1

CONTENTS

1. Executive Summary.................................................................................................................2 2. Introduction..............................................................................................................................2

2.1. The Limitations of Legacy Technology ...........................................................................3 2.2. The Next Generation Challenge .....................................................................................3

3. 3GPP Bearer- Independent Circuit-Switched Core Network Architecture ..............................4 3.1. 3GPP Release 4 Architecture.........................................................................................4

3.1.1 Mc interface............................................................................................................5 3.1.2 Nc interface ............................................................................................................6 3.1.3 Nb Interface............................................................................................................6

3.2. Rel- 4 Network Elements ................................................................................................7 3.2.1 MSC Server............................................................................................................7 3.2.2 GMSC Server.........................................................................................................7 3.2.3 Media Gateway ......................................................................................................8

3.3. GSM to UMTS Evolution.................................................................................................8 4. Transmission Network.............................................................................................................8

4.1. Transmission Network Solutions ....................................................................................8 4.2. ATM or IP........................................................................................................................9 4.3. Packet Voice Transmission Efficiency..........................................................................10 4.4. Compression in Wireless ..............................................................................................11 4.5. Quality of Experience....................................................................................................11

5. Beyond R4 – IP Multimedia Subsystem (IMS) ......................................................................12 5.1. Architecture Overview...................................................................................................14

6. Conclusions ...........................................................................................................................15 Acknowledgments......................................................................................................................16

2

1. EXECUTIVE SUMMARY In Release 4, 3GPP introduces a bearer-independent core network architecture that enables packet networks as the bearer, in addition to the TDM bearers supported in current networks. Both IP and ATM are supported.

This architecture allows the splitting of the monolithic MSC network elements into MSC Servers that handle the control plane, and Media Gateways that handle the user plane.

The architecture supports all existing circuit-switched mobile services, which means that it will enable the operators to provide all existing services to end users while reaping the benefits of the split architecture and a packetized core network.

The separation of the control and user planes enables each function to be scaled independently of the other, and be geographically independent of the other.

Utilizing packet networks in the user plane allows any-to-any node connectivity without exponentially increasing the amount of connections, thus providing transmission savings. Redundant capacity in the network can therefore be minimized.

Most of the new services introduced in emerging networks will be based on packet technology. Utilizing a common packet network for both the legacy circuit-switched services and new services eliminates the need of running parallel networks.

2. INTRODUCTION 3rd Generation wireless standards have defined an open architecture for the packetization of wireless telephony networks, giving wireless operators a clear alternative to traditional TDM technologies. The packetization of existing wireless telephony services is the first step toward achieving the ‘all packet’ network architecture, widely recognized as the ultimate goal for network operators. This new architecture is defined in the 3GPP Release 4 Bearer Independent Core Network (BICN).

This solution provides the same service capabilities as are available using traditional TDM technologies. However, packet voice technology enables an operator to deliver these services at a much lower cost. This substantially lower cost base enables an operator to be either more competitive in their chosen market or to more profitably address new ‘lower revenue’ markets. The lower cost base is achieved through both capital and operational cost savings.

The consolidation and simplification of the core network into fewer ‘higher capacity’ and ‘higher density’ network elements brings a variety of cost savings which are discussed in more detail later. The consolidation and simplification of the core network is at the heart of the principles of scalability and efficiency. These principles enable several benefits from a business perspective:

• Distributed (flat-architecture) packet networks require less equipment than hierarchical TDM networks, reducing overall capital investment in the network and the cost of ownership associated with each network node.

• The use of highly scalable network elements enables the network to be built using far fewer nodes, thereby reducing internal network overhead and greatly improving network efficiency.

• Floor space always has a cost associated with it and the use of high-density packet technology instead of traditional TDM equipment greatly reduces the floor space needed. (This is the application of Moore’s Law.)

• Packet networks enable more efficient use of transmission capacity facilitating the scalability of network interfaces. The use of packet-based interfaces also has a direct bearing on the scalability of network nodes.

3

• Network equipment no longer has to be at legacy ‘central office’ sites at geographically constrained locations, but rather can be geographically distributed and scaled accordingly.

• One common and scalable packet network is used for everything - voice, data and signaling – simplifying network operation so that there is no need for multiple over-lay networks, thereby reducing network complexity and the operational overhead.

