GPRS System Survey GPRS Overview We are Developing Produced by:

GPRS System Survey GPRS Overview We are Developing Produced by:
MSC Performance Group Operations and Engineering Department Vodafone Egypt We are Developing GPRS System Survey GPRS Overview How are you?

Contents Chapter 1 : Introduction to GPRS
Chapter 2 : GPRS Air Interface Chapter 3 : GPRS BSS Chapter 4 : GPRS Backbone Network Chapter 5 : Traffic Cases Chapter 6 : GPRS Charging

Chapter 1 : Introduction to GPRS

The Future : Data or Voice ?
Introduction to GPRS The Future : Data or Voice ? GPRS System Survey Introduction to GPRS All telecommunication network operators are providing to their customers both voice and data services. PSTN networks allow their subscribers to dial up to the internet. ISDN networks are specially designed to enhance the PSTN capabilities in data transmission. ADSL Leased lines are increasing. GSM networks provide SMS, WAP and Data transmission services. Can we predict the demand and future growth of data communication ?

Some past predictions Introduction
GPRS System Survey Introduction to GPRS I think there is a world market for maybe five computers Thomas Watson, Chairman of IBM 1943 There is no reason anyone would want a computer in his home Ken Olson, Chairman of Digital Equipment Corp. 1977 640 K (RAM) ought to be enough for anybody Bill Gates 1981

The Future : Data or Voice ?
Introduction The Future : Data or Voice ? GPRS System Survey Introduction to GPRS Tbit/ day 150 Data 125 100 75 Voice 50 25 1998 1999 2000 2001

Mobiles & Internet Parallel Growth
Introduction Mobiles & Internet Parallel Growth GPRS System Survey Introduction to GPRS 1,000 800 600 (millions) Mobile Internet 400 The New Telecoms World 200 1996 1998 2000 2002 2004

Penetration Rates of Mobile Phone Users
Introduction Penetration Rates of Mobile Phone Users GPRS System Survey Introduction to GPRS Year - end 1998

Data Communication over GSM
Introduction Data Communication over GSM GPRS System Survey Introduction to GPRS Circuit switched. Services available only when connected. Consumes large resources of the telecommunication operator.

Data Communication over GSM
Introduction Data Communication over GSM GPRS System Survey Introduction to GPRS GSM provides 4 types of services Voice service. SMS service Fax service. Data service

Limitations of GSM data services
Introduction Limitations of GSM data services GPRS System Survey Introduction to GPRS 1. Slow data rates PSTN networks provide rate of 56 kb/s to its users ISDN networks provide multiples of 64 kb/s to its users What was the initial rate offered by GSM networks ? 9.6 kbps

Introduction Limitations of GSM data services GPRS System Survey Introduction to GPRS 1. Slow data rates Enhancements of GSM data rates: HSCSD Introducing GSM Phase 2+ allows for Multi-slot capability, a service known as High Speed Circuit Switched Data, HSCSD. Using this service allows the assignment of maximum 4 circuit switched time slots to the same user over the air interface. Thus the rate of 4 x 9.6 = 38.6 kbps is achievable The capability of the MS to use this service is dictated by a feature called the Multi-Slot Class of the MS. It decides how many timeslots will be assigned to the MS in each direction. For Internet Model, the uplink and downlink assignment may not be symmetric. i.e Timeslots assigned in the Rx direction are greater than those assigned in the Tx direction.

Introduction Limitations of GSM data services GPRS System Survey Introduction to GPRS 1. Slow data rates Enhancements of GSM data rates: Coding Schemes Channel Coding is used in the aim of attaining a reliable data link over the air interface. This is achieved by adding extra bits to the actual bits to be sent. These bits will be used to detect the presence of errors and order retransmission. Coding Scheme 1 (CS1) was the first CS to be used and it adds a large number of coding bits causing the user rate to be low. Rate of data over GSM using this CS is 9.6 Kbps To increase the rate more data will be sent Instead of strong error correction. This makes the link less reliable but increases the rate. Coding Scheme 2 (CS2) uses a less number of coding bits allowing the user rate to reach 14.4 Kbps.

Introduction Limitations of GSM data services GPRS System Survey Introduction to GPRS 1. Slow data rates Enhancements of GSM data rates: HSCSD + Coding Schemes Combining the effect of of the HSCSD and CS2 will jump with the rate to reach 14.4 x 4 = 57.6 kbps which is comparable to the PSTN rate. Yet, this bit rate is still low for some applications and consumes large number of resources creating congestion situations plus, the service will be expensive to the user.

Introduction Limitations of GSM data services GPRS System Survey Introduction to GPRS 2. Data transfer Communication : Circuit Switching B C A D

Introduction Limitations of GSM data services GPRS System Survey Introduction to GPRS 2. Data transfer Communication : Packet Switching B Info C Info Info A D

Circuit Switched or Packet Switched
Introduction Circuit Switched or Packet Switched GPRS System Survey Introduction to GPRS Circuit Switched communication is suitable for data traffic where one or more of the following cases apply: Constant band width data flow Sensitivity to even small connection delays. For example, circuit switched communication should be used for video conferences. Packet Switched communication is suitable for data traffic where one or more of the following cases apply: Data sent in bursts Sensitivity to errors. For example packet switched communication should be chosen for , dispatch traffic, telemetry applications and point of sale.

General Packet Radio Services
Introduction General Packet Radio Services GPRS System Survey Introduction to GPRS As the mobile data market develops, users will seek out high performance mobile networks that provide optimal handling of “bursty” data applications, with alternative tariffing i.e. volume based rather than time based charging. GPRS will address these user needs.

What is GPRS ? Introduction
GPRS System Survey Introduction to GPRS GSM-PLMN IP Enhancement of GSM data transfer capabilities A new set of bearer services A new kind of “data-pipe” Focus on IP-interworking Quality of Service categories Packet switching technology Efficient use of air interface resources Volume based Charging Always connected High data rate

GPRS End-user Benefits
Introduction GPRS End-user Benefits GPRS System Survey Introduction to GPRS Always connected, always on-line No need for frequent log on/log off Easier to access data services Higher speeds Volume based charging New application

GPRS Operator Benefits
Introduction GPRS Operator Benefits GPRS System Survey Introduction to GPRS New packet data services Attract various segments Efficient radio usage Low investment cost New business model Content Exclusivity E-commerce Wireless ISP Connectivity Bearer services Full Service Provider (FSP)

GPRS Applications Introduction
GPRS System Survey Introduction to GPRS Applications & services now used with a fixed network, can be used anywhere. Mobility will enable completely new applications & services. The parallel developments in software and hardware technology will be the key factors in the acceptance of these applications by the market.

GPRS Applications: Remote Office
Introduction GPRS Applications: Remote Office GPRS System Survey Introduction to GPRS Users get access to their corporate intranet in Europe from a mine site in South-East Asia. They can read files and download information, just as if they were in the office. GPRS enables this because it is based on the TCP/IP protocol, the same as the Internet and intranets.

GPRS Applications: Cars
Introduction GPRS Applications: Cars GPRS System Survey Introduction to GPRS GPRS makes it easy to send information to and from cars. Drivers could subscribe to a service for traffic updates, maps, travel information as well as Internet access. Car manufacturers and dealers could check up on vehicles remotely, and inform the driver when the next service is due.

GPRS Applications: Image Transfer
Introduction GPRS Applications: Image Transfer GPRS System Survey Introduction to GPRS The GPRS packet data platform is ideal for ensuring the integrity of the image and reducing cost. The journalist does not pay for online time only for the data transmitted.

Other GPRS Applications
Introduction Other GPRS Applications GPRS System Survey Introduction to GPRS Vending Machines ATM Banking Machines Connectivity Download billboard advertisement Mobile access to medical data

Point To Point (PTP) Applications
Introduction Point To Point (PTP) Applications GPRS System Survey Introduction to GPRS Typical PTP Applications Messaging (e.g. ). Remote (and mobile) access to corporate networks. Internet WEB-browsing. Credit card validation (point of sales). Utility meter readings (e.g. electricity, water). Road toll applications. Automatic Train Control (ATC).

Point To Multipoint (PTM) Applications
Introduction Point To Multipoint (PTM) Applications GPRS System Survey Introduction to GPRS Typical PTM Applications PTM multicast (PTM-M) Message to any subscriber located within a geographical area. No knowledge about which subscribers that will get the message. Anyone can be a subscriber of a certain group. PTM group (PTM-G) Message to a given set of subscribers located in a geographical area. Complete control over which subscribers that will get the message. Only appointed members can be a subscriber of a certain group.

