UNIT II – MOBILE TELECOMMUNICATION SYSTEM
GSM – Architecture – Protocols – Connection Establishment – Frequency Allocation –
Routing – Mobility Management – Security –GPRS- UMTS- Architecture
- List the standards similar to GSM. [May 2012]
GPRS
IS-95
IS-2000
UMTS
LTE - What is frequency range of uplink and downlink in GSM network? [May 2018]
The frequency range of uplink in GSM network is 890-960 MHz
The frequency range of downlink in GSM network is 935-960 MHz - State the pros and cons of GSM. [Nov 2011]
Advantages
Total mobility
Worldwide connectivity
High capacity
High transmission quality
Security functions
Disadvantages
No end-to-end encryption of user data
Reduced concentration while moving
Electromagnetic radiation
High complexity of system
Card-type
Serial number
A list of subscribed services - List the subsystems of GSM. [Nov 2018]
A GSM system consists of three main subsystems:
o Radio Subsystem (RSS)
o Networking and Switching Subsystem (NSS)
o Operation Subsystem (OSS) - What is the information stored in SIM? [May 2018]
A Mobile Station (MS) is also called as Cellular Phone
It contains two main parts: SIM and Mobile Device
SIM (Subscriber Identity Module) Card
o It is made up of microcontroller to store data.
o It has ROM for contacts storage, etc
o It has card type, serial number, PIN (Personal Identification Number), PIN
unblocking key (PUK), Authentication key, IMSI. - Name the Teleservices provided by GSM. [May 2017, Nov 2019]
Telephony
o High quality digital voice transmission of bandwidth 3.1 kHz.
o Special codecs are also used for voice transmission.
Emergency number
o Even when out of coverage area, subscriber can call some emergency
numbers.
o The same number is used throughout an area..
o This service is free of cost and mandatorily provided by all service
providers.
o This connection will automatically be set up with the closest emergency
center.
Short Messaging Service
o Using signaling channels, full duplex SMS can be sent and received of size
160 characters.
Fax
o Analogue fax data can be converted to digital data using MODEM and
transmitted over analog telephone network. - Write about the supplementary services in GSM. [Nov 2016]
User identification, call redirect, call forward, etc.
Standard ISDN features such as ‘close user group’ and ‘multiparty’
communication are available. - State the purpose of Home Location Register (HLR). [Nov 2018]
It is a database to store important information of each subscriber.
It contains prepaid (or) postpaid number.
It contains static information like Mobile Subscriber ISDN Number (MSISDN),
IMSI, Current Location Area (LA) of the MS, Mobile Subscriber Roaming
Number (MSRN). - What is Equipment Identity Register? [Nov 2013]
It is a database to track handsets using IMEI number.
It helps to block calls from stolen, unauthorized, or defective mobiles. - Give the block diagram of subscriber authentication in GSM architecture. [May
2014] - List the 3 important features of GSM security. [May 2016]
Security in GSM is broadly supported at three levels: operator’s level, customer’s
level, and system level.
These three levels help oversee aspects such as correct billing to the customer,
avoiding fraud, protecting services, and ensuring anonymity.
The three important features of GSM security are:
o Access control and authentication.
o Confidentiality.
o Anonymity. - What is handoff? List out its characteristics. [May 2013]
The mobile (MS) moves out of one cell to another it must be possible to retain the
connection. The process by which this occurs is known as handover or handoff.
Handover should not cause a cut-off, also called call drop. GSM aims at
maximum handover duration of 60 ms. - Differentiate soft and hard handoff. [Nov 2011]
- Draw a model to illustrate the effect of handoff. [May 2012]
- Define handoff. What are its types? [Nov 2012, Nov 2017]
Handoff is defined as a process of handling over the radio interface of a mobile
station from one cell to another cell.
This process should be started before the signal is weak in one cell, to avoid the
disconnection.
Types:-
o Hard handoff: When mobile station is moving, the handoff is made, but call
is disconnected in-between or disturbed.
o Soft handoff: Handoff is made without any disturbance. - What are the reasons for handover? [Nov 2013]
When MS moves away from BTS, signal strength decrease, increase in error rate
and quality of radio cell diminishes.
Load balancing – Traffic in one cell is too high and shift some MS to other cells
with a lower load. - What is the functionality of GGSN? [May 2014, Nov 2018]
GGSN is the internetworking unit between the GPRS network and PDN.
GGSN contains routing information for GPRS users, performs address connection
and securely tunnels data to a user through encapsulation.
GGSN is connected to an external network and it transfers packets to SGSN
through IP-based GPRS backbone network. - Draw the GPRS transport plane. [May 2012]
- What are the advantages of GPRS? [Nov 2012]
Advantages
Machine-to-machine data communication
lower service charges
Compatible with E-mail, broadcast services, and web browsing
Web-based services, e-Commerce, and advertising is also supported (High
speed packet-switched communication supported by GPRS)
Limitations
Reduced cell capacity
Transmission delay
No storage mechanism - Identify the services offered by GPRS. [Nov 2017, May 2019]
Point-to-Point (PTP) service
The PTP service is between two users and can either be connectionless or
connection-oriented.
Point-to-Multipoint (PTM) service
The PTM is a data service from one user to multiple users.
There are two types of PTM services.
Multicast PTM – The data packets are broadcast in a certain area.
Group calls PTM – The data packets are addressed to a group of users. - In which way GPRS is better than GSM? [Nov 2019]
Advanced with packet data transport for internet applications.
In GSM, it is charged for duration of connection, but in GPRS, it is charged
for amount of data packets transmitted.
Data transfer rate up to 150 kbps.
It allows broadband broadcast, multicast and unicast.
It works on packet switching. - What are the main elements of UMTS? [May 2016]
The three main elements of UMTS are:
User Equipment (UE),
Radio Network Subsystem(RAN)
Core Network. - List out the advantages of UMTS networks over 2G networks. [May 2019]
Higher speech quality
Fast Internet & Higher data rate: 2Mbps
Virtual Home Environment
Increased capacity when compared to 2G
Smooth multimedia messaging
Enhanced location based services
Enhanced communication (Email, IM, File sharing)