Thursday, December 17, 2009
gprs Summary
The GPRS is a very important step in the evolution of second generation mobile systems towards third generation systems. It offers packet switching of packet data along with the conventional circuit switching of voice data. The billing is friendly, the data rates are high and call setup time is very low. The system is optimized for packet switched data and is transition from the circuit switched cellular network to totally packet switched cellular networks.
Radio Resource Management and Logical Channels
GPRS uses the same frequency spectrum as GSM i.e. 890-960MHz for up-link and 935-960MHz for down-link. There are 124 channels of 200kHz each and one channel is left as guard band. Some of these channels are allocated to GPRS arbitrarily. The channel allocation in GPRS is much more flexible than GSM. The channel is allocated to MS only when it needs to send data. More than one slot can be given to a single MS leading to maximum data rate of 172kbit/s.
GPRS uses similar logical channel structure as the GSM. The channel can be divided in two categories: traffic channels and signaling channels. The different channels are:- PDTCH (Packet Data Traffic Channel) is used for user data transfer.
- PBCCH (Packet Broadcast Control Channel) is unidirectional point-to-multipoint signaling channel from BSS to MS. It is used by BSS to broadcast control information to all MS in cell.
- PCCCH (Packet Common Control Channel) is bidirectional point-to-multipoint signaling channel which transports the signaling information for network access management.
- PRACH (Packet Random Access Channel) is used by MS to request one or more PDCH.
- PAACH (Packet Access Grant Control Channel) is used to allocate one or more PDTCH to MS.
- PPCH (Packet Paging Channel) is used by BSS to find out the location of a MS (paging) prior to down-link packet transfer.
- PNCH (Packet Notification Control Channel) is used to inform the MS of incoming PTM message (multicast or group call).
- PACCH (Packet Associated Control Channel) is used for sending signaling information related to one particular MS (e.g. power control information).
- PTCCH (Packet Timing advance control Channel) is used for adaptive frame synchronization.
Session, Mobility and Location Management
Before MS can use any type of GPRS services it must ``attach'' to network. Attach involves registration and authentication with network. Similarly it performs ``detach'' when it no longer needs the service. Before the Mobile station can talk to any external PDN it must get a PDP context after an attach. PDP context contains the IP address of MS, requested QoS and address of serving GGSN. PDP can be static (IP address assigned permanently by PLMN) or dynamic (address allocated by visited network). The figure below shows the PDP activation procedure.
The MS requests to SGSN with message ``activate PDP context request''. The SGSN after the authentication forewords this request to affected GGSN. The GGSN responds with ``create PDP context response'' message to SGSN which updates its PDP context table and confirms to MS with ``activate PDP context accept'' message.
The purpose of location management is to keep track of MS so that the incoming packets can be routed to it without ``paging''. But there is trade off of battery power Vs the frequency of location update and a compromise is the good solution. For this reason the MS maintains it state in one of the three states as shown in figure The location update frequency is dependent upon the state of MS.
In IDLE state the MS is not reachable and no location update is performed. After an ``attach'' the MS gets into READY state and may perform ``detach'' to go back to IDLE state. The STANDBY state is reached when the MS does not send any packets for a long time, and READY timer expires.
In READY state the MS sends Location update information to SGSN every movement to a new cell. For location management in STANDBY state GSM location area is divided in several Routing Areas (RA) consisting of several cells. Whenever a MS moves from one RA to another, it sends a ''routing area update'' to the associated SGSN. Inter SGSN and Intra SGSN RA updates are possible. Sometimes RA is combined with GSM LA.
The purpose of location management is to keep track of MS so that the incoming packets can be routed to it without ``paging''. But there is trade off of battery power Vs the frequency of location update and a compromise is the good solution. For this reason the MS maintains it state in one of the three states as shown in figure The location update frequency is dependent upon the state of MS.
In READY state the MS sends Location update information to SGSN every movement to a new cell. For location management in STANDBY state GSM location area is divided in several Routing Areas (RA) consisting of several cells. Whenever a MS moves from one RA to another, it sends a ''routing area update'' to the associated SGSN. Inter SGSN and Intra SGSN RA updates are possible. Sometimes RA is combined with GSM LA.
GPRS Services
The bearer services of GPRS offer end-to-end packet switched data transfer. Of the two types of bearer services offered by GPRS only the point-to-point (PTP) service is available now and the point-to-multipoint (PTM) service will be made available in future releases of GPRS.
The PTP service offers transfer of data packets between two users. It is offered in both connectionless mode (PTP connectionless network service (PTP-CLNS), e.g., for IP) and connection-oriented mode (PTP connection-oriented network service (PTP-CONS), e.g., for X.25).