2.1. THE LIMITATIONS OF LEGACY TECHNOLOGY

Many mature legacy wireless network operators are experiencing high operational costs due to the inefficiency and complexity of their legacy networks. With wireless markets continuing to become more and more competitive, these operators are naturally looking for ways to lower their costs. This is not only relevant to operators in mature networks but also to operators building Greenfield networks, and those looking for some reassurance that their network capacity investments will be future proof.

The traditional circuit-switched network architecture is based on monolithic network elements which has close coupling of the control and bearer planes. This close coupling has fundamentally limited the scalability of traditional network elements, such as in a MSC. Close coupling of the control and bearer plane has also meant that a complete MSC must be installed in each geographical area to be covered. Consequently, when MSC capacity limits are reached or further geographical coverage is needed, network growth would be achieved by adding more and more MSCs.

There are two types of growth to consider: growth due to increased geographical coverage, and growth due to increased subscriber penetration. When the capacity of an MSC is exceeded, the only solution is to add another MSC. In the early days, when the number of MSCs was low and the geographical area covered by an MSC was quite large, adding more MSCs was not a major problem. However, as subscriber numbers increased and switch coverage areas shrank, the number of nodes in the network steadily increased, with each MSC needing to communicate with all of the other MSCs in the network. So every time another MSC was added to the network, the complexity of inter-MSC communications increased exponentially.

This is also a common networking issue in wireline networks, often referred to as ‘The N2 Problem’. In wireless networks, the complexity of this communications mesh is compounded by the need to maintain up-to-date mobility information for both active and inactive subscribers - the more mobility information to be kept up-to-date, the greater the network inefficiency from the N2 Problem. This is at the heart of the inefficiency of legacy wireless networks, which has a direct bearing on the efficiency savings from more scalable equipment.

The ‘scalability limitations’ of circuit switches constrains network growth as it becomes increasingly difficult to implement a full physical mesh at only one network layer. To overcome this problem, a whole new hierarchy of circuit switches has to be added to provide ‘transit layer’ interconnection of the MSCs. These transit layers typically do not provide end user services and consequently represent increased operational cost for no extra service revenue to the operator. Transit network layers are often implemented for both bearer and signaling traffic, creating multiple overlay networks with corresponding capital and operational costs. Using closely coupled circuit switches in a mature wireless network becomes a spider’s web of hierarchical complexity. In the end, a high proportion of the network’s capability is simply focused on maintaining this level of complexity, rather than on earning service revenue for the operator.

2.2. THE NEXT GENERATION CHALLENGE

The challenge for the target network architecture is ‘how to enable an operator to grow from the early network to the mature network’ without adding the complexity and inefficiency. Clearly, complexity and inefficiency in a network is closely related to the lack of scalability of a MSC and its interfaces, as measured by the added number of MSCs needed to match network growth. The answer to this seeming conundrum is buried in the close coupling of circuit switches and the two types of network growth.

4

First, the new target network architecture must decouple the control and bearer plane. This means that the control plane and the bearer plane should scale independently of each other, rather than limit the scalability of each as they do in traditional circuit switches. Bearer capacity must scale according to the traffic needs of the geographical area that is to be covered. This covers anywhere from low capacity levels in ‘new market’ scenarios, all the way through to high capacity levels in high-penetration mature markets - all achieved without nodal proliferation. This enables efficient network expansion for geographical coverage followed by efficient nodal growth as penetration rates increase.

Decoupling removes the geographical constraints of the control plane capacity from the bearer plane, and eliminates the need for local presence when extending geographical coverage. Once this is achieved, control plane capacity is free to scale as a network wide resource, scaling from the early to late market as needed. The geographical independence of the control plane frees the operator from any constraints of circuit switching, enabling control plane capacity to scale in the most cost effective way. In practical terms, this might include the divestiture or consolidation of property portfolios, as well as a more efficient application of highly skilled and costly labor.

This target architecture is further defined in 3GPP Release 4 Bearer Independent Core Network standards.

3. 3GPP BEARER- INDEPENDENT CIRCUIT-SWITCHED CORE NETWORK ARCHITECTURE

3.1. 3GPP RELEASE 4 ARCHITECTURE

Within 3GPP Release 4, the concept of a Bearer-Independent Circuit-Switched (CS) Core Network was introduced. This built upon Release 99 and provides for a flexible architecture with the option for ATM or IP transport for the core network. The network architecture is specified in 3GPP TS 23.002 Network Architecture and 3GPP TS 23.205 Bearer-Independent Circuit-Switched Core Network. The option for IP bearer support on the Iu interface from the core network to the radio network was added in 3GPP Release 5. 3GPP Release 4 is completed and has been stable since 2003.

