HUAWEI EQUIPMENT INSTALLATION

OMQ000001 GPRS Fundamentals ISSUE 1.0 OMQ000001 GPRS Fundamentals ISSUE 1.0 Table of Contents Table of Contents Chapter GPRS Fundamentals 1.1 GPRS Overview 1.2 Evolution of GPRS Standards and Services 1.3 Comparison Between GPRS and HSCSD 1.4 EDGE Overview 1.5 Advantages and Disadvantages of the GPRS .2 Chapter GPRS Network Architecture 2.1 Overall GPRS Structure 2.2 Logical System Architecture of the GPRS 2.3 Major Network Entities of GPRS Chapter GPRS Protocol Layers 3.1 GPRS Data Transmission Plane 3.2 GPRS Signaling Plane 10 3.3 GPRS Network Interface Protocols 12 3.3.1 Um Interface .12 3.3.2 Gb Interface 17 3.3.3 Gs Interface 19 3.3.4 Gn/Gp Interface 19 3.3.5 Gi Interface .21 3.3.6 Gr Interface .21 3.3.7 Gd Interface 21 3.3.8 Gc Interface 21 3.3.9 Gf Interface .21 Chapter GPRS Radio Subsystem 22 4.1 GPRS Radio Interface Channels 22 4.2 Channel Coding 24 4.2.2 Channel Coding of GPRS PDTCH 24 4.2.3 Channel Coding of EGPRS PDTCH 26 4.2.4 Channel Coding for PACCH, PBCCH, PAGCH, PPCH, PNCH and PTCCH/D .33 4.2.5 Channel Coding for the PRACH 33 4.3 Media Access Control Mode .34 4.4 Multislot Capability of MS 34 4.4.1 Multislot Configuration 34 4.4.2 MS Classes for Multislot Capability 34 4.5 Power Control 37 4.6 Paging Handling 37 4.6.1 Packet Paging 37 4.6.2 Paging Co-ordination .38 4.6.3 Network Operation Modes .38 4.7 Packet Access Modes 39 4.8 GPRS Cell Selection and Reselection .40 4.8.1 Relationship Between GPRS Cell Selection and GSM Cell Selection 40 4.8.2 Relationship Between GPRS Cell Reselection and GSM Cell Reselection 40 4.8.3 Network Control Modes 40 Chapter GPRS Contents and Quality .42 5.1 Bearer Services 42 5.2 GPRS Supplementary Services 43 5.3 Applications of GPRS Services 43 5.4 Relations Between GPRS Network and Circuit Switching Service 44 5.5 GPRS Service Quality 45 Confidential Information of Huawei No Spreading without Permission i OMQ000001 GPRS Fundamentals ISSUE 1.0 Table of Contents Chapter GPRS Numbering Plan and Functions 49 6.1 IMSI .49 6.2 P-TMSI 50 6.3 NSAPI/TLLI 50 6.4 PDP Address and Type .51 6.5 Tunnel Identifier (TID) 51 6.6 Routing Area Identifier (RAI) .51 6.7 Cell Identifier .52 6.8 GSN Address and Numbering 52 6.9 Access Point Name (APN) 52 Chapter GPRS Entity Information Storage 53 7.1 HLR 53 7.2 MS 54 7.3 GGSN 54 7.4 SGSN 55 Chapter GPRS Mobility Management Flow 57 8.1 Overview 57 8.2 MM Status and MM Context .57 8.3 GPRS Attach/Detach 60 8.3.1 GPRS Attach 60 8.3.2 GPRS Detach 60 8.4 GPRS Location Management Function 60 8.4.1 Cell Updating Procedure 61 8.4.2 Routing Area Updating Procedure 61 8.4.3 Periodical RA/LA Updating Procedure .62 8.4.4 User Data Management Procedure 62 8.4.5 MS Class Mark Processing Function .62 8.5 Security Management 63 8.5.1 GPRS Authentication and Encryption 63 8.5.2 P-TMSI Reallocation 63 8.5.3 User Data and GMM/SM Signaling Privacy 63 Chapter GPRS PDU Transmission 65 Appendix Frame Relay 67 A.1 Frame Relay Concept 67 A.2 Frame Relay Structure .68 A.3 Frame Relay Working Principle 68 A.4 Congestion Control 69 A.5 Frame Relay Technical Feature 70 A.6 FR Application on GPRS Gb Interface 71 ii Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Χηαπτερ Chapter GPRS Mobility Management Flow GPRS Fundamentals 1.1 GPRS Overview The General Packet Radio Service (GPRS) allows GSM subscribers access to data communication applications such as e-mail, and Internet using their mobile phones The GPRS introduces the packet switching and transmission capabilities to the existing GSM network As one of the contents implemented by GSM Phase2.1 standard, the GPRS offers higher data rate than the 9.6 kbit/s of existing GSM network By utilizing the same frequency band, band width, burst structure, radio modulation standards, frequency hopping rule and TDMA frame structure as the GSM, the GPRS features the following:     High resource utilization Always online and always connected High transmission rate Reasonable cost 1.2 Evolution of GPRS Standards and Services As the second generation of digital mobile cellular communication system, the GSM has found wide application across the world But with the development of mobile communication technologies and service diversification, the demand for data service is continually on the rise To address this demand, the GSM, primarily supporting the voice service, proposes two types of high-speed data service models in PHASE2 and PHASE2+ specifications, that is, the High Speed Circuit Switched Data (HSCSD) based on high-speed data bit rate and circuit switching, and the GPRS based on packet switching Early in 1993, operators in Europe have taken the lead in proposing the concept of deploying the GPRS over the GSM network In 1997, great progress has been made on the GPRS standardization In October of the same year, the ETSI released the GSM02.60 GPRS Phase1 service description By the end of 1999, the GPRS Phase2 was finalized The GPRS standards contain three phases, during which 18 new standards are established and dozens of existing standards revised to implement the GPRS Table 1.1 lists the three phases of the GPRS standards: Table 1.1 Three phases of GPRS standards Phase 02.60 service description 　 　 　 Phase 03.60 system description and network structure 03.64 radio interface description 03.61 point-tomultipoint-broadcast service 03.62 point-tomultipoint group call Phase 04.60 RLC/MAC protocol 04.61 PTM-M service 04.62 PTM-G service 04.64 LLC 04.65SNDCP Major revised standards 01.61 encryption requirement; SAGE algorithm; lawful interception 03.20 security 03.22 idle mode program 04.04–07 GPRS system and time schedule information 04.08: MAC, RLC and layer3 mobility management Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Phase Phase 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 Chapter GPRS Entity Information Storage Phase 07.60 user interworking 08.14 Gb layer-1 08.16 Gb-layer network service 08.18 BSSGP and Gb interface 09.16 Gb layer-2 09.18 Gb layer-3 09.60 Gn&Gp interface 09.61: External network interworking Major revised standards 05 series: Radio interface physical layer 08.58&08.60: Abis interface and TRAU frame structure change 09.02: Add the Gr and Gd protocols 11.10: TBR-19 MS test 11.2X BSS test 11.11 SIM 