Horizontal and Vertical Applications
Introduction Horizontal and Vertical Applications GPRS System Survey Introduction to GPRS

Horizontal and Vertical Applications
Introduction Horizontal and Vertical Applications GPRS System Survey Introduction to GPRS Horizontal Vertical Business Internet Intranet/Wan access /Fax Database Access Conferencing Voice IP phone Consumer /messaging Internet access E-commerce News Operations Job Dispatch Delivery Fleet Management Taxi Police Field Service Emergency Field Sales Automation Car tolls Telemetry Vending machines Meter reading Surveillance Position tracking

GSM and TDMA/AMPS Coverage
Introduction GSM and TDMA/AMPS Coverage GPRS System Survey Introduction to GPRS January 1999

3G Data Transfer Time Introduction GPRS System Survey
Introduction to GPRS

GPRS Architecture Introduction Gr Gd Internet Gf PLMN Corporate LAN Gi
GPRS System Survey Introduction to GPRS HLR AUC SMSC Gd Gp Gf Gr Gb Gi Gn X.25 Network Corporate LAN Internet EIR ISDN PLMN PSTN SGSN GGSN GWMSC MSC/VLR Gs IP Backbone network PLMN BSC/TRC + PCU BSC/TRC Traffic BTS TE MT Signaling

GPRS Interfaces Introduction Gr Gd Internet Gf Corporate LAN Gs
GPRS System Survey Introduction to GPRS HLR AUC SMSC Gr X.25 Network Corporate LAN Internet Gd EIR Gf SGSN GGSN MSC/VLR Gs IP Backbone network PLMN SS7 MAP Gr Register Interface Gf Fraud Interface Gd Data Interface BSC/TRC + PCU SS7 BSSAP+ Gs Switching System Interface

GPRS Interfaces Introduction Internet Corporate LAN X.25 Network Gb
GPRS System Survey Introduction to GPRS HLR AUC SMSC X.25 Network Corporate LAN Internet EIR SGSN GGSN MSC/VLR Gb IP Backbone network PLMN BSSGP over Frame Relay Gb BSS Interface BSSGP . NSC Frame Relay E1 BSC/TRC + PCU

GPRS Interfaces Introduction GTP over IP Gn Network Interface GTP .
GPRS System Survey Introduction to GPRS HLR AUC SMSC GTP over IP Gn Network Interface GTP TCP/UDP . IP p Eth/FR/ATM X.25 Network Corporate LAN Internet EIR SGSN GGSN MSC/VLR Gi IP Gi Internet Interface Application . TCP/UDP . IP p Eth/FR/ATM IP Backbone network PLMN Gn BSC/TRC + PCU Gp

GPRS Architecture Introduction Terminal Equipment (TE)
GPRS System Survey Introduction to GPRS Terminal Equipment (TE) The Terminal Equipment is the computer terminal that the end-user works on. This is the component used for the GPRS system to transmit and receive end-user packet data. The TE could be for example a laptop computer. The GPRS system provides IP connectivity between the TE and an Internet Service Provider or Corporate LAN connected to the GPRS system. From the TE point of view, you could compare the MT to a modem, connecting the TE to the GPRS system.

GPRS Architecture Introduction Mobile Terminal (MT)
GPRS System Survey Introduction to GPRS Mobile Terminal (MT) The Mobile Terminal (MT) communicates with a TE, and over the air with a BTS. The MT must be equipped with software for the GPRS functionality when used in conjunction with the GPRS system. The MT is associated with a subscriber in the GSM system. The MT establishes a link to an SGSN. Channel reselection is provided at the radio link between the MT and the SGSN. The IP connection is static from the TE point of view, that is the TE is not aware of being mobile and retains its assigned IP address until the MT detaches.

GPRS Architecture Introduction Mobile Station (MS)
GPRS System Survey Introduction to GPRS Mobile Station (MS) The combination of a TE and an MT is a MS (Mobile Station). The term MS is used when discussing the GPRS features. It can be concluded from the context which parts would relate to the MT or the TE parts. Note that the MT and TE parts could actually be in the same piece of equipment.

GPRS Architecture Introduction Mobile Classes
GPRS System Survey Introduction to GPRS Mobile Classes GPRS MSs can operate in three different modes depending on the MS and the network capabilities: Class A mode of operation It allows a MS to have a circuit switched connection at the same time as it is involved in a package transfer. Class B mode of operation It allows a MS to be attached to both CS and PS but it can not use both services at the same time. However, MS that is involved in a package transfer can receive a page for circuit switched traffic. The MS can then suspend the packet transfer for the duration of the circuit switched connection and afterwards resume the package transfer. Class C mode of operation It allows an MS only to be attached to one service at the time. An MS that only supports GPRS and not circuit switched traffic will always work in class C mode of operation.

GPRS Architecture Introduction Base Station System (BSS)
GPRS System Survey Introduction to GPRS Base Station System (BSS) The Base Station System (BSS) consists of a Base Station Controller (BSC) and a Base Transceiver Station (BTS). The BTS is the radio equipment which transmits and receives information over the air to let the BSC communicate with MSs in the BSCs service area. A group of BTSs is controlled by a BSC. The BTS must contain GPRS-specific software. The BSC provides all the radio-related functions. The BSC has the functionality to set up, supervise and disconnect circuit-switched and packet-switched calls. It is a high capacity switch that provides functions including handover, cell configuration data, and channel assignment. The BSC must be equipped with GPRS hardware and software when used for GPRS. One or several BSCs are served by an MSC, and a number of BSCs are served by an SGSN. The BTS separates the MS-originated circuit-switched calls from packet data communication, before the BSC forwards CS calls to the MSC/VLR, and PS data to the SGSN. The protocols towards the BSC are standard GSM protocols, for the desired compatibility.

GPRS Architecture Introduction Mobile Services Switching Center (MSC)
GPRS System Survey Introduction to GPRS Mobile Services Switching Center (MSC) The Mobile services Switching Center (MSC) performs the telephony switching functions of the GSM circuit-switched system, like the SGSN switches the GSM packet-switched traffic. It controls calls to and from other telephony and data systems, such as the Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Public Land Mobile Network (PLMN), Public Data Networks, and possibly some private networks. The SGSN Routing Area (RA) is a subset of the MSC (CS) Location Area (LA). The SGSN Routing Area is the part of the network that is covered by one SGSN. An MSC Location Area is a group of BSS cells. The system uses the LAs to search for subscribers in the active state. An LA is the part of the network in which a MS may move around without reporting its location to the network. There can be several MSCs corresponding to one SGSN. One MSC can also be connected to several SGSNs.

GPRS Architecture Introduction
GPRS System Survey Introduction to GPRS Visitor Location Register (VLR) Functionality in SGSN and in MSC The Visitor Location Register (VLR) database contains information about all mobile stations currently located in the MSC location area or SGSN routing area respectively. The SGSN contains the VLR functionality for packet-switched communication. Similarly, Ericsson MSC contains the circuit-switched VLR as an integrated part. The VLR contains temporary subscriber information needed by the MSC or SGSN to provide services for visiting subscribers. When a mobile station roams into a new MSC location area or SGSN routing area, the VLR of that MSC or SGSN requests and stores data about the mobile station from the HLR. If the mobile station makes a call at another time, the VLR will then already have the information needed for that call setup.

GPRS Architecture Introduction
GPRS System Survey Introduction to GPRS Visitor Location Register (VLR) Functionality in SGSN and in MSC The Gs interface is used for dealing efficiently with terminals that are attached to both GPRS (Packet-Switched) and to GSM (Circuit-Switched) traffic. The Gs interface thus connects the databases in the MSC/VLR and the SGSN. The Gs interface is used to coordinate the location information of MSs that are attached to both GPRS and the CS network. The Gs interface is also used to convey some CS procedures via the SGSN. An example is that the Class-A and Class-B MSs connect to the MSC/VLR over the SGSN via the combined CS and PS Mobility Management procedures, if there is a Gs interface. The Gs interface is essential for supporting the Network operation mode I and Mobile Station (MS) mode of operation A and B. This includes combined IMSI and GPRS attach and detach, identification and mobility management.

GPRS Architecture Introduction Serving GPRS Support Node (SGSN)
GPRS System Survey Introduction to GPRS Serving GPRS Support Node (SGSN) The Serving GPRS Support Node (SGSN) is a primary component in the GSM network using GPRS and is a new component in GSM. The SGSN forwards incoming and outgoing IP packets addressed to/from a mobile station that is attached within the SGSN service area. The SGSN provides: Packet routing and transfer to and from the SGSN service area. Ciphering and authentication, Session management Mobility management Logical link management towards the MS Connection to HLR, MSC, BSC, SMS-GMSC, SMS-IWMSC, GGSN Output of charging data. The SGSN collects charging information for each MS related to the radio network usage.

GPRS Architecture Introduction Gateway GPRS Support Node (GGSN)
GPRS System Survey Introduction to GPRS Gateway GPRS Support Node (GGSN) Like the SGSN, GGSN is a primary component in the GSM network using GPRS and is a new component. The GGSN provides: The interface towards the external IP packet networks. Therefore it contains access functionality that interfaces external ISP functions like routers and RADIUS servers (Remote Access Dial-In User Service). From the external IP network’s point of view, the GGSN acts as a router for the IP addresses of all subscribers served by the GPRS network. The GGSN thus exchanges routing information with the external network GPRS session management; communication setup towards external network Functionality for associating the subscribers to the right SGSN Output of charging data. The GGSN collects charging information for each MS, related to the external data network usage.

GPRS Architecture Introduction The Co-Located SGSN and GGSN
GPRS System Survey Introduction to GPRS The Co-Located SGSN and GGSN The SGSN and GGSN functionalities may be combined in the same physical node (network element), or they may reside in different physical nodes.

GPRS Architecture Introduction Home Location Register (HLR)
GPRS System Survey Introduction to GPRS Home Location Register (HLR) The Home Location Register (HLR) is the database that holds subscription information for every person who has bought a subscription from the GSM/GPRS operator. The HLR stores information for CS and for PS communication. The HLR contains information about supplementary services, authentication parameters, and whether or not packet communication is allowed. In addition, the HLR includes information about the location of the MS. For GPRS, subscriber information is exchanged between HLR and SGSN. Note that the authentication triplets for GPRS are fetched directly from the HLR to the SGSN, i.e. does not use the MSC/VLR like for CS GSM.

