GPRS

蔡佩倪2010/10/29

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Outline

Introduction GSM system architecture GPRS network architecture GPRS/GSM mobile classes GPRS attach procedure PDP context activation GPRS Protocol Stack GPRS channels Summary

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Introduction

The General Packet Radio Service (GPRS) is an European Telecommunications Standard Institute (ETSI) standard for packet data transmission using the core GSM (Global System for Mobile Communications) radio access network.

It provides switched packet data transfer to efficiently utilize the radio resources.

It provides a quick session set up and fast data transmission speeds. Supports immediacy (no dial-up connection is necessary)

theoretically supports maximum speeds of up to 171.2 kbps

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BSS

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AUCHLR

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VLR

VLRMSC

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GC

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PSTN PSDN ISDN

otherGSMPLMN

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GSM System Architecture - I

與固定網路間之介面

BTS

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GSM 系統之行動臺 (Mobile Station ，簡稱 MS) 是由一「行動話機」及一「客戶識別模組」 (Subscirber Identity Module ，簡稱 SIM)所組成。

HLR 為一大型資料庫，其內主要儲存系統所有行動用戶之相關資料，以做為行動用戶漫遊辨識、記帳之用途。

行動交換中心 (MSC) 是整個 GSM 行動通信系統的中樞，負責行動用戶與行動用戶間之交換接續，及行動用戶與固定網路 ( 如PSTN ， ISDN ， PSDN 等 ) 間之銜接，並與 VLR ， LR/AUC ， EIR 等相連接，以取得行動用戶之相關資料。

「訪客位置記錄器 VLR 」主要負責儲存目前漫遊 (Roaming) 到此一 VLR 服務區之來訪行動用戶之相關資料，俾使行動用戶漫遊到此一 VLR 服務區時，仍可繼續享有 GSM 行動通信的服務。

「設備識別記錄器」 (EIR) 提供系統經營者具備核對「國際行動台設備識別碼」 (IMEI) 之能力，以避免讓已遭竊或未經授權之行動台設備進接入其 GSM 系統。

GSM System Architecture - II

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More about VLR

訪客位置記錄器 (Visitor Location Register, VLR)負責儲存目前漫遊 (Roaming) 到此一 VLR 服務區之來訪

行動用戶之相關資料，包括 國際行動用戶識別碼 (International Mobile Subscriber Identity,

IMSI): 為國際唯一之號碼 (stored in SIM card, sent by phone to

BS)

行動台漫遊號碼 ( Mobile Subscriber Roaming Number, MSRN)

行動台最新註冊之位置區 (Location Area, LA)

暫時行動用戶識別碼 (Temporary Mobile Subscriber Identity,

TMSI): 由 VLR 指配，較 IMSI 短，具節省無線資源及保密等優點

用戶資料… 適時向 HLR 擷取用戶資料 (thru IMSI)

負責執行認證、位置更新、加密之支援、用戶註冊 / 解註冊程序、用戶增添服務之處理、 IMSI 及 TMSI （取代 IMSI 避免被竊取）之管理，可單獨存在亦可與 MSC 結合在一起。

IMSI MSRN LAC TMSI Subs. Info.

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More about HLR

本籍位置記錄器 (Home Location Register, HLR)為一大型資料庫，儲存系統所有用戶之相關資料，做為漫

遊辨識、記帳之用，包括 行動台 ISDN 號碼 (Mobile Station ISDN Number, MSISDN): 如

886-932123456 IMSI 呼叫路由選擇所需之暫時位置訊息 ( 即 VLR 之 ID) MSRN 用戶登記資料

執行位置註冊提供用戶登記資料給 VLR提供 MSRN 給 MSC認證與加解密之支援與 VLR 、 MSC 、 AUC 間之信號傳送可單獨存在，亦可與其他元件合併。 ( 大多數廠商均將

HLR 與 AUC 合併裝設 )

MSISDN IMSI VLR ID MSRN Subs. Info.

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GPRS network architecture

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GPRS network architecture

The gateway GPRS support node (GGSN) provides a gateway between the GPRS

network and the public packet data network (PDN) or other GPRS networks.

provides authentication and location management functions, connects to the home location register (HLR) by means of the Gc interface, and counts the number of packets transmitted for accurate subscriber billing.

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GPRS network architecture

The serving GPRS support node (SGSN) controls the connection between the

network and the mobile station (MS). provides session management and GPRS

mobility management functions such as handovers and paging. It also counts the number of packets routed.

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GPRS network architecture

Functions of the packet control unit (PCU) converting packet data into a format

that can be transferred over the air interface

managing radio resources implementing quality of service (QoS)

measurements

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GPRS/GSM mobile classes

Class A (GSM/GPRS) Class A mobiles can attach to the GPRS and

GSM network simultaneously. Class B (GSM/GPRS)

This class is similar to class A with the exception that Class B mobile phones will not support simultaneous traffic.

Most GPRS mobile devices are Class B. Class C (GSM or GPRS)

This class of mobile phones will have both GSM and GPRS functionality but will attach to only one network at a time.

