Telecom Network

8/6/2019 Telecom Network

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TELECOM NETWORK

2G Network

2G (or 2-G) is short for second-generation wireless telephone technology. Second generation 2G cellular

telecom networks were commercially launched on the GSM standard in Finland by Radiolinja (now part

of Elisa Oyj) in 1991. Three primary benefits of 2G networks over their predecessors were that phone

conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum

allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile,

starting with SMS text messages.

GSM is a cellular network, which means that mobile phones connect to it by searching for cells in theimmediate vicinity. There are five different cell sizes in a GSM networkmacro, micro, pico, femto and

umbrella cells. The coverage area of each cell varies according to the implementation environment.

The network is structured into a number of discrete sections:

y The Base Station Subsystem (the base stations and their controllers).

y The Network and Switching Subsystem (the part of the network most similar to a fixed network).

This is sometimes also just called the core network.

y The GPRS Core Network (the optional part which allows packet based Internet connections).

y The Operations support system (OSS) for maintenance of the network.


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Figure 1: 2G Architecture

COMPONENTS:


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Figure 2: 2G Components

Mobile Station (MS)

It consists of two parts, the Mobile Equipment (ME) and an electronic smart card called a SubscriberIdentity module (SIM).

The ME is the hardware used by the subscriber to access the network. The hardware has an

identity number associated with it, which is unique for that particular device and permanently

stored in it. This identity number is called the International Mobile Equipment Identity (IMEI)

and enables the network operator to identify mobile equipment which may be causing problems

on the system.

The SIM as mentioned previously is a smart card which plugs into the ME and contains

information about the MS subscriber hence the name Subscriber Identity Module.

The SIM contains several pieces of information:

o International Mobile Subscriber Identity (IMSI): This number identifies the MS

subscriber. It is only transmitted over the air during initialization.

o Temporary Mobile Subscriber Identity (TMSI): This number identifies the

subscriber. It is periodically changed by the system management to protect the

subscriber from being identified by someone attempting to monitor the radio

interface.

o Location Area Identity (LAI): Identifies the current location of the subscriber.


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o Subscriber Authentication Key (Ki): This is used to authenticate the SIM card.

o Mobile Station International Services Digital Network (MSISDN): This is the

telephone number of the mobile subscriber. It is comprised of a country code, a

network code and a subscriber number.

Base Station System (BSS)

The GSM Base Station System is the equipment located at a cell site. It comprises a combination of

digital and RF equipment. The BSS provides the link between the MS and the MSC.

The BSS communicates with the MS over the digital air interface and with the MSC via 2 Mbit/s links.

The BSS consists of three major hardware components:

y The Base Transceiver Station BTSThe BTS contains the RF components that provide the air interface for a particular cell.

This is the part of the GSM network which communicates with the MS. The antenna is included

as part of the BTS.

y The Base Station Controller BSC

The BSC as its name implies provides the control for the BSS. The BSC communicates

directly with the MSC. The BSC may control single or multiple BTSs.

y The Transcoder XCDR

The Transcoder is used to compact the signals from the MS so that they are more

efficiently sent over the terrestrial interfaces. Although the transcoder is considered to be a part

of the BSS, it is very often located closer to the MSC. The transcoder is used to reduce the rate

at which the traffic (voice/data) is transmitted over the air interface. Although the transcoder is

part of the BSS, it is often found physically closer to the NSS to allow more efficient use of the

terrestrial links.

Network Switching System

The Network Switching System includes the main switching functions of the GSM network. It also

contains the databases required for subscriber data and mobility management. Its main function is to

manage communications between the GSM network and other telecommunications networks.

The components of the Network Switching System are listed below:

y Mobile Services Switching Centre MSC

The MSC is included in the GSM system for call-switching. Its overall purpose is the same as

that of any telephone exchange.The MSC will carry out several different functions depending upon its position in the

network. When the MSC provides the interface between the PSTN and the BSSs in the

GSM network it will be known as a Gateway MSC. In this position it will provide the

switching required for all MS originated or terminated traffic.

The functions carried out by the MSC are listed below:

o Call Processing: Includes control of data/voice call setup, inter-BSS and inter-MSC

handovers and control of mobility management (subscriber validation and location).


