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All drawings appearing in this Recommendation have been done in Autocad.
Recommendation E.711
USER DEMAND
1 Introduction
1.1 Traffic offered to layers 1-3 of the ISDN can be modelled by distributions
of arrival times and holding times (traffic variables). This Recommendation
describes how these traffic variables are related to user demands at higher
levels.
2 General structure
2.1 This section describes the general process by which the distributions of
arrival times and holding times (traffic variables) which determine the offered
traffic to layers 1-3 may be derived from user demands. The process is
illustrated in Figure 1/E.711 and described in detail in Annex B.
2.2 Through the mediation of Customer Premises Equipment (CPE), user demands
are translated into sequences of requests for applications, teleservices, and
bearer services.
2.3 An application in an ISDN is a sequence of teleservice and bearer service
requests, predefined in order to satisfy a global communications need.
2.4 A call pattern is a specific sequence of events and inter-event times
generated by a call demand and modelled by traffic variables as described in S 3
of this Recommendation. Each teleservice class can be modelled by a mix of call
patterns, each corresponding to a set of teleservice attributes.
2.5 A connection pattern is a specific set of information transfer and general
attributes which are significant for traffic engineering. Information transfer
and general attributes are described in Recommendation I.210. Each call pattern
can be served by one or more connection patterns.
Figure 1/E.711
Fascicle II.3 - Rec. E.711 PAGE1
2.6 A teleservice has attributes that can be selected by the user, negotiated
or selected by the service provider. The result of this selection procedure is a
sequence of requests for connection patterns.
2.7 Annex A outlines the relations between user demands, applications,
teleservices, bearer services and traffic significant attributes.
2.8 The mix of connection patterns determined by the process in turn
determines the distributions of arrival times and holding times.
3 Traffic variables
3.1 Traffic variables are expressed as distributions of arrival times and
holding times. For traditional circuit switched services, the shapes of some
distributions are such that they can be represented by the mean values. A
discussion of traffic variables in the ISDN context is given in the following
sections.
3.2 Call variables
3.2.1 Arrival process
For traditional circuit switched services, the call attempt rate has, for
practical purposes, been considered equivalent to the call demand rate. In the
ISDN, on the contrary, this equivalence can no longer be assumed. Many
teleservices will have attributes such that complex call attempt sequences are
generated for each call demand. This will require the introduction of additional
considerations such as:
- number of call attempts per call demand;
- number of negotiations per call demand;
- number of call demands requiring reservation.
The entire subject of call attempts sequences requires further study.
3.2.2 Holding times
For traditional circuit switched services, call holding time t1 is the
only variable of interest. For reservation services, additional variables are
needed to characterize reservation time t2, completion time t3 and request time
t4. See Figure 2/E.711. (New holding times require further study.)
Figure 2/E.711
PAGE10 Fascicle II.3 - Rec. E.711
3.3 Transaction variables
Additional information beyond S 3.2 is needed for packet switching
services.
For packet-switched services, the information content at the user level
during a call may be produced in discrete transactions (intervals during which a
user is continuously producing information). This subdivision is significant from
a traffic point of view. See Figure 3/E.711.
3.3.1 Arrival process
The arrival process for transactions within a call is for further study.
3.3.2 Transaction length
The transaction length as expressed in bits represents the workload
offered by the transaction through the user/network interface. The distribution
of transaction lengths is for further study.
Note - For transport purposes, the workload as related to single
transactions within a specific call may undergo one or more segmentation stages.
The entire subject of workload segmentation is for further study.
Figure 3/E.711
4 Examples
4.1 Traditional telephone service with lost calls cleared is usually
characterized by mean arrival rate and mean holding times.
4.2 Telephone service in the ISDN, with a fast signalling system (Signalling
System No. 7) and capabilities for automatic repetition, needs the introduction
of a supplementary variable, namely the repetition rate, to evaluate the number
of call attempts per call demand.
4.3 Personal computer communication using reservation services, associated
with the supplementary services of automatic repetition and call waiting, is a
teleservice giving rise to a complex call attempt sequence as illustrated in
Figures 4/E.711 and 5/E.711.
In relating this service to user demand, many additional variables are
needed as discussed in S 3. The control and user plane traffics must take into
account not only the mean values but also other parameters characterizing the
distributions.