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GPRS Routing Example 1

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GPRS Routing Example 2

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GPRS Routing Example 3

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The GPRS attach procedure

A GPRS attach is a GPRS mobility management (GMM) process that is always initiated by the mobile phone.

Depending on the settings of the mobile phone, the GPRS attach may be performed every time the phone is powered on, or it may be initiated manually by the user.

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The GPRS attach procedure

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PDP context activation

A PDP context activates a packet communication session with the SGSN.

During the activation procedure, the mobile phone either provides a static IP address or requests a temporary one from the network.

It also specifies the access point name (APN) with which it wants to communicate.

The mobile requests a desired quality of service (QoS) and a network service access point identifier (NSAPI).

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PDP context activation

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GPRS Protocol Stack

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Transmitting the packet data units

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GPRS logical channels

Logical channels are pre-defined functions supported by frames within a physical channel.

GPRS physical channels generally carry two types of information: control signaling for establishing and maintaining a GPRS service, and user data traffic.

GPRS logical channels can be classified as packet control channels and packet traffic channels.

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GPRS logical channels

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GPRS logical channels

PBCCH (packet broadcast control channel) is used to broadcast packet data system

information to all GPRS mobiles in a cell. The PBCCH might not be present for

certain channel combinations, in which case the BCCH will be used to broadcast packet system information.

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GPRS logical channels

PCCCH (packet common control channel) a set of logical channels used for common

signaling between the mobile station and the base station. (PRACH, PPCH, PAGCH, PNCH)

PRACH (packet random access channel) is used only in uplink to initiate uplink transfer.

PPCH (Packet Paging Channel) is used to page a mobile prior to downlink

packet transfer.

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GPRS logical channels

PAGCH (packet access grant channel) is used in the packet transfer

establishment phase to send resource assignment messages to a mobile prior to packet transfer.

PNCH (packet notification channel) is used to send a point-to-multipoint

multicast notification to a group of mobiles prior to point-to-multipoint multicast packet transfer.

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GPRS logical channels

PTCH (packet traffic channel) PDTCH (packet data traffic channel)

is allocated for data transfer. It is dedicated temporarily to one or a group

of mobiles for multicast applications. PACCH (packet associated control channel)

is used to convey signaling information related to a given mobile

PTCCH (packet timing advance control channel)

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GPRS physical channels

Radio channels of GPRS are the same as GSM

Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8

Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8

Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8

… …

… …

Frequency 1

Frequency 2

Frequency 124

Timeslot 1 2 3 4 5 6 7 8

TDMA frame = 4.615 ms

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GPRS physical channels

The physical channel dedicated to packet data traffic is called a packet data channel (PDCH).

The logical channels are mapped over physical channels using the technique of “multiframing.”

The GPRS multiframe length is 52 TDMA frames, and it is organized into 12 blocks of 4 consecutive TDMA frames, plus 4 idle frames.

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The 52-multiframe structure

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52-multiframe for four time slots

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Mapping logical channels tophysical channels

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Mapping logical channels tophysical channels Example on downlink

Example on uplink

PBCCH

PAGCH

PDTCH

PACCH

PAGCHPDTCHPACCH

PBCCH

PAGCH

PDTCH

PACCH

PPCHPBCC

H

PAGCH

PDTCH

PACCH

PPCHPBCC

H

PAGCH

PDTCH

PACCH

PPCH

B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11

PRACH

PRACH

PRACHPDTCHPACCH

PRACH

PRACHPDTCHPACCH

PRACHPDTCHPACCH

PRACH

PRACHPDTCHPACCH

PRACHPDTCHPACCH

PRACH

PRACHPDTCHPACCH

PRACHPDTCHPACCHB0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11

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Resource allocation

TS 0 TS1 TS2 TS3 TS4 TS5 TS6 TS7

TS 0 TS1 TS2 TS3 TS4 TS5 TS6 TS7

GSM only GPRS only

GSM & GPRSGSM only GPRS only

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Summary

GPRS technology adds packet-switching capability to GSM PCU, GGSN, SGSN

Time slot, frame 1 TDMA frame = 8 Time slot

52-multiframe structure 12 Radio blocks

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References

Agilent Understanding General Packet Radio Service (GPRS) http://cp.literature.agilent.com/litweb/pdf/5988-2598EN.pdf

S. Emmanuel, S. Patrick, P. Pierre-Jean, GPRS for Mobile Internet, Artech House, 2003.

Kai-Wei Ke, Chen-Nien Tsai, and Ho-Ting Wu, “Performance analysis for hierarchical resource allocation in multiplexed mobile packet data networks,” Computer Networks, Vol. 54, Issue 10, 2010, pp. 1707-1725.

General Packet Radio Service (GPRS) Overview http://www.pcs.csie.ntu.edu.tw/course/pcs/2007/reference/08_GPRS_Overview.pdf

廖宏祥，鐘嘉德。整合分封無線服務 (GPRS) 簡介。暨大電子雜誌。 http://beaver.dlc.ncnu.edu.tw/projects/emag/show.aspx?dataId=98d2571b-481d-483b-8804-f64ed720c38b

邱弘斌。行動網際網路技術與應用上課投影片。

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THANK YOU Q & A