The PTM service offers transfer of data packets from one user to multiple users. There exist two kinds of PTM services:
- Using the multicast service PTM-M, data packets are broadcast in a certain geographical area. A group identifier indicates whether the packets are intended for all users or for a group of users.
- Using the group call service PTM-G, data packets are addressed to a group of users (PTM group) and are sent out in geographical areas where the group members are currently located.
It is also possible to send SMS over GPRS. In fact the 160 character limit in GPRS is not applicable in GPRS as in GSM. It is also planned to have other supplementary services like call forwarding unconditional (CFU), call forwarding on mobile subscriber not reachable (CFNRc), and closed user group (CUG).
Moreover, a GPRS service provider may provide a number of other non-standardized services built over IP like access to databases, messaging service, electronic monitoring and surveillance systems, whether forecast, traffic information broadcast etc.
GPRS also provides the facility to use both packet and circuit switched services simultaneously depending upon the class of the MS. Class A can use both services simultaneously, class B can register for both but use only one at a time whereas class C can at a time attach for only one type of service.
GPRS Interfaces
Different network components of the GPRS are connected together by well defined interfaces. Some new interfaces to GSM have been added in GPRS to support packet switched data mainly between GGSNs, SGSNs and other network components. The following interfaces have been defined:
- Um interface between MS and BTS is very similar to GSM and defines the modulation type, error correction/detection technique, power control information etc.
- A interface between BTS and BSC defines the channel allocation, power measurement information etc.
- Gb interface connects BSCs to SGSN.
- Gn interface is used between GSNs of same PLMN to exchange user profile when the user moves from one SGSN to another.
- Gp interface is defined between two GSNs of different PLMN for exchanging the user profile and other signaling information between a SGSN and GGSN of another area.
- Gf interface is used between SGSN and EIR to query the IMEI information if a MS tries to register with the network.
- Gr interface between SGSN and HLR is used to get the user profile, the current SGSN address and the PDP address(es) for each user in PLMN.
- Gc interface between GGSN and HLR is used by GGSN to query user's location and profile to update its location register.
- Gi interface connects GGSN to external PDN (e.g. X.25 or IP).
- Gs interface between SGSN and MSC/VLR is used to perform paging request of circuit switched GSM call for combined attachment procedure.
- Gd interface between SMS-Gateway (SMS-GMSC) and SGSN is used to exchange short message service (SMS) messages.
All GSNs are connected over a GPRS backbone network over IP. Within this backbone the GSNs encapsulate and transmit PDN packets by using GPRS Tunneling Protocol (GTP). This backbone network is of two types:
- Intra-PLMN backbone connects the GSNs of same PLMN and are therefore private IP based networks of the service provider.
- Inter-PLMN backbone connects the GSNs of different PLMNs if there is a roaming agreement is between them. The gateways between these PLMNS are called border gateways and perform security functions apart from regular functions to protect the private information against unauthorized usage.
GPRS System Architecture
The GPRS is an enhancement over the GSM and adds some nodes in the network to provide the packet switched services. These network nodes are called GSNs (GPRS Support Nodes) and are responsible for the routing and delivery of the data packets to and form the MS and external packet data networks (PDN). The figure below shows the architecture of the GPRS system.
The most important network nodes added to the existing GSM networks are:
- SGSN (Serving GPRS Support Node).
- GGSN (Gateway GPRS Support Node).
The serving GPRS support node (SGSN) is responsible for routing the packet switched data to and from the mobile stations (MS) within its area of responsibility. The main functions of SGSN are packet routing and transfer, mobile attach and detach procedure (Mobility Management (MM)), location management, assigning channels and time slots (Logical Link Management (LLM)), authentication and charging for calls. It stores the location information of the user (like the current location, current VLR) and user profile (like IMSI addresses used in packet data networks) of registered users in its location register.
The gateway GPRS support node (GGSN) acts as interface between the GPRS backbone and the external packet data network (PDN). It converts the GPRS packet coming from the SGSN into proper packet data protocol (PDP) format (i.e. X.25 or IP) before sending to the outside data network. Similarly it converts the external PDP addresses to the GSM address of the destination user. It sends these packets to proper SGSN. For this purpose the GGSN stores the current SGSN address of the user and his profile in its location register.The GGSN also performs the authentication and charging functions. In general there may be a many to many relationship between the SGSN and GGSN. However a service provider may have only one GGSN and few SGSNs due to cost constraints. A GGSN proved the interface to several SGSNs to the external PDN.