GPRS Architecture Introduction SMS-GMSC and SMS-IWMSC
GPRS System Survey Introduction to GPRS SMS-GMSC and SMS-IWMSC The Short Message Service Gateway MSC (SMS-GMSC) and Short Message Service Inter-working MSC (SMS-IWMSC) are connected to the SGSN to enable GPRS MSs to send and receive SMS over GPRS radio channels. The Short Message Service Center (SC or SM-SC) is connected to the GPRS network via the SMS-GMSC and the SMS-IWMSC. The SMS-MSCs are not changed for GPRS use.

Chapter 2 : Air Interface

Air Interface Routing Area GPRS System Survey Air Interface

Air Interface GPRS Protocol Stack GPRS System Survey Air Interface

Multi-frame Structure
Air Interface Multi-frame Structure GPRS System Survey Air Interface Header User Data Packet Network Layer Header Tail Information field LLC PDU LLC Layer RLC Information RLC Header USF BCS RLC Information RLC Information Header USF BCS Radio Blocks RLC/MAC Layer Ciphering is performed between the MS and the SGSN directly over the LLC layer unlike the GSM. The MS is making cell selection and reselection on its own. It represents the logical link between the MS and the SGSN even though the MS moves from one BSC to another. LLC adds the Temp. Logical Link Identifier TLLI. Normal Burst GSM RF (Physical Layer) B0 B1 B2 T B3 B4 B5 I B6 B7 B8 B9 B10 B11

Um Interface MAC (Medium Access Control) Air Interface
GPRS System Survey Air Interface MAC (Medium Access Control) It controls the access signaling across the air interface, including shared transmission resources management (assignment of the radio block to multiple users on the same timeslot). MAC achieves these functionalities by placing a header in front of the RLC header in the RLC/MAC data and control blocks. The MAC header contains several elements,some of which are direction-specific, referring to the downlink or uplink.

Um Interface MAC (Medium Access Control) Air Interface
GPRS System Survey Air Interface MAC (Medium Access Control) The key parameters of MAC header are: Uplink status flag (USF),is sent in all downlink RLC/MAC blocks and indicates the owner or use of the next uplink radio block on the same timeslot. Relative reserved block period (RRBP),identifies a single uplink block in which the mobile phone will transmit control information. Payload type (PT),the type of data (control block or data block)contained in the remainder of the RLC/MAC block. Countdown value (CV),is sent by the mobile to allow the network to calculate the number of RLC data blocks remaining in the current uplink TBF.

Um Interface Um Interface MAC (Medium Access Control) Air Interface
GPRS System Survey Air Interface GPRS System Survey Air Interface MAC (Medium Access Control) TS 4 5 6 7 USF 1 USF=3 f1 B0 B1 B2 T B3 B4 TS6 BTS PCU TS 4 5 6 USF 2 3 f1 B0 B1 B2 T B3 B4 Data TS 5 6 7 USF 2 3

Um Interface RLC ( Radio Link Control ) Air Interface
GPRS System Survey Air Interface RLC ( Radio Link Control ) It is responsible for a number of functions: Transferring LLC-PDUs between the LLC layer and the MAC function Segmentation of LLC-PDUs into RLC data blocks and re-assembly of RLC data blocks to fit into TDMA frame blocks Segmentation and re-assembly of RLC/MAC control messages into RLC/MAC control blocks Backward error correction for selective transmission of RLC data blocks.

Um Interface RLC ( Radio Link Control ) Air Interface
GPRS System Survey Air Interface RLC ( Radio Link Control ) The RLC segmentation function is a process of taking one or more LLC-PDUs and dividing them into smaller RLC blocks. The LLC-PDUs are known collectively as a temporary block flow (TBF) and are allocated the resources of one or more packet data channels (PDCH). The TBF is temporary and is maintained only for the duration of the data transfer. Each TBF is assigned a temporary flow identity (TFI)by the network. The RLC data blocks consist of an RLC header, an RLC data unit, and spare bits. The RLC data block along with a MAC header may be encoded using one of four defined coding schemes.The coding scheme is critical in deciding the segmentation process.

Um Interface RLC ( Radio Link Control ) Air Interface All use TS 6
GPRS System Survey Air Interface RLC ( Radio Link Control ) TFI = 1 f1 B0 B1 B2 T B3 B4 TS6 Data TFI 1 BTS PCU All use TS 6 TFI 2 TFI 3

Air Interface Scheduling GPRS System Survey Air Interface

Um Interface RLC / MAC Data Block Air Interface GPRS System Survey

Um Interface RLC / MAC Control Block Air Interface GPRS System Survey

456 bits in each radio block
Air Interface Channel Coding GPRS System Survey Air Interface Radio Block Header Info bits + Coding bits M bits in RLC/MAC block 456 - M bits of Coding 456 bits in each radio block Coding Max no of info bits Max data rate per TS (kbps) Target C/I (dB) CS-1 CS-2 CS-3 CS-4 160 241 293 401 8 12 14 20 ~6 ~9 ~12 ~17

Logical Channels Air Interface
GPRS System Survey Air Interface A number of new logical channels, similar to the existing ones, but for GPRS only, have been standardized. The logical channels are mapped onto the physical channels that are used for dedicated packet data. These physical channels are called Packet Data Channel (PDCH). The logical channels in GPRS are divided into: Packet Common Control Channels Packet Broadcast Channel Packet Traffic Channels

Logical Channels Air Interface Packet Common Control Channels
GPRS System Survey Air Interface Packet Common Control Channels PRACH Packet Random Access Channel Uplink PPCH Packet Paging Channel Downlink PAGCH Packet Access Grant Channel Downlink PTCCH Packet Timing advance Control Channel Uplink / Downlink PNCH Packet Notification Channel Downlink Packet Broadcast Channel PBCCH Packet Broadcast Control CHannel Downlink Packet Traffic Channels PDTCH Packet Data Traffic Channel Uplink / Downlink PACCH Packet Associated Control Channel Uplink / Downlink BNCH are used for PTM-G services. e.g When we want to inform a set of mobiles that preemption will take place. Not implemented yet.

Logical Channels Air Interface
GPRS System Survey Air Interface In Ericsson terminology, a Packet Data Channel (PDCH) carrying PCCCH and PBCCH is called the Master PDCH If master PDCH is present the following channels will be available in the cell: PRACH PPCH PAGCH Master PDCH can carry PDTCH and PACCH

GPRS System Information
Air Interface GPRS System Information GPRS System Survey Air Interface BCCH GPRS supported or not on the cell. GPRS Radio Resources allocated or not. The position of the PDCH carrying PBCCH and PCCCH. PBCCH GPRS BA list, Frequency Hopping information. Cell Selection parameters. MS Power Control parameters. Discontinuous Reception (DRX) parameters. Discontinuous Reception (DRX) parameters.  Corresponding to MFRMS in GSM used for paging groups and sleeping periods.

PDCH Allocation Air Interface
GPRS System Survey Air Interface f1 1 2 3 4 5 6 7 f2 BTS f3 f4 BSC / PCU The PCU is responsible for assigning channels to the different GPRS MSs. The PDCHs can be allocated in different ways: Dedicated: allocated and released by operator command. On-demand: serving as temporary dynamic GPRS resources. Allocated and released depending on GPRS traffic demand. RLGSC:FPDCH=,CELL=; PDCH carrying PCCCH Master PDCH PDTCH CCCH, TCH or free time slot

GPRS System Survey Air Interface Channels that are allocated for GPRS (PDCH) are allocated in sets of maximum four consecutive time slots. Such a set is called a PSET, and can consist of both dedicated and on-demand PDCH. All channels in a PSET are on the same frequency or hop the same frequency hopping set. A mobile station can only be assigned PDCHs from one PSET. At present this limits the maximum number of assigned time slots to four. There is no additional limit on the number of PDCHs that can be allocated in a cell, except the number of available TCHs.

GPRS System Survey Air Interface f1 1 2 3 4 5 6 7 f2 BTS f3 f4 BSC / PCU 4 5 6 7 MS 1 TS 4,5,6,7 on f4 In this example, each time slot will serve 3 subscribers. This means that the timeslot will carry information belonging to 3 different TBFs. Block: ROEPC TBFDLLIMIT 8 TBFULLIMIT 6 MS 2 MS 3 MS 1 MS 4 MS 2 TBF LIMIT TS 4,5,6 on f4

GPRS System Survey Air Interface Maximum TBF limit in the uplink direction is 6 Maximum TBF limit in the downlink direction is 8

PDCH Allocation Air Interface Dedicated PDCH
GPRS System Survey Air Interface Dedicated PDCH Dedicated PDCHs can only be used for GPRS. The operator can specify zero to eight dedicated PDCHs per cell. Dedicated PDCHs ensure that there are always GPRS resources in a cell. The operator can specify to some extent where he wants his dedicated PDCH(s) to be located. From a radio point-of-view, non-hopping channels on the BCCH (Broadcast Control Channel) carrier are generally not equivalent to quality to traffic channels on other frequencies. The BCCH frequencies may have a separate frequency plan, and bursts on the BCCH frequency are not power-regulated. The operator can decide if the PDCH shall be allocated on the non-hopping BCCH frequency as primary or secondary choice, or with no preference. BCCH is non hopping so its C/I is low The coding scheme determines the quality of service and CS1 can use low C/I .. In this case it will be better to allocate the BCCH carrier to the GPRS with CS1 and benefit from hopping to the GSM calls. Command RLGSC determines the preference.

