Radio and Core Network Protocols in UMTS

Presented by:

Naveen Jakhar, ITS

Topics:

UMTS Network Architecture

OSI Communication model

UMTS Protocol stack

Circuit switched-control plane/user plane

Packet switched-control plane/user plane

Generic protocol model for UTRAN interfaces

Iu-CS interface protocol structure

Iu-PS interface protocol structure

Iur interface protocol structure

Iub interface protocol structure

Summary

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UMTS Network Architecture3

OSI Communication model

• Each layer communicates only with two adjacent layers and its peer on the other side

• Each layer receives services from the layer below and provides services to the layer above

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• Intermediate communication nodes

require layers 1 through 3

• Internal operation within each layer is

independent of the internal operation

in any other layer

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical LayerPhysical Layer

Data Link Layer

Network Layer

Physical Medium Physical Medium

Node A Node B Node C

Peer to peer protocols • WCDMA interfaces

described using OSI model

• OSI = Open System

Interconnect

• Developed by ISO as a

general model for computer

communication

• Used as a framework for

development and

presentation of most

contemporary

communication standards

Note: WCDMA covers Layers 1-3 of OSI Model

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UMTS Protocol stack

• First three layers of the

protocol stack are part of

UTRAN

Note: SMS exists on both circuit switched and packet switched side

NAS or the Non Access Stratum is a set of protocols in the

UMTS that is used to convey non-radio signalling between the User

Equipment (UE) and the core network.

From a protocol stack perspective, the NAS is the highest stratum of

the control plane

The NAS procedures consist of MM, CC, GMM, SM

Access Stratum signalling is between UTRAN and the terminal.

Eg. RRC Connection setup

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UMTS CS protocols – control plane

• RNC terminates

the Access

Stratum (AS)

• RRC, RLC and

MAC terminate at

RNC

• PHY terminates at

Node B except for

outer loop power

control

• RAN (access

stratum) acts as

transport for NAS

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Note: UTRAN protocols are layered in an architecture that follows OSI model

RRC: RRC connection management(setup, release, reconfiguration), –

Radio Bearers management(setup, release, reconfiguration),

Management of radio resources for the RRC connection, RRC

connection mobility functions, Paging/notification

Radio Link Control (RLC): The RLC protocol offers logical link control

over the radio interface for the transmission of higher layer-signalling

messages and SMS. RLC is defined in TS 25.322.

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UMTS CS protocols – user plane

• User plane –

caries user

data

• Application –

end to end

protocol

• Access stratum

the same for

both control

plane and user

plane

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UMTS PS protocols – control plane

• Control plane

for packet data

• Very similar to

control plane

for PS

• Identical

access stratum

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UMTS PS protocols – user plane

• Additional protocol

PDCP

• PDCP –

compression of IP

headers

• PDCP may or may

not be used

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• PDCP:

– provides protocol transparency

(wrt the underlying radio-

interface protocols) for higher-

layer protocols

– support for e.g., IPv4, PPP and

IPv6 (easy introduction of new

higher layer protocols)

– compression of control

information (header

compression)

– no user data compression in Iu

mode

■ RLC:

– RLC protocol provides logical link control over the radio interface.

■ MAC

– MAC protocol controls the access signaling(request and grant) procedures for the radio channel

Figure :Generic protocol model for UTRAN interfaces

The structure consists of two horizontal layers:

1)The Radio Network Layer and

2) The Transport Network Layer.

The Radio Network Layer is concerned with application information

to be carried either user data and control information.

The Transport Network Layer is concerned with the transport

technologies used for the UTRAN interfaces.

The two layers are logically independent of each other. This makes it

possible to change the Transport Network Layer without affecting

Radio Network Layer, if required. In Release 99, the Transport

Network Layer is based on ATM. In Release 5, IP is used.

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•The user plane includes the user data between the UE and the

network and the data bearers. The user data consists of data streams

characterized by frame protocols specific to a UTRAN interface.

•The control plane includes the application protocols and the signaling

bearers, which transport the control information.

The application protocols used at different UTRAN interfaces are:

■ Iu-CS: Radio access network application protocol (RANAP)

■ Iu-PS: RANAP

■ Iub: Node B application protocol (NBAP)

■ Iur: Radio network system application protocol (RNSAP)

•The transport network control plane includes the access link control

application protocol (ALCAP). ALCAP is used to set up transport

bearers to carry user and control plane information. It is not visible to the

Radio Network Layer.

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Figure : Iu-CS interface protocol structure.16

IUcs interface protocol structure

• In UMTS, the interface between RAN and CN is Iu.

•Iu-CS is the interface specified between the RAN and the 3G MSC.

•The Iu-PS interface is defined between the RAN and the 3G SGSN.

•In order to have uniformity, 3GPP specifies a single protocol at Radio Network Layer for the Iu-CS and the Iu-PS interfaces.

