GSM DATA SERVICES ECE 2526 – MOBILE COMMUNICATION Monday, February 17, 2020
BASIC GSM SERVICES 1. Teleservices 3. Bearer Services (a) Voice full-rate (13kbs) (a) 2.4 -9.6 Data transmission (b) Voice Half-rate (6.5 kbps) (b) Full duplex/half duplex (c) SMS (up to 160 characters) (c) Synchronous/Asynchronous (d) MMS (e) Fax (f) Bearer Services 2. Supplementary (a) Call Forwarding (b) Caller ID (c) Connected Line ID (d) Call Hold (e) Call barring (f) Call charge advice
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 (9.6Kb/s) – Data Packet Duplex (9.6 Kb/s)
GSM BEARER DATA SERVICES 1. To offer bearer services, a circuit switched connection is established to connect the MS to an interface in the PSTN. 2. A radio channel and a wire-line circuit are reserved even if the data 9.6kbps is not transferred. Data Network 3. An alternative would be to release the resource when the data is not being transferred. 4. However, GSM call set-up is too long to be tolerated by many data applications.
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 high 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 are then 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 Available to Kbps when all 8 time slots are used. Voice callers } } 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 number of channels used per second (or per minute).
GENERAL PACKET RADIO SERVICE (GPRS) 1. G eneral P acket R adio S ervice (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) S erving G PRS S ervice N ode ( SGSN ) (b) G ateway G PRS S upport N ode( GGSN )
GENERAL PACKET RADIO SERVICE (GPRS) ARCHITECTURE AuC VLR HLR S erving G PRS G ateway G PRS S upport N ode S ervice N ode
GSM/GPRS NETWORK ARCHITECTURE GPRS packet switched section uses the NSS for authentication, location management, and billing through this link.
THE SERVING GPRS SUPPORT NODE (SGSN) 1. SGSN takes care of some important tasks, including routing, handoff and IP address assignment. 2. Any packets that are lost during this process of handover are retransmitted. 3. The SGSN converts mobile data into TCP/IP protocol format.
GATEWAY GPRS SUPPORT NODE (GGSN) Gateway GPRS Support Node is the “last port of call” in the GPRS 1. 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 (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 multi-slot class 2. GPRS speeds range from 56 – 118 Kbps.
DEPLOYING GPRS OVER EXISTING GSM NETWORKS 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.
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.
GSM-GPRS INTERFACES (1) Gb: routes signaling, Gr: SS7 control, and user data to interface used or from the SGSN to the to provide BSC 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: SS7 interface which enables coordination between the MSC and the SGSN mobile allowing authentication and location updates.
GSM-GPRS INTERFACES (2) Gd: SS7 interface used to interface with the SMCC to enable GPRS mobiles to send and receive short messages. Gc: SS7 interface that is used to determine the SGSN serving mobiles. Ga: IP-based interface used to carry signaling and user data.
COMPARING GGSN WITH A CORPORATE SYSTEM 12 Mb/s Internet 12/24/72 Switch 12/24/72 Switch Router/Fire wall 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 3 1 2 MSC VLR HLR MS 4 5 USSD Gateway Application Server
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 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) ETI 2511 Monday, September 21, 2015
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.
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