PDCH Allocation Air Interface On-demand PDCH
GPRS System Survey Air Interface On-demand PDCH On-demand PDCH can be pre-empted by incoming circuit switched calls in congested cells. There is no physical limit on how many on-demand PDCHs there can be in a cell. The number of on-demand PDCHs depends on how much packet switched traffic there is, up to the limit where circuit switched traffic starts to preempt PDCH due to congestion. In a cell without any circuit switched traffic it would be possible to use all channels for GPRS traffic. A load supervision function is implemented so that in a cell with or without dedicated PDCH, new on-demand PDCHs are allocated when the number of GPRS users becomes too high

PDCH Allocation Air Interface Master PDCH
GPRS System Survey Air Interface Master PDCH A Master PDCH (MPDCH), is a PDCH carrying a PBCCH and a PCCCH, as well as GPRS traffic. The PCCCH carries all the necessary control signaling to initiate packet transfer. The first dedicated PDCH that is allocated according to the operator’s preferences regarding non-hopping BCCH will be configured as an MPDCH. The following PDCHs that are allocated will only carry GPRS traffic and associated signaling. If the operator decreases the number of dedicated PDCHs, the MPDCH is kept as long as there is at least one dedicated PDCH in the cell. In a cell with no MPDCH (no dedicated PDCH allocated) the ordinary control channels, like BCCH, RACH etc, will handle the broadcasting and signaling to the GPRS mobiles.

PDCH Allocation Air Interface Master present or not
GPRS System Survey Air Interface Master present or not The operator can decide if there shall be an MPDCH in a cell or not. In a cell with no MPDCH, the MS will listen to BCCH and PCH (Packet Channel) for broadcast information and paging messages. The paging message will contain information to distinguish CS pages from PS pages. The MS sends access bursts on the RACH. The MS specifies in this message if it is a request for a CS or a PS connection. Information about the allocated resources is then sent on the AGCH to the MS. In a cell with an MPDCH allocated, an MS only reads the BCCH to get information about the physical channel where the PBCCH and the PCCCHs can be found. The MS then listens to the PBCCH to get all system information it needs. The MS will listen to the PPCH for paging messages. The MS sends access bursts on the Packet Random Access Channel (PRACH) for request for PS services, but on the RACH if the request is for a CS service. The GPRS traffic and associated signaling, however, is always transmitted on GPRS-specific channels, regardless of whether an MPDCH is allocated or not.

Air Interface Multi-Slot Classes GPRS System Survey Air Interface

PS resources Allocation Strategy
Air Interface PS resources Allocation Strategy GPRS System Survey Air Interface TBF

CS resources Allocation Strategy
Air Interface CS resources Allocation Strategy GPRS System Survey Air Interface

GPRS MS States and Modes
Air Interface GPRS MS States and Modes GPRS System Survey Air Interface There are three GPRS mobility management states Idle state : The MS is turned on but not GPRS attached. The MS is “invisible” to GPRS network , e.g. if the MS is outside the coverage area for GPRS. Ready state : A packet transfer is ongoing or has recently ended. A ready timer defines how long time the MS shall remain in ready state after a transfer before being in the standby state. The time is decided by SGSN and can take values from zero to infinity. The MS sends cell update to SGSN every time it changes cell. In ready state there is no need to send a page to the MS. SGSN sends the LLC frames to the PCU and the PCU sends an assignment to the MS immediately, since the location is known. Standby state : The MS is GPRS attached and sends routing area updates to the SGSN every time it changes Routing Area. The SGSN knows the state of all MSs that are in standby or ready state.

Air Interface GPRS MS States and Modes GPRS System Survey Air Interface Idle Idle Standby timer Expiry GPRS Attach GPRS Detach Standby timer Expiry or Cancel Location GPRS Attach GPRS Detach Or Cancel Location Ready Ready Ready Timer Expiry or Force to STANDBY LLC PDU Transmission Ready Timer Expiry or Force to STANDBY Abnormal RLC Condition LLC PDU Reception Standby Standby MM State Model of MS MM State Model of SGSN

Air Interface GPRS MS States and Modes GPRS System Survey Air Interface

TLLI and NSAPI Air Interface TLLI Temporary Logical Link Identifier
GPRS System Survey Air Interface NSAPI TLLI TLLI Temporary Logical Link Identifier NSAPI Network Service Access Point Identifier

Air Interface TLLI and NSAPI GPRS System Survey Air Interface

Packet Transfer Air Interface Network Operation Mode
GPRS System Survey Air Interface Network Operation Mode The network may provide coordination of paging for circuit-switched and packet-switched services. Paging coordination means that the network sends paging messages for circuit-switched services on the same channel that is used for packet-switched services (on the GPRS paging channel or on the GPRS traffic channel), and the MS only needs to monitor that channel. Three network operation modes are defined: Network operation mode I Network operation mode II Network operation mode III

Packet Transfer Air Interface Network Operation Mode I
GPRS System Survey Air Interface Network Operation Mode I The network sends CS paging message for a GPRS-attached MS, either on the same channel as the GPRS paging channel (i.e. the packet paging channel or the Common Control Channel, CCCH, paging channel), or on a GPRS traffic channel. This means that the MS must only monitor one paging channel, and that it receives CS paging messages on the packet data channel when it has been assigned a packet data channel.

Packet Transfer Air Interface Network Operation Mode II
GPRS System Survey Air Interface Network Operation Mode II The network sends CS paging message for a GPRS-attached MS on the CCCH paging channel, and this channel is also used for GPRS paging. This means that the MS must only monitor the CCCH paging channel, but that CS paging continues on this paging channel, even if the MS has been assigned a packet data channel.

Packet Transfer Air Interface Network Operation Mode III
GPRS System Survey Air Interface Network Operation Mode III The network sends CS paging message for a GPRS-attached MS on the CCCH paging channel, and sends a GPRS paging message on either the packet paging channel (if allocated in the cell) or on the CCCH paging channel. This means that an MS that wants to receive pages for both circuit-switched and packet-switched services must monitor both paging channels if the packet channel is allocated in the cell. The network performs no paging coordination.

Packet Transfer Air Interface
GPRS System Survey Air Interface RAEPC:ID=GPRSNWMODE; Exchange Parameter Mode I Paging Coordination exist Gs interface exist Mode II No Paging Coordination No Gs interface No master PDCH Mode III No Paging Coordination No Gs interface Master PDCH exist

Packet Transfer Air Interface Paging
GPRS System Survey Air Interface Paging When an MS in class A or class B mode of operation is attached to both GPRS and CS, and the Gs interface between MSC and SGSN is available, the MSC sends the pages to the SGSN, via the Gs interface, instead of directly to the BSC. Since the SGSN knows the location of the MS on cell level when it is in ready state and on routing area level otherwise, the paging area will be of same size or smaller than when the page is sent directly to the BSC. SGSN sends the page to the affected PCU(s) with information of the cell or routing area. If the MS is involved in a packet transfer, the PCU sends the page on the control channel associated with the packet transfer, PACCH. Otherwise the page is sent out on PPCH, or on PCH if PPCH is not available.

Packet Transfer Air Interface Paging
GPRS System Survey Air Interface Paging It is possible to have a network without a Gs interface. In this case the MSC sends the page directly to the BSC. If the MS is in GPRS MS standby state, the downlink packet transfer is initiated by paging the MS in a Routing Area. This is initiated by the SGSN sending a BSSGP Paging Request to the PCU. The PCU will then calculate which paging group to which the MS belongs, and send the paging request in a time slot when the MS is awake (listening). The MS responds to the page by sending a Paging response message to the SGSN. This is done using the uplink packet transfer procedure. The message is transparent to BSS and looks like an ordinary LLC frame. The MS is now in ready state and the SGSN can start to send LLC frames to the PCU with the cell and MS identity. The SGSN repeats the Paging up to 5 times. As a result of the Paging response the MS state will change from S/B to ready.

Packet Transfer Air Interface
GPRS System Survey Air Interface Discontinuous Reception and Paging Groups Max 704 paging groups (15 Seconds) 81 groups in GSM In GPRS the MS can select the Paging Group by negotiation the DRX value with the SGSN In GSM it is an IMSI property

Establishment of uplink TBF
Air Interface Establishment of uplink TBF GPRS System Survey Air Interface The MS has no TBF established If an MS has no TBF established, the MS sends a Packet Channel Request message to the PCU. In the Ericsson implementation there are two main ways to allocate resources after receiving a Packet Channel Request message from the MS: The MS is assigned resources on one or several timeslots for a longer time using the dynamic allocation method. For each timeslot, the MS is assigned a value of the Uplink State Flag (USF). The TFI is used in signaling to identify the MS. This is called a one-phase access. A single timeslot is reserved for the sending of one RLC block. This can be used to let the MS send a Packet Resource Request message, to further specify its capabilities and/or demands. This is called a two- phase access. The single RLC block could also be used when the MS only has a very short LLC frame to send. At two-phase access, the MS sends a Packet Resource Request on the allocated timeslot. With the new information received, the PCU assign resources and sends a new Packet Uplink Assignment to the MS.

