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Radio Network Controller
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<h2 id="interfaces">Interfaces</h2> <p>The logical connections between the network elements are known as interfaces. The interface between the RNC and the Circuit Switched Core Network (CS-CN) is called Iu-CS and between the RNC and the Packet Switched Core Network is called Iu-PS. Other interfaces include Iub (between the RNC and the Node B) and Iur (between RNCs in the same network). Iu interfaces carry user traffic (such as voice or data) as well as control information (see § Protocols), and Iur interface is mainly needed for <a href="/facts/Soft_handover/2GBmEnr0">soft handovers</a> involving 2 RNCs though not required as the absence of Iur will cause these handovers to become hard handovers. </p><p>Until 3gpp R4, all the interfaces in the <a href="/facts/UTRAN/pft9MQse">UTRAN</a> are implemented using <a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a> only, except the <a href="/facts/Universal_Mobile_Telecommunications_System/lhy2RrMw">Uu (air) interface</a> which uses <a href="/facts/WCDMA/lhy2RrMw">WCDMA</a> technology. Starting R5, <a href="/facts/Internet_Protocol/Qq6VeEal">IP</a> bearers can be used over <a href="/facts/Ethernet/nMfhU8tU">Ethernet</a> instead. Physically, these interfaces can be carried over <a href="/facts/Synchronous_Digital_Hierarchy/G3LgtGS6">SDH</a> over optical fiber, <a href="/facts/E-carrier/h0MXcgXN">E1</a> (sometimes referred to as <a href="/facts/Plesiochronous_Digital_Hierarchy/oTrEENKx">PDH</a>) - over a copper wire or <a href="/facts/Microwave_radio_relay/bz9H9Ete">microwave radio</a>. Several E1s can be bundled to form an <a href="/facts/Inverse_Multiplexing_for_ATM/Fg4zWcaj">IMA</a> Group. Since the interfaces are <i>logical</i>, many interfaces can be multiplexed onto the same transmission line. The actual implementation depends on the <a href="/facts/Network_topology/rBYE0kke">network topology</a>; examples are chain, distant star, mesh and loop configurations. </p> <h2 id="protocols">Protocols</h2> <p>Iub, Iu and Iur protocols all carry both user data and signalling (that is, control plane). </p> <ul><li>Signalling protocol responsible for the control of the Node B by the RNC is called NBAP (Node-B Application Part). NBAP is subdivided into Common and Dedicated NBAP (C-NBAP and D-NBAP), where Common NBAP controls overall Node B functionality and Dedicated NBAP controls separate cells or sectors of the Node B. NBAP is carried over Iub. In order for NBAP to handle common and dedicated procedures, it is divided into: NodeB Control Port (NCP) which handles common NBAP procedures and Communication Control Port (CCP) which handles dedicated NBAP procedures.</li> <li>Control plane protocol for the <a href="/facts/Transport_layer/UmIGUCeK">transport layer</a> is called ALCAP (Access Link Control Application Protocol). Basic functionality of ALCAP is multiplexing of different users onto one AAL2 transmission path using channel IDs (CIDs). ALCAP is carried over Iub and Iu-CS interfaces.</li> <li>Signalling protocol responsible for communication between RNC and the core network is called <a href="/facts/RANAP/LBmEFKYe">RANAP</a> (Radio Access Network Application Part), and is carried over Iu interface.</li> <li>Signalling protocol responsible for communications between RNCs is called <a href="/facts/RNSAP/962FVom4">RNSAP</a> (Radio Network Subsystem Application Part) and is carried on the Iur interface.</li></ul> <h2 id="rnc-roles">RNC roles</h2> <p>In a relationship to a <a href="/facts/UE_(wireless_telephone)/bMTNPWXV">UE</a> (in a <a href="/facts/Soft_handover/2GBmEnr0">soft handover</a> situation) an RNC can play two different roles. These are: </p> <ul><li>D-RNC: Drift RNC</li> <li>S-RNC: Serving RNC</li></ul> <p>However, as far as the NodeB is concerned, the RNC may play a third role: </p> <ul><li>C-RNC: Controlling RNC</li></ul> <p>It is important to know that one RNC can assume more than one role at any time. </p><p>An RNC also controls the power of a NodeB. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Operations_and_Maintenance_Centre/hh7nLIL3">Operations and Maintenance Centre</a></li> <li><a href="/facts/Radio_Resource_Control/tpD0qUs9">Radio Resource Control</a></li> <li><a href="/facts/UMTS/lhy2RrMw">UMTS</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://www.3gpp.org/ftp/Specs/html-info/25433.htm">NBAP Specifications</a></li> <li><a href="http://www.3gpp.org/ftp/Specs/html-info/25413.htm">RANAP Specifications</a></li> <li><a href="http://www.3gpp.org/ftp/Specs/html-info/25423.htm">RNSAP Specifications</a></li> <li><a href="http://www.3gpp.org/ftp/Specs/html-info/25331.htm">RRC Specifications</a></li></ul>