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UMTS Layers, Interfaces, Protocols - Iub interface.

Just to remind - Iub interface connects Node B (RBS) and RNC. As for general view (general info) in this interface one can describe layers (i.e. Radio and Transport Network Layer), planes (i.e. user and control plane) and some protocols within those planes.

Figure 1. Iub Control Plane - ATM transport.

NBAP - Node Application Part SSCF-UNI - Service Specific Coordination Function for support of signaling at the User Network Interface [ITU-T 2130] SSCOP - Service Specific Connection Oriented Protocol AAL5 - ATM Adaptation Layer 5

Simplified UMTS network architecture

Figure 1 shows simplified UMTS network architecture.

Figure 1. Simplified UMTS network architecture.

Note: Not all nodes and interfaces are included in this picture.

Abbreviations used in the picture:
RNC - Radio Network Controller
MSC - Mobile Switching Center
Ue - User Equipment
SGSN - Serving Gprs Support Node
PDN - Packet Data Network
PSTN - Public Switched Telephony Network

UMTS Layers, Interfaces, Protocols - General

Previous post was a short introduction for general information regarding layers, protocols, interfaces and planes.
In UMTS one can find all mentioned objects and divisions.

As for the layers the Figure 1 shows what layers are defined for UMTS.

Figure 1. UMTS network protocols layers [1]
As mentioned in each layer may have its User and Control Plane. Each layer has dedicated protocol to work in proper plane. Detailed description of theses protocols will be placed in next posts.

Figure 2. General Layer, Plane and Protocol Model for interfaces in UTRAN [2]
Signaling bearers for Transport Network User Plane and for Transport Network Control Plane may be different but may be the same. It is up to configuration if the same Signaling Bearers would be used [2]

Based on:
[1] UMTS System Telefonii Komórowej Trzeciej Generacji - J. Kołakowski, J. Cichocki. WKŁ 2006
[2]  3GPP TS 25.401

Protocols, interfaces, User Plane and Control Plane

When two devices would like to communicate with each other they would use a defined protocol. Protocol is set of rules describing how those two devices can communicate in way that receiver would understand what sender “had in mind” while sending message. Protocol description is usually description of messages (signals) that can be sent and received, it is also description for particular procedures and functions.
Now, our two devices know “how to talk” to each other, but they need to be connected somehow. For this purpose an Interface would be defined. Interface would be generally another device, with or without dedicated software, that would allow connecting, inter-working and changing messages(signals) between our devices – connected using this interface.
Sometimes when connecting two devices using interface there is a need for two protocols. First protocol would allow first device to control how works the second one. This kind of protocol is part of control plane. Second protocol wo…

Radio Interface (UMTS)

Simplified radio interface (Uu) architecture.

MAC, RLC and RRC communicate with each other using some signals/messages called primitives.

Based on 3GPP 25.321.

Question and Answers

Questions and Answers concerning particular and often very detailed issues given without introduction.
Comments, questions are of course welcome!!!

Q: Why AAL2 on Iu interface needs ALCAP and AAL5 does not need this signaling protocol ?
A: AAL5 is using PVC configured by O&M, hence there is no need to establish, release or maintain this connections. AAL2 is not using PVC but VC/VP which need to be established, released and maintained by separate signaling protocol i.e. ALCAP.
Q: What is the meaning of PDU and SDU and what is the difference between them ?
A: PDU is Protocol Data Unit and SDU is Service Data Unit. Difference between them and their role should describe following figure
Q: What means NNI and UNI ? This two terms can be seen together with SAAL layer.
A: NNI means Network-to-Network Interface also known as Network-Node Interface. UNI means User-to-Network Interface.

NAS: Non-Access Stratum

This post is to give short description of NAS protocols, procedures and functions.
NAS is a layer for communication between Ue and Core Network (CN). This communication is transparent for underlaying Access Stratum.
NAS protocols:
GMM - GPRS Mobility ManagementMM - Mobility Management SM - Session ManagementCC - Call Control SS - Supplementary Services SMS - Short Message Services SM, SMS, SS and CC form a group of protocols called Connection Management.