Air Interface Establishment of uplink TBF GPRS System Survey Air Interface The MS has no TBF established

Air Interface Establishment of uplink TBF GPRS System Survey Air Interface The MS has a downlink TBF If the MS already has a downlink TBF established, the MS sends a Packet Resource Request message on the control channel associated with the downlink TBF, the Packet Associated Control Channel (PACCH). The PCU has to consider the downlink allocation when allocating uplink resources. The Packet Uplink Assignment message is then sent to the MS on the PACCH.

Establishment of downlink TBF
Air Interface Establishment of downlink TBF GPRS System Survey Air Interface When the PCU receives LLC frames from the SGSN, the PCU checks whether the addressed MS is already involved in a packet transfer. The checking result may be that: The MS is in the Standby Mode The MS has a downlink TBF The MS has an uplink TBF The MS is ready but has no TBF established

Air Interface Establishment of downlink TBF GPRS System Survey Air Interface The MS is in the Standby mode If the MS is in GPRS standby state, the downlink packet transfer is initiated by paging the MS in a Routing Area. This is initiated by the SGSN sending a BSSGP Paging Request to the PCU. The PCU will then calculate which paging group the MS belongs to and send the paging request in a timeslot when the MS is awake (listening). The MS responds to the page by sending a Paging response message to the SGSN. This is done by use of the uplink packet transfer procedure. The message is transparent to BSS and looks like an ordinary LLC frame. The MS is now in ready state and the SGSN can start to send LLC frames to the PCU with the cell and MS identity. Non DRX mode. The MS will be ready after Paging response. The PCU doesn’t need to wait for the MS turn to send the assignment, instead it will send the assignment on the first vacant access grant block (Replacing any paging block).

Air Interface Establishment of downlink TBF GPRS System Survey Air Interface The MS has a downlink TBF If the MS already has a downlink TBF, the new LLC frame is put in the queue with the other LLC frames to that MS.

Air Interface Establishment of downlink TBF GPRS System Survey Air Interface The MS has an uplink TBF If the MS already has an uplink TBF, the PCU has to take this into consideration. Probably the PCU will allocate downlink resources on the same time slots (or at least partially) as the MS has uplink resources. This makes it possible for the MS to use both the uplink and downlink resources at the same time. The MS multi-slot class notes the capability of the MS regarding how many PDCH it can handle in each direction at the same time. The Packet Downlink Assignment message is sent on the control channel that is associated with the uplink assignment, the Packet Associated Control Channel (PACCH).

Air Interface Establishment of downlink TBF GPRS System Survey Air Interface The MS is ready but has no TBF established If the MS has no TBF established, a Packet Downlink Assignment message is sent on a timeslot that the MS listens to, according to its paging group. A certain time after the MS has been involved in a packet transfer it remains in non-DRX mode. That means that it is awake and there is no need to wait for its paging group. The message can be sent immediately. The Packet downlink assignment message consists of a list of the channels that will be used and a TFI to address the MS.

Acknowledgement Air Interface
GPRS System Survey Air Interface Radio blocks can be sent in acknowledged or unacknowledged RLC mode. Actually Ack/Nack messages are sent in both modes, but packets are only retransmitted over the air interface in acknowledged RLC mode. The reason for sending acknowledgements in unacknowledged mode can be several: To check that the communication has not been broken. To get knowledge about the transmission quality, in order to use the coding scheme that gives the best performance. To prioritize MS depending on link quality.

Air Interface Acknowledgement GPRS System Survey Air Interface

Ending a TBF Air Interface Ending a downlink TBF
GPRS System Survey Air Interface Ending a downlink TBF When there are no more LLC frames to a certain MS in the PCU (but there may be more in the SGSN), the downlink TBF is released. If a new LLC frame arrives immediately after, a new assignment corresponding to a new TBF is sent to the MS. The MS is still in ready state, so there is no need to page the MS. Ending an uplink TBF When the MS has only a few more RLC blocks to send, this is signaled to the network, and a countdown procedure begins. After all blocks have been sent and acknowledged, the uplink TBF is released. If the MS has more packets to send after the countdown procedure has been initiated, a new TBF has to be established. The MS is not allowed to continue to send more packets than it had when initiating the countdown procedure.

Air Interface Ending a TBF GPRS System Survey Air Interface

Cell Selection and Reselection
Air Interface Cell Selection and Reselection GPRS System Survey Air Interface Comparing GPRS with circuit switched In a GSM network the BSC governs the cell selection behavior of MS in idle and active mode by different methods. Idle mode MSs autonomously perform cell reselection by using the C1/C2 criteria. In active mode, non-GPRS MSs are steered by the locating functionality implemented in the BSC. That means that the BSC initiates handovers to other cells. In GPRS, the MS determines the base station with which it will communicate. GPRS MS manages both the idle packet and transfer packet mode behaviors.

Air Interface Cell Selection and Reselection GPRS System Survey Air Interface Comparing GPRS with circuit switched

Air Interface Cell Selection and Reselection GPRS System Survey Air Interface The cell selection and reselection algorithms used for controlling idle/transfer mode behaviors are governed by GPRS cell selection and reselection parameter settings broadcast in the packet system information on PBCCH in each GPRS capable cell with allocated PBCCH (MPDCH). If no PBCCH is allocated in a cell, the GPRS MS will read the system information broadcast on BCCH and use the C1/C2 criteria for cell selection and reselection as in the circuit switched idle mode case. The GPRS cell selection and reselection algorithms are governed by parameter settings. These parameters, C31 and C32, are different from the corresponding parameters for the circuit switched case. In Ericsson implementation, GPRS cell selection parameters are automatically mapped on those for cell selection/locating known from the circuit switched case. This achieves the same cell selection behavior for GPRS and enables an easy rollout of GPRS in the network. The standard allows the network to take over cell reselection for a specific MS or for all MS. This is called Network Controlled Cell Reselection and is not implemented.

Air Interface Cell Selection and Reselection GPRS System Survey Air Interface Cell reselection, a small traffic case In this example, the MS is involved in a downlink packet transfer. The MS discovers that another cell is a better choice according to its own measurements and to the cell selection parameters broadcast on PBCCH or BCCH. The MS stops listening to the old cell and starts to read the necessary system information in the new cell. Then the MS accesses the new cell and sends a cell update to the SGSN. This message is transparent to the PCU. The SGSN receives the cell update and discovers that there was already an ongoing downlink packet transfer. The SGSN sends a flush message to the PCU responsible for the old cell. The flush message contains the addresses of both the old and the new cell, as well as the MS identity.

Air Interface Cell Selection and Reselection GPRS System Survey Air Interface Cell reselection, a small traffic case The PCU checks whether it is also responsible for the new cell. If the PCU is responsible for the new cell, all buffered LLC frames that have not been acknowledged or not sent are moved to a queue towards the new cell. The PCU assigns new resources to the MS in the new cell and transmission is restarted. If the PCU is not responsible for the new cell, it will delete all LLC frames destined to that MS and leave the retransmission to higher layers.

Power Regulation Air Interface Cell reselection, a small traffic case
GPRS System Survey Air Interface Cell reselection, a small traffic case Open loop MS power control is implemented. The value of the parameter Gamma is set per cell by the operator. The value of the Parameter Alpha is set per BSC. Alpha and Gamma are used with the received power signal strength to decide its output signal strength.

Quality of Service Profile
Air Interface Quality of Service Profile GPRS System Survey Air Interface There are a number of parameters defined as QoS parameters or attributes. The following concerns BSS: Precedence Class. At congestion, all packets with the lowest class are discarded. Then packets with the second lowest class are discarded, etc. This is not implemented in BSS. Reliability Class. The part that concerns BSS is the RLC Block mode. Both acknowledged and unacknowledged mode supported. Peak Throughput Class. Maximizes the throughput for a MS. Nothing is guaranteed. This is not implemented in BSS. Radio Priority HGPDI. Check parameter QOS

Chapter 3 : GPRS BSS

Structure and Interfaces of BSS
GPRS BSS Structure and Interfaces of BSS GPRS System Survey GPRS BSS BSC SGSN PCU CCU Gb Abis PCU Packet Control Unit (Hardware and Software) CCU Channel Control Unit (Software) The PCU is responsible for packet routing in the BSC. It implements the following protocol layers: Physical layer of the Abis interface. Radio Link Control (RLC) and Medium Access Control (MAC) layers of the Um interface. Gb interface towards SGSN.

The PCU, Simplified GPRS BSS E1/T1 Gb interface GPRS System Survey
GPRS Signaling Links (GSL)

Network Service Control (NS Control)
GPRS BSS Gb Protocol Stack GPRS System Survey GPRS BSS BSSGP Network Service Control (NS Control) Network Service Frame Relay E1 T1 L1 bis

GPRS BSS Frame Relay GPRS System Survey GPRS BSS A layer-2 protocol specified for accessing Wide Area Networks. Error correction and flow control is the responsibility of the higher layers. High throughput and small delays due to small overheads and simple switching mechanisms. Statistical multiplexing and port sharing. Dynamic bandwidth allocation. Suitable for use on digital-transmission technology over high quality reliable transmission links.

