home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Internet Standards
/
CD2.mdf
/
ccitt
/
1992
/
e
/
e720.asc
< prev
next >
Wrap
Text File
|
1991-12-30
|
7KB
|
142 lines
All drawings appearing in this Recommendation have been done in Autocad.
Recommendation E.720
ISDN GRADE OF SERVICE CONCEPT
1 Introduction
This Recommendation outlines the general considerations for the ISDN Grade
of Service (GOS) concept and provides guidelines for selecting GOS parameters. In
this Series of Recommendations, the term GOS always refers to traffic Grade of
Service parameters as defined in Recommendation E.600.
ISDN GOS parameters are given in subsequent Recommendations in the E.720
Series.
2 GOS concept
GOS uses a number of traffic engineering parameters to provide a measure
of adequacy of plant under specified conditions; these GOS parameters may be
expressed as probability of blocking, probability of delay, etc. Blocking and
delay are caused by the fact that the traffic handling capacity of a
network/network component is finite and that the demand traffic is stochastic by
nature.
The users of telecommunication services can experience the effects of GOS
parameters depending on their perception of events such as:
1) failure of a call demand or excessive delay to satisfy a call demand;
2) failure of call attempts or excessive delay to satisfy call attempts;
3) failure of automatic re-attempts or excessive delay to satisfy
automatic re-attempts.
Events of the first class are always perceived by the user. Events of the
other two classes may be perceived by the user depending on the capability of the
terminal equipment to transmit signalling information to the calling user.
In all three classes the ability to distinguish GOS depends on having
distinct indications of called user conditions and network conditions.
GOS may be distinguished as the user GOS, network GOS and network component GOS as shown in
Figure 1/E.720. User GOS relates to user call demands. Network GOS
relates to any call attempts including both user generated call
attempts and terminal generated automatic reattempts. Network
component GOS relates to bids for the utilization of a specific
network component including both bids generated by call attempts
and bids generated by call attempts and bids generated by internal
retrials in the network. Parameters related to user GOS and network
component GOS are for further study.
Recommendation E.721 defines network GOS parameters based on
any call attempt. Subsequent Recommendations in the E.720 Series
will define other GOS parameters. Recommendations in the E.740
series will define traffic measurement and performance monitoring
requirements.
User GOS performance effects and other traffic-independent,
user-perceived effects such as availability and service integrity
contribute to Quality of Service (QOS). Network GOS parameters and
their values provide information on the traffic aspects of the QOS.
3 Principles to select ISDN GOS parameters
3.1 ISDN traffic characteristics
ISDN has many characteristics different from the existing dedicated
networks such as Public Switched Telephone Network (PSTN), Circuit Switched
Public Data Network (CSPDN), Packet Switched Public Data Network (PSPDN), etc.
The following characteristics are taken into account when defining GOS parameters
for ISDN:
- ISDN provides integrated access to a wide variety of telecommunication
services through a small set of standardized user-network interfaces.
- Services have heterogeneous traffic demand profiles and diverse
performance requirements.
- The traffic streams generated by user demands for bearer services and
teleservices utilize layer 1, 2 and 3 resources.
- The configuration and implementation of a user's terminal and its
man-machine interface may vary from one service to another service and
one user to another user.
- Out-of-band signalling and call control capability, based on D-channel
and Signalling System No. 7 (S.S. No. 7) are provided.
Figure 1/E.720 - T0201181-88
Fascicle II.3 - Rec. E.720 PAGE1
3.2 Parameter selection principles
The GOS parameters defined in the E.720 series of Recommendations applies
to the first phase of ISDN. The definitions of these parameters may be expanded
or additional GOS parameters defined to accomodate future evolution of ISDN
architecture and services. Considering the above characteristics in ISDN, the
following principles are recommended for selecting GOS parameters in ISDN:
i) A minimum common set of GOS parameters is defined for attempts on
layers 1, 2 and 3 - such attempts belonging to different services may
or may not share the same out-of-band call set-up and release
procedures. (See Note.)
ii) The GOS parameters are defined and specified in such a way that the GOS
can be derived at well-defined reference points (traffic significant
points).
iii) The GOS parameters should be specified with reference to traffic
load conditions in the sense of Recommendation E.500.
iv) Blocking GOS parameters may in the future need to take account of
repetitions due to network status, but are presently based on
lost-call-cleared assumptions.
v) GOS parameters related to the user plane information transfer phase are
for further study.
Note - To assess the performance directly perceived by a user, other
additional parameters which are specific to the user's terminal equipment may
also be necessary.
3.3 GOS standard setting principles
GOS standard setting principles will take into account the current
standards for voice and data services so that when the user migrates from a
dedicated network to the ISDN, the user does not encounter a marked undesirable
contrast.
PAGE2 Fascicle II.3 - Rec. E.720