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INTERNATIONAL TELECOMMUNICATION UNION
ITU-T RECOMMENDATION SUMMARY
Rec. No. : E.525
Title : Designing networks to control grade of service
Study Group : II - Network Operation
Version : Revised
Date of adoption : 1992
Notes :
Network design may have two objectives to control grade of service
(GOS). One is to provide an overall GOS for all traffic offered to the
network. This can be achieved by the choice of a routing scheme that
reduces the effect of adverse network conditions. Routing schemes that
allow more flexible routing choices generally provide greater
resilience, especially in the case of forecast errors or focused
overload, than traditional hierarchical routing methods.
The second objective is to control the grade of service for certain
streams of traffic by restricting the access to circuit groups.
Several service protection methods are available, with the common
feature that they may reject certain call attempts when the considered
circuit group has little idle capacity. Service protection is
generally used in alternative routing networks to restrict overflow
traffic, but can also be used to give priority service to one class of
traffic over another.
Failure or overload conditions may require temporary changes to
service protection parameters. This is considered to be network
management action which is described in the E.400-Series
Recommendations.
Recommendation E.525 comprises the following issues:
Applications of service protection methods:
Cluster and end-to-end engineering concepts;
Appropriate dimensioning algorithms.
The choice between available methods will generally depend on
performance characteristics and ease of implementation.
Flexible and/or dynamic routing schemes can be viewed as "network
level" methods. Service protection methods can be viewed as "circuit
group level" methods. It is possible to provide methods on one of the
levels only or to provide both levels in conjunction with each other.
To order the complete text of this Recommendation, please use the
Order Form for ITU-T Recommendations. An electronic version of this
form is available on ITUDOC (Winword: UPI=ITU-5265; ASCII: UPI=ITU-2488).