for serveability performance of networks.

Annex

(to Question 19/II)

Call oriented models for the serveability performance
of networks

Introduction

This annex is one of a set of closely related documents concerned with
the accessibility and retainability and integrity of telecommunication
services, as listed below.

The material in this annex is provisional and is for study by those
involved in telex, telephony, data and ISDN services.

The CCITT,

considering

(a) that there is a need for a comprehensive and uniform evaluation of
telecommunication services;

(b) that there is a desire to establish overall objectives for the
serveability performance of networks;

(c) that such objectives can then be used as a basis for the design,
planning, operation and maintenance of telecommunication networks
and their component parts;

(d) that Recommendation E.800 contains terms and definitions for the
serveability performance and related characteristics of services and
networks;

(e) that Recommendation E.810 shows the model of a basic telephone
call and its serveability performance.

recommends

that the call oriented models given in this annex shall be used by
administrations to evaluate design, plan, operate and maintain their
networks which for the international telephone service the objectives
have to be taken into account which are given in Recommendations:

E.845 Connection accessibility objective for the international
telephone service;

E.850 Connection retainability objective for the international
telephone service;

E.855 Connection integrity objective for the international telephone
service;

E.830 Models for the allocation of international telephone connection
retainability objectives.

Objectives for other telecommunication services are under study; in
principle these may be derived from appropriate Recommendations of
the I, X and F-Series.

1. Models of a basic call in various telecommunication services and the
components of serveability performance.
The following models are presented:

-Simplified model of a virtual call (Packet Terminal)

-Simplified model of a virtual call (Non-packet Asynchronous Terminal)

-Simplified model of a basic circuit-switched call in ISDN based on
"overlap sending"

-Simplified model of a basic circuit-switched call in ISDN based on "en
bloc sending"

-Simplified model of a basic telex message.

The simplified models illustrate the principal phases of a basic call in
various services. It also interrelates these phases to the service
related
performance concepts and their principal measures as well as to the
main causes of failure in the establishment and retention of such a call
and its subsequent billing.

The models also indicate where, in this series of phases, user actions
or mistakes may influence the call.

1) Network accessibility and connection accessibility combined into
service accessibility.
2) The shaded extension shows that a premature release can occur
during the time to await Call Connected packet.
3) This packet has two meanings, local and end-to-end.
4) The release of a call is not a separate phase in this model.
A release failure may result in network inaccessibility for a new call.
5) The billing integrity has been shown for completeness, but is not a
part of serveability performance.

FIGURE 2-a

Model for serveability performance on a virtual call (Packet Terminal)

1) Network accessibility and connection accessibility combined into
service accessibility.
2) The shaded extension shows that a premature release can occur
during the time to await Call Connected packet.
3) This packet has two meanings, local and end-to-end.
4) The release of a call is not a separate phase in this model.
A release failure may result in network inaccessibility for a new call.
5) The billing integrity has been shown for completeness, but is not a
part of serveability performance.

FIGURE 2-b

Model for serveability performance on
a virtual call (non-packet asynchronous terminal)

1) Network accessibility and connection accessibility combined into
service accessibility.
2) The routing of the call may start before all digits have been
received
(overlap).
3) The shaded area shows that a premature release can occur during
the time to answer.
4) The release of a call is not a separate phase in this model.
A release failure may result in network inaccessibility for a new call.
5) The billing integrity has been shown for completeness, but is not a
part of serveability performance.

FIGURE 3-a

Model for serveability performance on
a basic circuit-switched call in ISDN based on "overlap sending"

1) Network accessibility and connection accessibility combine into
service accessibility.
2) The shaded area shows that a premature release can occur during
the time to answer.
3) The release of a call is not a separate phase in this model.
A release failure may result in network inaccessibility for a new call.
4) The billing integrity has been shown for completeness, but is not a
part of serveability performance.

FIGURE 3-b

Model for serveability performance on
a basic circuit-switched call in ISDN based on "en bloc sending"

1) Network accessibility and connection accessibility combined into
service accessibility.
2) The shaded area shows that a premature release can occur during
the time to answer.
3) The release of a call is not a separate phase in this model.
A release failure may result in network inaccessibility for a new call.
4) The billing integrity has been shown for completeness, but is not a
part of serveability performance.

FIGURE 4

Model for serveability performance on a basic
telex-message (Telex-subscribers connected to a type aaa exchange)