Mobile 2G/3G Workshop

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Mobile 2G/3G Workshop

  1. 1. Mobility Workshop2G/3G Network ArchitectureOctober 5th, 2010
  2. 2. 2G GSM2 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  3. 3. 2G GSM Network Architecture SMSG E MSC EIR F C RAN B D BSS VLR (TDM) E HLR H EIR F AuC D Um Abis A MS BTS BSC B C MSC VLR NSS E PSTN GMSC Abis interface is comprised of multiple T1s (TDM). Signaling between elements is carried out over an SS7 or SIGTRAN (SS7oIP) network.Slide # 3 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  4. 4. GSM Node DefinitionsMS: Mobile Subscriber  The subscriber and the mobile device.BTS: Base Station Transceiver  Mobile wireless transceiver used to aggregate discrete mobile systems in the BSS.BSC: Base Station Controller  BTS aggregator and controller. Termination point for the Abis interface.BSS: Base Station Subsystem  The MS, BTS and BSC.MSC: Mobile Switching Center  Main call processing element in the mobile wireless network. Equivalent to a Class 5 switch.VLR: Visitor Location Register  A database that stores information related to the MSs associated with the MSC to which it is attached.HLR: Home Location Register  A central database that stores the subscriber information for all mobile subscribers authorized to use a given GSM network.EIR: Equipment Identity Register  A database that stores information regarding specific mobile subscriber equipment (used for blocking access and tracking stolen equipment, etc.).AuC: Authentication Center  A central database used to authenticate each SIM that attempts network access.Slide # 4 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  5. 5. GSM Interface DefinitionsA Interface  TDM interface connecting BSC to MSC. Carries all bearer and signaling traffic associated with GSM mobile services.Abis Interface  The BSS-based TDM interface connecting the BTS to the BSC.B Interface  TDM signaling interface between the MSC and VLR. Used to access subscriber account information.C Interface  Interface between the HLR and a GMSC or SMSG. Every call originating from the PSTN has to go through a gateway to obtain routing information using the MAP/C protocol.D Interface  TDM signaling interface between the VLR and HLR. Used to pass master subscriber account information from the HLR to the VLRE Interface  TDM bearer interface connecting MSCs or MSC gateways (GMSC, SMS Gateway). Used to transport voice bearer traffic.F Interface  TDM signaling interface between the MSC and EIR. Used to access equipment registration information.G Interface  Interconnects two VLRs that belong to different MSCs and uses the MAP/G protocol to transfer subscriber information (such as during a location update procedure).H Interface  TDM signaling interface between the HLR and AuC. Used to authenticate subscribers.Um Interface  The air interface used for communication between the MS and a BSS. LAPDm (modified version of ISDN LAPD), is used for signaling.Slide # 5 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  6. 6. GPRS OverviewGeneral Packet Radio Service (GPRS)  Generally referred to as 2G  Developed specifically for the transmission of data in mobile wireless networks  Maximum theoretical data rate of 171.2 kbps  Uses the same underlying RF technology as GSMCore Services  Point-to-point IP applications  Point-to-multipoint IP applications (relatively uncommon)  Internet applications for smart devices through WAP and IP  SMS  MMS  Push-to-talk over Cellular (PTT/PoC) Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  7. 