AV Generation . . . .6.26 Authentication Functions in the USIM . . . .6.27 Action on Synchronization Failure . . . .6.28 VHE (Virtual Home Environment). . . .6.29 CAMEL (Customized Applications for Mobile network Enhanced Logic) . . . .6.30 LCS (Location Services). . . .6.31 Access Networks . . . .6.32 GERAN (The GSM/EDGE Radio Access Network) . . . .6.33
GSM and UMTS Core Network
At the end of this section you will be able to:
OBJECTIVES
Introduction to the System Architecture
■
■ highlight the differences between CS calls in a 3GPP Release 99 core network and 3GPP
Release 4 core network
■
■ list the bearer and teleservices in UMTS ■
■ describe the evolution to a third-generation system
■
■ outline the service requirements of a UMTS system ■
■ identify the role of the core network in authentication
■
GSM and UMTS Core Network
Introduction to the System Architecture
The Third-Generation Concept
The term ‘third generation’, or 3G, relates to the progression and development of mobile cellular networks from their inception in the early 1980s to the present day.
The first systems were based around a digital core network, but they only offered telephony services through an analogue air interface. These systems, which were limited in their service capability, roaming capability and security functions, are referred to as ‘first-generation systems.
By the early 1990s, first-generation systems were being superseded by 2G systems. Principal among these on a worldwide basis is the GSM. However, there are several other 2G systems that are used on a regional basis. All these systems are characterized by signalling and service types that are similar to those of the ISDN. They also have roaming capability and much improved security functions. The GPRS is an upgrade to the GSM network. It is a packet-based service that allows data to be sent and received across the GSM network and is referred to as 2.5G. EDGE uses the 8PSK modulation scheme to improve data rates across GSM networks.
3G systems, which include the UMTS, promise an improved and more flexible service profile. They are designed to be fully compatible with 2G systems, so subscribers can enjoy a seamless migration. The flexibility of service provision is intended to provide for innovation and differentiation between operators. This should be complemented with full subscriber and service roaming capability.
HSPA, which was introduced in Release 6 of UMTS, includes high-speed downlink and high-speed uplink access. HSPA+(HSPA Evolved) was introduced in Release 7 of UMTS and boasts of speeds up to 42 Mbit/s on the downlink and 22 Mbit/s on the uplink.
3GPP LTE takes the data rates ‘Beyond 3G’ (B3G) and offers downlink speeds of about 100 Mbit/s and 50 Mbit/s on the uplink. A further evolution, LTE Advanced, is expected to be part of Release 10, for which peak download rates of 1 Gbit/s have been specified.
Phase 1 Phase 2 Phase 2+ Release 8 Release 7 Release 6 Release 5 Release 4 Release 99 (UMTS phase1) Release 98 Release 96 2006 2004 2002 2000 1990 1992 1994 1996 1998 2008 2010 2012 GSM 2G GPRS 2.5G EDGE 2.75G UMTS R99 3G HSPA 3.5G HSPA+ 3.75G LTE/SAE 3.9G/4G
6.2
GSM and UMTS Core Network
UMTS Phasing
UMTS was designed to be implemented in phases. Phase 1’s requirements were met by the capabilities of GSM Phase 2+ Release 99, including specific enhancements for UMTS. The specifications for UMTS Phase 1 were therefore written to interwork with GSM phase 2+ Release 99 specifications; the main difference between them is the is the support of high-bit-rate bearer services and the ability to negotiate traffic and Quality of Service (QoS) characteristics.
UMTS Phase 1 supports bursty and asymmetric traffic in an efficient way. This allow UMTS Phase 1 to support single- and multimedia Narrowband ISDN (N-ISDN) applications and single- and multimedia IP applications. GSM Release 1999 UMTS Release 5 GSM Release 1998 GSM Release 1997 Second Generation Third Generation UMTS Phase 1 UMTS Release 1999 UMTS Release 4 Other Releases
Introduction to the System Architecture
3GPP (3rd Generation Partnership Project)
3GPP comprises five TSGs (Technical Specification Groups), each with a specific area of interest. Each TSG is responsible for defining and producing the specifications for the group.
The RAN group is responsible for defining the architecture and protocols for the radio access network of UMTS.
The Core Network group is responsible for defining call control protocols, supplementary services, IMS (IP Multimedia Subsystem) protocols and architecture and interconnection to external networks.
