Mobile Wireless Overview
A fast-paced technological transition is occurring today in the world of internetworking. This transition is marked by the convergence of the telecommunications infrastructure with that of IP data networking to provide integrated voice, video, and data services.
As this transition progresses, the standards are continuing to evolve and many new standards are being developed to enable and accelerate this convergence of telecommunications and IP networking to mobilize the internet and provide new multimedia services.
The Cisco IOS Mobile Wireless Configuration Guide discusses the technologies implemented in the Cisco IOS software that support mobile wireless communication and IP data services in a mobile wireless environment.
This chapter includes the following sections:
•Introduction to Mobile Wireless Technology
•Model for IP Integration into Mobile Wireless
•Mobile Wireless in Cisco IOS Software
Introduction to Mobile Wireless Technology
The technologies related to wireless communication can be complex to differentiate. Wireless technology has been around for a while; however, there has been a relatively recent and rapid surge in the evolution of new wireless standards to support the convergence of voice, video and data communication. Much of this rapid evolution, or revolution, is a result of people seeking ubiquitous and immediate access to information and the assimilation of the internet into business practices and for personal use. People "on the go" want their internet access to move with them, so that their information is available at anytime, anywhere.
There are many factors that can be used to characterize wireless technologies:
•Spectrum, or the range of frequencies in which the network operates
•Transmission speeds supported
•Underlying transmission mechanism, such as frequency division multiple access (FDMA), time division multiple access (TDMA), or code division multiple access (CDMA)
•Architectural implementation, such as enterprise based (or in-building), fixed, or mobile
In addition, the mobile wireless technologies [such as Global System for Mobile Communications (GSM), TDMA, CDMA] are differentiated by a number of different factors, including some of the following:
•Control of the transmitted power
•Radio resource management and channel allocation
•Network topology and frequency reuse
The Cisco IOS Mobile Wireless Configuration Guide focuses on technologies that are directly related to the mobile wireless segment of wireless communication. As suggested by its name, mobile wireless communication addresses those wireless technologies that support mobility of a subscriber, which provide seamless and real-time services without interruption. Mobile wireless technologies support network access whether subscribers roam within or outside their home wireless coverage area.
Overview of Basic Network Elements Associated with Cellular Networks and Mobile Wireless
This section provides a brief introduction to a few of the basic network components associated with the existing telecommunications infrastructure. It specifically discusses the existing mobile wireless network infrastructure components for TDM-based wireless networks, some of which eventually will be replaced by new IP-based components.
In the early 1980s, support for mobile wireless communications was introduced using cellular networks, which were based on analog technologies such as AMPS. Many of the telecommunications entities associated with cellular networks still play a vital role in today's wireless networks. As wireless communications technologies continue to progress and IP data networking is further integrated into the existing infrastructure, some of the functions of these entities might still exist within the network, but will be implemented in different and more effective ways.
The following network elements are part of a typical cellular telecommunications network:
•Public Switched Telephone Network (PSTN)
•Mobile Switching Center (MSC)
•Base Station (BS)
•Radio Access Network (RAN)
•Home Location Register (HLR)
•Visitor Location Register (VLR)
•Authentication Center (AC)
Public Switched Telephone Network (PSTN)
The PSTN is the foundation and remains the predominant infrastructure that currently supports the connection of millions of subscribers worldwide. The PSTN has several thousands of miles of transmission infrastructure, including fixed land lines, microwave, and satellite links. After the introduction of cellular telephone systems in the early and mid-1980s, and with the rapid development of mobile wireless communication services, the PSTN still provides the fixed network support using the Signaling System Number 7 (SS7) protocol to carry control and signaling messages in a packet-switched environment.
Mobile Switching Center (MSC)
The MSC, usually located at the Mobile Telephone Switching Office (MTSO), is part of the mobile wireless network infrastructure that provides the following services:
•Switches voice traffic from the wireless network to the PSTN if the call is a mobile-to-landline call, or it switches to another MSC within the wireless network if the call is a mobile-to-mobile call.
•Provides telephony switching services and controls calls between telephone and data systems.
•Provides the mobility functions for the network and serves as the hub for up to as many as 100 BSs.
More specifically, the MSC provides the following functions:
•Mobility management for the subscribers (to register subscribers, to authenticate and authorize the subscribers for services and access to the network, to maintain the information on the temporary location of the subscribers so they can receive and originate voice calls).
In GSM, some of the functionality of the MSC is distributed to the Base Station Controller (BSC). In TDMA, the BSC and the MSC are integrated.
•Call setup services (call routing based on the called number). These calls can be to another mobile subscriber through another MSC, or to a landline user through the PSTN.
•Connection control services, which determine how calls are routed and establishes trunks to carry the bearer traffic to another MSC or to the PSTN.
•Service logic functions, which route the call to the requested service for the subscriber, such as an 800 service, call forwarding, or voicemail.