Figure 4/E.711
Figure 5/E.711
Fascicle II.3 - Rec. E.711 PAGE1
ANNEX A
(to Recommendation E.711)
Relation between user demands and attributes
A.1 Introduction
This Annex provides concrete examples relating user demands (applications,
teleservices and bearer services) to attributes which are important for traffic
engineering purposes. Tables are provided for illustrative purposes but it must
be noted that these are based on a selective summarization of key attributes
related to the I.200 Series of Recommendations. Thus they should be only
interpreted as illustrations of the process.
A.2 User demand attributes
User demands are described by the following attributes:
- user service selections;
- access channels and rates (see Figure A-1/E.711);
- layer 7 to 1 protocols.
A.3 Application characteristics
Applications are described by the following characteristics:
- teleservices supporting the application;
- bearer services supporting the application;
- bearer capabilities supporting teleservices and bearer services.
Table A-1/E.711 gives the teleservices recommended in Recommendation I.240
together with the attributes which are important from a traffic engineering point
of view. These comprise:
- information transfer mode;
- information transfer rate;
- information transfer capability;
- establishment of communication;
- symmetry;
- communication configuration.
As other teleservices are introduced into ISDN (e.g. electronic shopping)
in the future, the traffic engineering attributes may expand (e.g. information
handling processes).
Table A-2/E.711 lists representative bearer services from which those
required to support an application may be chosen.
A.4 Teleservices
According to Recommendation I.210, a teleservice is the result of one of
the following combinations:
- one basic teleservice;
- one basic teleservice plus one or more supplementary services.
Furthermore, a teleservice is implemented using bearer capabilties.
Figure A-1/E.711
TABLE A-1/E.711 is in file named TA1-711E.DOC. It must be printed on landscape.
PAGE10 Fascicle II.3 - Rec. E.711
TABLE A-2/E.711
Bearer services
Circuit mode (Recommendation I.231)
64 kbit/s, unrestricted, 8 kHz structured
64 kbit/s, 8 kHz structured, usable for speech
information transfer
64 kbit/s, 8 kHz structured, usable for 3.1 kHz audio
information transfer
Alternate speech / 64 kbit/s unrestricted, 8 kHz
structured
2 x 64 kbit/s unrestricted, 8 kHz structured
384 kbit/s unrestricted, 8 kHz structured
1536 kbit/s unrestricted, 8 kHz structured
1920 kbit/s unrestricted, 8 kHz structured
Packet mode (Recommendation I.232)
Virtual call and permanent virtual circuit
Connectionless
User signalling
ANNEX B
(to Recommendation E.711)
Traffic characterization
B.1 Introduction
B.1.1 This Annex describes a methodology for relating user demands to the
traffic offered to layers 1-3 of the ISDN. The basic approach is to relate the
mix of user demands to call patterns and connection patterns. These latter
concepts are defined in SS 2.4 and 2.5 and repeated below; between them, they
contain all of the information needed to derive the distributions of arrival
times and holding times.
B.1.2 Call patterns and connection patterns are the means by which the effects
of user demands are described as they affect layers 1-3 of the ISDN network.
A call pattern is a specific sequence of events and inter-event times
generated by a call demand and modelled by traffic variables as described in S 3
of this Recommendation.
A connection pattern is a specific set of information transfer and general
attributes which are significant for traffic engineering. Information transfer
and general attributes are described in Recommendation I.210.
Call patterns describe what happens at the user-network interfaces.
Connection patterns describe what types of resources are used. Each call pattern
can be served by one or more connection patterns.
B.2 User/customer premises equipment characterization
B.2.1 User classes
The population of users can be divided into user classes characterized by
the user selections of applications, teleservices and bearer services, and their
rates of occurrence. Each class is associated with a penetration in the
population.
B.2.2 Customer premises equipment (CPE) classes
The actual application, teleservice and bearer service requests presented
to the network as a result of user selections are determined by the user's CPE
type. Each user class can be subdivided into CPE classes characterized by the
penetration of CPE types in that user class.
B.3 Application characterization
For further study.
B.4 Teleservice characterization
B.4.1 Teleservice classes
The population of teleservices requested by user/CPE combinations may be
subdivided into classes defined by the values of attributes significant for
traffic engineering.