The Services and System Aspects group is responsible for security and confidentiality. It also specifies the user services and general architecture of the UMTS Network
The Terminal group is responsible for defining the structure of the USIM and the functions and conformance tests for UMTS terminals.
The GERAN group is responsible for defining the protocols for the GERAN, which is the evolved radio access network of GSM that combines the GSM and EDGE modulation schemes.
3GPP Technical Specification Group (TSG)
Terminals
GSM EDGE Radio Access Network
(GERAN) Radio Access Network
(RAN)
Core Network
6.4
GSM and UMTS Core Network
UMTS Releases: R99 to R5
The first phase of UMTS, Phase 1 Release 99, specified a new WCDMA (Wideband CDMA (Code Division Multiple Access)) air interface. The core network did not differ greatly from the GSM core network; the Mobile-services Switching Centre used in UMTS is generally the same as that used in GSM, having been upgraded to support UMTS protocols.
After Phase 1, the naming structure was changed to release numbers, and Release 4 followed on from Phase 1. A significant change in Release 4 was the introduction of the All-IP core network, otherwise known as the ‘split architecture’. Transport and control were split and handled separately by an IP softswitch such that the control was handled by an MSC Server and the media was handled by an Media Gateway (MGW). Release 5 introduced the IMS as part of the UMTS core network. The IMS has since become access independent. Flexible RANs were also introduced, which allow a RNC (Radio Network Controller ) to connect to multiple MSCs and SGSNs. Before this was introduced, a one-to-one mapping meant one RAN node to one CN node. One advantage of flexible RANs is that multiple MSCs or SGSNs share loads. Also, they also reduce the need for signalling updates when a UE moves between location areas and routing areas. HSDPA (High Speed Downlink Packet Access) includes additional UMTS logical and physical channels, allowing a maximum bit rate of 14.4 kbit/s. Release 5 also enhanced LCS with A-GPS (Assisted GPS). UMTS Release 8 LTE SAE-EPS IMS enhancements IP Node B UMTS Release 7
TISPAN requirements for IMS A-GNSS HSPA+ UMTS Release 6 Network sharing IMS services WLAN interworking MIMO HSUPA MBMS UMTS Release 5
IP Multimedia Subsystem (IMS) Flexible RANs
Iu Flex HSDPA
LCS enhancement with A-GPS
UMTS Release 4
Separate transport and control in CS domain Split architecture
MSC server and media gateway UMTS all IP core network
UMTS Release 99
Phase 1 UMTS
GSM RAN replaced by UTRAN WCDMA
High bandwidth (up to 2 Mbit/s) Soft handover
Introduction to the System Architecture
UMTS Releases: R6 to R8
Release 6 introduced a network sharing support enhancement mechanism that allows operators to share RAN network elements. Some IMS services were defined such as Video Sharing and Immediate Messaging. Interworking between UMTS and WLANs (Wireless Location Area Networks), which allows WLAN UEs to utilise resources and access services in UMTS, was also introduced. Release 6 also saw the introduction of HSUPA (High Speed Uplink Packet Access), which allows a maximum uplink bit rate of 5.76 Mbit/s.
MIMO (Multiple Input Multiple Output) and MBMS (Multimedia Broadcast Multicast Service) were also introduced at Release 6. MIMO achieves high data rates by using more than one antenna to send and receive two or more unique data streams over the same channel at the same time. MBMS is a technology for broadcast services over cellular networks.
In Release 7, TISPAN (Telecommunications and Internet Converged Services and Protocols for Advanced Networking) worked with 3GPP in defining requirements for fixed line access to IMS. 3GPP started to address A-GNSS (Assisted Global Navigation Satellite System) techniques, GNSS having been designed by the European Union so that access to the system cannot be denied or performance degraded by a foreign power. Also at Release 7 the standards for HSPA+ were finalized, supporting uplink speeds of 42 Mbit/s and downlink speeds of 22 Mbit/s.
