7.General Description of RNC

Version 0 Revision 1 JTO PH II (3G) Ericsson

General description of RNC

Radio Network Controller (RNC) in a Radio Access Network (RAN) that uses Wideband Code Division Multiple Access (WCDMA) technology. The RNC exercises radio network control functions on Radio Base Stations (RBSs) and User Equipment (UE). The RNC is also connected to the Core Network (CN), the RAN Operation Support System Radio and Core (OSS-RC), and the Network Management System (NMS).

Fig 1. Overview of RNC

BRBRAITT, Jabalpur, Issued in SEPT- 2009 7-1


Common Platform:

The RNC is based on CPP, Connectivity Packet Platform. The platform consists of a transport system, a distributed real-time telecommunication control system, and a management support system. Cell switching is used for communication between boards and subracks. Between nodes a range of different communication standards are supported.

Hardware

The RNC consists of one or two cabinets with a set of almost identically equipped subracks. The first cabinet i the Main Cabinet and the second the Extension Cabinet. The two types of subracks, the Main Subrack (MS) and the Extension Subrack (ES), use a limited set of board types

Software

The RNC software, apart from the common platform software, consists of three layers: resource, encapsulation, and service.

RNC Roles

For each connection between a UE and the UTRAN, an RNC can act as a Serving RNC (SRNC) or a Drift RNC (DRNC):

An single SRNC controls all radio connection between a UE and the UTRAN. The SRNC terminates the Iu interface for this UE.

A DRNC supports the SRNC with radio resources when the connection between the UTRAN and the UE need to use one or more cells controlled by this RNC.

The RNC owning the Signalling link towards a basestation is called Controlling RNC (CRNC).

Main services and functions

The RNC provides a number of services and functions that represent segments of high-level Universal Mobile Telecommunications System (UMTS) services. The end-user services comprise the following:

Mobile telephony (voice) Unrestricted digital information Packet data, including High-Speed Downlink Packet Access (HSDPA) Short Message Service (SMS) Mobile positioning and localization Ciphering (security)



The end-user functions provided by the RNC are as follows:

Radio Access Bearer (RAB) service, establishment, release, modification, identification, coordination, and maintenance

Mobility within UTRAN

In addition to these end-user services and functions, the RNC provides O&M, radio network, and transmission services.

Hardware Structure

Figure 2 RNC Main and Extension Cabinets Hardware Location

The letters in the figure above denote the following:

A - Power connections B - ESs



C - MS D - Interface Connection Field (ICF)

Subracks

The MS includes all funcitons required of the RNC. ESs may be added for increased traffic capability and connectivity. ESs are connect to the MS using a 1+1 internal link redundancy.

The processing capacity of the RNC is scalable in relation to the number of ESs.

The Figure 3 shows a typical RNC hardware structure and its connections

MS Functions

An RNC always includes an MS. The MS interconnects all other subracks in the RNC and includes all functions of an ES as well as functions common to the RNC. Functions of the MS comprise the following:

Termination of the Mur interface with OSS-RC Termination of the lu interface with the CN Termination of the Iur interface with another RNC Termination of the lub interface with the RBSs



External transmission interfaces Attachment of synchronization sources Duplicated non-blocking Cell switch Duplicated high-speed links to interconnect with the ESs Duplicated timing signals for the node Input for GPS signals Pool of processors for user plane processing and control

Most boards work in pools where the loss of one board only marginally reduces the total pool capacity. In remaining cases there is a standby board for each active, taking over with full capacity in case the primary should fail.

ES Functions:

ESs has interfaces with the RBSs. The functions of an ES comprise the following:

Termination of the lub interface with the RBSs External transmission interfaces Duplicated high-speed links between subracks and the MS Duplicated non-blocking Cell switch Pool of processors for user plane processing and control

Most boards work in pools where the loss of one board only marginally reduces the total pool capacity. In remaining cases there is a standby board for each active, taking over with full capacity in case the primary should fail.

RNC Modules:

The RNC modules divide an RNC into smaller resource units. An RNC module comprises the following:

One General purpose Processor Board (GPB) One or more Special purpose Processor Boards (SPBs) Supporting software

The MS comprises two RNC modules and an ES comprises five RNC modules.

Table RNC Function GroupsFunction Group DescriptionControl System Functions

Provide platform processor resources and data storage such as debug support, file system and storage media, MP load control, and processor system.

Terrestrial Transport Functions

Provide terrestrial physical interfaces and switching such as local access and physical line termination SDH PDH 1.5 Mbps, 2 Mbps, 34 Mbps, 45 Mbps and 155 Mbps and 1Gbit Ethernet.

Bearer Functions Transfer, split, and combine user or control data with a set of service attributes including service attribute conversion. Bearer functions are divided into three groups: Radio network, Transport network, and Management network.

Synchronization Functions

Provide correct timing of data and prevent loss of data due to slip of information transmitted through the system. Synchronization



functions comprise network, node, and frame synchronization.Control Functions After stimuli from the end-user or the core network, these

functions support the process of initiating, maintaining, and terminating user connections with a specific bearer service.