Figure - Inter protocols communication MS side [3GPP 24.007]

SM - its functions is to activate, deactivate or modify PDP contexts which are sessions for PS traffic in UMTS/GPRS networks

Figure 1 - Simplified PDP context activation procedure

Figure 2 - Inter protocol communication for PDP context activation - MS side

CC - its functions is to establish, maintain and finally release CS calls in UMTS/GPRS/GSM networks

Figure 3- Simplified CS call proceeding

Figure 4 - Inter protocol communication for CS call setup

EPS - Network architecture

This is simplified network architecture for EPS (Evolved Packet System)

There are two main parts of EPS: LTE (Long Term Evolution) and SAE (System Architecture Evolution).
Actually those two parts have also different names and LTE is known as E-UTRAN and SAE is known as EPC (Evolved Packet Core).
MME - Mobility Management Entity S-GW - Serving Gateway HSS - Home Subscriber Server PCRF - Policy Control and Charging Rules Function PDN-GW - Packet Data Networks Gateway


CAMEL - Customised Applications for Mobile network Enhanced Logic
This is simplified CAMEL entities configuration. Based 3GPP 23.002 Release 9.


In UMTS/GSM networks the whole area covered by network coverage is divided into smaller parts. The smallest and base entity is cell that is area controlled by base station (BTS/Node B). One or more cells form UTRAN Registration Area. RNC controls URA. One or more URA forms Routing Area (RA). The area controlled by SGSN. One or more RA can be part of Location Area (LA). This is controlled by MSC/VLR.

Another concept is Service Area (SA). Service Area is a subset of Location Area. Several cells may be grouped into Service Area. This area used by RAN helps to find out UE location within LA.



Location Area
Location Area is one or more cells. Location Area is controlled by VLR. Each time MS changes LA it needs to inform VLR about this with Location Update Procedure.

NAS - Non-Access Stratum
Set of protocols (i.e. MM, GMM, SM, CC, SS, SMS) and functions for communication between Ms (or Ue) and Core Network (both CS and PS domain).

Routing Area
Routing Area is one or more cells. Routing Area is controlled by SGSN. Each time Ms changes RA it needs to inform SGSN about this with Routing Area Update procedure.

Service Area
Service Area is one or more cell belonging to the same LA. It is used by RAN when location request comes from CN.

Network Architecture Release 99

This is simplified network architecture described in 3GPP 23.002 Release 99.

Multiple Access Methods

The problem is each wireless system has to have its bandwidth that needs to be shared among several users. That is the reason that multiple access techniques have been designed.

FDMA - Frequency Division Multiple Access
TDMA - Time Division Multiple Access
CDMA - Code Division Multiple Access

FDMA - Each user has its part of overall frequency band i.e. the whole bandwidth is divided for many users. TDMA - The whole bandwidth is reserved for particular user for only specified period of time.
CDMA - User can use whole bandwidth for all time but has to use different code.
As for explanation of difference between these three multiple access technologies there is an example of room with people talking in pairs. When they would use FDMA the room (whole bandwidth) should be divided into smaller rooms and each room would represent one frequency. Walls would be the separation of these frequencies hence people in pairs would have a chance to talk at the same time without disturbi…


3GPPThird Generation Partnership Project
AALATM Adaptation Layer
ADCHAssociated DCH
ADSLAsymetric Digital Subscriber Line
ALCAPAccess Link Control Application Part
ARFCNAbsolute Radio Frequency Channel Number
ARQAutomatic Repeat reQuest
ATMAsynchronous Transfer Mode
BCCHBroadcast Control Channel
BCHBroadcast ChannelBERBit Error RateBICCBearer Independent Call ControlBLERBlock Error RateBPSKBinary Phase Shift KeyingBSCBase Station ControllerBSSBase Station SubsystemBTSBase Transceiver StationCAMELCustomised Applications for Mobile network Enhanced Logic
CCCall Control
CCCHCommon Control Channel
CDMCode Division Multiplexing
CDMACode Division Multiple Access
CNCore Network
CMConnection Management
CPICHCommon Pilot Channel
CQIChannel Quality Indicator
CRCCyclic Redundancy Check
C-RNTICell Radio Network Temporary Identifier
CSCirciut Switch
CRNCControlling Radio Network Controller
DCHDedicated Channel
DNSDomain Name Server
DL-SCHDownlink Shared Channel
DRNCDrift Radio Network Controller

GPRS Network Architecture

Simplified GPRS network architecture.

GPRS - General Packet Radio Service
SGSN - Serving GPRS Support Node
GGSN - Gateway GPSR Support Node
PLMN - Public Land Mobile Network

GSM Network Architecture

Simplified GSM network architecture

Ms - Mobile Station
BTS - Base Transceiver Station
MSC - Mobile Switching Center
HLR - Home Location Register
VLR - Visitor Location Register
EIR - Equipment Identity Register
G-MSC - Gateway MSC

This blog has beencreated as a place for somegeneral and somedetailedinformationabout mobile networkssuch as GSM, GPRS, UMTS and LTE.

Best Regards