Introduction

The development of mobile technology began with the intention to relieve the dependency of the user on a particular location. With the evolution of mobile networks, mobile data access was offered, and relatively quickly it has begun to represent an important revenue generator for the typical mobile service provider (SP).

Mobile networks have become very complex. The following sections of this article present a brief overview of each of these technology solutions.

The long-term goal of the providers of mobile data technology is to offer data-transfer rates comparable to those of fixed broadband. Recent market research shows a growing gap between the statistical rates of data usage for mobile versus fixed data (database, throughput etc.). These changes are the direct result of the gradual migration of data users from fixed to mobile data services.

Enhancements on the radio access side (3G and 4G) have ensured the exclusion of radio data access as a network bottleneck. It is worth mentioning that the average quantity of data transmitted over a network by a user has changed rapidly, since nowadays data-users' habits are related to more diverse and often heavy loads.

While tremendous change has happened on the radio access side, bringing high-bandwidth capacity to widespread end users, it has triggered other evolutionary improvements to wireless networking. New, easily available services have emerged, imposing themselves as the revenue generator.

Mobile data services are still considered as the desire of the audience, the goal of investors, and the source of value-added applications for service providers.

Mobile access evolution

Due to constant improvement of coding schemes on the radio access side, capacity throughput has been enhanced significantly over the past 12 years.

Figure 1 (Source: Cisco)

Different data-rates shown with the access technology evolution

The Global System for Mobile Communications (GSM) has used the Time-Division Multiplexing (TDM) channel for either voice or data traffic, whereas the General Packet Radio Service (GPRS) uses coding schemes CS-1 through CS-4, and Enhanced Data Rates for GSM Evolution (EDGE) improves them to modulation coding schemes (MCS) – Gaussian Minimum Shift Keying (GMSK) and 8-Phase Shift Keying (8-PSK). The Universal Mobile Telecommunications System (UMTS) with HSPA capacity improvements such as Quadrature Amplitude Modultaion (16QAM) employ Wideband Code Division Multiple Access (WCDMA), while Long Term Evolution (LTE) has benefited from Orthogonal Frequency-Division Multiplexing (OFDM).

There are two main limiting aspects of throughput on 3G radio access:

Radio conditions related to the user's physical position and relative speed of the user's equipment.

Due to the limited number of channels per radio carrier, throughput is in inverse proportion to the number of available channels. In other words, a user who is allocated greater throughput reduces available resources for other users in the same cell.

IP RAN – Aggregation and mobile backhaul

A single network might use several transport technologies (SDH, ATM, FR etc.). In order to optimize such a variety, and improve the capacity and simplicity of the transport infrastructure, operators tend to introduce IP Radio Access Network (IP RAN) solutions as an intermediary step that allows them to make the most of 2G/3G technology that uses non-IP-based interfaces. As a carrier, IP RAN typically uses Dense Wavelength-Division Multiplexing (DWDM) transport. On top of this, an IP Multiprotocol Label Switching (IP/MPLS) cloud could be built, as the high-performance choice; or a pure IP transport could be used to carry pseudowires of a different nature (TDM, ATM, ETH etc.). The mobile transport network could be used as part of the common Carrier Ethernet Transport, which could include some other possible uses of the pseudowires (PBX, VoIP etc.) belonging to the same service provider, or rented to another operator.

Figure 2 (Source: Cisco)

Example of pre-aggregation and aggregation levels in IP RAN

Evolved Packet Core (SGSN, GGSN)

The Gateway GPRS Support Node (GGSN) acts as the gateway between the GSM network and the external packet data network, or Internet. It is a Network Access Server (NAS) for GPRS/UMTS users, communicating with the Authentication, Authorization and Accounting (AAA) server for user identification, and with the charging facilities for prepaid or postpaid users.

The Serving GPRS Support Node (SGSN) is responsible for the termination of bearer and signaling and delivery of data packets to and from the mobile stations within its geographical service area. The SGSN handles mobility management (attach/detach and location management), logical link management, and authentication in home-location register (HLR) and possibly also charging functions.

Typically, but not necessarily, GGSNs are more centrally located with HLR/VLR/MSCs, while SGSNs are more often geographically distributed with BSC/RNCs.