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GSM System Architecture
In GSM system the mobile handset is called Mobile Station (MS). A cell is formed by the coverage area of a Base Transceiver Station (BTS) which serves the MS in its coverage area. Several BTS together are controlled by one Base Station Controller (BSC). The BTS and BSC together form Base Station Subsystem (BSS). The combined traffic of the mobile stations in their respective cells is routed through a switch called Mobile Switching Center (MSC). Connection originating or terminating from external telephone (PSTN) are handled by a dedicated gateway Gateway Mobile Switching Center (GMSC). The architecture of a GSM system is shown in the figure below.
In addition to the above entities several databases are used for the purpose of call control and network management. These databases are Home Location Register (HLR), Visitor Location Register (VLR), the Authentication Center (AUC), and Equipment Identity Register (EIR).
Home Location Register (HLR) stores the permanent (such as user profile) as well as temporary (such as current location) information about all the users registered with the network. A VLR stores the data about the users who are being serviced currently. It includes the data stored in HLR for faster access as well as the temporary data like location of the user. The AUC stores the authentication information of the user such as the keys for encryption. The EIR stores stores data about the equipments and can be used to prevent calls from a stolen equipments.
All the mobile equipments in GSM system are assigned unique id called IMSI (International Mobile Equipment Identity) and is allocated by equipment manufacturer and registered by the service provider. This number is stored in the EIR. The users are identified by the IMSI (International Module Subscriber Identity) which is stored in the Subscriber Identity Module (SIM) of the user. A mobile station can be used only if a valid SIM is inserted into an equipment with valid IMSI. The ``real'' telephone number is different from the above ids and is stored in SIM.
In addition to the above entities several databases are used for the purpose of call control and network management. These databases are Home Location Register (HLR), Visitor Location Register (VLR), the Authentication Center (AUC), and Equipment Identity Register (EIR).
Home Location Register (HLR) stores the permanent (such as user profile) as well as temporary (such as current location) information about all the users registered with the network. A VLR stores the data about the users who are being serviced currently. It includes the data stored in HLR for faster access as well as the temporary data like location of the user. The AUC stores the authentication information of the user such as the keys for encryption. The EIR stores stores data about the equipments and can be used to prevent calls from a stolen equipments.
All the mobile equipments in GSM system are assigned unique id called IMSI (International Mobile Equipment Identity) and is allocated by equipment manufacturer and registered by the service provider. This number is stored in the EIR. The users are identified by the IMSI (International Module Subscriber Identity) which is stored in the Subscriber Identity Module (SIM) of the user. A mobile station can be used only if a valid SIM is inserted into an equipment with valid IMSI. The ``real'' telephone number is different from the above ids and is stored in SIM.
System Architecture
In order to understand the GPRS system architecture it is helpful to first understand the architecture of GSM system. We therefore discuss the architecture of GSM system prior to discussing the architecture of GPRS.
Subsections
GPRS: General Packet Radio Service
The introduction of second generation cellular mobile systems witnessed an impressive growth in the number of mobile subscribers. The most popular second generation systems are GSM and IS-95. The GSM system is based on FDMA-TDMA technology and is widely used in Europe, many parts of Asia and Africa. The IS-95 system is based on CDMA technology and is used in North America. With the increasing popularity of these systems there was an increasing demand for the data services over the wireless. These systems were designed for supporting circuit switched voice data and supported packet data on limited basis, but could not meet of today's traffic requirements. In future it is expected that the wireless systems would be able to provide various kind of services like Internet access over wireless, streaming audio and video, text and multimedia messaging services.
Existing cellular systems do not fulfill the current data needs. The data rates are slow, the connection setup time is long and the services are too expensive. The reason for this is that these systems are designed primarily to handle circuit switched voice data and a channel is dedicated to a single user for the entire duration of the call. This leads to inefficient channel utilization for the packet switched data since it is bursty in nature and many calls could utilize same channel. If packet switched bearer service is provided, the channels can be allocated to the users when needed, leading to sharing of the physical channel (Statistical multiplexing) and thus efficient channel utilization.
The General Packet Radio Service (GPRS) has been developed to address the above inefficiencies and to simplify the wireless access to packet data network. It applies packet radio principles to efficiently transfer data between GSM mobile stations and external packet data network. GPRS supports both X.25 and IP (IPv4 as well as IPv6) networks. GPRS offers session establishment time below one second and data rates up to several tens kbit/s. It also provides for user friendly billing since the billing is based on the amount of transmitted data as against GSM where user is billed based on the duration of the call. This is suitable for applications with bursty traffic (e.g. web browsing) where user can be ``online'' for longer period of time but will be billed based on transmitted data volume.
