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INTRODUCTION TO
GSM DATA SERVICES
ECE 2515 – WIRELESS COMMUNICATION
Monday, October 4, 2021
BLOCK DIAGRAM OF GSM MOBILE STATION
GENERAL BLOCK DIAGRAM OF A GSM PHONE
SAMSUNG J5 BLOCK DIAGRAM
BASIC GSM SERVICES
1. Teleservices
(a) Voice full-rate (13kbs)
(b) Voice Half-rate (6.5 kbps)
(c) SMS (up to 160 characters)
(d) MMS
(e) Fax
2. Supplementary
(a) Call Forwarding
(b) Caller ID
(c) Connected Line ID
(d) Call Hold
(e) Call barring
(f) Call charge advice
3. Bearer Services
(a) 2.4 -9.6 Data
transmission
(b) Full duplex/half duplex
(c) Synchronous/
Asynchronous
GSM 2 BASIC DATA SERVICES
• GSM Phase 2 standard supports two data
service groups:
1. Short-Message Services (SMS)
– usually offered as part of basic subscription
2. Bearer Data Services-
– Data Circuit Duplex (up to 9.6Kb/s)
– Data Packet Duplex (up to 14 Kb/s)
CLASS DISCUSSION
• The channel data rate for all 8 time
slots/channels is 270.833 kbit/s, and the
frame duration is 4.615 ms.
• What are the overheads? Look at the
normal traffic burst presented in earlier
lecture.
• Stand-alone Dedicated Control Channel
- SDCCH
Uplink and Downlink
• Used for call setup, authentication,
ciphering location update and SMS.
10
HOW SMS IS SEND/RECEIVED
BEARER DATA SERVICES
1. To offer bearer services, acircuit switchedconnection is establishedto connect the MS to aninterface in the PSTN.
2. A radio channel and awire-line circuit arereserved even if the datais not transferred.
3. Resources are releasedthe resource when thedata is not beingtransferred.
4. GSM call set-up is toolong to be tolerated bymany data applications.
Internet
9.6kbps
GSM PHASE 2+ SYSTEMS
1. SMS and Bearer data services under Phase 2
could not support Internet protocols such as
FTP in an efficient manner.
2. Later, new Protocols were developed as apart
of the GSM 2+ standard as follows:
a) High Speed Circuit Switched Data (HSCSD) for such
services as speed file transfer and mobile video
transmission.
b) General Purpose Radio Service (GPRS) for packet
switched data services such as Internet applications.
FEATURES OF HIGH SPEED CIRCUIT SWITCHED DATA
(HSCSD)
1. HSCSD is a 2+ generation high
speed circuit switched protocol
used for large file transfer and
multimedia applications.
2. It uses the same physical layer
as that used in GSM 2.
3. By improving on error
correction, HSCSD supports a
speed of 14.4 Kbps (up from
9.6Kbps)
4. Data rates can be increased by
using multiple time slots (up to
8) instead of one time slot.
HIGH SPEED CIRCUIT SWITCHED DATA – USE OF MULTIPLE
TIMESLOTS
1. By using multiple timeslots, HSCSD can support speed of up to 115
Kbps.
2. This however Increases the Blocking Rate of the system as it reduces
time slots that could be used to carry voice.
Data Rate
14.4 kbps/slot x 8 time-slots = 115 kbps
HSCSD ILLUSTRATION
By using multiple timeslots, HSCSD can support up to 115
Kbps when all 8 time slots are used.
Problem of multiple time slot allocation:
1. HSCSD reduces the number of available channels to subscriber in a
cell since one terminal can use all the timeslots in an ARFCN.
2. Charges are higher – most operators charge based on the resources,
i.e channels used.
Available to
Voice callers
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1. General Packet Radio Service (GPRS) is a
packet switched protocol designed to
support web applications.
2. Because, it is packet switched, it requires
additional components to be added to the
basic GSM 2.0 architecture.
3. The added components are:
(a) Serving GPRS Service Node (SGSN)
(b) Gateway GPRS Support Node(GGSN)
GENERAL PACKET RADIO SERVICE (GPRS)
HLR
GENERAL PACKET RADIO SERVICE (GPRS) ARCHITECTURE
Serving GPRS
Service Node
GGSN
Gateway GPRS
Support Node
SGSN
THE SERVING GPRS SUPPORT NODE (SGSN)
1. SGSN takes care of routing, handover and IP address assignment.
Any packets that are lost during handover are retransmitted.
2. The SGSN converts mobile data into TCP/IP protocol format.
GATEWAY GPRS SUPPORT NODE (GGSN)
1. Gateway GPRS Support Node is the “last port of call” in the GPRS network before a connection between an ISP or corporate network’s router occurs.
2. The GGSN is basically a gateway, router and firewall rolled into one.
Packet Control Unit
PACKET CONTROL UNIT
Packet Control Unit (PCU) is
a logical network element
that is responsible for:
1. Air-interface access
control
2. Packet scheduling on the
air interface
3. Packet assembly and
reassembly
GPRS CLASSES
Devices supporting GPRS are divided into three classes:
1. Class A
– Class A terminals have 2 transceivers which allow them to send / receive data and voice at the same time.
