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.



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