The radio access network application protocol (RANAP) is the Radio Network Layer protocol for the Iu interface. The RANAP peer entities reside in 3G MSC/SGSN and the SRNC. The RANAP functions are specified in 3GPP TS 25.413 in detail. In summary, RANAP procedures support the following key functions:

■ Radio access bearer (RAB) management including RAB setup, modification, and release

■ Iu connection management

■ Facilitate general UTRAN procedures from the core network, e.g., paging requests from the CN to UE

■ Services to upper layers including the transportation of upper layer nonstratum protocols (i.e., call control, session management, and mobility management) messages between the UE and CN

■ Overload and error handling

■ SRNS relocation

■ UE location reporting 17

The Service Connection and Control Part (SCCP) offers both connectionless and

connection-oriented services. Each active UE is assigned a separate logical link in case of

connection-oriented service between two RANAP entities.

The SCCP utilizes services provided by the lower layers to transport messages between two

entities.

Layer 3 Broadband Message Transfer Part (MTP3b) provides message routing,

discrimination, and distribution. It also provides link management functions including load

sharing between linksets.

The SSCF-NNI(Service-Specific Coordination Function for Signaling at the Network Node

Interface) maps the requirements of above layers to the requirements of SSCOP.

The SSCOP (Service-Specific Connection-Oriented Protocol)provides the mechanism for

the establishment and release of connections and the reliable exchange of signalling

information between the signalling entities.

In cases where the IP transport option is chosen, the services are provided by M3UA(MTP 3

User Adaptation Layer), SCTP (Stream Control Transmission Protocol) and IP.

AAL5 (ATM Adaptation Layer 5)is used to adapt the upper layer protocol to the

requirements of the lower ATM cells.

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As described in the previous section, the purpose of the transport network

control plane is to set up, maintain, and release bearers to transport the data

via the user plane.

The AAL2 signaling protocol capability set 1 (ALCAP), which is described in

ITU-T specification Q.2630.1, is used. ALCAP(Access Link Control Application

Part ) is a Layer 3 protocol. Its responsibility is to set up and manage ATM

Adaptation Layer 2 (AAL2) connections.

In the user plane, ATM Adaptation Layer 2 (AAL2) is used as the user data

bearer. AAL2 has been specifically designed to transport short-length packets.

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Figure: Iu-PS interface protocol structure. 20

IUps interface protocol structure

The Iu-PS interface is specified between the RAN and the 3G SGSN.

As described in the previous section, 3GPP specifies a single protocol at

the Radio Network Layer for the Iu-CS and the Iu-PS interfaces, i.e.,

RANAP for the control plane and Iu for the user plane.

No transport network control protocol is needed. Unlike GPRS, where

the GTP tunnel ends at the SGSN, the GTP tunnel in UMTS extends up

to RNC. The tunnel ID and IP address, which is required to establish a

tunnel, is included in the upper layer protocols.

Like GPRS, GTP-U uses UDP/IP. AAL5 is used to carry the packet-

switched user traffic over the Iu-PS interface.

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Figure :Iur interface protocol structure. 22

Iur interface protocol structureIur is the interface between the RNCs.

One of the RNCs assumes the controlling role and is termed the serving

RNC (SRNC); the other RNC is termed the drifting RNC (DRNC).

The Radio Subsystem Application Part (RNSAP) is a Radio Network Layer

protocol used at the Iur interface. RNSAP includes procedures for network

control signaling between two RNC nodes:

■ Radio link management and reconfiguration

■ Radio link supervision

■ Common control channel (CCCH) signaling transfer

■ Paging

■ Relocation execution

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RNSAP uses the services of the Transport Layer for reliable

transfer of signaling messages in both connectionless and

connection-oriented modes.

The SCCP allows a separate independent logical connection with

individual UE. If the ATM transport option is chosen between two

RNCs, the SCCP uses MTP3-B, SSCF-NNI, and SSCOP services

for networking and routing of messages.

In cases where the IP transport option is chosen, these services

are provided by the M3UA, SCTP, and IP.

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Iub interface protocol structureIub is the interface between the Node B and the RNC .

The Node B application protocol (NBAP) is a Radio Network Layer control

plane protocol at the Iub interface. NBAP includes the procedures to manage

the logical resources at Node B. NBAP procedures support the following

functions:

■ Cell configuration management

■ Radio link management and supervision

■ Common transport channel management

■ System information management

■ Configuration verification/alignment

■ Measurement of common and dedicated resources System network

protocols26

Summary

•UTRAN in WCDMA covers Layers 1-3 of OSI Model

•Complete UMTS architecture is divided into Non Access Stratum and Access

Stratum

•The application protocols used at different UTRAN interfaces are:

■ Iu-CS: Radio access network application protocol (RANAP)

■ Iu-PS: RANAP

■ Iub: Node B application protocol (NBAP)

■ Iur: Radio network system application protocol (RNSAP)

•In order to have uniformity, 3GPP specifies a single protocol at Radio Network Layer for

the Iu-CS and the Iu-PS interfaces.

•UMTS protocol structure is divided into horizontal layers and vertical planes

1)Radio network layer 1)User Plane

2)Transport network layer 2)control plane

3) Transport Network control Plane

•In Release 99, the Transport Network Layer is based on ATM. In Release 5, IP is used.

•There is no Transport Network control Plane in Iu-PS interface

•Unlike GPRS, where the GTP tunnel ends at the SGSN, the GTP tunnel in UMTS

extends up to RNC.

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Thank You!