12.XX O&M OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Mobility Management Flow 3) Technical advantages of the GPRS By introducing the packet-switched transmission mode, the GPRS brings radical changes to the original circuit-switched-based GSM data transmission and features the following:  High resource utilization In the circuit-switched mode, an MS connected to the system shall occupy a radio channel even if there is no data transmission In the packet-switched mode, an MS only occupies radio resource during data transmitting or receiving This means several MSs can share the same radio channel, enhancing the resource utilization  High transmission rate The GPRS provides a transmission rate up to 115 kbit/s (maximum rate: 171.2 kbit/s, excluding the FEC) The circuit-switched data service rate is only 9.6 kbit/s The GPRS users can quickly access Internet and browse web pages with portable computers as the ISDN users, and make possible the transmission-rate-sensitive mobile multimedia applications  Always online The GPRS features “Always online”, that is, the subscriber is always connected with the network When an MS accesses the Internet, the MS receives and transmits data on the radio channel Then the MS releases the occupied radio channel for other users and enters the “Quasi-dormant” state in the case of no data transmission In that case, the MS logically connects with the network and requests a radio channel from the network when the MS has the need for data transmission  Short access time The access time of packet switching is less than one second, greatly enhancing the efficiency of processing some transactions (for example, credit card check and remote monitoring) It also enables convenient and smooth Internet applications (for example, E-mail and Internet access) 4) Disadvantages of the GPRS Though the GPRS dramatically enhances the spectrum utilization in comparison with the existing non-voice data service, yet it still cannot get rid of the following disadvantages:  Actual transmission rate is lower than the theoretical one: To reach the theoretical transmission rate of 171.2 Kbps, a subscriber shall occupy the whole TSs without any error protection program In practice, it is impossible for a single GPRS subscriber to occupy all TSs In addition, there are constraints on the TS support capability of the GPRS terminals Therefore, the theoretical maximum rate needs re-proving by taking account of the practical environmental constraints  The terminal does not support the wireless termination function After a subscriber confirms the volume-based charging for the service contents when enabling the GPRS, the subscriber has to pay for undesired spam contents Whether the GPRS terminal supports the wireless termination threatens the application and market exploration of the GPRS  The modulation is not optimal The GPRS adopts the GMSK modulation mode The EDGE employs a new modulation mode eight-phase-shift keying (8 PSK), and allows higher bit rate on the radio interface The PSK modulation is also used in the UMTS  Transmission delay: The GPRS packet switching technology transmits data in different directions but to reach the same destination, so the data of one or several packets may be lost during the radio link transmission Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Χηαπτερ Chapter GPRS Entity Information Storage GPRS Network Architecture 2.1 Overall GPRS Structure When constructing the GPRS on the existing GSM network, you only need to perform software upgrade for most of the parts on the GSM network instead of hardware changes To build the GPRS system, you need to:  5) 6) 7)  Introduce major components to the GSM network: Serving GPRS Supporting Node (SGSN) Gateway GPRS Support Node (GGSN) Packet Control Unit (PCU) Perform software upgrade of related components of the GSM network Figure 1.1 shows the GPRS network architecture: Circuit-switched service path MSC PSTN ISDN PLMN Other GPRS networks BSC PCU GPRS network SGSN Internet X.25 GGSN Packet-switched service path GTP Figure 1.1 GPRS network architecture As shown in the above figure, the portable computer connects to the GPRS cellular phone through serial or radio mode The GPRS cellular phone communicates with the BTS Different from the circuitswitched data calls, the GPRS packets are transmitted from the BTS to the SGSN instead of being transmitted to the voice network through the MSC The SGSN communicates with the GGSN The GGSN handles the packet data before transmitting them to the destination network, for example, the Internet or X.25 network Upon receiving the IP packets from the Internet with the MS address, the GGSN forwards them to the SGSN which then transmits the packets to the MS Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Mobility Management Flow 2.2 Logical System Architecture of the GPRS The GPRS is implemented by adding two nodes SGSN and GGSN and the PCU to the GSM network New interfaces shall be defined after these network nodes are added Figure 1.1 shows the logical system architecture of the GPRS Figure 1.1 Logical system architecture of the GPRS Table 1.1 lists the interfaces defined in the GPRS network architecture Table 1.1 List of interfaces defined in the GPRS network architecture Interface Description The reference point between the Mobile Terminal (MT) (for example, mobile phone) and the Terminal Equipment (TE) (for example, the portable computer) The interface between the SGSN and BSS The interface between the GGSN and HLR The interface between SMS and GMSC; the interface between SMSIWMSC and SGSN The interface between the GPRS and external packet data The interface between SGSNs and between SGSN and GGSN in the PLMN The interface between GSNs of different PLMNs The interface between the SGSN and HLR The interface between the SGSN and MSC/VLR The interface between the SGSN and EIR The interface between MS and GPRS network side R Gb Gc Gd Gi Gn Gp Gr Gs Gf Um 2.3 Major Network Entities of GPRS The major network entities of the GPRS include the GPRS MS, PCU, GPRS Support Node (GSN), Charging Gateway (CG), Border Gateway (BG), Domain Name Server (DNS), and Remote Authentication Dial-In User Service (RADIUS) server 8) GPRS