Release 8 introduced Long Term Evolution (LTE), which will support uplink speeds of over 100 Mbit/s. The core network evolves to the EPS (Evolved Packet System) to support the high data rates across the access network. UMTS Release 8 LTE SAE-EPS IMS enhancements IP Node B UMTS Release 7
TISPAN requirements for IMS A-GNSS HSPA+ UMTS Release 6 Network sharing IMS services WLAN interworking MIMO HSUPA MBMS UMTS Release 5
IP Multimedia Subsystem (IMS) Flexible RANs
Iu Flex HSDPA
LCS enhancement with A-GPS
UMTS Release 4
Separate transport and control in CS domain Split architecture
MSC server and media gateway UMTS all IP core network
UMTS Release 99
Phase 1 UMTS
GSM RAN replaced by UTRAN WCDMA
High bandwidth (up to 2 Mbit/s) Soft handover
6.6
GSM and UMTS Core Network
UMTS Services
There are three principal types of service in UMTS networks: bearer services, teleservices and supplementary services.
Bearer services provide the capabilities to transmit signals between two access points. A bearer service does not include descriptions of the applications using it or the terminal equipment functions. It is defined in terms of characteristics such as data rate, bit error ratio, transfer delay, delay variation and bit integrity. A bearer services is a ‘bit pipe’ for the transfer of information bits; it is not concerned what information the bits comprise.
Teleservices are built on underlying basic bearer services, but also describe the full capability including terminal functions. A range of teleservices are defined in UMTS.
Supplementary Services complement teleservices. They are not offered as standalone services but only as supplements to existing teleservices.
Teleservices and Supplementary Services
Bearer Service Internet PSTN Core Network Radio Access Network Streaming Server Phone
Introduction to the System Architecture
UMTS Service Structure
Teleservices and supplementary services are end-to-end services, and therefore have a bearer service requirement. This comprises a local bearer service, a UMTS bearer Service and an external bearer service.
The local bearer service is the connection between the phone and the application, which could be either internal or exist as a connection between the phone and a computer via cable or Bluetooth .
The UMTS bearer service is composed of a RAB (Radio Access Bearer) service and a core network bearer service and thereby requires interworking between radio protocols and core network protocols to provide end-to-end QoS.
The RAB service consists of a radio bearer set up between the UE and the UTRAN (Universal Terrestrial Radio Access Network) and an Iu bearer set up between the UTRAN and the core network node (the MSC for a CS call or the SGSN for a PS call). The radio bearer is set up over the WCDMA air interface using either FDD (Frequency Division Duplex) or TDD (Time Division Duplex). The Iu bearer service uses ATM virtual circuits between the UTRAN and the core network.
In UMTS Release 4, the core network bearer service has an IP-based backbone network. This will be engineered to support the requirements of the services supported by the network.
UMTS TE MT UTRAN CN Iu EDGE NODE CN Gateway TE End-to-End Service TE/MT Local
Bearer Service UMTS Bearer Service External Bearer Service
Radio Access Bearer Service CN Bearer Service
Radio Bearer
Service Iu Bearer Service CN Bearer Service
UTRA FDD/TDD
Service
Physical Bearer Service
6.8
GSM and UMTS Core Network
Bearer Service Attributes
Some bearer service attributes in the core network do have the same corresponding attributes in the RAB and will depend on implementation and network dimensioning. The attributes are listed and explained briefly below.
The maximum bit rate (kbit/s) is the maximum number of bits delivered by the UMTS network within a period of time, divided by the duration of the period. The maximum bit rate is the maximum data rate that will be expected to or from a UE across the network bearers. This parameter will be policed and shaped at the ingress points to the network.
The guaranteed bit rate (kbit/s) is the guaranteed number of bits delivered by a UMTS network within a period of time divided by the duration of the period.
In-sequence delivery (y/n) indicates whether the UMTS bearer provides in-sequence delivery of the data or not. Some applications require in-sequence delivery to function properly.
Maximum SDU (Service Data Unit) size is the maximum allowed size of the SDU across the bearer.
SDU format information (bits) is the exact format of the SDU payloads and it is retrieved from the codec used in the core network media gateway. The UTRAN needs this information to be able to operate in support mode for predefined SDU size, which is beneficial to spectral efficiency.
The SDU error ratio indicates the acceptable fraction of SDUs lost or discarded by the network because of detected errors.
The residual bit error ratio indicates the undetected bit error ratio in the delivered SDUs. If no error detection is requested then the Residual bit error ratio indicates the bit error ratio in the delivered SDUs.
Delivery of erroneous SDUs (y/n/-) indicates whether SDUs detected as erroneous are to be delivered or discarded. This depends on the requirements of the application using the bearer.
The transfer delay (ms) indicates maximum delay for 95th percentile of the distribution of delay for all delivered SDUs during the lifetime of a bearer service.
