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Understanding GPRS: The
GSM Packet Radio Service
Brahim Ghribi2 and Luigi Logrippo3
School of Information Technology and
Engineering,
University of Ottawa, Ottawa ON Canada
K1N 6N5
Abstract
• The General Packet Radio Service
(GPRS), a data extension of the mobile
telephony standard GSM
• Is the first true packet switched
architecture to allow mobile subscribers to
benefit from high-speed transmission rates
and run data applications from their mobile
terminals.
Introduction
• The market is witnessing a remarkable
explosion of cellular and mobile
technologies leading to demand that data
applications become available to mobile
users.
• GSM offers data services already but they
have been constrained by the use of
circuit switched data channels over the air
interface allowing a maximum bit rate of
14.4 k bit/s.
• The HSCSD (High-Speed Circuit-Switched
Data) is one solution that addresses this
requirement by allocating more time slots
per subscriber and thus better rates
• GPRS subscribers to use several time
slots (packet data channels)
simultaneously reaching a bit rate of about
170kbit/s
• Volume-based charging is possible
because channels are allocated to users
only when packets are to be sent or
received
Basic overview of the GSM
Network
Accessing the GPRS Network
• The outcome is the establishment of a
logical link between the MS and a single
SGSN and the creation of a mobility
management context
MM Context
• The MS in GSM can be in one of two
states: Idle or Dedicated.
• Idle State
• Ready State
• Standby State
GSM/GPRS Service Interactions
Limitations of GPRS
Despite its potential, GPRS remains
constrained by the following limitations:
• GPRS transmission rates are much lower
than in theory.
• GPRS relies on packet switching
• GPRS relies also on re-transmission and
data integrity protocols to ensure that data
packets transmitted over the radio air
interface are not lost or corrupted.
• Although it is possible theoretically to
specify a high QoS profile, traffic over
radio imposes severe constraints on the
Quality of Service.
• The protocols between the BSS and the
SGSN support mainly asynchronous data
transfer applications making it a challenge
to implement real-time interactive traffic.
~END~
DSP創思設計競賽
• 使命必達
• 電話傳輸信號模擬器
• 主動式遠距監控與定位救援手杖實作
使命必達
• 作品功能
• 包括「使用者端」與「遠端照護端」二部
分。「使用者端」以ARM-based嵌入式平
台安裝Linux作業系統，並以C語言撰寫開
發應用程式完成，提供需長期量測心電訊
號之病患使用；
• 「遠端照護端」以PC安裝Windows 7作業
系統，並以Visual C++撰寫應用程式完成，
提供醫療院所之醫護人員即時監看及即時
救援使用。同時也以平板電腦完成與PC監
看的相同功能，便於醫療人員攜帶使用，
達到行動醫療的功能。
• 實現了以下四個功能
• (1)顯示心電圖與即時估算心跳數
• (2)心電訊號儲存
• (3)透過網際網路實現遠距離照護救援
• (4)應用GPS及GSM於救援導航系統。
主動式遠距監控與定位救援手杖實作
• 作品功能
• 使用心跳資訊做為判斷是
否有緊急警報，當心跳的
數值超過的正常的數據會
發出訊息給醫護人員做判
斷
• 跌到的判斷則是由手機內的三軸感應器部
分，當三軸感應器的數值異常於本實驗的
設定範圍內會即時的通報給醫護人員以及
發出求救訊號給附近的人員來讓使用者得
到第一時間的協助。
電話傳輸信號模擬器
• 模擬產生各種電話線上信號，如撥號音、
忙線音、回鈴音等，本作品是以現有信號
處理軟體： Audaciey，依據各種音源信號
規格，加以合成編修而產生。