7. EDGE Overview Enhanced Data rates for GSM Evolution (EDGE)  Also known as EGPRS  Generally referred to as 2.5G Characteristics:  Uses the same base RF attributes as GPRS  Enhances data rates by applying enhancement to carrier modulation – GMSK used by GSM/GPRS – GMSK + 8PSK used by EDGE – EDGE produces 3-bit words for every change in phase – Effectively triples the gross data rate – Theoretical maximum data rates: - 2 timeslots == 118.8 kbps - 4 timeslots == 236.8 kbps - 8 timeslots == 473.6 kbps – Most carriers deploy 2 or 4 timeslots and reserve the remainder for voiceSlide # 7 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  8. 8. GPRS vs. EDGE Comparison GPRS EDGE Modulation GMSK 8PSK/GMSK Symbol Rate 270 ksym/s 270 ksym/s Modulation Bitrate 270 kbps 810 kbps Radio Data Rate Per Timeslot 22.8 kbps 69.2 kbps User Data Rate Per Timeslot 20 kbps (CS4) 59.2 (MCS9) 160 kbps 473.6 kbps User Data Rate (8 Timeslots) (182.4 kbps) (553.6 kbps)Slide # 8 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  9. 9. 2.5G GPRS/EDGE Network Architecture Gi Remote Internet GTP PLMN GGSN GRX Gp SGSN Gn Gi Local PSN Internet RAN PLMN BSS Gb Gs GGSN (TDM) GTP PCU EIR Gr F D Um Abis A HLR MS BTS BSC B H MSC VLR AuC E C PSTN GMSCSlide # 9 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  10. 10. Serving GPRS Support Node (SGSN) The SGSN is responsible for delivery of packets to and from mobile stations within a geographical service area. Common SGSN Functions:  Detunnel GTP Packets from the GGSN (downlink).  Tunnel IP Packets in GTP towards the GGSN (uplink).  Carry out Mobility Management as standby mode mobile moves from one Routing Area to another Routing Area.  Billing user data.  Lawful intercept.  Encrypt down-link data, decrypt up-link data to/from mobiles.  Logical Link management  Authentication  Stores temporary data such as location information and user profiles in the serving Visiting Location Registrar (VLR).Slide # 10 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  11. 11. Gateway GPRS Support Node (GGSN) The GGSN is the main component of the GPRS core network.  GGSN is the IP anchor point for mobile data traffic  Responsible for interworking between the mobile network and external networks such as the Internet.  From the external network’s point of view, the GGSN is a router to a subnetwork. Common GGSN Functions:  Tunnels/de-tunnels GTP protocol packets from the SGSN.  Manages PDP Contexts.  Responsible for IP address assignment.  Responsible for quality of service.  Acts as default gateway for the mobile.Slide # 11 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  12. 12. GPRS/EDGE Node DefinitionsPCU: Packet Control Unit  An addition to the BSC that provides packet processing capabilities between the RAN and the SGSN.SGSN: Serving GPRS Support Node  An interworking element responsible for providing packet access between the RAN and the Packet Switched Network (PSN). Encapsulates subscriber traffic in GTP for transmission across the Gn interface.GGSN: Gateway GPRS Support Node  An IP element responsible for de-encapsulating GTP traffic from the Gn interface and interfacing with external networks (such as the Internet).GTP: GPRS Tunneling Protocol  The protocol used to tunnel user traffic across the PSN on the Gn interface.AP: Access Point  A distinct closed user group or VPN. Represents a group of users with some common criteria.APN: Access Point Name  The name used to designate a particular AP.PDP Context: Packet Data Protocol Context  The PDP Context describes the active session of an MS connected to a particular APN. The PDP Context is active on the SGSN and the GGSN.Slide # 12 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  13. 