Bearer Server Attributes Transfer Delay
(ms) Traffic Handling Priority SDUerror rates Allocation/ Retention Priority
Traffic Class Maximum bit rate (kbit/s) Guaranteed bit rate (kbit/s) In-sequence Delivery (Yes/No) Source Statistics descriptor (speech/unknown) Maximum SDU size (octets) SDU format Information (bits)
Introduction to the System Architecture
Bearer Service Attributes (continued)
The traffic handling priority specifies the relative importance for handling of all SDUs belonging to the UMTS bearer compared to the SDUs of other bearers.
Allocation/retention priority is a subscription parameter which specifies the relative importance of this bearer compared to other UMTS bearers for allocation and retention. During periods of congestion, a user with a higher allocation priority than another would be allocated a bearer in preference to the other user.
The source statistics descriptor (Speech/Unknown) specifies the characteristics of the source of submitted SDU’s. It is set to speech if the Radio Access Bearer transports compressed speech generated by the codec in the Media Gateway.
Bearer Server Attributes Transfer Delay
(ms) Traffic Handling Priority SDUerror rates Allocation/ Retention Priority
Traffic Class Maximum bit rate (kbit/s) Guaranteed bit rate (kbit/s) In-sequence Delivery (Yes/No) Source Statistics descriptor (speech/unknown) Maximum SDU size (octets) SDU format Information (bits)
6.10
GSM and UMTS Core Network
UMTS Traffic Classes
Traffic classes determine the type of application for which the bearer service is optimized. There are four traffic classes, Conversational, Streaming, Interactive and Background, which are explained below. Users of the Conversational class require real-time interaction between all active members of the conversation. This does not just include telephony-style calls, but also multimedia conferencing using VoIP (Voice over IP) and video calling. The aim of this class is to preserve the time relationship between generation and delivery of information with acceptable delay. It has a transfer delay of 100 ms across the bearer.
Streaming of information is not interactive in the sense of conversation but still has a near-real-time requirement. This may include real-time as well as recorded information. However, the listener/viewer cannot interact with the flow. An example of this is streamed audio from a radio web site or streamed video. This information may be buffered at the terminal equipment before being played to the user in order to achieve the time relationship between the information. It has a transfer delay of 250 ms across the bearer.
Information in the Interactive class does not have a real-time dependency, although there is interaction between end users. Examples of this are Internet chat rooms and general web browsing.
Background Class is for the transport of file information such as the upload/download of files from a FTP (File Transfer Protocol) server and emails.
UMTS Bearer UMTS Bearer UMTS Bearer UMTS Bearer Voice/video Streaming video Web browsing E-mails, telemetry Interactive Background Streaming Conversational
Introduction to the System Architecture
UMTS Teleservices
UMTS teleservices provide the full capabilities for communications by means of terminal equipment functions and network functions. UMTS supports a basic range of standard teleservices and a range of non-standardized teleservices.
Speech is one of the standard teleservices and uses the AMR (Adaptive Multi Rate) codec. The AMR codec is a single chip which supports eight speech rates from 4.75 kbit/s to 12.2 kbit/s and these rates can dynamically change every 20 ms. Both SMS and SMS cell broadcast are included as standard teleservices as well as transparent and non-transparent data, Internet access and video calling.
UMTS Teleservices
Fax Emergency Calls
Transparent and Non-transparent Data Speech (AMR) SMS SMS cell Broadcast Internet
6.12
GSM and UMTS Core Network
PS QoS Attributes
The end users care only about the issues that are visible to them. The QoS perceived by the end user is very important.
The 3GPP Recommendation 23.107 states that ‘QoS parameters should meet the following criteria:
■
■ The UMTS QoS mechanisms shall provide a mapping between application requirements and
UMTS services.
■
■ QoS behaviour should be dynamic, i.e., it shall be possible to modify QoS parameters during an
active session.
■
■ User QoS requirements shall be satisfied by the system, including when change of SGSN within
the Core Network occurs.
■
■ QoS mechanism allows efficient use of radio capacity.
The main distinction between the PS QoS classes is how delay sensitive the traffic is.
Conversational class is very delay sensitive decreasing to background class, which is the most delay- insensitive traffic class.
Priority refers to the relative handling of SDUs belonging to a UMTS bearer compared to the SDUs of other bearers.
Peak throughput and mean throughput refer to maximum and guaranteed bit rate provided by the network for an application process.