GPRS BSS Frame Relay GPRS System Survey GPRS BSS

Frame Relay Virtual Circuits
GPRS BSS Frame Relay Virtual Circuits GPRS System Survey GPRS BSS Frame relay technology is based on the concept of using Virtual Circuits (VCs). VCs are two-way, software-defined data paths between two endpoints There are two types of Frame Relay Virtual Connections: Permanent Virtual Circuits (PVC) PVCs are set up and released manually by the network operator on a permanent basis. They have two operational states: Data Transfer and Idle. Used by GPRS Switched Virtual Circuits (SVC) SVCs are set up and released automatically by the network on a call-by- call basis. They have four operational states: Call Setup, Data Transfer, Idle and Call Termination. Not used by GPRS

How does the Frame Relay work ?
GPRS BSS How does the Frame Relay work ? GPRS System Survey GPRS BSS Check the integrity of the frame using the Frame Check Sum (FCS). If it indicates an error, discard the frame. Look up the DLCI in the distribution table of the node. If the DLCI is not defined for this link, discard the frame. Relay the frame towards its destination by sending it on the outgoing port or trunk specified in the distribution table.

Frame Relay Routing GPRS BSS Virtual Connection 1 Virtual Connection 2
GPRS System Survey GPRS BSS Virtual Connection 1 Virtual Connection 2 Virtual Connection 3 LAN Router DLCI 3 B DLCI 2 DLCI 5 DLCI 6 A C DLCI 1 DLCI 8 DLCI 4 DLCI 9 DLCI 7 Router LAN Router LAN Router LAN

Network Service Control
GPRS BSS Network Service Control GPRS System Survey GPRS BSS NS Control adds GPRS specific node management functionality to Frame Relay PVCs. It identifies one end-to-end NSVC for each Frame Relay PVC. It provides load sharing function to distribute BSSGP traffic on the available NSVCs between the PCU and the SGSN. It identifies one NSE for every PCU, and identifies in the SGSN as many NSEs as the number of PCUs connected to it. An NSE communicates over the Gb interface with only one peer NSE using the same NSEI. BSSGP Network Service Control (NS Control) Network Service Frame Relay E1 T1 L1 bis

Network Service Control
GPRS BSS Network Service Control GPRS System Survey GPRS BSS BSC1 BSC2 BSC3 SGSN NSEI=1 NSEI=2 NSEI=3 NSVCI=1 DLCI=100 DLCI=105 DLCI=107 DLCI=106 NSVCI=2 DLCI=108 DLCI=109 NSVCI=3

BSS GPRS Protocol (BSSGP)
GPRS BSS BSS GPRS Protocol (BSSGP) GPRS System Survey GPRS BSS BSSGP identifies, for every cell in the BSC, an end-to-end communication path between the PCU and the SGSN that is called PtP-BVC. These BVCs are used for traffic routing to/from the cells, Each PCU will have a signaling BVC towards the SGSN, which will carry the BSSGP management messages used for establishment of the PtP-BVCs. The traffic for all the BVCs is multiplexed automatically on the available NSVCs.

BSSGP Virtual Connections
GPRS BSS BSSGP Virtual Connections GPRS System Survey GPRS BSS

Chapter 4 : GPRS Backbone

Introduction GPRS Backbone Internet GPRS Backbone network Intranet
GPRS System Survey GPRS Backbone Billing System NMS SGSN GPRS Backbone network GGSN Internet FW Corporate LAN BG GSGSN Intranet Server PLMN FW DNS

Internet Protocol GPRS Backbone
GPRS System Survey GPRS Backbone IP is a connectionless protocol that is primarily responsible for addressing and routing packets between network devices. Connectionless means that a session is not established before data is exchanged. IP is quite unreliable because packet delivery is not guaranteed. IP makes what is termed a ‘best effort’ attempt to deliver a packet Also an acknowledgement is not required when data is received. Thus it doesn’t keep copy of the sent packets. Instead it fires and forgets the packets. Packets then, may be lost, delivered out of sequence, duplicated or delayed. The sender or receiver is not informed when a packet is lost or out of sequence. The acknowledgement of packets is the responsibility of a higher-layer transport protocol, such as the Transmission Control Protocol (TCP). IP is also responsible for fragmenting and reassembling packets.

Internet Protocol GPRS Backbone IP IP IP Packet Packet Packet
GPRS System Survey GPRS Backbone Host B Host A Reliability and sequencing Reliability and sequencing IP Fires and forgets IP Routes if possible IP Delivers as received Network Interface Network Interface Packet Packet Packet Fragments

Internet Protocol Suite and OSI Model
GPRS Backbone Internet Protocol Suite and OSI Model GPRS System Survey GPRS Backbone Application FTP,TELNET,DNS, SNMP,SMTP Transport TCP or UDP Internet Protocol Network Interface LAN-ETH,TR,FDDI WAN-Serial Lines,FR,ATM

IP Packet Structure GPRS Backbone IP Header 20 Bytes Long 1 Byte
GPRS System Survey GPRS Backbone 1 Byte Version IHL Type of Service Total Length Identification Flags Fragment Offset IP Header 20 Bytes Long Time To Live Protocol Header Checksum Source Address Destination Address Options + Padding Data

Internet Header Length (IHL)
GPRS Backbone IP Packet Structure GPRS System Survey GPRS Backbone Field Length in Bits Description Version 4 Specifies version of the IP protocol, and hence format of the IP header being used, for example IPv4 or IPv6. This field can also be used with IPsec. Internet Header Length (IHL) Length of header in 32-bit words. Minimum value is five, which is the most common header. Header must be at least 20 bytes long. Type of Service 8 Indication of the quality of service requested for the IP packet. It specifies reliability, precedence, delay and throughput parameters. Typically not used Total length 16 Total packet length, including header and data, in bytes. Identification. Unique number assigned by the sending device to aid in reassembling a fragmented packet. Primary purpose is to allow the destination device to collect all fragments from a packet, since they will all have the same identification number. Flags 3 Provides the fragmentation control fields. First bit is not used and is always 0. If second bit is 0, it means ‘May fragment’. If it is 1, it means ‘Don’t fragment’. If the third bit is 0, it means ‘Last fragment’. If it is 1, it means ‘More fragments’.

IP Packet Structure GPRS Backbone GPRS System Survey GPRS Backbone
Fragment Offset 13 Used with fragmented packets to aid in reassembling the full packet. The value is the number of 8-byte pieces (header bytes are not counted) that are contained in earlier fragments. In the first fragment, or in a unique fragment, this value is always zero. Time to Live 8 Contains time(s), that packet is allowed to remain on an internetwork. Each IP device that the packet passes through will decreases the value by the time it takes it to process the IP header. All routers must decrease this value by a minimum of one. If value drops to zero the packet is discarded. This guarantees that packets cannot travel around an IP network in a loop, even if routing tables become corrupt. Protocol Indicates the higher-level protocol to which IP should deliver the data in the packet, for example, UDP is 17 and TCP is 6. Header Checksum 16 This is a checksum on the header only, which ensures integrity of header values. Sending IP device performs a calculation on the bits in the IP header, excluding the header checksum field, and places the result in the header checksum field.

IP Packet Structure GPRS Backbone GPRS System Survey GPRS Backbone
Source Address 32 This is the 32-bit IP address of the sending device. Dest. Address This is the 32-bit IP address of the receiving device. Options Var These are not required in every packet. They are mainly used for network testing or debugging. Data The total length of the data field plus header is a maximum of bytes.

Original IP Packet Data area
GPRS Backbone IP Packet Structure GPRS System Survey GPRS Backbone Fragmentation IP Header Original IP Packet Data area Data 1 Data 2 Data 3 IP Header 1 Data 1 IP Header 2 Data 2 IP Header 3 Data 3 MTU = 1500 Bytes Router 1 Router 2 Router MTU = 4500 bytes MTU = 4500 bytes Ethernet

IP Addressing GPRS Backbone IP Header 20 Bytes Long 1 Byte Version IHL
GPRS System Survey GPRS Backbone 1 Byte Version IHL Type of Service Total Length Identification Flags Fragment Offset IP Header 20 Bytes Long Time To Live Protocol Header Checksum 1 Byte Source Address Destination Address Options + Padding Data

IP Addressing GPRS Backbone
GPRS System Survey GPRS Backbone Every network interface on a TCP/IP device is identified by a globally unique IP address. Host devices, for example, PCs, typically have a single IP address. Routers typically have two or more IP addresses, depending on the number of interfaces they have. Each IP address is 32 bits long and is composed of four 8-bit fields, called octets. The address is normally represented in ‘dotted decimal notation’ by grouping the four octets and representing each one in decimal form. Each octet represents a decimal number in the range For example, is known as

IP Addressing GPRS Backbone
GPRS System Survey GPRS Backbone Each IP address consists of a network ID and a host ID. The network ID identifies the systems that are located on the same network. The network ID must be unique to the internet work. The host ID identifies a TCP/IP network device (or host) within a network. The address for each host must be unique to the network ID. In the example above, the PC is connected to network ’ ’ and has a unique host ID of ‘.5’.