The purpose of the Bearer-Independent Circuit-Switched Core Network architecture is to provide the capability to split the control and user planes into separate network entities and to enable usage of a packet-switched backbone in the network. To ensure service continuity, it was important that all end user services (such as supplementary services, SMS and bearer services) as well as network services (such as IN, mobility management, and location services) be unaffected.

At the same time and to ease deployment, the architecture needed to minimize the impact on other network domains, e.g. the access network (BSS and RAN), the SS7 network, the customer care and billing systems, the IN network entities, and the location service entities.

5

MGW

Signalling and Data TransferInterface

SignallingInterface

UTRAN PSTN/Legacy/External

HLRApplications& Services

MSC server GMSC server

Mc

D C

MGWNb

Nc

Iu

Iu

CAPCAP

Mc

GERAN

A

A

Figure 1: CS Core Network Logical Architecture

The Bearer-Independent Circuit-Switched Core Network (see Figure 1) enables the support of different transports (e.g. ATM or IP) in a bearer-independent fashion. For the ATM and IP transport, there is a strict separation between the call control level and the bearer control level. In the case of ATM or IP transport, the passage of compressed speech at variable bit rates is possible through the CS core network.

In order to split the control and user plane, the monolithic MSCs from Release 99 have been separated into the MSC server, GMSC server and media gateways (see Figure 1). The GMSC server and MSC server provides the call control and mobility management functions, and the media gateway provides the bearer control and transmission resource functions, and contains the stream manipulating functions. The GMSC server and MSC server are connected to the media gateway via the Mc reference point. The MSC server and GMSC server are connected to each other with the Nc reference point. There may be a number of call control transit nodes between the MSC server and GMSC server in the Nc reference point. The MGWs are connected with the Nb reference point.

By simply splitting the existing MSCs and defining interfaces between the MSCs and MGWs, while maintaining the existing interfaces to other nodes (e.g. interfaces to the SCP, HLR), there is no impact on existing services. Hence, the users connected to the Bearer-Independent Circuit-Switched Core Network are not aware whether a MSC server/media gateway combination is used, or a monolithic MSC is used.

The architecture can thus be seen as a CS core internal issue without impact on the other reference points, network elements and subsystems.

3.1.1 MC INTERFACE

The Mc reference point defines the interface between the (G)MSC server and the MGW. The H.248 protocol, together with 3GPP specific extensions (i.e. packages), is used over this Mc interface.

H.248/MEGACO has been jointly developed within the ITU-T and the IETF, and supports a separation of call control entities from bearer control entities, and a separation of bearer control entities from transport entities. H.248 is used on the Mc interface between the (G)MSC servers and the media gateway.

6

3.1.2 NC INTERFACE

The Nc reference point defines the interface between MSC servers. The Bearer Independent Call Control (BICC) protocols defined by ITU-T are used over the Nc interface.

The BICC architecture as described in ITU-T Q.1902 consists of the following types of protocols: call control protocol, bearer control protocols and a resource control protocol.

The call control protocol is based on ISUP and enables setting up different types of bearers required in the Nb interface between MGWs.

3.1.3 NB INTERFACE

The Nb reference point defines the interface between MGWs. Bearer control and transport are performed over the Nb reference point, which may be RTP/UDP/IP or AAL2/ATM for the transport of user data. Both IPv4 and IPv6 can be used.

The user plane protocol used between two media gateways in the CS core network is referred to as the Nb UP protocol. The Nb UP protocol is very similar to the Iu UP protocol used between RNC and MGW.

The Nb UP framing is identical to the Iu UP framing (i.e. the same PDU types are valid for both protocols).

MGWMGW

NbIu

Transport Layer

SRNC

Radio Protocols

Iu UP Iu UP Nb UP

Nb UP

Figure 2: Nb UP Protocol Layer Occurrence in Overall Architecture

Figure 2 shows the logical location of the Nb UP protocol layer in relation to the Nb interface. Nb UP defines initialization, rate control and time alignment procedures in addition to user data transport.

The AAL2 Signaling Protocol defined in ITU-T Q.2630.2 is used for the establishment of AAL2 connections.

The ITU-T Recommendation Q.1970 “BICC IP Bearer Control Protocol” (IPBCP) is used for IP bearer establishment. IPBCP is transported over the Mc and Nc interface by means of the ITU-T Recommendation Q.1990 “BICC Bearer Control Tunneling Protocol”.