MS Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Entity Information Storage The GPRS MS consists of the TE and MT The MS is actually an integrated MT after the TE functions are integrated into the MT  TE The TE, used to transmit and receive the packet data of the end user, refers to the computer operated and used by the end user The TE can either be a stand-alone desktop computer, or integrated with the handset MT In a sense, the GPRS network provides all functions for the sake of establishing a path between the TE and external data network to transmit packet data  MT The MT on the one hand communicates with the TE and on the other hand communicates with the BTS over the air interface The MT can establish a logical link to the SGSN The MT of the GPRS must be configured with the GPRS functional software to enable the GPRS From the perspective of the TE, the MT acts as a modem for TE in the GPRS network The functions of both MT and TE can be integrated to one physical device  MS The MS can be regarded as the device that integrates the functions of both MT and TE It can either be an independent entity or two entities (TE + MT) The MS can be classified into the following three categories based on the capabilities of the MS and network: Class-A GPRS MS: The Class-A MSs can attach to the GSM and GPRS network simultaneously, activate and receive system messages from two systems, and implement Packet Switched Service (PS) and Circuit Switched Service (CS) concurrently Class-B GPRS MS: The Class-B MSs are similar to Class A MSs with the exception that Class-B MSs will not support simultaneous traffic If there is a circuit-switched call incoming to a Class-B MS, the MSC/VLR sends a “Suspend” message to the SGSN Upon receiving the “Suspend” message, the SGSN suspends (temporarily terminates) the GPRS connection After the circuit switching, the MSC/VLR then sends a “Restore” message to the SGSN to restore the GPRS connection Class-C GPRS MS: The Class-C GPRS MSs cannot attach to the GPRS and GSM networks concurrently, and they only support manual switching between the PS and CS 9) Packet Control Unit (PCU) As a processing unit added on the BSS side, the PCU implements the PS processing on the BSS side and management of packet radio channel resources Currently the PCU networking structure includes the following three types: A Integrated into the BTS; B Integrated into the BSC; C Independently configured, as shown in Figure 1.1 Huawei GPRS adopts the type C networking mode Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Mobility Management Flow Gb Um CCU BSC BTS GSN PCU A CCU Abis CCU BSC BTS B PCU CCU CCU GSN BTS BSC GSN C PCU CCU Gb Figure 1.1 PCU networking 10) GPRS Support Node (GSN) As the most important node in the GPRS network, the GSN contains all functions that support the GPRS Several GSNs can be present in one GSM network The GSN can be classified into the following two types: SGSN and GGSN The SGSN is the node that provides services for the MS (that is, the Gb interface is supported by the SGSN) The SGSN establishes a mobility management environment, containing the mobility and security information of the MS, when the GPRS is activated The SGSN records current location information of the MS, and transmits and receives packet data between the MS and SGSN The SGSN can transmit location information to and receive the paging request from the MSC/VLR over any Gs interface The GGSN is the gateway for the GPRS network to connect with external PDN It may connect with different data networks, for example, ISDN and LAN The GGSN is also known as the GPRS router The GGSN can implement protocol translation for the GPRS packet data packets in the GSM network, and then transmit them to the remote TCP/IP or X.25 network The GGSN can be accessed by the Packet Data Network (PDN) through configuration of a PDP address It stores the routing information of the GPRS subscriber, and transmits the PDU to current Service Access Point (SAP) of the MS, that is, the SGSN, by utilizing the tunnel technology The GGSN can query current address information of the subscriber from the HLR over the Gc interface The functions of both SGSN and GGSN can either by integrated into one physical node or implemented on different nodes They both shall support the IP routing function and can connect with the IP router When the SGSN and GGSN are located in different PLMNs, they are interconnected over the Gp interface 11) Charging Gateway (CG) The CG implements the collection, combination and pre-processing of the bills from the GSNs and provides communication interface to network with the billing center Originally there is no CG in the GSM network The bill for Internet access of a GPRS Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Χηαπτερ Chapter GPRS Mobility Management Flow GPRS Mobility Management Flow 8.1 Overview The mobility management can be classified into two types: GMM specific function and GMM security function They are described as follows: 1) 2) The GMM specific function includes: GPRS attach/detach, cell updating, and RA updating The GMM security function includes: GPRS authentication and encryption, PTMSI re-allocation, user data, and GMM/SM signaling confidentiality 8.2 MM Status and MM Context Subscriber mobility management is described by three MM status Each status describes the function and information allocation of a certain layer This information is stored in the MM context of the MS and the SGSN The three MM status: IDLE, STANDBY, and READY The MS and the SGSN converts the status among the three based on the triggering of different events The MM context is the context of the mobility management It is the database created for the GPRS MS in the SGSN and the MS It is associated with the mobility status When an MS is attached to the GPRS network, the SGSN creates an MM context for the MS If the MS is attached to the GPRS network again, the SGSN searches the user database and then re-creates an MM context based on the existing one The MM context contains some contents of the subscriber mobility management such as IMSI, MM status, P-TMSI, MSISDN, Routing Area, Cell identity, New SGSN Address, and VLR Num 1) DILE status In GPRS IDLE status, the subscriber is not attached to the GPRS