– This class of device takes full advantage of GPRS and GSM.
– You can be taking a call and receiving data all at the same time.
2. Class B
– Can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at a given time.
– During GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded.
– Most GPRS mobile devices are Class B.
3. Class C
– Are connected to either GPRS service or GSM service (voice, SMS). Must be switched manually between one or the other service.
GPRS SPEEDS
1. The upload and download speeds that can be
achieved in GPRS depend on a number of
factors such as:
– the number of BTS TDMA time slots assigned by the
operator
– the channel encoding used.
– the maximum capability of the mobile device
expressed as a GPRS multislot class
2. GPRS speeds range from 56 – 118 Kbps.
GPRS COSTS
1. Support for IP/TCP thus allowing seamless connection to the internet.
2. GSM network providers do not have to start from scratch to deploy GPRS.
3. GPRS is an upgrade to the existing network that sits along side the GSM network. This makes it easier to deploy.
4. Most updates are software so they can be administered remotely
5. There is little or no downtime of the existing GSM network whilst implementation takes place.
6. This allows GSM providers to add value to their business at relatively small costs.
COMPLETE GSM 2+ SYSTEM WITH GPRS SUPPORT
COMPARISON HSCSD/GPRS
1. HSCSD users are usually charged at a rate higher than a normal phone call (e.g., by the number of time slots allocated) for the total period of time that the user has a connection active.
2. GPRS has lower pricing (based on amount of data transferred rather than the duration of the connection), has become more common than HSCSD.
3. Being circuit switched, HSCSD has a lower average radio interface latency compared to GPRS which is packet switched.
GPRS INTERFACES
SIGNALLING
• Gb passes signaling, control, and user data to or from the SGSN.
• Gr is a SS7 interface is used to provide location updates to the HLR for GPRS mobiles and to retrieve mobile information for any mobile that is located in the service area of the SGSN.
• Gs a SS7 interface which enables coordination between the MSC and the SGSN mobile that support both circuits witched services (voice) controlled by the MSC and packet-data services controlled by the SGSN.
• Gd is a SS7 interface used to interface with the SMCC to enable GPRS mobiles to send and receive short messages.
• Gn is an IP-based interface used to carry signaling and user data.
• Gc is a SS7 interface that is used to determine the SGSN serving mobiles.
COMPARING GGSN WITH A CORPORATE SYSTEM
60 Mb/s
Internet
Router/Fire
wall
12/24/72
Switch
12/24/72
Switch
12/24/72
Switch
12/24/72
Switch
12/24/72
Switch
12/24/72
Switch
SAFARICOM BUNDLE BILLING
SAFARICOM OFFERS
SAFARICOM: VOICE TARIFF
UNSTRUCTURED SUPPLEMENTARY SERVICE DATA (USSD)
1. After the initial launch of GSM 2.0, new services started
evolving.
2. To support these new services, Supplementary Service
Data Services (USSD) was introduced in GSM 2.90.
3. A USSD string consists of:
a) Asterisks symbol *
b) Digits (2 – 4)
c) Harsh symbol #
4. Example: *217# - used to access Nairobi County
Parking Service
IMPLEMENTATION OF USSD
MSC VLR HLR
USSD
Gateway
Application
Server
MS
1 2 3
4
5
TAKE HOME QUESTIONS
1. How is the 3-time slot delay between up-link and downlink maintained in GSM?
2. Why is it necessary to have a training sequence in GSM?
3. DO HSCSD and GPRS introduce new handoff issues in GSM?
4. Which of the algorithms A3, A5 and A8 are specific to a mobile operator? Why?
5. Discuss the advantages and disadvantages of using HSCSD vs and GPRS to access a corporate database.
6. Discuss how the GSM system can programmed to effectively provide service to data and voice users in a location in an efficient manner using HSCSD.
ENHANCED DATA RATES FOR
GSM EVOLUTION (EDGE)
ECE 2526
ENHANCED DATA RATES FOR GSM
EVOLUTION (EDGE)
1. Also referred to as Enhanced GPRS (EGPRS)
2. EDGE is a digital mobile phone technology
that allows improved data transmission rates
as a backward-compatible extension of GSM.
3. EDGE is considered a pre-3G radio technology
and is part of ITU's 3G definition.
4. EDGE was deployed on GSM networks
beginning in 2003
UPGRADING TO EDGE
1. EDGE requires no hardware or software changes to be made in GSM core networks.
2. Howver, EDGE-compatible transceiver units must be installed and the base station subsystem needs to be upgraded to support EDGE.
3. If the operator already has (2) in place, which is often the case today, the network can be upgraded to EDGE by activating an optional software feature.
4. EDGE is supported by all major chip vendors for both GSM and WCDMA/HSPA.
CAPACITY OF EDGE
• EDGE can carry a bandwidth up to 236.8 kbit/s
for 4 timeslots (theoretical maximum is 473.6
kbit/s for 8 timeslots) in packet mode.
• This means it can handle four times as much
traffic as standard GPRS.
• EDGE meets the ITU’s requirement for a 3G
network, and has been accepted by the ITU as
part of the IMT-2000 family of 3G standards.