Nb supports AMR, EFR and G.711 codecs.

7

MGW MGW

MSC-Server MSC-ServerNc

Mc

Nb

Mc

TS 29.232

BICC: Q.765.5

Tunnel: Q.1990

IPBCP: Q.1970

Figure 3: Transport of IPBCP

3.2. REL- 4 NETWORK ELEMENTS

3.2.1 MSC SERVER

The MSC Server mainly comprises the call control (CC) and mobility control parts of a MSC. It is also integrated with a VLR to hold the mobile subscriber's service data and CAMEL-related data. The MSC Server is responsible for the control of mobile-originated and mobile-terminated CC CS domain calls.

The MSC server terminates the user-network signaling (see 3GPP TS 24.008) and translates it into the signaling over the Nc interface. It also terminates the signaling over the Mc interface with the media gateway. The MSC server controls the parts of the call state model that pertain to connection control for media channels in an MGW. It also contains the 'Call Control Function' in the BICC model.

3.2.2 GMSC SERVER

The GMSC server mainly comprises the call control and mobility control parts of a GSM/UMTS GMSC as described in 3GPP TS 23.002.

The GMSC server terminates the signaling over the Nc interface and the call control interfaces to the external networks. It also terminates the signaling over the Mc interface towards the media gateway. The GMSC server controls the parts of the call state model that pertain to connection control for media channels in an MGW. It also contains the 'Call Control Function' in the BICC model.

If a network delivering a call to the PLMN cannot interrogate the HLR, the call is routed to a MSC. The MSC will interrogate the appropriate HLR and then route the call to the MSC where the mobile station is located. The MSC, which performs the routing function to the actual location of the MS, is called the Gateway MSC (GMSC).

The choice of which MSCs can act as Gateway MSCs is for the operator to decide (i.e. all MSCs or certain designated MSCs).

8

3.2.3 MEDIA GATEWAY

The media gateway (MGW) terminates the signaling over the Mc interface from the (G)MSC servers. It also terminates the bearer part of the signaling over the Iu interface and the Nb interface. A MGW terminates bearer channels from a circuit-switched network and media streams from a packet network (RTP streams in an IP network or AAL2 channels in an ATM network).

The MGW bearer control and payload processing capabilities also needs to support mobile specific functions such as SRNS relocation/handover and anchoring. The MGW supports 3GPP bearer and supplementary services. This means that it should support 3GPP specific CS data handling, as well as have support for services such as conferencing, tones, DTMF detection/generation and announcements.

For support of Iu interface, the MGW supports AMR codec. EFR support is also useful, as an option for Iu, and also provided for codec compatibility in 2G to 3G relocation. For support of Nb interface, AMR and G.711 codecs are supported over the NbUP.

At a minimum, echo cancellation and automatic level control are required for speech quality. Regulatory requirements such as Lawful Interception (i.e. CALEA) are also supported.

3.3. GSM TO UMTS EVOLUTION

The CS services in GSM and UMTS are nearly identical. The most notable difference relates to the capability of UMTS to support transparent 64 kbit/s synchronous CS data services that enables services such as video calling. Thus, from the service control and control plane points of view, the CS core provides excellent evolution possibilities. In most cases, the same infrastructure can be used.

For the user plane, the UMTS architecture differs slightly from GSM with the transcoder being located in the core network (vs. the access network with the GSM access). However, in most cases the location of the codec is a minor issue compared to the support of the CS-related bearer and supplementary services. Despite this difference, the Bearer-Independent Circuit-Switched Core Network supports both UMTS and GSM networks. More information can be found in the 3GPP Technical Report TR 23.977.

Introducing UMTS as an overlay network and the recommendation to utilize excess capacity in GSM CS Core Network are common and valid approaches for supporting UMTS access.

4. TRANSMISSION NETWORK The data networking industry has been debating whether to use IP or ATM in Carrier Data Networks for many years now. Strong opinions are routinely voiced on both sides of this argument and several ‘claims of victory’ have already been made prematurely. In reality, there are still no signs of this debate reaching a conclusion. Strong sales of both types of Carrier Data products have continued, even through the depths of the telecommunications economic downturn.