The Packet Control Unit (PCU) performs encapsulation/decapsulation of packet-related resource and process packets between RLC/LLC and BSSGP protocols (on the radio bearer).

Figure 3 (Source: Cisco)

GPRS architecture elements

Content charging, policy control, real-time billing

Revenue is based not only on user subscriptions or usage, but on the nature of the content. The main reason for this innovation was the fact that mobile SP revenues were being outpaced by infrastructure investments. Different content related to the particular applications could be charged at individual rates to increase revenues.

For this purpose, operators introduce deep packet inspection (DPI) on the Gi interface, and GTP prime (GTP') tunnels for real-time billing (closely related to mobile prepaid data access) and Charging Data Record CDR repository on the Ga interface.

Figure 4 (Source: Cisco)

Functional position of DPI element

The DPI function is a network resource that provides high-throughput analysis of all the traffic with no latency. It might be combined with the Policy Server on the Gx interface; for example, in order to impose different rates to users dynamically. The same Policy Server could operate on the Rx interface, providing a similar function over the IP Multimedia Subsystem (IMS) cloud.

With the increasing commercial success of mobile data access, similar needs have occurred in other broadband technologies, such as the need for statistical overview of traffic and filtering/policing. However, the main need recently is the ability to control increasing peer-to-peer traffic, which avoids standard charging and payment for the use/purchase of intellectual property. Network elements such as DPI are put in the way of the traffic, from the subscriber side toward the network side, controlling both directions.

Service Delivery Platform

Creative business models focus on revenue generation that benefits from translating marketing ideas into the systems used by the mobile SPs. The globalization benchmark would allow potential service users to access anything, anywhere in the cloud, without the need for a physical presence, and not limited to a particular country. This goal rapidly increases the number of users and transactions, but with a huge impact on the infrastructure.

The goal of service delivery platforms (SDPs) is to provision and monetize these services faster, modifying them as they grow. This capability gives the mobile SP a competitive value-add advantage over the competition.

The SDP's task is to integrate customer-related applications such as CRM, billing, provisioning, inventory and service activation over standardized interfaces, propagating changes to the network core components. This important role takes into account both service-oriented architecture (SOA) and real-time billing.

The total SDP global market has reached a value of approximately $3 billion U.S.—the exact number forecast about two years ago. The current forecast for the next four years doubles that value (http://www.researchandmarkets.com/reports/1071153/service_delivery_platforms_market_review.htm).

Mobile users are expected to spend more money on the other applications or products delivered in addition to each user's costs for the subscription or traffic volume. SDP is a fundamental part of the 3G/IMS-based network design that delivers these revenues.

Figure 5 (Source: Teligent)

SDP introduces multi-purpose missing layer

Services are available across a wide variety of transmission methods:

Short Message Service (SMS): Banking, news, stock market, sports-related, quizzes

Multimedia Messaging Service (MMS): Ringtones, animated content, audio/video content

Wireless Application Protocol (WAP) and GPRS: Gaming, betting, browser downloads, e-mail, financial (banking)

Streaming: Broadcast of live radio, TV programs, audio/video on demand

IMS architecture

IMS architecture was developed to provide multimedia support to the end user connected over broadband access. It may be found more often in the mobile environment, although this is likely a consequence of the larger average revenue per user (ARPU) and faster subscriber database growth of mobile services. Fixed broadband might use similar but less expensive platforms, with reduced functionality. If a service provider wants to introduce fixed mobile convergence (FMC), the IMS platform could enable it.

To bring multimedia content (audio, video, messaging, etc.) to the user, Session Initiation Protocol (SIP) was developed as a (text-based) signaling protocol, and it holds a key position within the IMS architecture. SIP enables not only the usual communication session control, but also controls the sessions for advanced services (such as ringtone generation) that work with the external servers over SIP. For negotiation and description of the sessions' capabilities, SIP benefits from the Session Description Protocol (SDP).

The signaling control is focused on the Call Session Control Function (CSCF) element of IMS.

Since the initiation of the session is determined by the user's location, SIP is responsible for determining the location – therefore, SIP supports the user's mobility. Furthering the market requirement for user mobility, combined with retaining the same network resources offered by the mobile SP, a new IETF standard has been developed: Mobile IP (described in detail in the following section).

