Release 4

The main focuses of R4, with respect to R3, are the following:
• Hybrid architecture—ATM-based UTRAN (currently a workgroup
is busy defining IP-based RAN) and IP/ATM-based CN;
• GERAN (support for GSM radio including EDGE);
• Enhanced services provided using toolkits (e.g., CAMEL, MExE,
SAT, VHE/OSA);
• Backwards compatibility with R99 services; • Enhancements in QoS (real-time PS services), security, authentication,
and privacy;
• Support for interdomain roaming and service continuity.In R4, the
circuit-switched domain is split into a separate signaling plane
(MSC server) and transport plane [media gateway (MGW)], which
means introduction of new entities. Standardized protocols will be
used:
• Q.BICC or SIP-T (for inter-MSC signaling);
• H.248/MeGaCo (for MSC server to MGW signaling).
This enables cost reduction by optimizing transport resources. The
splitting of MSC into MSC server for signaling and MGW for transport
makes R4 scalable, reliable, and cost efficient with respect to R3 (see Figure
2.5). A MSC server is able to support several MGWs. If the serving MGW
for a specific connection goes down, the MSC server is in state to reroute the
traffic through a different MGW. As an implementation option, it is possible
to have a many-to-many (m:n) relationship between MSC servers and MGWs. This allows for an efficient allocation of user plane resources as the
MSC servers can loadbalance between multiple MGW.