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o Operations and Maintenance Support: Includes database management, traffic

metering and measurement, and a manmachine interface.

o Internetwork Interworking: Manages the interface between the GSM network and

the PSTN.

o Billing: Collects call billing data.

y Home Location Register HLR

The HLR is the reference database for subscriber parameters.

Various identification numbers and addresses are stored, as well as authentication

parameters. This information is entered into the database by the network provider when a

new subscriber is added to the system.

The HLR database contains the master database of all the subscribers to a GSM PLMN.

The data it contains is remotely accessed by all the MSCs and the VLRs in the network and,

although the network may contain more than one HLR, there is only one database record

per subscriber each HLR is therefore handling a portion of the total subscriber database.

The subscriber data may be accessed by either the IMSI or the MSISDN number. The data

can also be accessed by an MSC or a VLR in a different PLMN, to allow inter-system and inter-

country roaming.The various data stored by the HLR are listed below:

o Subscriber ID (IMSI and MSISDN)

o Current subscriber VLR (current location)

o Supplementary services subscribed to

o Supplementary service information (e.g. current forwarding number )

o Subscriber status (registered/deregistered)

o Authentication key andAUCfunctionality

o Mobile Subscriber Roaming Number

y Visitor Location Register VLR

The VLR contains a copy of most of the data stored at the HLR. It is, however, temporarydata which exists for only as long as the subscriber is active in the particular area covered

by the VLR. The VLR database will therefore contain some duplicate data as well as more

precise data relevant to the subscriber remaining within the VLR coverage.

The VLR provides a local database for the subscribers wherever they are physically located

within a PLMN, this may or may not be the home system. This function eliminates the

need for excessive and time-consuming references to the home HLR database.

The additional data stored in the VLR is listed below:

o Mobile status (busy/free/no answer etc.).

o Location Area Identity (LAI).

o Temporary Mobile Subscriber Identity (TMSI).

o Mobile Station Roaming Number (MSRN).

y Short Message Service Entities SMSE

In order to provide SMS, the core network has three distinct entities. The first of these is the

Short Message Service Centre(SM-SC). The SM-SC is responsible for the relaying and store-

and forwarding of a short message between as MS and a Short Message Entity (SME). The

SME is any entity that can send or receive SMS message.


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An EC is used on the PSTN side of the MSC for all voice circuits. Echo control is required at

the switch because the inherent GSM system delay can cause an unacceptable echo

condition, even on short distance PSTN circuit connections.

2.5G Network

2.5G is a stepping stone between 2G and 3G cellular wireless technologies. The term "second and a half

generation is used to describe 2G-systems that have implemented a packet-switched domain in

addition to the circuit-switched domain. It does not necessarily provide faster services because bundling

of timeslots is used for circuit-switched data services (HSCSD) as well.

The first major step in the evolution of GSM networks to 3G occurred with the introduction of General

Packet Radio Service (GPRS). CDMA2000 networks similarly evolved through the introduction of 1xRTT.The combination of these capabilities came to be known as 2.5G.

GPRS could provide data rates from 56 Kbit/s up to 115 Kbit/s. It can be used for services such as

Wireless Application Protocol (WAP) access, Multimedia Messaging Service (MMS), and for Internet

communication services such as email and World Wide Web access. GPRS data transfer is typically

charged per megabyte of traffic transferred, while data communication via traditional circuit switching is

billed per minute of connection time, independent of whether the user actually is utilizing the capacity

or is in an idle state.

1xRTT supports bi-directional (up and downlink) peak data rates up to 153.6 Kbit/s, delivering an

average user data throughput of 80-100 Kbit/s in commercial networks.[3] It can also be used for WAP,SMS & MMS services, as well as Internet access.


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Figure 3: 2.5G Architecture

COMPONENTS:

Serving GPRS Support Node (SGSN)

The function of SGSN in the GPRS network is quite similar to that of the MSC/VLR in GSM network. Thus,

an SGSN maintains subscriber information obtained from the HLR and provides packet routing functions

to/ from GGSN. An SGSN controls one or more Routing Area(s) (RA).