mobility management The MM context in the MS and the SGSN does not contain the valid location and routing information of the subscriber In this case, the mobility management cannot be implemented Under this condition, data cannot be transmitted between the SGSN and the subscriber The GPRS MS is regarded unreachable To set up the MM context between the MS and the SGSN, the MS must be attached to the GPRS mobility management 2) STANDBY status In STANDBY status, the MS is attached to the GPRS mobility management and the MM context is set up between the MS and the SGSN The MS can receive the PS paging and the CS paging through the SGSN However, the data cannot be transmitted between the MS and the SGSN In this status, the MS can perform the GPRS RA updating and GPRS cell selection and reselection When moving to a new RA, the MS implements the mobility Confidential Information of Huawei No Spreading without Permission 57 OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Entity Information Storage management to notify the SGSN When moving from one cell to another in the same RA, the MS does not notify the SGSN Therefore, the SGSN MM context contains the GPRS RAI location information only In STANDBY status, the MS can activate or deactivate the PDP context Before sending or receiving the data, the MS must activate a PDP context When the MS is in STANDBY status, the paging is implemented in the RA level When receiving a paging of the PDP or the PTM-G data but the MS is in STANDBY status, the SGSN checks whether the paging proceed flag (PPF) is reset If yes, the SGSN sends the paging request message to the RA where the MS resides; If not, the SGSN does not send the request If the MS answers the paging, its MM context changes to READY status After the SGSN receives the paging response message, its MM context changes to READY status Similarly, if the MS sends the data or signaling, its MM context changes to READY status After the SGSN receives the data or signaling, its MM context changes to READY status When the MS or the network await-order timer expires, the SGSN implements the implicit detachment to change the MM identifier of the MS to IDLE status After that, the SGSN removes the MM of the MS and the PDP context 3) READY status In READY status, the SGSN implements the mobility management on the MS in a specific cell level Through the mobility management process, the MS provides its current cell information to the network The selection and reselection of the GPRS cell can be implemented by the MD or by the SGSN The cell global identification (CGI: containing RAC and LAC) is contained in the BSSGP header of the packet sent by the MS In this status, the MS can send or receive the PDP PDU and the SGSN can initiate non-GPRS paging to the MS The data sent by the SGSN is forwarded by the BSS to the GPRS cell where the MS resides In READY status, the MS can activate or deactivate the PDP context When the MS is in READY status, the paging is implemented in the cell level During the packet data transmission, the MM context is in READY status When the data transmission is complete, the MM context is still in READY status READY status is controlled by a ready timer (T3314) If the timer expires, the MM context changes from READY status to STANDBY status When the MS initiates GPRS detach, the MM context changes from READY status to IDLE status 58 Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Mobility Management Flow IDLE IDLE GPRS Attach GPRS Detach Implicit Detach or Cancel Location READY READY timer expiry or Force to STANDBY GPRS Detach or Cancel Location GPRS Attach PDU transmission READY READY timer expiry or Force to STANDBY or Abnormal RLC condition PDU reception STANDBY STANDBY MM State Model of MS MM State Model of SGSN Figure 1.1 Conversion of three status in mobility management The conversion among the status is as follows: 1) From IDLE to READY GPRS attach: The MS requires accessing the GPRS service and sets up a logical link to the SGSN The MM context is created in the MS and the SGSN respectively 2)   3)   4)  From STANDBY to IDLE Implicit detach: The MM context in the SGSN returns to IDLE status and the PDP context returns to INACTIVE status The MM and PDP contexts in the SGSN and the PDP context in the MS will be removed Location removal: After receiving a MAP location removal message from the HLR, the SGSN removes the MM and PDP contexts From STANDBY to READY PDU sending: The MS sends an LLC PDU message to the SGSN as the response to the paging PDU receiving: The SGSN receives an LLC PDU sent by an MS From READY to STANDBY Ready timer timeout: The MM contexts in the MS and the SGSN return to Confidential Information of Huawei No Spreading without Permission 59 OMQ000001 GPRS Fundamentals ISSUE 1.0   5)   Chapter GPRS Entity Information Storage STANDBY status Forced to STANDY status: Before the ready timer expires, the SGSN sends a message, indicating the MM context to return to STANDBY status Abnormal RLC: To avoid radio interface transmission failure or irrevocable radio transmission faults, the MM context of the SGSN returns to STANDBY status From READY to IDLE GPRS detach: The MS or the network requires that the MM context returns to IDLE status, and the PDP context returns to INACTIVE status The SGSN removes the MM and PDP contexts The PDP context in the SGSN is removed Location removal: After receiving a MAP location removal message from the HLR, the SGSN removes the MM and PDP contexts 8.3 GPRS Attach/Detach 8.3.1 GPRS Attach The GPRS attach falls into common GPRS attach and combined GPRS attach The common GPRS attach is to attach the IMSI of the MS to the GPRS service The combined GPRS attach is to attach the IMSI of the MS to both the GPRS and nonGPRS services Most of the current networks adopt combined GPRS attach 8.3.2 GPRS Detach The GPRS detach function enable the MS sends GPRS or IMSI detach request to the network and the network sends GPRS or IMSI detach request to the MS The detach types are as follows:    IMSI detach GPRS detach Combined GPRS/IMSI detach (initiated by MS only) The MS GPRS detach can be either explicit detach or implicit detach   Explicit detach: The network or the MS sends the explicit detach request Implicit