Legacy Connectivity (3GPP Rel-4)

There are support for legacy network but first we need to understand Dial-up connections and GPRS. Both basically related to initial development of 3GPP standards (up to Rel-5). 

Specially for mobile user, which are used for providing information on small screen of mobile. So WAP was not fully compatible to public internet so WAP Gateways are used to get data and send request over public internet.

Dial up Connection:

Figure 1: GSM circuit switched access connection

While connecting with dial-up connection we use a E-164 number to dial to operator who connects to a WAP server or third party service provider. In initial deployment we have used RADIUS protocol so when a user dials up E-164 NAS number, user request of NAS connects to gateway, so at gateway there is authorization check is made and if allowed to access public internet, Gateway provide a private IP address to User terminal. By this way  a user can connect to public internet as Gateway publish a Public IP of user for other network and by getting data from that end , it map address of public identity to user private IP Address.

GPRS connectivity:

The GPRS nodes of each operator are interconnected on a private IP network.  The access connection (the technical name is PDP Context) can be thought of as a “flexible tunnel” through the GPRS networks that is established by the GPRS Tunneling Protocol (GTP). The arrangement is shown in Figure 2. The GTP tunnel extends from the SGSN to the GGSN. A mobile may support several PDP Contexts simultaneously.

Figure 2: The GPRS access connection
 

A GPRS user can access the following types of access point:

·        a Virtual Private Network connected to their home mobile operator (APN = <name of VPN>.mnc.mcc.gprs)

·        a third party ISP connected to their home mobile operator  (APN = <name of ISP>.mnc.mcc.gprs)

·        the Internet using either normal Internet protocols or WAP via the visited network’s connection to the Internet (APN = “Internet”).

APN name is an IP address of access point. APN is not URL of information source which user wants to interrogate, it is a access point by which a user can access many information source.

For the tunnel between the SGSN and the GGSN, i.e. the section across the GPRS backbone, there is a tunnel  identifier (TID) distinguishing each user’s tunnel. The tunnel ID relates to the GTP protocol running between the SGSN and the GGSN, and there are IP addresses for the source and destination SGSN/GGSN interfaces at each end of the tunnel. So this approach is known as circuit switching communication.

General Information Elements

Wireless system Analysis is based on two part. Radio Access Network part and Core technologies.

In the Radio Part, the technologies are evolving towards higher efficiency ( i.e. being able to encode/or send more data on the same radio signal ( or the carrier frequency). The movement is from TDM/FDM ( or 2G GSM), CDMA (IS95, CDMA 1x ) to WCDMA ( 3G) to OFDM (4G & LTE) .
In the Core, technologies are evolving from circuit switched to being packet switched. This basically means that instead of reserving a whole circuit for the duration of the call, you are dividing it in to data packets , which are re-assembled at the recieving end. IMS has multiple releases and stages, through which this move is being achieved.

IP Multimedia Service (IMS) is an architectural framework for delivering Internet Protocol (IP) multimedia services. It was originally designed by the wireless standards body 3rd Generation Partnership Project (3GPP), as a part of the vision for evolving mobile networks beyond GSM. Its original formulation (3GPP R5) represented an approach to delivering "Internet services" over GPRS.

Relational Analysis of LTE, IMS, SAE, EPC

LTE (Long Term Evolution) is the 4G wireless access technology from 3GPP like UMTS was the 3G or GPRS the 2.5G. Because it provides IP based only access and a lot of bandwidth 3GPP decided to study what converged architecture will support it. The study was called System Architecture Evolution (SAE).
The Evolved Packet Core is the result of this study. It is the All-IP architecture to which LTE and other 3GPP (UMTS,GPRS) and non-3GPP (WiMAX,HRPD,WLAN etc) access systems connect to. The EPC provides a converged solution for Security, QoS , Mobility and connection to the IP based services (IMS or the Internet).Sometimes the term Evolved Packet System (EPS) is also used but it just refers to the EPC and the LTE access network (E-UTRAN) together.
IMS is on top of the EPC but its just considered one of the possible IP Services layer. There is a data interface (SGi) from the main gateway of the EPC (the PDN-Gw) to IMS and also a signaling/control interface (Rx) from the application function (the P-CSCF in IMS) to the main session controller in charge of the authorization, admission control, resource reservation, QoS (PCRF).

Basics of LTE Understanding

Before we start discuss anything first come to knowledge that IMT has set some requirements that must be fulfilled to qualify for 4G naming.
IMT-Advanced standard requirements

The main purpose of these processing is to provide better speed and reliability on wireless side of mobile communication.

• Peak download rates of 326.4 Mbit/s for 4x4 antennae, and 172.8 Mbit/s for 2x2 antennae (utilizing 20 MHz of spectrum).
• Peak upload rates of 86.4 Mbit/s for every 20 MHz of spectrum using a single antenna.
• Five different terminal classes have been defined from a voice centric class up to a high end terminal that supports the peak data rates. All terminals will be able to process 20 MHz bandwidth.
• At least 200 active users in every 5 MHz cell. (Specifically, 200 active data clients)
• Sub-5 ms latency for small IP packets.
• Increased spectrum flexibility, with supported spectrum slices as small as 1.4 MHz and as large as 20 MHz (W-CDMA requires 5 MHz slices, leading to some problems with roll-outs of the technology in countries where 5 MHz is a commonly allocated amount of spectrum, and is frequently already in use with legacy standards such as 2G GSM and cdmaOne.) Limiting sizes to 5 MHz also limited the amount of bandwidth per handset
• In the 900 MHz frequency band to be used in rural areas, supporting an optimal cell size of 5 km, 30 km sizes with reasonable performance, and up to 100 km cell sizes supported with acceptable performance. In city and urban areas, higher frequency bands (such as 2.6 GHz in EU) are used to support high speed mobile broadband. In this case, cell sizes may be 1 km or even less.
• Good support for mobility. High performance mobile data is possible at speeds of up to 350 km/h, or even up to 500 km/h, depending on the frequency band used.
• Co-existence with legacy standards (users can transparently start a call or transfer of data in an area using an LTE standard, and, should coverage be unavailable, continue the operation without any action on their part using GSM/GPRS or W-CDMA-based UMTS or even 3GPP2 networks such as cdmaOne or CDMA2000)
• Support for MBSFN (Multicast Broadcast Single Frequency Network). This feature can deliver services such as Mobile TV using the LTE infrastructure, and is a competitor for DVB-H-based TV broadcast

E-UTRAN Air Interface

E-UTRAN is the air interface of LTE. Its main features are:

• Peak download rates up to 292 Mbit/s and upload rates up to 71 Mbit/s depending on the user equipment category.
• Low data transfer latencies (sub-5 ms latency for small IP packets in optimal conditions), lower latencies for handover and connection setup time than with previous radio access technologies.
• Support for terminals moving at up to 350 km/h or 500 km/h depending on the frequency band.
• Support for both FDD and TDD duplexes as well as half-duplex FDD with the same radio access technology
• Support for all frequency bands currently used by IMT systems by ITU-R.
• Flexible bandwidth: 1.4 MHz, 3 MHz, 5 MHz, 15 MHz and 20 MHz are standardized.
• Support for cell sizes from tens of metres radius (femto and picocells) up to 100 km radius macrocells
• Simplified architecture: The network side of EUTRAN is composed only by the enodeBs
• Support for inter-operation with other systems (e.g. GSM/EDGE, UMTS, CDMA2000, WiMAX...)
• Packet switched radio interface.