13. GPRS/EDGE interface definitionsGb Interface  A Frame Relay interface between the BSC and the SGSN.Gn Interface  IP-based interface between the SGSN and internal GGSNs. Uses GTP protocol.Gp Interface  IP-based interface between the SGSN and external GGSNs. Also uses GTP protocol.Ga Interface (not shown)  Interface that serves the Call Data Records (CDRs) which are written in the SGSN and sent to the Charging Gateway (CG). This interface uses a subset of the GTP protocol called GTP’ (GTP Prime).Gr Interface  Interface between the SGSN and the HLR. Messages going through this interface use the MAP3 Protocol.Gd Interface (not shown)  Interface between the SGSN and the SMS Gateway (SMSG). Can use either MAP1, MAP2 or MAP3.Gs Interface  Interface between the SGSN and the MSC/VLR. Uses BSSAP+ Protocol. This interface allows paging and station availability when it performs data transfer. When the station is attached to the GPRS network, the SGSN keeps track of which Routing Area (RA) and Location Area (LA) to which the station is attached. When a station is paged this information is used to conserve network resources. When the MS initiates a PDP Context, the SGSN knows which BTS the MS is attached to.Gi Interface  The IP-based interface between the GPRS/EDGE network and the Internet.Slide # 13 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  14. 14. GPRS Tunneling Protocol (GTP) GPRS Tunneling Protocol (GTP) is a group of IP-based protocols used to carry data traffic within GSM and UMTS networks. GTP is really composed of 3 separate protocols:  GTP-C – The control portion of the GTP standard. When a subscriber requests a PDP Context, the SGSN sends a Create PDP Context Request message to the GGSN. The GGSN will respond with a Create PDP Context Response message. – UDP port 2123  GTP-U – The user portion of the GTP standard that is used to tunnel IP traffic within and between mobile operator networks. Each subscriber may have one or more tunnels to support different connections or different quality of service requirements. – UDP port 2152  GTP’ (pronounced GTP Prime) – The charging data portion of the GTP standard. Used to transfer charging data from the SGSNs and GGSNs to the Charging Gateway Function (CGF). – TCP or UDP port 3386Slide # 14 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  15. 15. PDP Context The Packet Data Protocol (PDP) Context is a data structure which contains the subscriber’s session information when an active session exists on the network. It usually contains the following:  Subscriber’s IP address  Subscriber’s IMSI (International Mobile Subscriber Identity)  Subscriber’s Tunnel Endpoint ID (TEID) at the SGSN  Subscriber’s Tunnel Endpoint ID (TEID) at the GGSN The TEID is a random number allocated by the SGSN/GGSN which identifies the tunneled data related to a particular PDP Context. 2 kinds of PDP Contexts:  Primary – Has a unique IP address associated with it.  Secondary – Shares an IP address with the Primary Context. – Created based on the Primary Context. – Secondary PDP contexts may have different quality of service settings.Slide # 15 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  16. 16. Access point Name (APN) 3GPP has the concept of virtual private networks that represent communities of interest. These VPNs are called Access Points (APs) and are identified by Access Point Names (APNs).  An APN defines a service description and routing for GPRS/EDGE/UMTS data.  All traffic within and APN is routed in a similar manner.  When an SGSN sends user traffic in a GTP tunnel, it sends that traffic to a GGSN that services the APN the subscriber’s traffic belongs to. Examples of APNs:  wap.cingular  epc.tmobile.com  blackberry.net  pp.vodafone.co.ukSlide # 16 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  17. 17. SGSN-to-GGSN Routing How does an SGSN know which GGSN serves a particular APN?  APN names look suspiciously like DNS name… and this is precisely what it is.  When an SGSN wants to connect a subscriber to an APN, it performs a DNS lookup on the APN name (e.g. wap.cingular)  This query is sent to a special DNS infrastructure called Gn DNS.  