detach: When the MS or timer expires or irrevocable radio link connection fails, the network initiates the detachment without notifying the MS In the explicit detach, a detach request (containing cause value) can be sent from the SGSN to the MS or from the MS to the SGSN The MS can implement the IMSI detach in one or two modes based on whether it is one GPRS attach The MS attached to the GPRS sends a detach request to the SGSN to notify the IMSI detach It can be applied to the combined GPRS detach to detach the IMSI of the MS that is not attached to the GPRS In the MS detach request message, there is a value indicating whether the MS is powered off This indication determines whether to return the detach acknowledge message The GPRS detach can be initiated by the MS or the network 8.4 GPRS Location Management Function The location management function provides the following: 60 Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0    Chapter GPRS Mobility Management Flow Solution of selecting the cell and PLMN Solution of obtaining the RA of the MS that is in STANDBY and READY status Solution of obtaining the cell identifier of the MS that is in READY status The MS periodically compares the CGI and RAI in the MM context with those in the message received from the system, thus generating the cell updating and RA updating requests In addition, the MS periodically initiates RA updating request The location management procedure falls into the following:    Cell updating procedure Routing area updating procedure Combined RA/LA updating procedure 8.4.1 Cell Updating Procedure 1) IDLE mode cell updating procedure when MS is in READY status When an MS that is in READY status moves from one cell to another in the same RA, the MS initiates the cell updating procedure The cell updating procedure is described as follows: The MS sends a free-type upstream LLC frame that contains the MS ID to the SGSN to initiate the cell updating procedure After receiving the LLC frame, the BSS adds the CGI (RAC+LAC) of the new cell to the header of the BSSGP frame and then sends the frame to the SGSN After receiving the BSSGP frame, the SGSN saves the CGI of the new cell to the MM context of the MS The services sent to the MS are directly transmitted to this cell 2) Transmission mode cell updating procedure when MS is in READY status During packet data transmission, if the MS finds another more suitable adjacent cell through signal measurement or cell selection parameters broadcasted on the PBCCH/BCCH, it stops receiving the system messages from the previous cell but starts to receiving the system messages from the new cell Then the MS enters this new cell and sends a CELL UPDATE message to the SGSN This message is transparently transmitted to the PCU When the SGSN receives the CELL UPDATE message and identifies that the MS is receiving the downstream packets, it sends a PURGE message (containing the BVCIs of both the previous and new cells and the TLLI of the MS) to the PCU to notify the PCU that the MS moves from one cell to another The PCU finds the previous cell through the BVCI of the previous cell After that, the PCU exports or transfers the TLLI-related LLC frames that are not transmitted or not confirmed from the previous cell to the transmission queue of the new cell After that, the PCU reallocates resources for the MS in the new cell The new TBF stream is set up for the MS in the new cell and then the data transmission is started Note: If the cell updating procedure is implemented in different BSSs, the PCU removes the TLLIrelated LLC frames from the previous cell If the data transmission is implemented in LLC confirm mode, the LLC-PDUs removed by the PCU will be retransmitted If the cell reselection procedure is implemented in LLC non-confirm mode, the LLC-PDUs removed by the PCU will be discarded 8.4.2 Routing Area Updating Procedure The RA updating procedure falls into the following: Intra-SGSN RA updating, interSGSN RA updating, intra-SGSN combined RA/LA updating, and inter-SGSN Confidential Information of Huawei No Spreading without Permission 61 OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Entity Information Storage combined RA/LA updating When the IMSI-attach and GPRS-attach MS moves to an RA that works in network operation mode I, the combined RA/LA updating occurs The RA that works in other network operation modes does not support the paging coordination, so it is meaningless for the MS to initiate the combined RA/LA updating procedure In addition, different types of MSs support different updating procedures The MS of class A initiates only the RA updating procedure rather than combined RA/LA updating procedure during the CS service The MS of class B does not initiate any updating procedure during the CS service The MS of class C never initiates the combined RA/LA updating procedure 8.4.3 Periodical RA/LA Updating Procedure All GPRS-attach MSs (except the MS of class B during the CS service) must initiate periodical RA update procedure The periodical RA updating procedure is equal to the intra-SGSN RA updating procedure (except for updating type) The IMSI-attach but GPRS-detach MS must initiate the periodical LA updating procedure For the IMSI-attach and GPRS-attach MS, the updating procedure is determined by the network operation mode:   In mode I: periodical RA updating procedure only In mode II or III: respectively the periodical RA updating procedure and periodical LA updating procedure 8.4.4 User Data Management Procedure If the user subscription data (QoS file or VPLMN address) in the HLR is modified or removed, the HLR can implement the inserting user data procedure or removing user data procedure to notify the SGSN In addition, through the inserting user data procedure the HLR can notify the SGSN to insert one or more PDP contexts or modify one or more existing PDP contexts 8.4.5 MS Class Mark Processing Function The GPRS adopts a different way from the GSM for processing the MS class mark When an MS is attached to the GPRS, its class mark contained in the MM message is sent to the network The class mark is stored in the network until the MS changes to GPRS-detach status This saves radio resources by avoiding the MS class mark being transmitted on