Chap01 gprs intro_03_kh


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Chap01 gprs intro_03_kh

  1. 1. Chapter 1 The GPRS Network Contents: 1.1 GPRS and GSM 1. GPRS and GSM 1.2 Network elements and functions 1. The GSM PLMN 2. GPRS Network Architecture 3. Functions of GGSN 4. Functions of SGSN 5. Additional PS core entities 6. Modifications for GPRS in the BSS 7. GPRS MS 1.3 Services and Network evolution 1. GPRS Network Services 2. Network evolution into GERAN 3. GERAN reference architecture (Rel 5) 1
  2. 2. Chapter 1.1 The GPRS Network 1.1 GPRS and GSM 1. GPRS and GSM 2
  3. 3. GPRS and GSM higher flexibility on High Speed Circuit Enhanced Enhanced radio interface! Switched Data (HSCSD) Data rates Circuit for GSM Switched channel bundling Evolution Data 115.2 (EDGE) (ECSD) up to higher kbps efficiency new coding schemes: up to 14.4 kbps/TS 348 higher new up to kbps throughput modulation and GSM coding Phase 2+ General Packet Radio schemes Enhanced Service (GPRS) General Packet channel bundling 171.2 up to Radio kbps Service new coding schemes: (EGPRS) up to 21.4 kbps/TS + capacity on demand 476 + multiplexing of subscribers up to kbps on one phy. channel 3
  4. 4. The GSM PLMNThe GSM Public Land Mobile Networks (PLMN) consists out of a Network Switching Subsystem (NSS) and aBase Station System (BSS). NSS A E BTS TC MSC/VLR GMSC Ater PSTN C Ext BSC F DMS BTS Abis BSS (H) EIR HLR AuC SCP CSE SMSC SS7Main element in the NSS is the Mobile Switching Center (MSC) which contains the Visitor Location Register (VLR).The MSC represents the edge towards the BSS and on the other side the Gateway MSC (GMSC), the connectionpoint to all external networks, like the Public Switched Telephone Network or ISDN. GSM is a circuit switchednetwork, there are physical links to transport control information (signalling) and user data. The signalling links areSS7 based and circuits (voice channels) are switched through the MSC (or GMSC).HLR Home Location Register, a main database that contains data for each subscriber like IMSI, MSISDN, subscribed services, access rights etc.EIR Equipment Identity Register, if supported, may be integrated in the HLR.AuC Authentication Center, provides Authentication Triplets for every subscriber to perform authentication and ciphering (performed by MSC/VLR).SCP Service Control Point, a database for Intelligent Network services.CSE CAMEL Service Entity, a database for PLMN specific Intelligent Services, e.g. charging of roaming subscribers.SMSC Short Message Service Center, used for transfer of short messages. 5
  5. 5. GPRS Network Architecture GERAN NSS BSS E Ext BTS A MSC/VLR GMSC Ater TC PSTN BSC BTS PCU Abis F D C BTS Home Subscriber Gs (H) EIR HLR AuC Server (HSS)MS Rel 5 BSS BTS TC Gf Gc Gr GPRS PS Core Network BTS Abis BSC Gb Gn IPvX PCU SGSN backbone GGSN ISP BTS Gi 6
  6. 6. Functions of GGSN GMSC Gateway GGSN Gateway GPRS Support Node Mobile services Switching Centre • signalling evaluation (SS7) • signalling evaluation (IP header) • switching (cs traffic) • routing and tunneling of packet data (ps traffic) • operational tasks incl. • operational tasks incl. - collection of traffic statistics - collection of traffic statistics - alarms - alarms - generation of charging records - generation of charging records • interrogation of HLR • interrogation of HLR • often interfacing external networks, such as • interfaces external IP networks PSTN, ISDN • Interfaces internal IP network (IP BB) • Allocates dynamic or static IP addresses to mobiles either by itself or with the help of a DHCP or a RADIUS server Gateway GPRS Support Node is an IP router that provides access to various PDP networks, 7 e.g. the Internet
  7. 7. Functions of SGSN (V)MSC/VLR SGSN Visited MSC/ Serving Visitor Location GPRS Support Node Register • signalling evaluation (SS7) • signalling evaluation (IP header) • switching (cs traffic) • routing (ps traffic) • operational tasks incl. • operational tasks incl. - collection of traffic statistics - collection of traffic statistics - alarms - alarms - generation of charging records - generation of charging records • Mobility Management, incl. authentication, • GMM (GPRS Mobility Management), incl. authorisation, location area updates authentication, authorisation, routing area updates • Connection Management, incl. call control, SMS, supplementary • SM (Session Management), services incl. PDP (Packet Data Protocol) context management and SMS • Paging (CS) • Paging (PS –and CS as option) • Protocol conversion between IP backbone and BSS protocols e.g. data compression for IP-Header and IP payload (V.42 bis, RFC 1144). 8
