A radio network controller manages hundreds of Node B transceiver stations while switching and provisioning services off the Mobile Switching Center and 3G data network interfaces. The connection from the RNC to a Node B is called the User Plane Interface Layer and it uses T1/E1 transport to the RNC. Due to the large number of Node B transceivers, a T1/E1 aggregator is used to deliver the Node B data over channelized OC-3 optical transport to the RNC. The OC-3 pipe can be a direct connection to the RNC or through traditional SONET/SDH transmission networks.

A typical Radio Network Controller may be built on a PICMG or Advanced TCA chassis. It contains several different kinds of cards specialized for performing the functions and interacting with the various interfaces of the RNC.

Figure 2: RNC Interfaces

Controller Cards
The controller card controls the entire chassis and performs application-level functions complementary to the other line cards. It also interfaces to the Element Management System (EMS). Because this role is so critical, typically a pair of redundant cards is used.

Radio Access Network (RAN) Line Cards
This card is a Node B controller. A Node B aggregates T1/E1 uplinks and forwards OC-3 optical data to the RNC.

Core Network (CN) Cards
These cards provide OC-12 connections to the back-end circuit-switched and packet-switched infrastructure. The CN card provides the bandwidth to manage the Node B traffic from the RAN line cards.

Real Time Unit (RTU) Line Cards
This card implements real-time user stream processing that is complementary to the other line cards. These control functions span all RAN and CN interfaces in and out of the RNC. Multiple RTU cards with redundant Gigabit Ethernet links are required to support the bi-directional traffic.

Ethernet Switching Modules
These cards provide the Gigabit Ethernet fabric for the chassis. Every line card in the system contains one or more connections to each switching module, depending on the individual bandwidth requirement for each line card.