Mobility Functions Provide the ability for the end-user to move within the radio network by changing the serving network element or resource. The mobility functions comprise cell update, hand over evaluation, inter-radio access technology cell change, inter-radio access technology hand over, inter-frequency hand over, soft and softer hand over, as well as the ability to determine the geographical position of the UE.

Capacity Management Functions

Optimize the radio resource usage and prevent the system from overloading. The functions control admission, congestion, and power control.

Configuration Management Functions

Provide the ability to set system parameters, initialize and terminate Managed Objects (MOs), and collect configuration and status information.

Fault Management Functions

Detect, localize, isolate, correct, store, and send alarms of abnormal operation of MOs.

Performance Management Functions

Collect, store, and report statistics regarding the effectiveness of RNC functions.

Security Management Functions

Prevent unauthorized use of the system by administration of security services and mechanisms including reporting of security relevant events. The functions comprise user authentication and authorization.

User Interface Functions

Provide tools and functions for the operator to interact with the system. This function is also known as the Element Manager (EM).

External Interfaces:

The RNC connects to other nodes and networks over the Iu, Iur, Iub, Uu, and Mur interfaces. Besides these interfaces. In addition human interaction with the RNC occurs over a Visual and Mechanical Interface (VMI) comprising indicators, switches, buttons, cables, and so on, and through O&M applications



Fig 4. External Interfaces

lu

The lu is the interface between the RNC and Circuit-Switched (CS) or Packet-Switched (PS) CN. The Radio Access Network Application Part (RANAP) protocol is used for traffic-related control signaling to the CS and PS CN, and for GTP-U protocols to the PS CN. Signalling is supported over ATM and IP (ET-MFG). GTP-U may use IP over ATM or Ethernet (ET-MFG).

lur

The lur is the interface between two RNCs. This interface carries the Radio Network Subsystem Application Part (RNSAP), used for traffic-related control signaling. For user data Frame Protocols are used. Signalling is supported over ATM and IP (ET-MFG).

lub

The lub is the interface between the RNC and an RBS. This includes the Node B Application Part (NBAP), used for traffic related control signaling. For user data Frame Protocols are used.

Uu

The Uu is the air interface between the RNC and the CN, on the one hand, and the UE, on the other hand. The interface is divided into three layers. The different layers terminate in different nodes of the RAN as follows:



Layer 1 terminates partly in the RBS and partly in the RNC. Layer 2 terminates mainly in the RNC. Layer 3 terminates mainly in the RNC, while many messages are transparently

transferred between the UE and the CN. Broadcast Channel (BCH) terminates in the RBS.

Mur

The Mur management interface provides element and network management of the RNC. Users of the interface are the RNC Element Manager, OSS-RC, or an external Management System.

Upgrade and Expansion

The RNC can be expanded by adding subracks or cabinets to increase the traffic capacity.

The traffic capacity of the RNC can also be enhanced by adding or upgrading individual GPB boards and additional transmission options can be achieved by adding or replacing ET boards

Software StructureThe RNC comprises a number of resource layers shown in Figure 5. A layer represents a hierarchical level offering services to the layer or layers above through a well-defined interface.



Figure 5 RNC Software Layers

RNC software layers are described in Table 2.

Table 2 RNC Resource LayersLayer Description

Operation & Maintenance

Provides the overall O&M functionality for the RNC, including management interface services and access to the O&M support in the Platform layer.

Service Provides the control services offered by the RNC, such as the following:

Radio Network control

Functions for paging of UE

Signaling connection handling

Radio Access Bearer service handling

This layer isolates the more abstract functions from the user plane functions and resources.

Encapsulation Reserves and releases resources in the Resource layer for dedicated and common channel connections. The layer includes functions that enable the user of the Mur interface to configure devices and their use.

Resource Provides user and control plane resources controlled and administered by RNC. Examples of such resources are resources for Iu/Iub Frame Protocol handling and Uu Layer 2 protocol handling.

Platform Provides services to the other layers, for example, operating system, database, equipment control, internal communication, fault recovery, and upgrade mechanisms



Program restart

In the unusual situation of an abnormal program execution, the RNC will recover by restarting the program. A program restart can also be a part of a SW update. The program restart has usually no impact on ongoing traffic. The program restart takes a few seconds.

Board restart

A more severe incident will escalate to a board restart. This means that the board will restart the processor(s) and all programs running on the board. Board restart is also used when introducing a new board, or when upgrading the SW to a newer version. The impact of a board restart on the service and on ongoing traffic depends on the role of the board and its processors, see Table 1. Note that for completeness, the table also includes all active parts of the RNC, i.e., also other components than boards.

Node restart

A node restart may occur as a last resort in extraordinary fault situations. A node restart may also be triggered manually in extraordinary circumstances. During a node restart, all traffic is terminated, and no service is available until the node has restarted and re-established connections to the RBSs and to the Core Network.


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7.General Description of RNC