Question 9/XVIII - Performance objectives for ISDN availability

Note 1 - Consideration should be given to Recommendation X.137 and the
E.800Series.

Note 2 - To be studied in close consultation with Study Group II and
other related Study Groups.

1. What definitions of "availability" and models for its calculation are
appropriate for ISDNs, including broadband aspects?

Note - Quotation marks are used to indicate that the term "availability"
is taken to have wider applicability than implied by the definition in
Recommendation G.106.

2. What levels of connection processing performance, packet performance,
and circuit performance will be used in determining the "availability"
of an ISDN connection?

Note - Specific reference should be made to the work done on Questions 5
and 7.

3. What "availability" parameters should be recommended for ISDNs?

Note - These parameters will be measured at connection element
boundaries.

4. What reference connections should be used in the consideration of
values for these parameters?

5. What values and measurement conditions should be recommended for
"availability" performance on connections through ISDNs?

6. What rules should be adopted for apportioning the overall values to
the constituent parts of the connections?

Note - Specific reference should be made to Recommendation G.921.

7. What guidance can be given to the other competent Study Groups
regarding use of the recommended values?

Note - The study should take account of the following:

a) that circuit mode connections can be completed over many alternative
routes through the network;

b) that the failure of any one route or link does not prevent the
connection from being established;

c) that traffic load will vary in time, thus impacting the accessibility
of a particular route or link;

d) that an end-user will not be able to distinguish these two
conditions;

e) that a failure of the access line will, in general, make the
connection unavailable;

f) that many of the same observations apply to packet mode connections
as well.