4.1. TRANSMISSION NETWORK SOLUTIONS

One of the key criteria behind the choice of VoIP or VoATM is the nature of the transmission network infrastructure that is available to the wireless operator. One of the business drivers for many operators is ‘how to achieve operational cost reduction through transmission capacity savings’. Next Generation Networks can enable operators to achieve substantial efficiency gains, which becomes an important factor when choosing the technology to use. As a business driver, the relative transmission network efficiency of each technology must be considered.

9

Many wireless operators have traditionally taken the view that their business is concerned more with wireless service provision than with transmission network provision. Consequently, this has often been ‘outsourced’ to other network operators who have specialized in this kind of business. For this reason many wireless networks use leased line transmission capacity, which represents a recurring operational cost to the business. An advantage to this approach is that the wireless operator is free to focus on its core business of wireless service provision without diversionary distractions into other business directions. If transmission network capacity is abundant or transmission costs are low, the operator may not be concerned by this operational cost.

However, if capacity is scarce or expensive, or if the distances involved are long, then a Next Generation Networking business driver might be to achieve transmission cost savings. In this case, the efficiency of the protocol used becomes important. There is no simple rule that can be applied; however, as the cost of transmission capacity can vary enormously between countries, and even within the same country. In recent years, some countries have seen substantial capital investment in transmission capacity, which has led to increased competition and lower transmission capacity prices.

Even so, some operators have chosen to invest in their own optical fiber infrastructure, which requires substantial capital investment. This financial justification is often based on the savings of transmission network costs that was discussed above. The availability of existing capacity and its corresponding pricing trends must clearly be considered.

Next Generation Networks provide an alternative solution to implementing an optical network. Wireless operators or their parent companies that have already implemented an optical network are effectively exchanging the ongoing recurring operational cost of leased lines for an immediate capital investment in their own optical infrastructure. In many cases this could be classified as diversification from wireless into the transmission network business. Looking at where investment in an optical network has already been made, the wireless operator has created access to abundant low cost transmission capacity. It should be noted that in this scenario, the operator is typically not necessarily concerned with packet voice transmission efficiency.

4.2. ATM OR IP

In 3GPP Release 4, both IP and ATM transport is supported in the CS core network. In the Iu CS interface, IP-based transport is introduced by 3GPP Release 5. From a standards point of view, both transport solutions are valid choices.

ATM is the more conventional approach, with well-understood QoS mechanisms containing hard guarantees. ATM is used as transport in current WCDMA access networks and Iu interfaces, and is thus widely supported. It is also available in most markets. In the user plane, 3GPP defines the usage of AAL2 to enable efficient utilization of bandwidth - with AAL2 channels being created on a call-by-call basis.

However, ATM network management is inherently more complex. To be able to set up AAL2 channels on a call-by-call basis, ATM VCC must exist before the AAL2 channel can be set up. This means that SVCs cannot be used on the ATM level. Network planning and management is further complicated in big networks due to the limited number of ATM switches capable of switching on the AAL2 level that are deployed or available. ATM is also generally perceived as more expensive from the capital expenditure point of view.

IP transport on the other hand is often perceived as lacking on its ability to provide guaranteed QoS solutions. This is partly based on perception, but also reflects how IP networks typically have been designed and managed. With proper design and management, IP QoS is not an issue on current networks. Since traffic is generated by elements controlled by the network operators, the problem is further minimized when considering IP transport in the CS core. With admission control at the edges of the network (in A- or Iu-interface and the PSTN-interface), the traffic type and behavior is more predictable than, for example, the Internet. Due to the nature of IP, the networks can be significantly simpler from a management point of view.

10

From a network evolution perspective, IP is a more natural fit when considering current development trends in networks and backbone infrastructure. This applies both to service development trends, as well as technology development trends. ATM and IP co-existence, and ATM to IP(/MPLS) migration issues are also well understood and supported by all major backbone vendors.

Thus, it can be concluded that both ATM and IP (or a mix of technologies) are all valid options. ATM might be more relevant in cases where a more conventional and familiar approach is preferred, and might even be dictated by deployed infrastructure. IP on the other hand might be preferred from a strategic viewpoint when taking operational and capital expenditure considerations into account.

4.3. PACKET VOICE TRANSMISSION EFFICIENCY

The most efficient way to transport digital speech is through conventional TDM techniques, primarily because there is no additional header information needed in TDM and consequently a 64kpbs constant bit rate voice stream is all that is needed. However, significant capacity savings can be achieved by compressing speech or by suppressing “unnecessary” traffic, such as silence. When this is achieved, the digital speech is no longer a constant bit stream of 64kbps, but is a highly bursty ‘variable bit rate’ bit stream. With silence, the bit rate can be close to zero. But if this were to be transmitted in the conventional TDM way, the full 64kbps would still need to be used, even if the actual compressed speech bit rate was close to zero.