IMS layered architecture and protocols:

SIP: application layer text-based protocol for creating, modifying and terminating IMS sessions

SIP I/T: SIP enhancement for public switched telephone network (PSTN)/public land mobile network (PLMN) interworking with IP networks

DIAMETER: AAA, policy negotiation and Quality of Service (QoS) negotiation

H.248/Media Gateway Control Protocol (Megaco): control mechanism protocol allowing the media gateway controller or equivalents to control the media gateway

Real-time Transport Protocol (RTP): standard format for audio and video delivery over the Internet

Real-time Transport Control Protocol (RTCP): protocol for out-of-band control information and QoS information for an RTP flow

XML Configuration Access Protocol (XCAP): set of conventions for mapping XML documents and document components into HTTP Uniform Resource Identifiers (URIs); XCAP allows a client to read, write and modify application configuration data stored in XML format on a server

The main purpose of the Session Border Controller (SBC) is the protection of the owner network from potential attacks from other networks and malicious users. The SBC contains a firewall and other security functionalities. Also, the SBC could be used for billing purposes after being integrated with billing platforms.

This level of protection could be used between two SPs, or between the SP and its client. A SIP-aware enterprise level of the Session Border element creates a demarcation between the SP and the enterprise client's responsibility – it's a signaling contact point.

Mobile IP Standard

The need for uninterrupted location-independent access to the user's home IP address and infrastructure created a new standardization task.

The Mobile IP standard (RFC 3344) allows mobile users to stay attached to their home network, regardless of the current “foreign“ connection location or technology, via proven mobility over WLAN, satellite, GPRS, CDMA2000, OFDM-4G, WiMAX, etc.

Much of the VPN tunnel-like style found an appropriate appliance, avoiding obstacles and preventing user discomfort due to unavailability of the service.

Figure 6 (Source: Cisco)

There is a similarity between Mobile IP and GPRS tunneling

Uninterrupted access is provided by creating a tunnel between the home network and the visiting network. The endpoints of the IP-in-IP tunnel are the Home Agent and the Foreign Agent. After encapsulation/decapsulation of the tunneled content, the mobile user keeps the same internal IP address (as seen from the user's home network perspective). As a result, all the services offered will work without any issues, and the SP can control the handover process.

A mobile node, such as a personal digital assistant (PDA), a laptop computer or a data-ready cellular phone, uses a “Home Address“ for internal communication between the endpoints, and a temporary “Care Of Address“ for external routing over the access networks.

Figure 7 (Source: Cisco)

The tunnel over Internet is created between HA and FA

Mobile Router (MR) - host or router that changes its point of attachment from one network or subnetwork to another

Home Agent (HA) - router located on the mobile node's home network

Foreign Agent (FA) [one hop away from MR] - devices on a network that are capable of acting as a detunneling point for datagrams to the mobile node

Care of Address (CoA) [Tunnel Endpoint] - address used temporarily by a mobile node as a tunnel’s exit point when the mobile node is connected to a foreign link

Correspondent Node (CN) - node on the network

Security Association (SA) [SPI/Key] - authentication between MR and HA

ICMP Internet Router Discovery Protocol (IRDP) [Advertisement]

Registration Request (RRQ)

There is one considerable drawback to this solution: overhead due to added tunnel headers.

Figure 8 (Source: Cisco)

The Home Agent acts as an anchor point for mobility support of the mobile nodes

In the next-generation network with Mobile IP support, the same IP address and the network resources will be available regardless of the access technology.

Conclusion

We are currently on the eve of the circuit-switching fixed or mobile SP networks, and the introduction of all-IP next-generation networking (NGN), based on high capacity and strong performance network resources, is creating a completely new business developing plan.

An important commercial driver of mobile technology is the market offer of revolutionary portable devices such as laptops or PDAs with 3G/WLAN connection. The most popular PDAs or smartphones are Nokia's Symbian-based devices (dominant), iPhones, Google's Android-based devices, RIM's Blackberries and Windows Mobile PDAs with similar capabilities. Such mobile devices are bringing the services into the focus – newly developed, attractive and well-promoted, easy to understand and helpful.

This could well imply in the future an even more dominant position for mobile technology players (vendors, integrators SPs), based on IP networks.