the radio interface The MS class mark falls into the following: radio access class mark and SGSN class mark The radio access class mark indicates the MS radio access capability such as frequency band, multiple slots, and power level In addition, it indicates some other information required by the BSS to implement the radio resource management The SGSN class mark indicates other capabilities irrelevant to the radio access, such as encryption The SGSN regards the radio class mark as an information field and provides it to the BSS in each downstream BSSGP PDU The SGSN stores the SGSN class mark and transmits it to the new SGSN To improve the efficiency, the initial access stage is advanced in the specifications for 62 Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Mobility Management Flow the BSS to directly obtain the simple radio access class mark from the MS In this case, the BSS does not need to obtain the entire radio access class mark from the SGSN, thus quickly implementing transmission triggering for the MS The simplified class mark can be contained in the initial random access message or in the first upstream radio block 8.5 Security Management The security management falls into the following:    Preventing unauthenticated GPRS service application (authentication and service request confirmation) Providing subscriber identification privacy (temporary identification authentication and encryption) Providing user data privacy (encryption) 8.5.1 GPRS Authentication and Encryption The procedure of the GPRS authentication and encryption is the same as that of the GSM The difference is: In the GPRS service, this procedure is implemented by the SGSN The GPRS authentication and encryption procedure contains user authentication, encryption algorithm selection, and encryption synchronization The authentication triplet is stored in the SGSN The MSC/VLR does not authenticate the IMSI attach or location updating but implements the authentication during the CS connection setup 8.5.2 P-TMSI Reallocation The allocation of the P-TMSI is to protect the subscribe identification, that is, prevent the subscriber from being identified or located The P-TMSI is valid only within an RA Different RAs are distinguished uniquely through the RAI When the RA of an MS changes, the P-TMSI reallocation procedure must be implemented The reallocation procedure is generally after the authentication and encryption procedure is complete It can be contained in the attachment procedure or RA updating procedure 8.5.3 User Data and GMM/SM Signaling Privacy Encryption scope Compared with the GSM encryption (single local channel between BTS and MS), the GPRS implements the encryption from intra-SGSN to intra-MS The encryption is implemented at the LLC layer on radio path from the MS to the BTS in GSM mode GPRS encryption algorithm The GPRS encryption adopts a new algorithm The SGSN does not know the TDMA frame number, so it adopts the LLC frame number to replace the TDMA frame number The encryption algorithm still adopts the standard Kc management procedure Identification verification procedure The procedure of the GPRS MS identification verification is the same as that of the Confidential Information of Huawei No Spreading without Permission 63 OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Entity Information Storage GSM The difference is: In the GPRS service, this procedure is implemented by the SGSN 64 Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS Fundamentals ISSUE 1.0 Χηαπτερ Chapter GPRS Mobility Management Flow GPRS PDU Transmission Application IP / X.25 IP / X.25 SNDCP LLC RLC MAC GSM RF Um SNDCP GTP LLC UDP / TCP BSSGP Relay MS GTP relay RLC BSSGP MAC Network Service GSM RF L1bis BSS Gb UDP / TCP IP IP Network service L2 L2 L1bis L1 SGSN L1 Gn GGSN Gi Figure 1.1 GPRS PDU transmission protocol layers This section describes how the PDU is transmitted from one side of the GPRS network to the other side and how the relevant protocol is implemented when the PDU is transmitted over the interface Take the case when a PC sends an E-mail to a GPRS MS for example The application layer (the PC here) generates an IP packet and sends it to the GGSN through the external network (IP network or X.25 network) When the IP packet reaches the GGSN, it is called network packet data unit (N-PDU) The N-PDU will be transmitted orderly on the layers of the protocol stack after being added a header at each layer After a GTP header is added to the N-PDU on the GTP layer, the N-PDU becomes the G-PDU The GTP is the interface protocol bearing the N-PDU between the GSNs On the signaling platform, it specifies the channel management and control On the data transmission platform, it is used to transmit the user packet data through the established tunnel between the GSNs The tunnel is defined by the GTP header The TID of the GTP header indicates which tunnel the N-PDU belongs to The receiving GSN identifies the MM and PDP contexts through this TID Thus, the PDU is multiplexed between the GSNs through the GTP The N-PDU that contains the GTP header is transmitted to the transport layer In the GPRS specifications, the UDP/IP is used for transmitting the GTP signaling and the tunnel established on the UDP/IP connectionless path or the TCP/IP connectionoriented path is used for transmitting PDUs To be specific, the UDP/TCP layer adds the UDP/TCP header to the N-PDU The header contains the port address, flow control, and error prevention information The IP layer adds the IP header to the NPDU The header contains the sending and receiving GSN addresses, and routing information In addition, the IP layer performs the segmentation on the N-PDU to meet the maximum transmission unit (MTU) restriction of the IP layer After being added with the headers of every layer, the N-PDU is transmitted to the SGSN by physical circuits through the Gn interface When receiving the N-PDU, the protocol stack of the SGSN removes the headers layer by layer and then sends the N-PDU from the trunk layer to the SubNetwork Confidential Information of Huawei No Spreading without Permission 65 OMQ000001 GPRS Fundamentals ISSUE 1.0 Chapter GPRS Entity Information Storage Dependent Convergence Protocol (SNDCP) layer At this