The following are some of the important information elements maintained by the SGSN:

y IMSI

y One or more Packet-Temporary Mobile Subscriber Identity (P-TMSI)

y Zero or more Packet Data Protocol (PDP) addresses

y Routing Area (RA) where the MS is registered

y VLR number where the MS is registered

y GGSN address of each GGSN for which an active PDP context exists

SGSN performs the following functions using the information maintained by it:


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y GPRS mobility management. The SGSN maintains the registration status of MS, performs RA

updates, and obtains subscription information from the HLR.

y Session management. SGSN helps in activation/ deactivation of PDP context whereby the MS

gets an address (e.g. Internet Protocol (IP) address) for communication with a Packet Data

Network (PDN).

y

Security management. SGSN also performs important security management functions includingauthentication and ciphering. While authentication is used to validate the identity of the MS,

ciphering is performed during data transfer between the MS and SGSN.

y Packet routing. Apart from mobility management, the other important function of SGSN is to

also deliver packet to MS from GGSN and vice versa.

y Miscellaneous functions. SGSN also performs other function like charging data collection, data

compression, and logical link management.

Gateway GPRS Support Node (SGSN)

The GGSN provides an interface with the PDN. It converts the GPRS packets received from SGSN into the

appropriate format of the external network. In the reverse path, the GGSN coverts the incoming packet

to the GPRS packets and delivers it to the destined MS using the PDP context stored by it. The GGSN

connects with the SGSN through an IP backbone over which the packets are tunneled, using the GPRS

Tunneling Protocol (GTP). GGSN stores the current SGSN address of the user and subscriber profile in its

database for various operations.

3G Network

3G or 3rd generation mobile telecommunications, is a generation of standards for mobile phones and

mobile telecommunications services fulfilling the International Mobile Telecommunications-2000 (IMT

2000) specifications by the International Telecommunication Union. Application services include

wide-area wireless voice telephone, mobile Internet access, video calls and mobile TV, all in a mobile

environment. To meet the IMT-2000 standards, a system is required to provide peak data rates of at

least 200 Kbit/s. Recent 3G releases, often denoted 3.5G and 3.75G, also provide mobile broadband

access of several Mbit/s to smartphones and mobile modems in laptop computers.


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Figure 4: 3G Architecture

COMPONENTS:

Radio Network Sub-system (RNS)

One of the most important standardization accomplishments in the UMTS network is the

standardization of fully open Radio Network Sub-Systems (RNS). This is unlike BSS, which is based

primarily on proprietary solutions. The RNS, also known as Universal Terrestrial Radio Access Network

(UTRAN), comprises of one Radio Network Controller (RNC) and one or more Node B. The RNC is similar

to BSC while Node B is similar to BTS. The open interfaces of RNS enable RNC and Node B of different

vendors to interoperate with each other.

Radio Network Controller (RNC)The Radio Network Controller (RNC) controls one or more Node B. The important functions of RNC

include radio resource management, control of Node B, encryption decryption, admission control and

power control (downlink power control and uplink outer loop power control).

Depending upon its function, the RNC can assume various roles. These roles are: Controlling RNC, Drift

RNC and serving RNC. A Controlling RNC has overall control of the logical resources of a Node B. Thus,

the term Controlling RNC is always used in the context of the Node B that it controls.

From the point of view of a UE, RNC can assume two different roles: the Serving RNC and the Drift RNC.

The Serving RNC is the one that is in charge of the radio connections between the UE and the UTRAN. It

is not necessary that there be a direct connection between the Serving RNC and the UE. Instead, there

can be an intermediate RNC, called the Drift RNC, which works on behalf of the Serving RNC. More

formally, the Serving RNC terminates the Radio Access Network Application Part (RANAP) signaling with


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the Core Network over the Iu Interface. The Serving RNC also terminates the Radio Resource Control

(RRC) signaling with the UE over the air interface. The Drift RNC and Serving RNC communicate using the

Radio Network Sub-system Application Part (RNSAP).

Node B

The Node B works as per the instructions of RNC using the Node B Application Part (NBAP) protocol. Theprimary task of Node B is to interface with the UE over the air interface. A Node B serves one or more

cells.