IP Addressing GPRS Backbone Class A networks
GPRS System Survey GPRS Backbone Class A networks The high-order bit in a class A address is always set to zero. The next seven bits (completing the first octet) represent the network ID and provide 126 possible networks. The remaining 24 bits (the last three octets) represent the host ID. Each network can have up to hosts. Class A addresses were assigned to networks with a very large number of hosts. Class A networks Network ID Host ID

IP Addressing GPRS Backbone Class B networks
GPRS System Survey GPRS Backbone Class B networks The two high-order bits in a class B address are always set to binary 1 0 The The next 14 bits (completing the first two octets) represent the network ID and provide possible networks. The remaining 16 bits (last two octets) represent the host ID. Each network can have up to hosts. Class B addresses were assigned to medium-sized to large-sized networks. Class B networks 1 Network ID Host ID

IP Addressing GPRS Backbone Class C networks
GPRS System Survey GPRS Backbone Class C networks The three high-order bits in a class C address are always set to binary The next 21 bits (completing the first three octets) represent the network ID and provide possible networks. The remaining 8 bits (last octet) represent the host ID. Each network can have up to 254 hosts. Class C addresses were used for small networks. Class C networks 1 Network ID Host ID

IP Addressing GPRS Backbone Ranges from 1 - 126 Ranges from 128 - 191
GPRS System Survey GPRS Backbone Ranges from Ranges from Ranges from

IP Addressing GPRS Backbone Class D addresses
GPRS System Survey GPRS Backbone Class D addresses Class D addresses are employed for multicast group usage. A multicast group may contain one or more hosts, or none at all. The four high-order bits in a class D address are always set to binary The remaining bits designate the specific group, in which the client participates. When expressed in dotted decimal notation, multicast addresses range from through There are no network or host bits in the multicast operations. Packets are passed to a selected subset of hosts on a network. Only those hosts registered for the multicast operation accept the packet.

IP Addressing GPRS Backbone Class E addresses
GPRS System Survey GPRS Backbone Class E addresses Class E is an experimental address not available for general use. It is reserved for future use. The high-order bits in a class E address are set to

IP Addressing GPRS Backbone Addressing Guidelines
GPRS System Survey GPRS Backbone Addressing Guidelines The network ID cannot be 127. The class A network address is reserved for loop-back and is designed for testing and inter-process communication on the local device. When any device uses the loop-back address to send data, the protocol software in the device returns the data without sending traffic across any network. The network ID and host ID bits cannot all be 0s. If all bits are set to 0, the address is interpreted to mean ‘this network only’. The host ID must be unique to the local network.

IP Addressing GPRS Backbone Addressing Guidelines
GPRS System Survey GPRS Backbone Addressing Guidelines The network ID and host ID bits of a specific device cannot be all 1s. If all bits are set to 1, the address is interpreted as a broadcast rather than a host ID. The following are the two types of broadcast: If a destination address contains all 1s in the network ID and the host ID ( ) then it, is a limited broadcast, that is, a broadcast on the source’s local network. If a destination address contains all 1s in the host ID but a proper network ID, for example, , this is a directed broadcast, that is, a broadcast on a specified network (in this example network )

IP Addressing GPRS Backbone Private IP Address Space
GPRS System Survey GPRS Backbone Private IP Address Space Organizations should use private Internet address for hosts which require IP connectivity within the enterprise network, but do not require external connections to the global Internet. For this purpose the IANA has reserved the following three address blocks for private intranets: Class A networks Class B networks Class C networks Any organization that elects to use addresses from these reserved blocks can do so without contacting the IANA or an Internet registry. Since these addresses are never injected into the global Internet routing system, the address space can be used simultaneously by many organizations. The disadvantage of this addressing scheme is that it requires an organization to use a Network Address Translator (NAT) for global Internet access.

IP Addressing GPRS Backbone Subnet Mask
GPRS System Survey GPRS Backbone Subnet Mask A subnet mask is a 32-bit address used to: Block out a portion of the IP address to distinguish the network ID from the host ID. Specify whether the destination host’s IP address is located on a local network or on a remote network. The Subnet mask Blocks out a portion of the IP address to distinguish the Network ID from the host ID. It specifies whether the destination’s host IP address is located on a local network or on a remote network. The source’s IP address is ANDed with its subnet mask. The destination’s IP address is ANDed with the same subnet mask. If the result of both ANDing operations match, the destination is local to the source, that is, it is on the same subnet.

GPRS System Survey GPRS Backbone Subnet Mask A Default subnet masks or prefix lengths exist for class A, B and C addresses: Class A default mask (/8) Class B default mask (/16 Class C default mask (/24) For example, an IP device with the configuration below knows that its network ID is and its host ID is 10 Address Subnet Mask For convenience the subnet mask can be written in prefix length notation. The prefix-length is equal to the number of contiguous one-bits in the subnet mask. Therefore, the network address with a subnet mask can also be expressed as /24.

IP Addressing GPRS Backbone Subnet Mask GPRS System Survey

GPRS System Survey GPRS Backbone Subnet Mask The deployment of subnetting within the private network provides several benefits: The size of the global Internet routing table does not grow because the site administrator does not need to obtain additional address space, and the routing advertisements for all of the subnets are combined into a single routing table entry. The local administrator has the flexibility to deploy additional subnets without obtaining a new network number from the Internet. Rapid changing of routes within the private network does not affect the Internet routing table, since Internet routers do not know about the reachability of the individual subnets. They just know about the reachability of the parent network number.

IP Addressing GPRS Backbone Subnet Mask GPRS System Survey

IP Addressing GPRS Backbone Subnetting Example 01000000 00000000
GPRS System Survey GPRS Backbone Subnetting Example = 1………

Domain Name Resolution - DNS
GPRS Backbone Domain Name Resolution - DNS GPRS System Survey GPRS Backbone Internet addresses are hard for humans to remember, but easy for protocol software to work with. Symbolic names are more natural for humans, but hard for protocol software to work with.

GPRS Backbone Domain Name Resolution - DNS GPRS System Survey GPRS Backbone The DNS is based on a hierarchical scheme, with the most significant part of the name on the right. The leftmost segment is the name of the individual computer. Other segments in a domain name identify the group that owns the name. Basically, the Internet is divided into hundreds of top-level domains where each domain covers many hosts. Each domain is partitioned into subdomains, and these are further partitioned, and so on. There are two types of top-level domains: generic and country.

GPRS Backbone Domain Name Resolution - DNS GPRS System Survey GPRS Backbone The seven three-character generic domains are as follows: com commercial organization edu educational institution gov government organization mil military group net major network support center org organization other than those above int international organization Country domains consist of a two-letter entry for every country, as defined in ISO For example: eg Egypt. uk United Kingdom se Sweden

Internet Domain Name Space
GPRS Backbone Internet Domain Name Space GPRS System Survey GPRS Backbone Generic Countries int com mil edu gov net org uk se eg fr Yahoo EUN Groups News aun suez asunet Story

GPRS Backbone Domain Name Resolution - DNS GPRS System Survey GPRS Backbone The translation of a domain name into an equivalent IP address is called Name Resolution. The name is said to be resolved to an address. A host asking for DNS name resolution is called a resolver. Each resolver is configured with the address of a local domain name server. If a resolver wishes to become a client of the DNS server, the resolver places the specified name in a DNS request message and then sends the message to the local server. The resolver then waits for the server to send a DNS reply message that contains the answer

GPRS Backbone Domain Name Resolution - DNS GPRS System Survey GPRS Backbone Root Name Server Recursive query Iterative COM Name Server Local Name Server yahoo.com groups.yahoo.com DNS Client

GPRS Backbone Domain Name Resolution - DNS GPRS System Survey GPRS Backbone Internet name servers use name caching to reduce the traffic on the Internet and improve performance. Servers report cached information to clients, but mark it as a non-authoritative binding. If efficiency is important, the client chooses to accept the non-authoritative answer and proceed. If accuracy is important, the client chooses to contact the authority and verify that the binding between name and address is still valid. Whenever an authority responds to a request, it includes a time to live (TTL) value in the response. The TTL specifies how long the authority guarantees that the binding will be valid.

Transmission Control Protocol - TCP
GPRS Backbone Transmission Control Protocol - TCP GPRS System Survey GPRS Backbone TCP is a reliable, connection-oriented delivery service.There are exactly two endpoints communicating with each other on a TCP connection. Broadcasting and multicasting are not applicable to TCP. Processes or applications communicate with each other by having both the sending and receiving device create end points, called sockets. Each socket has a socket number (address) consisting of the IP address of the device and a 16-bit number called a port. A port is used by transport protocols to identify which application protocol or process they must deliver incoming messages to. A port can use any number between 0 and 65,536.

Transmission Control Protocol - TCP
GPRS Backbone Transmission Control Protocol - TCP GPRS System Survey GPRS Backbone TCP views the data stream as a sequence of octets or bytes that is divided into segments for transmission. Each segment travels across the network in a single IP packet. Reliability is achieved by assigning a sequence number to each segment. When TCP sends a segment it maintains a timer, waiting for the other end to acknowledge reception of the segment. If an acknowledgement is not received in time, the segment is retransmitted. TCP also provides flow control. Each end of a TCP connection has a finite amount of buffer space. A receiving TCP only allows the other end to send as much data as the receiver has buffers for. This prevents a fast host from taking all the buffers from a slower host. TCP also reacts to congestion on the network and automatically adjusts the transmission speed to the bandwidth available on the network.

Acknowledgement Number
GPRS Backbone TCP Packet Structure GPRS System Survey GPRS Backbone 1 Byte Source Port Destination Port Sequence Number Acknowledgement Number Offset Reserved Flags Window Checksum Urgent Pointer Options Padding Data

Well known TCP Port Numbers
GPRS Backbone Well known TCP Port Numbers GPRS System Survey GPRS Backbone

User Datagram Protocol - UDP
GPRS Backbone User Datagram Protocol - UDP GPRS System Survey GPRS Backbone User Datagram Protocol (UDP) provides a connectionless packet service that offers unreliable ‘best effort’ delivery. This means that the arrival of packets is not guaranteed, nor is the correct sequencing of delivered packets. UDP is used by applications that do not require an acknowledgement of receipt of data, for example, audio or video broadcasting. UDP is also used by applications that typically transmit small amounts of data at one time, for example, the Simple Network Management Protocol (SNMP). UDP provides a mechanism that application programs use to send data to other application programs. UDP provides protocol port numbers used to distinguish between multiple programs executing on a single device. That is, in addition to the data sent, each UDP message contains both a destination port number and a source port number. This makes it possible for the UDP software at the destination to deliver the message to the correct application program, and for the application program to send a reply.

