View source for Radio Network Controller

{{Short description|UTRAN component similar to a base station controller in GSM hierarchy}}
The '''Radio Network Controller''' ('''RNC''') is a governing element in the [[UMTS]] radio access network ([[UTRAN]]) and is responsible for controlling the [[Node B]]s that are connected to it.  The RNC carries out [[radio resource management]], some of the [[mobility management]] functions and is the point where encryption is done before user data is sent to and from the mobile. The RNC connects to the Circuit Switched Core Network through Media Gateway ([[Media gateway|MGW]]) and to the [[SGSN]] (Serving GPRS Support Node) in the [[Packet Switched Core Network]].

==Interfaces==
[[Image:Mobile network.jpg|thumb|RNC Interfaces]]
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 {{section link||Protocols}}), and Iur interface is mainly needed for [[soft handover]]s involving 2 RNCs though not required as the absence of Iur will cause these handovers to become [[hard handovers]].

Until 3gpp R4, all the interfaces in the [[UTRAN]] are implemented using [[Asynchronous Transfer Mode|ATM]] only, except the [[Universal Mobile Telecommunications System#Air interfaces|Uu (air) interface]] which uses [[WCDMA]] technology. Starting R5, [[Internet Protocol|IP]] bearers can be used over [[Ethernet]] instead. Physically, these interfaces can be carried over [[Synchronous Digital Hierarchy|SDH]] over optical fiber, [[E-carrier|E1]] (sometimes referred to as [[Plesiochronous Digital Hierarchy|PDH]]) - over a copper wire or [[Microwave radio relay|microwave radio]]. Several E1s can be bundled to form an [[Inverse Multiplexing for ATM|IMA]] Group. Since the interfaces are ''logical'', many interfaces can be multiplexed onto the same transmission line. The actual implementation depends on the [[network topology]]; examples are chain, distant star, mesh and loop configurations.

==Protocols==
Iub, Iu and Iur protocols all carry both user data and signalling (that is, control plane). 
* Signalling protocol responsible for the control of the Node B by the RNC is called '''NBAP''' ('''N'''ode-'''B''' '''A'''pplication '''P'''art). 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.
* Control plane protocol for the [[transport layer]] is called '''ALCAP''' ('''A'''ccess '''L'''ink '''C'''ontrol '''A'''pplication '''P'''rotocol). 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.
* Signalling protocol responsible for communication between RNC and the core network is called '''[[RANAP]]''' ('''R'''adio '''A'''ccess '''N'''etwork '''A'''pplication '''P'''art), and is carried over Iu interface.
* Signalling protocol responsible for communications between RNCs is called '''[[RNSAP]]''' ('''R'''adio '''N'''etwork '''S'''ubsystem '''A'''pplication '''P'''art) and is carried on the Iur interface.

==RNC roles==
In a relationship to a [[UE (wireless telephone)|UE]] (in a [[soft handover]] situation) an RNC can play two different roles. These are:
* D-RNC: Drift RNC
* S-RNC: Serving RNC

However, as far as the NodeB is concerned, the RNC may play a third role:
* C-RNC: Controlling RNC

It is important to know that one RNC can assume more than one role at any time.

An RNC also controls the power of a NodeB.

==See also==
* [[Operations and Maintenance Centre]]
* [[Radio Resource Control]]
* [[UMTS]]

==External links==
* [http://www.3gpp.org/ftp/Specs/html-info/25433.htm NBAP Specifications]
* [http://www.3gpp.org/ftp/Specs/html-info/25413.htm RANAP Specifications]
* [http://www.3gpp.org/ftp/Specs/html-info/25423.htm RNSAP Specifications]
* [http://www.3gpp.org/ftp/Specs/html-info/25331.htm RRC Specifications]

==References==
{{reflist}}

{{Mobile telecommunications standards}}

[[Category:3GPP standards]]
[[Category:UMTS]]
[[Category:Telecommunications infrastructure]]