Teleservices, as defined in Recommendation I.240, are teleservice classes
from the traffic point of view.
Of the attributes defined in Recommendation I.210, the following are
significant for traffic engineering:
- information transfer mode;
- information transfer rate;
- information transfer capability;
- establishment of communication;
Fascicle II.3 - Rec. E.711 PAGE1
- symmetry;
- communication configuration.
Each combination of attribute values defines a single teleservice class.
B.4.2 Teleservices
Within each teleservice class, individual teleservices are defined by
values of general attributes which are still under study in Study Group XVIII. Of
particular significance for traffic engineering is the attribute "Supplementary
services".
B.4.3 Demands for teleservice classes
Each user class/CPE class combination is characterized by rates of demand
for teleservice classes. This characterization may be represented as shown in
Table B-1/E.711. The contents of Table B-1/E.711 must be estimated by statistical
studies.
B.4.4 Teleservice demands
Combining the concepts of SS B.4.1 and B.4.2, the total request rate for
each teleservice class can be subdivided as shown in Table B-2/E.711.
The entries of Table B-2/E.711 must be estimated by statistical means.
B.4.5 Call patterns
For each individual teleservice there is one and only one corresponding
call pattern. However, the same call pattern may be representative of several
teleservices.
Multiplying the total rates in Table B-1/E.711 by the proportions shown in
Table B-2/E.711, rates for each call pattern are obtained as shown in Table
B-3/E.711.
TABLE B-1/E.711
Demands for teleservice classes
User class CPE class Teleservice class
(Note 1) 1 2 3 . . . . .
1 X
Y
PAGE10 Fascicle II.3 - Rec. E.711
Z
2 t
Z
Fascicle II.3 - Rec. E.711 PAGE1
. .
. .
. .
PAGE10 Fascicle II.3 - Rec. E.711
Totals
Note 1 - A given user class will not necessarily use all CPE classes.
Note 2 - Table entries are the rates at which the user/CPE combinations originate
requests for each teleservice class.
TABLE B-2/E.711
Demand for individual teleservices
Teleservice class General attribute combinations
1 2 3 . . . . .
1
Fascicle II.3 - Rec. E.711 PAGE1
2
.
.
.
PAGE10 Fascicle II.3 - Rec. E.711
Total
Note - Table entries are the proportions of total requests for
each teleservice class for each general attribute combination
(defining an individual teleservice). Each row adds to unity.
TABLE B-3/E.711
Call pattern demands
Teleservice class Call parttern
1 2 3 . . . . .
1
Fascicle II.3 - Rec. E.711 PAGE1
2
.
.
.
PAGE10 Fascicle II.3 - Rec. E.711
Total
Note - Table elements are the rates at which each teleservice class creates
a demand
for each call pattern.
B.5 Connection pattern characterization
Each call pattern can be served by one or more connection patterns. A
specific connection pattern corresponds to each set having as elements one value
for each applicable bearer service attribute.
The breakdown in Table B-4/E.711 of the call patterns on the connection
patterns is needed.
TABLE B-4/E.711
Breakdown of the call pattern on the connection patterns
Connection pattern
Packet mode Circuit mode
Call pattern On D-channel On B-channel (B-channel)
1 . i . 1
. . . .
Fascicle II.3 - Rec. E.711 PAGE1
. j . 1 . k .
. . . . . . . .
CP1
. . .
PAGE10 Fascicle II.3 - Rec. E.711
CPn
Total
Note 1 - Table entries are the proportions of the nth call pattern served by the
different connection patterns.
Note 2 - The total on the columns gives the total rate on each connection pattern.
Note 3 - The sums on the rows may be useful for designing priority classes.
Fascicle II.3 - Rec. E.711 PAGE1
Using Tables B-3/E.711 and B-4/E.711, Table B-5/E.711 can be obtained.
TABLE B-5/E.711
Rate of the call demands requiring a specific connection pattern
Connection patterns Rate
XP1
XP2
.
.
.
XPn
Total
Bibliography
BONATTI (M.), GIACOBBO SCAVO (G.), ROVERI (A.), VERRI (L.): Terminal exchange
access system for NB-ISDN: Key issues for a traffic reference model. Proc. 12th
ITC, paper 4.1A.3, Turin, 1988.
PAGE10 Fascicle II.3 - Rec. E.711