UE
Node-B
The Node-B is physical unit of radio transmission/reception with cells. It can support both TDD and FDD modes and can be colocated with GSM BTS to reduce implementation costs. It connects to UE via Uu W-CDMA radio interface and RNC via Iub ATM interface. The figure 3.3 below shows the Node B connected to UE and RNC.
The main task of Node B is the conversion to and from the Uu radio interface, including forward error correction (FEC), rate adaptation, W-CDMA spreading/despreading, and quadrature phase shift keying (QPSK) modulation on the air interface. It measures quality and strength of the connection and determines the frame error rate (FER), transmitting these data to the RNC as a measurement report for Handover and macro diversity combining. The Node B is also responsible for the FDD softer Handover. This micro diversity combining is carried out independently, eliminating the need for additional transmission capacity in the Iub.
The Node B also participates in power control, as it enables the UE to adjust its power using down-link (DL) transmission power control (TPC) commands via the inner-loop power control on the basis of up link (UL) TPC information. The predefined values for inner-loop power control are derived from the RNC via outer-loop power control.
The Node B also participates in power control, as it enables the UE to adjust its power using down-link (DL) transmission power control (TPC) commands via the inner-loop power control on the basis of up link (UL) TPC information. The predefined values for inner-loop power control are derived from the RNC via outer-loop power control.
RNC
The RNCs enables autonomous radio resource management (RRM) by UTRAN. The RNC and its associated Node-Bs form Radio Network Subsystem (RNS). The UTRAN consists of several such RNSs. RNCs also assist in Soft Handover of the UEs when a UE moves from one cell to another. In soft Handover, the UE is in communication with more than one Node-Bs and RAKE receiver technique can be used to achieve micro diversity, thus eliminating the fading. This is one of several features arising out of CDMA modulation technique. Other advantages of using CDMA technique are higher bandwidth, scalability in the number of users served, power control and easier logical link control (since Time slots are eliminated). The figure 3.2 below shows the RNC functions along with a soft Handoff scenario.
UTRAN
The UTRAN is the new Radio interface of UMTS. Its constituting element are RNC, Node-B and UE. These elements are described below.
Subsections
Subsections
UMTS Interfaces
The Core Network of UMTS is same as that of GPRS. The air interface is totally different. We therefore only discuss the air interface. The air interfaces in UMTS are listed below:
- Uu: UE to Node B (UTRA, the UMTS W-CDMA air interface
- Iu: RNC to GSM Phase 2+ CN interface (MSC/VLR or SGSN)
- Iu-CS for circuit-switched data
- Iu-PS for packet-switched data
- Iub: RNC to Node B interface
- Iur: RNC to RNC interface, not comparable to any interface in GSM
UMTS Architecture
UMTS system uses the same core network as the GPRS and uses entirely new radio interface. The new radio network in UMTS is called UTRAN (UMTS Terrestrial Radio Access Network) and is connected to the core network (CN) of GPRS via Iu interface. The Iu is the UTRAN interface between the Radio network controller RNC and CN. The figure shows the UMTS architecture.
The mobile terminal in UMTS is called User Equipment (UE). The UE is connected to Node-B over high speed Uu (up to 2 Mbps) Interface. The Node-B are the equivalent of BTS in GSM and typically serve a cell site. Several Node-Bs are controlled by a single RNCs over the Iub interface. The RNCs are connected to CN through Iu interface. The packet switched data is transmitted through Iu-PS interface and circuit switched data is transferred over Iu-CS interface. One of the new interfaces in UTRAN is Iur interface which connects two RNCs and has no equivalent in GSM system. The Iur interface facilitates handling of 100 percent of RRM (Radio Resource Management) and eliminates the burden from CN.
UMTS also supports GSM mode connections in which case the MS connect to the CN through Um interface to BSS and BSS connects through A (Gb interface in GPRS) interface to CN.
UMTS also supports GSM mode connections in which case the MS connect to the CN through Um interface to BSS and BSS connects through A (Gb interface in GPRS) interface to CN.
Monday, December 14, 2009
Technology
MTS combines three different air interfaces, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs.
Air interfaces
UMTS provides several different terrestrial air interfaces, called UMTS Terrestrial Radio Access (UTRA).[4] All air interface options are part of ITU's IMT-2000. In the currently most popular variant for cellular mobile telephones, W-CDMA (IMT Direct Spread) is used.
Please note that the terms W-CDMA, TD-CDMA and TD-SCDMA are misleading. While they suggest covering just a channel access method (namely a variant of CDMA), they are actually the common names for the whole air interface standards.[5]
Non-terrestrial radio access networks are currently under research.
