ISDN Protocol Administrator's and Developer's Guide ... - Intervoice

VN4 Call TransferVN4 ISDN layers 1, 2, and 3 use the same standards as Euro-ISDN.However, slight changes appear in supplementary services such as calltransfer and hold.For more information onthe VN4 ISDN protocol,refer to “VN4 ISDNProtocol,” Chapter 10.VN4 uses a “virtual line” for the outbound call in a call transfer. Avirtual line is one on which the inbound call is placed on hold, and theoutbound call is placed on the same physical port. All the supplementaryservices use the National Facility information element to invoke theservice.VN6 matches Euro-ISDN more closely than VN4 because it uses ETSIspecifications for supplementary services. The supplemental servicethat VN6 uses for call transfer is called Explicit Call Transfer (ECT).For more information about ECT, see “Explicit Call Transfer” onpage 3-5.The characteristics of VN4 call transfer are shown in Table 3-5.Table 3-5. VN4 Call Transfer CharacteristicsSpan Type Transfer Type connect UserDLL?E1 Single Line Transfer No3-6 ISDN Protocol Administrator’s and Developer’s Guide 60001262, First Edition