The important functions of Node B include channel coding, rate matching, spreading/dispreading and

inner-loop power control. Note the functions like spreading/dispreading and inner-loop power control

are new to UTRAN and are not performed by BTS.

4G Network

LTE advantages include high throughput, low latency, plug and play from day one, FDD and TDD in thesame platform, superior end-user experience and simple architecture resulting in low operating

expenditures (OPEX). LTE will also support seamless connection to existing networks, such as GSM,

CDMA and WCDMA. However LTE requires a completely new RAN and core network deployment and is

not backward compatible with existing UMTS systems.

A characteristic of next generation networks is that all connectivity and session control relies on TCP/IP.

Since different functional domains can now communicate and interact easily, the result is a richer

communications experience including enhanced voice, video, messaging services and advanced

multimedia solutions.

3GPP is defining IP-based, flat network architecture as part of the System Architecture Evolution (SAE)

effort. LTESAE architecture and concepts have been designed for efficient support of mass-market

usage of any IP-based service. The architecture is based on an evolution of the existing GSM/WCDMAcore network, with simplified operations and smooth, cost-efficient deployment. The main component

of the SAE architecture is the Evolved Packet Core (EPC), also known as SAE Core. The EPC will serve as

equivalent of GPRS networks (via the Mobility Management Entity, Serving Gateway and PDN Gateway

subcomponents).

The subcomponents of the EPC are:

y MME (Mobility Management Entity)

y S-GW (Serving Gateway)

y P-GW(PDNgateway)

The 3G RNC inherited from the 2G BSC has disappeared and the eNodeB is directly connected to the

Core Network using the S1 interface. As a consequence, the features supported by the RNC have been

distributed between eNodeB or the Core Network MME or Serving Gateway entities.


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Figure 5: LTE Architecture

COMPONENTS:

Mobility Management Entity(MME)

The MME is the key control node for the LTE access network. It is responsible for idle mode UE (User

Equipment) tracking and paging procedure including retransmissions. It is involved in the bearer

activation/deactivation process and is also responsible for choosing the SGW for a UE at the initial

attach and at time of intra-LTE handover involving Core Network (CN) node relocation. It is responsible

for authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS) signalling

terminates at the MME and it is also responsible for generation and allocation of temporary identities to

UEs. It checks the authorization of the UE to camp on the service providers Public Land Mobile

Network (PLMN) and enforces UE roaming restrictions. The MME is the termination point in the network

for ciphering/integrity protection for NAS signalling and handles the security key management. Lawful

interception of signalling is also supported by the MME. The MME also provides the control plane

function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the

MME from the SGSN. The MME also terminates the S6a interface towards the home HSS for roaming

UEs.


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Serving Gateway(S-GW)

The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user

plane during inter-eNB handovers and as the anchor for mobility between LTE and other 3GPP

technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW).

For idle state UEs, the SGW terminates the DL data path and triggers paging when DL data arrives for the

UE. It manages and stores UE contexts, e.g. parameters of the IP bearer service, network internalrouting information. It also performs replication of the user traffic in case of lawful interception.

PDNgateway(P-GW)

The PDN GW provides connectivity to the UE to external packet data networks by being the point of exit

and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one

PDN GW for accessing multiple PDNs. The PDN GW performs policy enforcement, packet filtering for

each user, charging support, lawful interception and packet screening. Another key role of the PDN GW

is to act as the anchor for mobility between 3GPP and non-3GPP technologies such as WiMAX and

3GPP2 (CDMA 1X and EvDO).

References

1. CP02 INTRODUCTION TO DIGITAL CELLULAR2. Heikki Kaaranen, AriAhtiainen, Lauri Laitinen, Siamak Naghian, Valtteri Niemi. UMTS Networks:Architecture,

Mobility and Services

3. Brough Turner & Marc Orange. 3G Tutorial4. Sumit Kasera, Nishit Narang, APPriyanka. 2.5G Mobile Networks: GPRS andEDGE5. Sumit Kasera, Nishit Narang. 3G Networks: Archituecture,Protocols andProcedures6. Antonis Hontzeas. Long Term Evolution7. Dr. Erik Dahlman. 3G Long Term Evolution

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