layer, the data is compressed and segmented to improve the channel utilization to meet the transmission requirement of the MTU of 1520 bytes at the NS layer of the Gb interface FR network The SN-PDU is classified into the connection-oriented SNDATA PAU and connectionless SN-UNIDATA PDU formats based on the transmission type (confirmation mode and non-confirmation mode) The segmentation and reassembly of the two formats are different In addition, the SNDCP implements the multiplexing (multiple PDUs use one NSAPI) and segmenting (one PDU uses multiple NSAPIs) of different types of PDUs After being added the NSDCP header, the NPDU is sent to the LLC layer The LLC layer compresses the SN-DATA PDU or SNUNIDATA PDU and then adds a header to the PDU to generate the LLC frame The LLC frame containing the SN-PDU is called LLC block The LLC layer provides a highly reliable encrypted logical link between the MS and the SGSN, which is uniquely identified by the TLLI The LLC frame header contains the control information unit, frame check sequence (FCS), and SAPI The SAPI indicates the frame associated with a certain PDP context This frame can be GMM, SMS, or SNDCP service The BSSGP interface is under the LLC layer, providing routing information for the NS layer It notifies the LLC block through which route the LLC block can access the FR physical layer The BSSGP also provides control parameters for the retransmission of the radio interface RLC/MAC The PDU is transmitted to the BSS through the Gb interface of the FR network After receiving the PDU, the BSS transfers all BSSGP information to the RLC layer The RLC layer segments the LLC block into smaller RLC block, that is, the TBFs The TBF exists only in data transmission Each TBF is uniquely identified by a TFI allocated The RLC block header added to the N-PDU contains the TFI and BSN The LLC information unit length of the RLC block is related to the coding scheme of the radio interface, that is, 22 (CS1), 32 (CS2), 38 (CS3), and 52 (CS4) Under the RLC layer is the MAC layer The MAC layer provides upstream and downstream signaling and data multiplexing It determines the contention and precedence among the channel access attempts initiated by the MSs The N-PDU is added with the MAC header and then transmitted to the MS through the radio interface physical network The MS orderly removes all headers added to the PDU based on the MS protocol and obtains the complete IP application layer data, that is, the E-mail sent by the PC 66 Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS/EDGE Fundamentals ISSUE 1.0 Appendix Frame Relay Appendix Frame Relay In the GPRS network, the Gb interface is defined between the GSS and the SGSN for the exchange of signaling information and user data In the hierarchical definition of the Gb interface protocol, layer one adopts the physical layer protocol, that is, physical circuits; layer two adopts the frame relay (FR) technology to establish the FR virtual circuit between the BSS and the SGSN for transmitting the upper-layer BSSGP PDU The FR is an important packet switching technology with complicated technical contents This appendix introduces the frame relay concept, frame relay structure, frame relay addressing, and technical features from the viewpoint of the frame relay principle A.1 Frame Relay Concept The FR is a fast PS technology developed on the basis of the X.25 PS technology It adopts the simple method at the data link layer to transmit and exchange the PDU The X.25 PS technology implements the functions of the lower three layers in OSI model while the FR only the functions of the lower two layers In addition, FR does not implement network error correction, retransmission, and flow control In this case, the processing of the network node is simplified, network throughput is improved, and communication delay is reduced The FR network is a PS network interconnected by FR switches A user (or a network, that is, FRAN) generates an FR frame through the frame relay access device (FRAD) and access the FR network The user-to-network interface (UNI) is adopted between the FRAN and the FR network The FR is based on the virtual circuit, currently, the permanent virtual circuit (PVC) The data link connection identifier (DLCI) is used to identify a PVC The DLCI in a frame structure determines which PVC this frame belongs to The network operator can provide the fixed virtual circuit to a subscriber A subscriber can apply for multiple virtual circuits Note: The virtual circuit is classified into the following: permanent virtual circuit (PVC) and switching virtual connection (SVC) The PVC is the fixed virtual circuit established between the subscribers for information transmission and exchange In SVC mode, no fixed circuit is established between the terminal users When there is a request for data transmission, the subscriber initiates the request for establishing the virtual circuit When the data transmission is complete, the request of clearing the virtual circuit is initiated Similar to the subscriber line of the telephony network, the network establishes the relevant virtual circuit through the calling request After the communication is complete, the virtual circuit is released through the signaling Virtual circuits are connection-oriented Confidential Information of Huawei No Spreading without Permission 67 OMQ000001 GPRS Fundamentals ISSUE 1.0 Appendix Frame Relay A.2 Frame Relay Structure The following figure shows the structure of a standard FR frame defined in the ITUT1.44/Q.921 recommendations Each frame is separated by a starting flag (F) of byte, similar to an X.25 frame An FR frame contains the header, information, and the trailer Compared with the X.25 frame, the FR frame header is much simplified, which reduces frame processing time | _Header _| byte byte Starting flag (F) 1~4096byte Address (A) 1 Information Information (I) 1 | Trailer _| byte 1byte FCS Ending flag (F) Figure 1.2 Frame relay frame structure Flag (F): Delimits the beginning and end of the frame The value of this field is represented as the 8-bit binary number 01111110 The flag is classified into starting flag and ending flag Data link connection identifier (DLCI): Indicates the virtual connection of the bearing