Please note that the terms W-CDMA, TD-CDMA and TD-SCDMA are misleading. While they suggest covering just a channel access method (namely a variant of CDMA), they are actually the common names for the whole air interface standards.[5]
Non-terrestrial radio access networks are currently under research.
W-CDMA (UTRA-FDD)
W-CDMA uses the DS-CDMA channel access method with a pair of 5 MHz channels. In contrast, the competing CDMA2000 system uses one or more arbitrary 1.25 MHz channels for each direction of communication. W-CDMA systems are widely criticized for their large spectrum usage, which has delayed deployment in countries that acted relatively slowly in allocating new frequencies specifically for 3G services (such as the United States).
The specific frequency bands originally defined by the UMTS standard are 1885–2025 MHz for the mobile-to-base (uplink) and 2110–2200 MHz for the base-to-mobile (downlink). In the US, 1710–1755 MHz and 2110–2155 MHz will be used instead, as the 1900 MHz band was already utilized. While UMTS2100 is the most widely-deployed UMTS band, some countries' UMTS operators use the 850 MHz and/or 1900 MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by AT&T Mobility, New Zealand by Telecom New Zealand on the XT Mobile Network and in Australia by Telstra on the Next G network.
The specific frequency bands originally defined by the UMTS standard are 1885–2025 MHz for the mobile-to-base (uplink) and 2110–2200 MHz for the base-to-mobile (downlink). In the US, 1710–1755 MHz and 2110–2155 MHz will be used instead, as the 1900 MHz band was already utilized. While UMTS2100 is the most widely-deployed UMTS band, some countries' UMTS operators use the 850 MHz and/or 1900 MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by AT&T Mobility, New Zealand by Telecom New Zealand on the XT Mobile Network and in Australia by Telstra on the Next G network.
UTRA-TDD HCR
UMTS-TDD's air interfaces that use the TD-CDMA channel access technique are standardized as UTRA-TDD HCR, which uses increments of 5MHz of spectrum, each slice divided into 10ms frames containing fifteen time slots (1500 per second)[7]. The time slots (TS) are allocated in fixed percentage for downlink and uplink. TD-CDMA is used to multiplex streams from or to multiple transceivers. Unlike W-CDMA, it does not need separate frequency bands for up- and downstream, allowing deployment in tight frequency bands.
TD-CDMA is a part of IMT-2000 as IMT CDMA TDD.
TD-CDMA is a part of IMT-2000 as IMT CDMA TDD.
TD-SCDMA (UTRA-TDD 1.28 Mcps Low Chip Rate)
TD-SCDMA uses the TDMA channel access method combined with an adaptive synchronous CDMA component [8] on 1.6 MHz slices of spectrum, allowing deployment in even tighter frequency bands than TD-CDMA. However, the main incentive for development of this Chinese-developed standard was avoiding or reducing the license fees that have to be paid to non-Chinese patent owners. Unlike the other air interfaces, TD-SCDMA was not part of UMTS from the beginning but has been added in Release 4 of the specification.
Like TD-CDMA, it is known as IMT CDMA TDD within IMT-2000.
Like TD-CDMA, it is known as IMT CDMA TDD within IMT-2000.
TD-SCDMA (UTRA-TDD 1.28 Mcps Low Chip Rate)
TD-SCDMA uses the TDMA channel access method combined with an adaptive synchronous CDMA component [8] on 1.6 MHz slices of spectrum, allowing deployment in even tighter frequency bands than TD-CDMA. However, the main incentive for development of this Chinese-developed standard was avoiding or reducing the license fees that have to be paid to non-Chinese patent owners. Unlike the other air interfaces, TD-SCDMA was not part of UMTS from the beginning but has been added in Release 4 of the specification.
Like TD-CDMA, it is known as IMT CDMA TDD within IMT-2000.
Like TD-CDMA, it is known as IMT CDMA TDD within IMT-2000.
Radio access network
UMTS also specifies the UMTS Terrestrial Radio Access Network (UTRAN), which is composed of multiple base stations, possibly using different terrestrial air interface standards and frequency bands.
UMTS and GSM/EDGE can share a Core Network (CN), making UTRAN an alternative radio access network to GERAN (GSM/EDGE RAN), and allowing (mostly) transparent switching between the RANs according to available coverage and service needs. Because of that, UMTS' and GSM/EDGE's radio access networks are sometimes collectively referred to as UTRAN/GERAN.
UMTS networks are often combined with GSM/EDGE, the later of which is also a part of IMT-2000.