In order to realize the capacity savings achieved through compression and silence suppression, the variable-bit-rate traffic must be sent in packet form. To accomplish this, a packet header must be attached to the payload, which has the opposite effect on compression in that it actually increases the amount of information that has to be sent. If the amount of header information is greater than the amount of bandwidth saved through compression, then the total capacity used would be less efficient than TDM. If saving bandwidth is the objective, then there may be no point in using packet speech in this case.

Mobile codec compression in the handset can be applied using high compression ratios to optimize the efficiency of the radio network interfaces used. Mobile codec compressed speech can provide significant savings against TDM networks even if large packet headers have to be attached. However, this is only possible if the speech stays compressed for the complete end-to-end speech path. To calculate the optimum bandwidth efficiency in the backbone for compressed speech, we need to compare the packet header efficiency of the different transport protocols for the whole protocol stack.

The transmission network capacity used by packet voice is influenced by several factors:

• The rate of compression for the call achieved by the voice codec (if it is used on the backbone).

• The voice sampling rate.

• Additional traffic reduction techniques, such as silence suppression.

• The efficiency of the packet network protocol used for the call. That is, the overhead cost varies depending on the protocol (e.g., VoIP or VoATM). Each protocol offers more than one implementation option, each with its own efficiency implications.

11

4.4. COMPRESSION IN WIRELESS

The discussion on transmission network efficiency provided above introduces the utilization of voice codecs in wireless voice transport. Wireless terminal devices compress speech prior to being transmitted over the radio interface in order to make optimum use of the available radio capacity. This is a major difference from wireline terminal equipment where this does not occur. Consequently, in wireless networks it makes sense to leave this pre-compressed speech in its compressed form since decompressing it would add to voice path delay, degradation in voice quality and an increase in the amount of bandwidth needed to carry it on the network. In the TDM networks operating today for both GSM and UMTS, these downfalls are prevalent. So unlike wireline networks where bandwidth saving is achieved by adding compression, in wireless networks it is achieved by simply avoiding decompression. This results in fewer delays, higher voice quality and less traffic on the network. This benefit is equally applicable to both VoIP and VoATM, and although is not a major consideration in the choice of packet protocol, it is a significant factor in choosing to move from TDM to packet.

4.5. QUALITY OF EXPERIENCE

Quality of Experience highlights important issues such as service continuity and Quality of Service.

From a service point of view, the 3GPP Rel-4 CS core network architecture provides seamless continuity. All Rel-99 and earlier services are supported. This includes tele-services, bearer services and supplementary services. The end user is unaware of which type of CS core network he is being served by.

Quality of Service in mobile networks is mainly affected by the nature of the radio interface (need for compression, packet loss, jitter and delay). These factors also apply to using packet-switched technologies for the fixed portion of the call.

The following table further elaborates on end user / application QoS requirements according to 3GPP TS 22.105 Service and Service Capabilities.

Table 1: End-user Performance Expectations - Conversational / Real-time Services

Medium Application Degree of symmetry Data rate Key performance parameters and target values

End-to-end one-way

delay

Delay variation within a

call

Information loss

Audio

Conversational voice

Two-way

4-25 kb/s

<150 msec preferred <400 msec limit Note 1

< 1 msec

< 3% FER

Video

Videophone Two-way 32-384 kb/s

< 150 msec preferred <400 msec limit Lip-synch : < 100 msec

< 1% FER

Data

Telemetry - two-way

control Two-way <28.8

kb/s < 250 msec N.A Zero

Data Interactive games Two-way < 1 KB < 250 msec N.A Zero

Data Telnet Two-way (asymmetric) < 1 KB < 250 msec N.A Zero

Note: The overall one-way delay in the mobile network (from UE to PLMN border) is approximately 100 msec.

12

In practice, there exists a delay of 80-100ms (UL) with the mobile and the access network, which means that even with no delay in the core network, the preferred values of <150ms will not be reached in a mobile-to-mobile call.

When using packet-switched transport in the CS core network, the core network introduces further delay. The delay mainly comprises packetization delay and jitter buffers required to keep the jitter within acceptable values. The IP or ATM backbone itself, as well as the routers and switches in the backbone, introduce insignificant delay compared with the delay of the end points and transmission.

