ABSTRACT: Over the past two decades, telecommunications suppliers have been designing and developing Digital Loop Carrier (DLC) equipment and selling their products to Local Exchange Carriers (LECs) for deployment in their networks. The generic requirements of TR-NWT-000057, Functional Criteria for Digital Loop Carrier Systems, Issue 2, January 1993, have provided the foundation for the voice frequency transmission and signaling of these systems. Since it's original publication to address the Universal Digital Loop Carrier applications, the criteria of TR-NWT-000057 have been applied (both directly and indirectly to other access technologies including: Integrated Digital Loop Carrier (IDLC), ADSL Digital Subscriber Line Access Multiplexers (DSLAM), and Fiber-in-the-Loop (FITL).

Technological advances included broadband access and packet voice have recently emerged in the access market. New service applications, such as Caller Identity Delivery on Call Waiting with multiple extension support, have also emerged on the market. GR-57 replaces TR-NWT-000057 in its entirety and includes updated voice frequency transmission and signaling criteria to address these and other market changes.

The GR includes new criteria to better support the momentary extension check function provided by Type 2/3 CPE and criteria allowing the use of balanced ringing on locally switched loop-start and coin lines. A number of unnecessary restrictive requirements have been modified to reflect the realities of today's public switched telephone network and the emerging packet-switched full service network. GR-57 provides the transmission and signaling criteria necessary to insure compatibility with today's telephone equipment and services, with an eye toward emerging access technology and applications.

All changes reference the previously released generic requirements document, TR-NWT-000057, Issue 2, January 1993.

When using GR-57, you may need to refer to GR-63, GR-78, GR-499, and GR-1089. You may also need to refer to GR-8, GR-66, TA-TSY-000077, TA-TSY-000083, TR-TSY-000177, GR-199, GR-303, GR-378, TR-NWT-000393, TR-NWT-000397, GR-436, GR-454, TR-TSY-000465, GR-472, GR-485, GR-487, GR-815, GR-820, TR-TSY-000824, TR-TSY-000827, GR-833, GR-834, GR-839, GR-840, MDP-326-140, ANSI T1.401.ANSI T1.403, and/or ANSI T1.405.

This GR also includes one or more Issue List Reports (ILRs) that details open or closed technical issues in the main document. The ILR(s) are automatically sent free of charge to the GR document purchaser.