UDP Packet Structure GPRS Backbone 1 Byte Source Port Destination Port
GPRS System Survey GPRS Backbone 1 Byte Source Port Destination Port Identification UDP Checksum Data

GPRS Tunneling Protocol - GTP
GPRS Backbone GPRS Tunneling Protocol - GTP GPRS System Survey GPRS Backbone 8 7 6 5 4 3 2 1 Version Reserved LFN Message type Length Sequence Number Flow Label LLC Frame Number x FN Reserved TID ( 8 Octets )

GPRS Tunneling Protocol - GTP
GPRS Backbone GPRS Tunneling Protocol - GTP GPRS System Survey GPRS Backbone TID = IMSI + NSAPI

GTP Encapsulation GPRS Backbone PDN1 TLLI PDN2 TID-1 NSAPI-1 GGSN 1
GPRS System Survey GPRS Backbone GTP Header IP Payload Payload IP Header Payload IP Header SNDCP BSSGP PDN1 TID-1 NSAPI-1 TID-2 GGSN 1 NSAPI-2 SGSN TLLI PDN2 GGSN 2

Remote Access Dial In user Server - RADIUS
GPRS Backbone Remote Access Dial In user Server - RADIUS GPRS System Survey GPRS Backbone Remote Authentication Dial In user Service (RADIUS) is a client / server protocol that enables the Remote Access Server (RAS) to communicate with a central server to authenticate dial in users and authorize their access to the requested system or service. RADIUS allows a company to maintain user profiles in a central database that all remote servers can share. It provides better security, allowing a company to set up a policy that can be applied at a single administered network point. Having a central service also means that it is easier to track usage for billing and for keeping network statistics. RADIUS was specified for user authentication and authorization, but RADIUS server can provide and administrate IP addresses for dial in users. RADIUS Server Remote Access Server Access Negotiation RADIUS Database

GPRS Backbone Remote Access Dial In user Server - RADIUS GPRS System Survey GPRS Backbone Inband RADIUS Corporate/ISP Operator Gi Domain GGSN Tunnel RADIUS Server

GPRS Backbone Remote Access Dial In user Server - RADIUS GPRS System Survey GPRS Backbone Outband RADIUS Corporate/ISP Operator Gi Domain GGSN Tunnel RADIUS Server

Dynamic Host Configuration Protocol – DHCP
GPRS Backbone Dynamic Host Configuration Protocol – DHCP GPRS System Survey GPRS Backbone DHCP supports three mechanisms for IP address allocation: Manual Allocation In this scheme, DHCP is simply used as a mechanism to deliver a predetermined network address and other configuration options to a host. There is a one-to-one mapping between the unique client identifier (generally the Ethernet address) offered by the client during DHCP initialization and the IP address returned to the client by the DHCP server. It is necessary for a network administrator to provide the unique client ID/IP address mapping used by the DHCP server. Automatic Allocation This is similar to manual allocation in that a permanent mapping exists between a host’s unique client identifier and its IP address. However, in automatic allocation this mapping is created during the initial allocation of an IP address. The IP addresses assigned during automatic allocation come from the same pool as dynamic addresses, but once assigned they cannot be returned to the free address pool without administrative intervention. Both automatic and manually assigned addresses are considered to have permanent leases. Dynamic Allocation DHCP assigns an IP address for a limited period of time. This IP address is known as a lease. This mechanism allows addresses that are no longer needed by their host to be automatically

Chapter 6 : Traffic Cases

Traffic Cases General GPRS System Survey Traffic Cases The following traffic cases are described to present the basic principles of a GPRS network: MS Attach and MS Detach PDP Context Activation and PDP Context Deactivation SGSN Routing Area Update.

Traffic Cases MS Attach GPRS System Survey Traffic Cases

MS initiated detach procedure
Traffic Cases MS initiated detach procedure GPRS System Survey Traffic Cases

SGSN initiated detach procedure
Traffic Cases SGSN initiated detach procedure GPRS System Survey Traffic Cases

HLR initiated detach procedure
Traffic Cases HLR initiated detach procedure GPRS System Survey Traffic Cases

PDP Context Activation
Traffic Cases PDP Context Activation GPRS System Survey Traffic Cases

PDP Context Activation
Traffic Cases PDP Context Activation GPRS System Survey Traffic Cases SGSN performs - Subscription Checking - QoS negotiation - APN  GGSN address translation via DNS - TID creation Activate PDP context Request [ APN,QoS, PDP- type(= IP), NSAPI, Protocol Configuration options ] GGSN performs - APN  ISP address translation via DNS - RADIUS client allocation. Create PDP context request [ APN, QoS, PDP- type(= IP), TID, Protocol Configuration options ] UDP-RADIUS Access Request [ Authentication, Configuration ] UDP-RADIUS Access Accept [ Authentication, Configuration ] RADIUS: Remote Authentication Dial In User Server In bound ( doesn’t belong to us but belongs to the ISP out bound ( Belongs to us) Allocates Dynamic IP address during the session duration. The IP address may be allocated statically as a part of the HLR data for the subscriber. Or dynamically through: RADIUS Remote Authentication Dial In User Server DHCP Dynamic Host Configuration Protocol GGSN The GGSN knows which node is going to assign an IP address. APN: Each has a pool of IP addresses MMS.Vodafone.net Internet.Vodafone.net WAP.Vodafone.com.eg Private Public Dynamic x x Static x GGSN stores the IP-address Activate PDP context Accept [ Protocol Configuration options ] M S SGSN GGSN ISP

Combined GPRS/IMSI Attach
Traffic Cases Combined GPRS/IMSI Attach GPRS System Survey Traffic Cases

MS initiated PDP Context Deactivation
Traffic Cases MS initiated PDP Context Deactivation GPRS System Survey Traffic Cases

SGSN initiated PDP Context Deactivation
Traffic Cases SGSN initiated PDP Context Deactivation GPRS System Survey Traffic Cases

GGSN initiated PDP Context Deactivation
Traffic Cases GGSN initiated PDP Context Deactivation GPRS System Survey Traffic Cases

SGSN Routing Area Update
Traffic Cases SGSN Routing Area Update GPRS System Survey Traffic Cases Intra-SGSN Routing Area Update

SGSN Routing Area Update
Traffic Cases SGSN Routing Area Update GPRS System Survey Traffic Cases Inter-SGSN Routing Area Update

Basic Roaming Scenarios
Traffic Cases Basic Roaming Scenarios GPRS System Survey Traffic Cases

Traffic Cases Basic Roaming Scenarios GPRS System Survey Traffic Cases Home GGSN: When using the home GGSN the traffic will always use the same gateway between the GPRS network and the external network, i.e. the traffic will always take the same way out from the GPRS network. Visited GGSN: The main advantage with using a visited GGSN is that the InterPLMN backbone is not used. This means that it saves capacity on the backbone, capacity that GPRS operators have to pay for, and by that the cost for the operator is lower if visited GGSNs are used.

Traffic Cases Basic Roaming Scenarios GPRS System Survey Traffic Cases ISP Roaming: When accessing a visited GGSN the external network could be the user’s world wide Intranet, the same ISP as in the home network or a new ISP. If the external network accessed is a corporate Intranet the Intranet performs the authentication. If the external network gives Internet access three scenarios can be identified: Visited ISP Multihomed ISP Proxy ISP The APN is built up like an Internet domain name (i.e. label1.label2.label3) and contains two parts, the Network Identifier and the Operator Identifier. “<network id>.mnc<MNC>.mcc<MCC>.gprs” Network ID Operator ID The Network ID is often sent to the network by the terminal, either inputted by the user or from a pre-configuration in the terminal, whereas the Operator ID often is added by the SGSN.

Traffic Cases Basic Roaming Scenarios GPRS System Survey Traffic Cases The InterPLMN backbone is a private network, not visible to the rest of the Internet. Only nodes that needs to communicate with nodes in other PLMNs needs to have public addresses and by that be visible on the InterPLMN backbone. If it is assumed that the internal backbone within an operator is considered secure, the part of the network between the Boarder Gateways needs to have an appropriate security level as well

Traffic Cases Basic Roaming Scenarios GPRS System Survey Traffic Cases Several international carriers exist and carry traffic from their clients (a GPRS operator) but they are also exchanging traffic between themselves (peering) so that a customer in one carrier’s network could reach a customer in another carrier’s network. The carrier makes Service Level Agreements (SLAs) with their customers and other carriers as well. An IP carrier fulfilling these requirements is called a GRX (GPRS Roaming eXchange) operator. Some advantages with the GRX approach are: A GPRS operator does not have to create dedicated connections to every roaming partner. Instead of tens or hundreds of separate connections, the operator can start offering the GPRS roaming service with number of roaming partners with only one connection to a GRX operator. A GPRS operator may choose to start with low quality and low capacity connection to GRX and upgrade the level of connectivity when it is economically feasible and there are traffic volumes and type of traffic that require more bandwidth and better quality.

Traffic Cases Basic Roaming Scenarios GPRS System Survey Traffic Cases

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