path on the subscriber network interface or network interface The length of a DLCI is 10, 16, or 23 bits In the address of two bytes, the length of a DLCI address is 10 bits, ranging 0–1023 Command/Response (C/R): It is not used currently and can be set to any value Extended address (EA): It can be set to or The value means another address byte follows the current address byte The value means this is the last byte of the address field To compatible with the ISDN, channel D can only adopt the 2-byte format The following table lists the bits complying with the 2-byte format FECN BECN C/R DE EA(0) EA(1) DLCI DLCI Forward explicit congestion notify (FECN): This bit is used to notify the end user of congestion for the purpose of preventing data loss Backward explicit congestion notify (BECN): This bit is used to notify the source user there is congestion in the opposite direction from the one the frame is traveling Discard eligibility (DE): When the network is congested, the frame may be discarded for bandwidth processing When it is set to 1, it indicates discard; when it is set to 0, it indicates not discard (for frames with higher precedence) A.3 Frame Relay Working Principle The FR network is based on the PVC The PVC routing table is saved in all network node equipment When a frame accesses the network, the node equipment identifies 68 Confidential Information of Huawei No Spreading without Permission OMQ000001 GPRS/EDGE Fundamentals ISSUE 1.0 Appendix Frame Relay the direction for the frame based on the DLCI in the routing table The FR virtual circuit is an end-to-end logical link made up by multiple DLCI logical connections When user data information is capsulated into the frame and sent to the network node equipment The node equipment analyses the DLCI in the frame and then queries the PVC routing table to find the DLCI of the next PVC, thus accurately sending the frame to the next node equipment The FR network subscriber interface supports up to 1024 virtual circuits The range of the DLCIs available to subscribers is 16–1007 The following figure illustrates the FR principle with one frame of a series of them that are sent from the local terminal to the network Suppose that there is an FR terminal connected to port X and the DLCI=a before FR switching When the switch begins to receive the frame, it checks the 2-byte FCS in the trailer to see whether the FCS is correct, length is proper, and CLCI=a is allocated If any information is incorrect, the frame is discarded If all information is correct, the switch queries the routing table and finds that the frame with DLCI=a received from port X should be sent from port Y It changes the DLCI from a to b, that is, DLCI=b In this case, the FCS must be recalculated before the frame is sent From the call setup, the routing tables of all switches that the frame is traveling must contain the entries as shown in the following figure During the transmission of the frame until it reaches the destination, the DLCI of the frame varies based on different links The figure illustrates one direction only It is the same with the other direction The transmission on two directions is independent from each other and can be configured with different pass rate RF principle FCS| Data| b FCS| Data| a Routing Selection Check Table Output Input Port Port Figure 1.3 Frame relay working principle The FR network is composed of FRADs and FR switching devices (FRSDs) The FR standard defines the following applications: interface protocol, network signaling protocol, and network services A.4 Congestion Control The simple data transmission protocol of the FR provides high transparency to higher-layer protocols This is the advantage of the FR compared with the X.25 technology Since flow control and error correction are not implemented between network nodes, the congestion may easily occur in case of heavy traffic or network failure In this case, the higher-layer protocol retransmits the discarded frames, thus causing more congestion or even system down In this case, flow control must be implemented in the FR network In the FR network, end user terminals are used to implement the flow control The FR implements the following congestion control mechanisms: Confidential Information of Huawei No Spreading without Permission 69 OMQ000001 GPRS Fundamentals ISSUE 1.0 Appendix Frame Relay 1) Congestion notification Explicit congestion notification: The congestion is detected by checking whether the FECN or BECN bit is set to After detecting the congestion, the system adjusts the window size to prevent the situation To be specific, when the FR node detects that the cache or processor is overloaded, it set the FECN bit to After detecting that the rate of “FECN=1” is over the threshold value, the receiving higher-layer protocol reduces the size of the receiving window to reduce the frame sending rate On the other side, when detecting that the cache or processor is overloaded, the FR node sets the BECN to to notify the sending party to reduce the frame sending rate Implicit congestion notification: When detecting that the frame is discarded or the delay is rather long, the user terminal sends the notification for the congestion In Huawei Gb interface configuration, the PCU and SGSN set the DE, FECN, and BECN to 2) Network access restriction The three broadband network control parameters applied by subscribers when accessing the FR network are: CIR, Bc, and Be Consent information rate (CIR): It indicates the ensured transmission rate (bit/s) at a time interval Tc (measuring period) when the network operation is normal Consent burst (Bc): It indicates the allowed maximum information volume (bit) at a time interval Tc (measuring period) Exceed burst (Be): It indicates the allowed maximum information volume (bit) that exceeds Bc at a time interval Tc (measuring period) Tc = Bc/CIR The FR monitors the information volume on the virtual circuit at each time interval (Tc) It determines whether a new access request is approved based on the transmission rate and network remaining bandwidth 3) Traffic volume forced restriction The FR forcedly restricts the traffic volume The restriction principles are as follows:  Within Tc, when user data transmission volume B