The UE (User Equipment) interface of the RAN (Radio Access Network) primarily consists of RRC (Radio Resource Control), RLC (Radio Link Control) and MAC (Media Access Control) protocols. RRC protocol handles connection establishment, measurements, radio bearer services, security and handover decisions. RLC protocol primarily divides into three Modes - Transparent Mode (TM), Unacknowledge Mode (UM), Acknowledge Mode (AM). The functionality of AM entity resembles TCP operation where as UM operation resembles UDP operation. In TM mode, data will be sent to lower layers without adding any header to SDU of higher layers. MAC handles the scheduling of data on air interface depending on higher layer (RRC) configured parameters.
Set of properties related to data transmission is called Radio Bearer (RB). This set of properties will decide the maximum allowed data in a TTI (Transmission Time Interval). RB includes RLC information and RB mapping. RB mapping decides the mapping between RB<->logical channel<->transport channel. Signaling message will be send on Signaling Radio Bearers (SRBs) and data packets (either CS or PS) will be sent on data RBs. RRC and NAS messages will go on SRBs.
Security includes two procedures: integrity and ciphering. Integrity validates the resource of message and also make sure that no one (third/unknown party) on radio interface has not modified message. Ciphering make sure that no one listens your data on air interface. Both integrity and ciphering will be applied for SRBs where as only ciphering will be applied for data RBs.
UMTS and GSM/EDGE can share a Core Network (CN), making UTRAN an alternative radio access network to GERAN (GSM/EDGE RAN), and allowing (mostly) transparent switching between the RANs according to available coverage and service needs. Because of that, UMTS' and GSM/EDGE's radio access networks are sometimes collectively referred to as UTRAN/GERAN.
UMTS networks are often combined with GSM/EDGE, the later of which is also a part of IMT-2000.
The UE (User Equipment) interface of the RAN (Radio Access Network) primarily consists of RRC (Radio Resource Control), RLC (Radio Link Control) and MAC (Media Access Control) protocols. RRC protocol handles connection establishment, measurements, radio bearer services, security and handover decisions. RLC protocol primarily divides into three Modes - Transparent Mode (TM), Unacknowledge Mode (UM), Acknowledge Mode (AM). The functionality of AM entity resembles TCP operation where as UM operation resembles UDP operation. In TM mode, data will be sent to lower layers without adding any header to SDU of higher layers. MAC handles the scheduling of data on air interface depending on higher layer (RRC) configured parameters.
Set of properties related to data transmission is called Radio Bearer (RB). This set of properties will decide the maximum allowed data in a TTI (Transmission Time Interval). RB includes RLC information and RB mapping. RB mapping decides the mapping between RB<->logical channel<->transport channel. Signaling message will be send on Signaling Radio Bearers (SRBs) and data packets (either CS or PS) will be sent on data RBs. RRC and NAS messages will go on SRBs.
Security includes two procedures: integrity and ciphering. Integrity validates the resource of message and also make sure that no one (third/unknown party) on radio interface has not modified message. Ciphering make sure that no one listens your data on air interface. Both integrity and ciphering will be applied for SRBs where as only ciphering will be applied for data RBs.
Core network
With Mobile Application Part, UMTS uses the same core network standard as GSM/EDGE. This allows a simple migration for exiting GSM operators. However, the migration path to UMTS is still costly: while much of the core infrastructure is shared with GSM, the cost of obtaining new spectrum licenses and overlaying UMTS at existing towers is high.
The CN can be connected to various backbone networks like the Internet, ISDN. UMTS (and GERAN) include the three lowest layers of OSI model. The network layer (OSI 3) includes the Radio Resource Management protocol (RRM) that manages the bearer channels between the mobile terminals and the fixed network, including the handovers.
The CN can be connected to various backbone networks like the Internet, ISDN. UMTS (and GERAN) include the three lowest layers of OSI model. The network layer (OSI 3) includes the Radio Resource Management protocol (RRM) that manages the bearer channels between the mobile terminals and the fixed network, including the handovers.
Core network
Over 130 licenses have already been awarded to operators worldwide (as of December 2004), specifying W-CDMA radio access technology that builds on GSM. In Europe, the license process occurred at the tail end of the technology bubble, and the auction mechanisms for allocation set up in some countries resulted in some extremely high prices being paid for the original 2100 MHz licenses, notably in the UK and Germany. In Germany, bidders paid a total €50.8 billion for six licenses, two of which were subsequently abandoned and written off by their purchasers (Mobilcom and the Sonera/Telefonica consortium). It has been suggested that these huge license fees have the character of a very large tax paid on future income expected many years down the road. In any event, the high prices paid put some European telecom operators close to bankruptcy (most notably KPN). Over the last few years some operators have written off some or all of the license costs. More recently, a carrier in Finland has begun using 900 MHz UMTS in a shared arrangement with its surrounding 2G GSM base stations, a trend that is expected to expand over Europe in the next 1–3 years.