As in traditional mobile CS networks, QoS is highly affected by the used codecs. 3GPP has defined Tandem Free Operation (TFO) to provide codec transparency when originating and terminating parties support the same codecs. TFO can also be supported over 3GPP Rel-4 CS core networks. 3GPP has further defined Out of Band Transcoder control (also called Transcoder Free Operation or TrFO) in UMTS access cases to provide both codec transparency and bandwidth savings when the Rel-4 CS core network architecture is used. In TrFO, the transcoders in the core network are effectively bypassed and inserted only when the core network needs it for inter-working reasons. 3GPP is currently working on providing similar benefits for a TFO type of solution for the TrFO, enabling the same level of service for GSM as for UMTS accesses.

5. BEYOND R4 – IP MULTIMEDIA SUBSYSTEM (IMS) The “Always On” subscriber is slowly coming of age. Ubiquitous broadband access is ushering in new consumer and lifestyle convergence – communication, entertainment, work, leisure, distance, and time. The demand for new and sophisticated ways of being in constant contact everyday, enlarging the “community” for leisure and entertainment anywhere and anytime, and enhancing the effectiveness and the efficiency in the workplace, have all dramatically increased. For operators, business success can no longer be guaranteed by making incremental improvements in their existing products, services and business models within this new environment.

The third generation body 3GPP is driving these rapid changes by specifying the IP Multimedia Subsystem (IMS), starting with Release 5, as the enabling vehicle by which this demand will be met. IMS is a new layer in the packet domain and will provide person-to-person, real and non real-time integrated multimedia services such as voice, video, instant messaging, on-line gaming, web sharing and many other services over a single IP network. IMS will bring the full potential of Internet technology to mobile users, allowing the creation of a new business cycle for wireless operators.

13

At network level ubiquity broadband access, Packet Switching technologies, SIP protocol, have been adopted as the multimedia convergence technologies. However, one of the key questions that the industry will need to ask itself is: to what extent will mobile services integrate and inter-operate with Internet services in order to satisfy these new market demands. Deploying profitable and cost effective solutions that enable multimedia services to be compelling, flexible and easy to use represents the new challenge for network operators.

GSM infrastructure providers are leveraging their own unique data and networks expertise to help this transformation by building convergent networks able to deliver services across various networks and media. This results in bringing new value to the end user experience and new streams of revenues to the operators.

• Enhanced Experience• Simplified usability• Seamless services access• Single User ID• Single bill

• Revenue generation• Stimulate data usage• Churn Reduction• Services control• OPEX/CAPEX optimized • Seamless services offer

end-user

operator

14

5.1. ARCHITECTURE OVERVIEW

The following diagram indicates the main components of the IMS architecture:

CSCF - Next generation call control: The Call State Control Function (CSCF) is an enhanced SIP proxy (i.e. an entity that routes SIP messages). Additional wireless capabilities are added (i.e. SIM-based authentication, billing, QoS control). Three "flavors" of CSCF have been defined (P-CSCF for Proxy, I-CSCF for Interrogating, and S-CSCF for Serving) potentially allowing a better repartition of the functionalities in different nodes, thereby providing more scalability, as well as roaming capabilities.

HSS - Centralized Subscriber Data/Authentication: The 3GPP IMS relies on the packet core for connectivity to the handset/client. The provisioning and authentication data is held at the HLR. The 3GPP IMS also needs its own provisioning and authentication information, therefore the HLR is extended to hold this information in one place – the Home Subscriber Server (HSS).

The Home Subscriber Server (HSS) is the master database for a given subscriber in the IMS domain. It is a key network element in the IMS network environment that facilitates mobility and service management for the IM-subsystem domain.

Open Applications Architecture: 3GPP defined a high-level architecture to allow SIP application servers, 3rd party applications and CAMEL SCPs to inter-work with the call control. This concept would allow the wireless operator to easily mix and match applications from different vendors and re-use legacy IN services. The service-triggering mechanism (through the standardized ISC interface) would offer the possibility of providing many different services based on a dedicated application server, controlled by either the wireless service provider or through a 3rd party. The ISC would also allow interfacing with OSA GW or existing IN/CAMEL platforms by means of the IM-SSF gateway.

