INTERNATIONAL TELECOMMUNICATION UNION ITU-T RECOMMENDATION SUMMARY Rec. No. : E.721 Title : Network grade of service parameters and target values for circuit-switched services in the evolving ISDN Study Group : II - Network Operation Version : Revised Date of adoption : 1991 Notes : Recommendation E.721 provides network Grade of Service (GOS) parameters for circuit-switched services in ISDN, based on the ISDN Grade of Service concept and guidelines for selecting GOS parameters provided in Recommendation E.720. The parameter values assume that the network and the components are fully operational and take account of the evolving nature of the ISDN and Signalling System No. 7 capabilities. Recommendation E.721 defines the following GOS parameters: - pre-selection delay; - post-selection delay (overlap or en-bloc sending); - answer signal delay; - call release delay; and - probability of end-to-end blocking 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).