  8. 8. Additional PS core entities Domain Name Server: DNS used to convert IP names into IP GPRS PS Core Network addresses or vice versa. Border Gateways: BGs are to interconnect operators GPRS backbone networks via a secure SGSN IPvX GGSN BG connection to support roaming backbone Charging Gateway: DNS LIG BG CG GPRS charging data records (CDR) are generated by SGSNs and GGSNs, and sent to the CG via interface Billing Ga. Inter-PLMN LEA Network Centre The Charging Gateway •collects all this data together CG •processes it •passes it to the Billing SystemLawful Interception Gateway: •Lawful interception is an action based on the law, which is performed by the GPRS network •It provides information for a Law Enforcement Agency (LEA) about some pre-defined target subscriber •Information could include •data sent and received by the interception target •location information LIG •subscriber information •etc. 9
  9. 9. Modifications for GPRS in the BSS BTS BSC site SGSN site CCU Abis Gb PCU CCU Ater PCU The PCU (Packet Control Unit): Performs radio specific functions (Radio Resource Management) •       Manages sub-multiplexing of multiple MS on one physical channel •       Decides which radio resources are dynamically allocated to packet switched or circuit switched use •       Is responsible for packet segmentation and re-assembly •       Guarantees reliable link to MS •       Terminates Gb interface In most vendors implementation the PCU is a part of the BSC, in principle it could be as well a standalone module or integrated in the BTS. Channel Codec Unit: CCU BTS SW upgrade for new Coding Scheme (CS 1-4 or CS 1+2). 10
  10. 10. GPRS MS simultaneous • attach Simultaneous CS and PS • activation class • attach class • monitor • invocation A • activation • monitor B • traffic class of GSM and GPRS pure GPRS or no simultaneous alternative use of C traffic GSM and GPRS onlyA class A MS may be attached to the CS and PS core simultaneously. While the MS is in packet transfer modeand there is an incoming call the MS can continue its packet session while making the call and enters the DualTransfer Mode (DTM). DTM requires additionally support by networks (BSS).A class B MS may be attached to the CS and PS core simultaneously. While the MS is in packet transfer modeand there is an incoming call the MS can take the call, the packet transfer has to be suspended and resumedafter the call is finished.A class C MS may be attached to the CS or PS core. While the MS is in packet transfer mode there can be noincoming call. Usually these MSs are PCMCIA cards. 11
  11. 11. GPRS Network ServicesThe objective of this training are the (E)GPRS signalling protocols, and to show, how a user data packet is transmitted through the GPRS network. The user data transmission can be seen from two points of view:• end users point of view: The subscriber wants to exchange user data packets between the mobile terminal (MT) attached to his MS (or internal) and an application server, located in a PDN. Application Server users point of view GPRS ISP ISP GGSN Inter- MS net Router• operators point of view: Router The operator is especially responsible to transmit the user data from one access point of the PLMN to another. The access points to and from the PLMN are the MS and the GGSN. The operator is required to offer a certain Quality of Service (QoS) in order to enable new services. Services are categorized into (Rel 99) Interactive class BSS NSS ISP Background class IP Streaming class PCU SGSN backbone GGSN 13 Conversational class
  12. 12. Network evolutions into GERAN 2G Network Support of Interactive and Support of streaming (Rel 4) and Background PS Services (Rel 99) conversational PS Services (Rel 5) GERAN (GSM/EDGE Radio Access Network) HSCSD ECSD In order to deliver the required QoS for a certain service the GSM existing networks are enhanced. ETSI standardized the GSM radio EGPRS interface and defined GSM, GPRS, GPRS classic EDGE access to PS Core Network (Rel 97, 98 ,99). Due to aspects of harmonization and interworking with 3G the specifications has been moved to 3GPP. Rel 99 has TDMA/136 + been adopted by 3GPP. Since then the GSM access network is referred to as GERAN. The evolution of GERAN is done in Rel TDMA/136HS EGPRS 4, 5, 6,... (along with the evolution TDMA/136 Outdoor compact of CN entities). Currently Rel 4, 5 and 6 features are adopted in order to fullfil the TDMA/136HS requirements for new services indoor 14
  13. 13. GERAN Reference architecture (Rel 5) Enhanced -Interactive, compared to Rel 99 GERAN -Background, (Support of Realtime BSS -Streaming Packet services) PS Services Iur-g Um A MS BTS To 2G CN (A/Gb mode) BSC Gb required for Rel 4 or older MSs MS BTS IuCS To 3G CN (Iu mode) Iur-g (cancelled) BSS IuPS -Interface carries only control signalling-no user Iur-g -Interactive, data -Background, -improved interworking UTRAN IuCS -Streaming To GERAN-UTRAN RNC 3G -Conversational IuPS -Radio specific CN PS Services procedures handled completely inside RAN GSM/UMTS Core Network A MS may operate in Gb mode (class A, B or C MS) or Iu mode. For Iu mode the MS may operate • CS/PS mode: correspondends to Class A in A/Gb mode • PS mode: MS can only operate packet switched services • CS mode: MS can only operate circuit switched services 15