The IP address returned by the Gn DNS is the destination address of the nearest serving GGSN. – Note that in order to scale the network and provide geo-redundancy, the Gn DNS may return different results depending on the source IP address of the SGSN. – Examples: - SGSNs from Region 1 have source IP addresses in the 172.16.1.0/24 range. - SGSNs from Region 2 have source IP addresses in the 172.16.2.0/24 range.  Gn DNS is a globally-connected infrastructure. – More details on this will be covered in the section on Data Roaming.Slide # 17 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  18. 18. Data RoamingNotice that Home PLMN•IP Anchor (GGSN) is in the home network•SGSN is in the visited network•LI and Charging can be done in both networks HLR Service Center Internet GGSN SS7/SIGTRAN Gn DNS GTP 3 PCU SGSN Root Gn DNSMS BTS BSC 2 1 GRX Gn DNS Visited PLMN Slide # 18 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  19. 19. 3G UMTS Copyright © 2009 Juniper Networks, Inc. www.juniper.netSlide # 19 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  20. 20. UMTS Family Air Interface Technologies UMTS - Universal Mobile Telecommunications System Wideband Code Division Multiple Access (W-CDMA)  Introduced in 3GPP R99  Max theoretical data rate of 1.92 Mbit/s in the downlink High-Speed Downlink Packet Access (HSDPA)  Based on 3GPP R5  Improves downlink data rate to speeds up to 14Mbit/s  Majority of deployments provide up to 7.2 Mbit/s in the downlink High-Speed Uplink Packet Access (HSUPA)  Based on 3GPP R6  Enhanced to increase the uplink data rate up to 5.8 Mbit/s Evolved High Speed Packet Access (HSPA+)  Based on 3GPP R7 & R8  Data rates up to 42 Mbit/s in the downlink and 11 Mbit/s in the uplink (per 5 MHz carrier)  Supports Multiple Input, Multiple Output (MIMO) technologiesSlide # 20 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  21. 21. 3G UMTS network architecture (R4)IuX Interfaces are ATM-based: Gi RemoteIuPS = AAL5 GTP Internet PLMNIuCS = AAL2 GGSN GRX Gp SGSN Gn Gi Local UTRAN PSN Internet PLMN IuPS Gs GGSN GTP EIR Uu IuB IuCS(S) HLR MS NodeB RNC MSCS VLR AuC IuCS(B) NxT1 ATM IMA MGW PSN PSTN MGWSlide # 21 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  22. 22. 3G UMTS network architecture (R5+)IuX Interfaces are IP-based Gi • Changes the Backhaul Routing and Internet Remote GTP PLMN Aggregation requirements • MX supports ethernet but not the (older) GGSN GRX ATM interfaces Gp SGSN Gn Gi Local UTRAN PSN Internet PLMN IuPS Gs GGSN GTP EIR Uu IuB IuCS(S) HLR MS NodeB RNC MSCS VLR AuC IuCS(B) MGW PSN PSTN MGWSlide # 22 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  23. 23. 3G UMTS network architectureNotes1. The IP anchor can be either in the home or visited network. • Pay attention this will come up again in LTE • Multiple concurrent APNs are generally not used in 3G Gi2. Later releases support “direct tunnel” which GTP Internet Remote PLMNallows the bearer traffic to bypass the SGSN GGSN • Greatly reduces SGSN bearer load GRX • Some bearer (e.g. LI and Roaming) still must go through the SGSN. Gp SGSN Gn Gi Local UTRAN PSN Internet PLMN IuPS Gs GTP GGSN Gn EIR GTP Uu IuB IuCS(S) HLR MS NodeB RNC MSCS VLR AuC IuCS(B) NxT1 ATM IMA PSN MGW PSTN MGW Slide # 23 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  24. 24. UMTS Node Definitions UE  User Equipment (the mobile device). NodeB  Analogous to the BTS in the GSM/GPRS BSS, the NodeB is responsible for Ue aggregation. Uses W-CDMA for the air interface. Radio Access Controller (RNC)  Analogous to the BSC in the GSM/GPRS BSS, the RNC aggregates Iub traffic from the NodeBs in a particular region of the RAN.  Responsible for air encryption, mobility management (handover), and voice/data transmission to the circuit-switched and packet-switched core. Call Server  A cut-down version of the MSC that is disassociated with the bearer path to reduce size and cost. Responsible for all voice signaling functions. Media Gateway (MGW)  The element responsible for interworking voice traffic between and among formats (e.g. ATM AAL2 RTP/IP).Slide # 24 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  25. 