Monday, September 14, 2009

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

Saturday, September 5, 2009


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 disturbing other pairs. As for TDMA each pair in the room would have some specific time to talk when other people should remain in silence. CDMA would allow to talk for all pairs but each of them would have to use different language (code).

This example as described in "UMTS". Javier Sanchez, Mamadou Thioune ISBN: 978-1-905209-71-2 January 2007, Wiley-ISTE

To increase system capacity it is common to use these technologies together. GSM would use for example TDMA together with FDMA.