The 2100 MHz UMTS spectrum allocated in Europe is already used in North America. The 1900 MHz range is used for 2G (PCS) services, and 2100 MHz range is used for satellite communications. Regulators have, however, freed up some of the 2100 MHz range for 3G services, together with the 1700 MHz for the uplink. UMTS operators in North America who want to implement a European style 2100/1900 MHz system will have to share spectrum with existing 2G services in the 1900 MHz band.
AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T Wireless in 2004 and has since then launched UMTS in select US cities. Cingular renamed itself AT&T and is rolling out some cities with a UMTS network at 850 MHz to enhance its existing UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones.
T-Mobile's rollout of UMTS in the US will focus on the 2100/1700 MHz bands, whereas UMTS coverage in Canada is being provided on the 850 MHz band of the Rogers Wireless network. In 2008, Australian telco Telstra replaced its existing CDMA network with a national 3G network, branded as NextG, operating in the 850 MHz band. Telstra currently provides UMTS service on this network, and also on the 2100 MHz UMTS network, through a co-ownership of the owning and administrating company 3GIS. This company is also co-owned by Hutchison 3G Australia, and this is the primary network used by their customers. Optus is currently rolling out a 3G network operating on the 2100 MHz band in cities and most large towns, and the 900 MHz band in regional areas. Vodafone is also building a 3G network using the 900 MHz band. The 850 MHz and 900 MHz bands provide greater coverage compared to equivalent 1700/1900/2100 MHz networks, and are best suited to regional areas where greater distances separate subscriber and base station.
Carriers in South America are now also rolling out 850 MHz networks.
The 2100 MHz UMTS spectrum allocated in Europe is already used in North America. The 1900 MHz range is used for 2G (PCS) services, and 2100 MHz range is used for satellite communications. Regulators have, however, freed up some of the 2100 MHz range for 3G services, together with the 1700 MHz for the uplink. UMTS operators in North America who want to implement a European style 2100/1900 MHz system will have to share spectrum with existing 2G services in the 1900 MHz band.
AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T Wireless in 2004 and has since then launched UMTS in select US cities. Cingular renamed itself AT&T and is rolling out some cities with a UMTS network at 850 MHz to enhance its existing UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones.
T-Mobile's rollout of UMTS in the US will focus on the 2100/1700 MHz bands, whereas UMTS coverage in Canada is being provided on the 850 MHz band of the Rogers Wireless network. In 2008, Australian telco Telstra replaced its existing CDMA network with a national 3G network, branded as NextG, operating in the 850 MHz band. Telstra currently provides UMTS service on this network, and also on the 2100 MHz UMTS network, through a co-ownership of the owning and administrating company 3GIS. This company is also co-owned by Hutchison 3G Australia, and this is the primary network used by their customers. Optus is currently rolling out a 3G network operating on the 2100 MHz band in cities and most large towns, and the 900 MHz band in regional areas. Vodafone is also building a 3G network using the 900 MHz band. The 850 MHz and 900 MHz bands provide greater coverage compared to equivalent 1700/1900/2100 MHz networks, and are best suited to regional areas where greater distances separate subscriber and base station.
Carriers in South America are now also rolling out 850 MHz networks.
Features of UMTS
UMTS, using W-CDMA, supports maximum theoretical data transfer rates of 21 Mbit/s (with HSDPA),[3] although at the moment users in deployed networks can expect a transfer rate of up to 384 kbit/s for R99 handsets, and 7.2 Mbit/s for HSDPA handsets in the downlink connection. This is still much greater than the 9.6 kbit/s of a single GSM error-corrected circuit switched data channel or multiple 9.6 kbit/s channels in HSCSD (14.4 kbit/s for CDMAOne), and—in competition to other network technologies such as CDMA2000, PHS or WLAN—offers access to the World Wide Web and other data services on mobile devices.
Precursors to 3G are 2G mobile telephony systems, such as GSM, IS-95, PDC, CDMA PHS and other 2G technologies deployed in different countries. In the case of GSM, there is an evolution path from 2G, to GPRS, also known as 2.5G. GPRS supports a much better data rate (up to a theoretical maximum of 140.8 kbit/s, though typical rates are closer to 56 kbit/s) and is packet switched rather than connection oriented (circuit switched). It is deployed in many places where GSM is used. E-GPRS, or EDGE, is a further evolution of GPRS and is based on more modern coding schemes. With EDGE the actual packet data rates can reach around 180 kbit/s (effective). EDGE systems are often referred as "2.75G Systems".
Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. Currently, HSDPA enables downlink transfer speeds of up to 21 Mbit/s. Work is also progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access (HSUPA). Longer term, the 3GPP Long Term Evolution project plans to move UMTS to 4G speeds of 100 Mbit/s down and 50 Mbit/s up, using a next generation air interface technology based upon Orthogonal frequency-division multiplexing.
The first national consumer UMTS networks launched in 2002 with a heavy emphasis on telco-provided mobile applications such as mobile TV and video calling. The high data speeds of UMTS are now most often utilised for Internet access: experience in Japan and elsewhere has shown that user demand for video calls is not high, and telco-provided audio/video content has declined in popularity in favour of high-speed access to the World Wide Web - either directly on a handset or connected to a computer via Wi-Fi, Bluetooth, Infrared or USB
Precursors to 3G are 2G mobile telephony systems, such as GSM, IS-95, PDC, CDMA PHS and other 2G technologies deployed in different countries. In the case of GSM, there is an evolution path from 2G, to GPRS, also known as 2.5G. GPRS supports a much better data rate (up to a theoretical maximum of 140.8 kbit/s, though typical rates are closer to 56 kbit/s) and is packet switched rather than connection oriented (circuit switched). It is deployed in many places where GSM is used. E-GPRS, or EDGE, is a further evolution of GPRS and is based on more modern coding schemes. With EDGE the actual packet data rates can reach around 180 kbit/s (effective). EDGE systems are often referred as "2.75G Systems".
Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. Currently, HSDPA enables downlink transfer speeds of up to 21 Mbit/s. Work is also progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access (HSUPA). Longer term, the 3GPP Long Term Evolution project plans to move UMTS to 4G speeds of 100 Mbit/s down and 50 Mbit/s up, using a next generation air interface technology based upon Orthogonal frequency-division multiplexing.
The first national consumer UMTS networks launched in 2002 with a heavy emphasis on telco-provided mobile applications such as mobile TV and video calling. The high data speeds of UMTS are now most often utilised for Internet access: experience in Japan and elsewhere has shown that user demand for video calls is not high, and telco-provided audio/video content has declined in popularity in favour of high-speed access to the World Wide Web - either directly on a handset or connected to a computer via Wi-Fi, Bluetooth, Infrared or USB
Introduction to UMTS
Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile telecommunications technologies, which is also being developed into a 4G technology. The first deployment of the UMTS is the release99 (R99) architecture. It is specified by 3GPP and is part of the global ITU IMT-2000 standard. The most common form of UMTS uses W-CDMA (IMT Direct Spread) as the underlying air interface but the system also covers TD-CDMA and TD-SCDMA (both IMT CDMA TDD). Being a complete network system, UMTS also covers the radio access network (UMTS Terrestrial Radio Access Network; UTRAN), the core network (Mobile Application Part; MAP) as well as authentication of users via USIM cards (Subscriber Identity Module).
Unlike EDGE (IMT Single-Carrier, based on GSM) and CDMA2000 (IMT Multi-Carrier), UMTS requires new cell towers and new frequency allocations. However, it is closely related to GSM/EDGE as it borrows and builds upon concepts from GSM. Further, most UMTS handsets also support GSM, allowing seamless dual-mode operation. Therefore, UMTS is sometimes marketed as 3GSM, emphasizing the close relationship with GSM and differentiating it from competing technologies.
The name UMTS, introduced by ETSI, is usually used in Europe. Outside of Europe, the system is also known by other names such as FOMA[1] or W-CDMA[nb 1][1]. In marketing, it is often just referred to as 3G.
Unlike EDGE (IMT Single-Carrier, based on GSM) and CDMA2000 (IMT Multi-Carrier), UMTS requires new cell towers and new frequency allocations. However, it is closely related to GSM/EDGE as it borrows and builds upon concepts from GSM. Further, most UMTS handsets also support GSM, allowing seamless dual-mode operation. Therefore, UMTS is sometimes marketed as 3GSM, emphasizing the close relationship with GSM and differentiating it from competing technologies.
The name UMTS, introduced by ETSI, is usually used in Europe. Outside of Europe, the system is also known by other names such as FOMA[1] or W-CDMA[nb 1][1]. In marketing, it is often just referred to as 3G.
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