This recommendation supports the 3GPP2 All-IP Step 1 Evolution Path by providing Stage-1, 2 and 3 for the architecture identified in Figure 3.1, "Legacy MS Domain Support for Circuit Mode IP Transport Call Delivery".

The Legacy MS Domain provides support for existing MSs (e.g., analog, IS-95-A, IS-95-B, IS-2000) in an IP core network environment. The Legacy MS Domain supports the features and capabilities provided in a legacy network in a manner transparent to the user. New features and capabilities supported by the IP core network may be made available to subscribers where they are supported by MS capabilities.

This document specifies signaling reference point zz (MSCe-to-MSCe). This reference point supports Media Gateway-to-Media Gateway bearer streams (i.e., yy reference point). The yy reference point is used as a bearer facility for legacy voice calls and is specified in [3GPP2-4].