25. UMTS Interface definitions Uu  Air interface connecting the UE to the NodeB. IuB  An ATM interface (R4) or IP interface (R5+) between the NodeB and RNC carrying all voice and data bearer and signaling traffic. IuR  An ATM interface (R4) or IP interface (R5+) connecting RNCs to one another. AN RNC may operate as an S-RNC (Serving RNC), D-RNC (Drift RNC), or C- RNC (Controlling RNC) Iu-PS  An ATM interface (R4) or IP interface (R5+) connecting the RNC with the SGSN. Used to transmit UE data traffic to the packet core. Iu-CS  An ATM interface (R4) or IP interface (R5+) connecting the RNC with the Call Server (Iu-cs(S)) and MGW (Iu-cs(B)). Used to transmit UE voice traffic (signaling and bearer) to the circuit core.Slide # 25 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  26. 26. Introduction to Handoff in 2G and 3G Target cells and all that fun stuff… Dang! These guys keep moving on me! Why dont they stand still and take their calls like a man!?Slide # 26 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  27. 27. The Simple Stuff- User is moving but not connected Re-selection (Packet Example) HLR 1. Mobile is “camped” on cell 1 2. Mobile device collects data on signal q Internet strength of nearby cells. GGSNPSTN 3. Mobile sees that cell 2 has a better signal MSC o and meets reselection criteria. SGSN n 4. Mobile tells network it is relocating. Rnc 5. Network accepts (or rejects) m 6. SGSN is updated for paging if needed (if the paging area changes). j 7. If SGSN needs to change with the cell this there is a proceedure. k jl k 8. IF needed HLR is updated so the user can be found for paging. (I.E. if SGSN is changes). 9. If this causes a change of SGSNs then the old SGSN tells the new SGSN and the HLR For more detail see: 3GPP TS 23.060 V10.0.0 Section 6.9 Page 80
  28. 28. Cell Update Examples This slide for Reference only(23.060 section 6.9) MS BSS new SGSN old SGSN GGSN HLR 1. Routeing Area Update RequestMS BSS SGSN 2. SGSN Context Request 1. Routeing Area Update Request 2. SGSN Context Response 2. Security Functions 3. Security Functions (A) 3. Routeing Area Update Accept 4. SGSN Context Acknowledge C1 4. Routeing Area Update Complete C1Intra SGSN Routing Area Update Procedure 5. Forward Packets 6. Update PDP Context Request (B) 6. Update PDP Context Response 7. Update Location 8. Cancel Location 8. Cancel Location Ack 9. Insert Subscriber Data 9. Insert Subscriber Data Ack 3GPP TS 23.060 V10.0 Section 6.9 10. Update Location Ack C2 11. Routeing Area Update Accept C3 12. Routeing Area Update Complete Inter SGSN Routing Area Update Procedure
  29. 29. Hard Handoff 2G Example Internet GGSN Connection is broken with original cellPSTN and established to a new (target) cell. MSC SGSN • Short interruption in bearer occurs • Generally not obvious to voice user BSC • Used for 2, 3 and 4G systems Internet GGSN PSTN MSC SGSN 1. Mobile device collects data on signal strength of nearby Cells 2. BSC sees current cell getting weak and target cell BSC getting strong. 3. BSC instructs mobile to retune to a new cell 4. Mobile breaks connection to old cell, retunes, and announces its presence on the new cell. 5. Bearer stream is sent to new cell. Slide # 29 Copyright © 2009 Juniper Networks, Inc. www.juniper.net
  30. 30. Soft Handoff 3G Example Internet Soft Handoff: GGSN • UE may be able to communicate with two cellsPSTN • Symbols (data) may be collected from both cells MSC SGSN • Downlink data is sent to both cells • Frame selector chooses best symbol on a symbol by symbol basis • Eventually one path becomes clearly better Frame Selector and the other path is dropped. • Used for most handoffs in 3G. Not used in RNC 2G or 4G Slide # 30 Copyright © 2009 Juniper Networks, Inc. www.juniper.net

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