Connectivity: Packet and Access enhancements – to allow real time services to work, many changes are required in the access and packet domains. This ensures appropriate Quality of Service (QoS) behavior for real time services (jitter and delay) and ensures the IP bearer is efficiently used. In addition, the packet core needs to be able to handle IPv6 addressing as defined by the 3GPP for the IMS.

PDF: Quality of Service and admission control – in the wireless domain, control of radio resources is critical. Hence, 3GPP has added procedures to ensure the application layer (CSCF) and bearer layer (GGSN) are well coordinated. The Policy Decision Function (PDF) is

GGSN

MGCF

Application Layer

Control Layer

Connectivity Layer MGW

HSS

Go

PSTN/PLMN

Internet/Intranet

I/S/P CSCF

R4 BICNMGW

MSC Server

Internet/Intranet

15

responsible for coordinating the set up of bearers (secondary PDP context establishment) with session setup (SIP “Invites”). In addition, application layer and bearer layer billing IDs are exchanges for billing correlation.

MGCF, IMS-MGW: Circuit Domain Inter-working – the 3GPP standards define the PSTN inter-working architecture in R5, with detailed call flows in R6. The Media Gateway Control Function (MGCF) is roughly equivalent to the Call Server in a R4 BICN architecture. It terminates SIP sessions and provides ISUP (or equivalent) signaling to the PSTN. The IMS-Media Gateway (IMS-MGW) provides inter-working and transcoding from IP bearer to TDM (or potentially VoIP or VoATM).

6. CONCLUSIONS Operators with mature wireless networks that have grown organically over several years will be familiar with the rising network costs at a time of limited revenue growth. The question of how to reverse this trend, or even simply contain it, is the focus of many operators today. However, this question is also relevant to operators of less mature networks and for those operators building Greenfield networks. Operators need to learn the lessons gained from the first generation of mature wireless networks.

A major component to the rising costs from mature networks has been identified as a function of network growth. Network growth has been achieved through the proliferation of multiple network nodes, versus scaling up of a smaller number of nodes. The proliferation of network nodes creates significant network overheads that enable network nodes to communicate with other networks nodes. This problem increases exponentially with the number of nodes in the network. Communication between nodes is necessary to maintain important functions such as location updates and active mobile handovers.

The large number of network layers further adds a dimension to this problem. The emerging wireless service proposition is no longer simply based on TDM telephony, but is a diverse package of services of which many will be based on packet technology. Implementing different network layers for each service type, network command and control means that the wireless operator is no longer operating a single network, but rather several networks at once. The consolidation of these multiple overlays into a single multi-service network is a key goal of the Wireless Next Generation Core Network.

Nodal scalability is also addressed through Wireless Next Generation Core Networks with the complete separation of the bearer and control plane, enabling each function to be scaled independently of the other and be geographically independent of the other. Containing the optimum number of network elements needed for geographical coverage and network resiliency ensures that the network cost model is optimized for the operators own circumstances. The scaling of each node in the network can then be implemented as growth requires it. Nodal scalability is achieved through the application of packet network techniques specifically to avoid the limitations of traditional TDM technology.

3G Americas believes that the application of Next Generation technology can bring a diverse range of benefits to operators of any type. GSM operators have the advantage by having 3GPP specifying the IP multimedia subsystem (IMS), starting with release 5. Long term benefits can be achieved through the simplification and consolidation of a network into smaller numbers of scalable network elements. This means that a mature network can be consolidated and simplified to contain escalating network costs. In the same way, less mature networks can avoid the pitfalls of network growth that were prevalent in first generation wireless networks.

IMS is a powerful network strategy providing GSM operators a new layer in the packet domain that will provide person-to-person, real and non-real time integrated multimedia services such as voice, video, instant messaging, online gaming, web-sharing, and other services over a single IP network.

16

ACKNOWLEDGMENTS

The mission of 3G Americas is to promote and facilitate the seamless deployment of GSM, GPRS, EDGE, and UMTS throughout the Americas for the benefit of consumers. 3G Americas' Board of Governor members include AT&T Wireless (USA), Cable & Wireless (West Indies), Cingular Wireless (USA), Ericsson, Gemplus, HP, Lucent Technologies, Motorola, Nokia, Nortel Networks, Openwave Systems, Research In Motion, Rogers Wireless (Canada), Siemens, T-Mobile USA, Telcel (Mexico), and Texas Instruments. We would like to recognize the significant project leadership and important contributions of Harshad Patel of Nortel Networks to this white paper.