•Transcoding functions, which decompress the voice traffic from the mobile device going to the PSTN and compresses the traffic going from the PSTN to the mobile device.
Base Station (BS)
The BS is the component of the mobile wireless network access infrastructure that terminates the air interface over which the subscriber traffic is transmitted to and from a mobile station (MS).
In GSM-based networks, the BS is called a Base Transceiver Station (BTS).
Radio Access Network (RAN)
The RAN identifies the portion of the wireless network that handles the radio frequencies (RF), Radio Resource Management (RRM), which involves signaling, and the data synchronization aspects of transmission over the air interface.
In GSM-based networks, the RAN typically consists of BTSs and Base Station Controllers (BSCs). User sessions are connected from a mobile station to a BTS, which connects to a BSC. The combined functions of the BTS and BSC are referred to as the Base Station Subsystem (BSS).
Home Location Register (HLR)
The HLR is a database that contains information about subscribers to a mobile network that is maintained by a particular service provider. In addition, for subscribers of a roaming partner, the HLR might contain the service profiles of visiting subscribers.
The MSC uses the subscriber information supplied by the HLR to authenticate and register the subscriber. The HLR stores "permanent" subscriber information (rather than temporary subscriber data, which a VLR manages), including the service profile, location information, and activity status of the mobile user.
Visitor Location Register (VLR)
The VLR is a database that is maintained by an MSC, to store temporary information about subscribers who roam into the coverage area of that MSC.
The VLR, which is usually part of an MSC, communicates with the HLR of the roaming subscriber to request data, and to maintain information about the subscriber's current location in the network.
Authentication Center (AC)
The AC provides handset authentication and encryption services for a service provider. In most wireless networks today, the AC is collocated with the HLR, and is often implemented as part of the HLR complex.
Wireless Standards Development
This section discusses the evolution of some of the wireless networking standards and the types of services they support.
The phased evolution of wireless networking standards are referred to as generations:
•1G—First generation. 1G refers to the initial category of mobile wireless networks that used only analog technology and were developed primarily for voice services. Advanced Mobile Phone Service (AMPS) is an example of a 1G mobile network standard.
•2G—Second generation. 2G refers generically to a category of mobile wireless networks and services that use digital technology. 2G wireless networks introduce support for data services. GSM, TDMA and CDMA are examples of 2G mobile network standards.
•2G+—Second generation plus. 2G+ refers generically to a category of mobile wireless networks that have a packet data overlay built on top of the circuit-switched voice network to support higher data rates than 2G mobile networks (2G networks support data in a circuit-switched model). General Packet Radio Service (GPRS) is an example of a 2G+ mobile network standard.
There is a similar packet data overlay concept for CDMA called Packet Data Services Node (PDSN), but this is considered 3G as part of the CDMA 1x solution.
•3G—Third generation. 3G refers generically to a category of next-generation mobile networks which operate at a higher frequency bandwidth (typically 2.1 GHz and higher) and have a larger channel bandwidth. This enables 3G networks to support very high data rates, up to 2 Mbps. With the higher bandwidth, more data and multimedia services are possible. 3G refers to the radio network and RF technology, and does not affect the switching core. The switching infrastructure for 3G is still based on MSCs and the TDM model.
The Universal Mobile Telephone Service (UMTS), based on the Wideband CDMA (W-CDMA) R-99 and CDMA 2000, are examples of 3G radio networks that are being developed to fulfill the requirements in the International Mobile Telecommunications-2000 (IMT-2000) standard by the International Telecommunication Union (ITU).
•3G+—Third generation plus. 3G+ refers to an advanced level of 3G that introduces the concept of an all-IP switching core. An all-IP switching core means that IP replaces the TDM-based MSC infrastructure with IP-based transport and IP-based signaling. IP-based signaling is implemented with new protocols like Session Initiation Protocol (SIP) and Media Gateway Control Protocol (MGCP). In 3G+ networks, the traditional MSC implementation goes away and the various MSC functions are redistributed to several other elements. A good example of this evolution in the switching core from TDM to packets is 3GPP's R4 and R5 architecture. 3GPP2 also has adopted a similar trend to transition to an all-IP network.
There are also initiatives under way to develop and migrate to a true end-to-end, all-IP mobile wireless network where both the switching core and the RAN are IP based. This evolution is being loosely referred to as R6 in 3G terminology.
Model for IP Integration into Mobile Wireless
The standards for the integration of IP data networking with the existing telecommunications infrastructure are rapidly developing and beginning to be realized in today's production networks.
Figure 1 shows a model for IP integration based upon the current industry direction and reflects some of the latest ideas within the Mobile Wireless Internet Forum (MWIF). The MWIF is a pre-standards consortium for service providers and suppliers to collaborate on the implementation of IP-based mobile wireless networks. The MWIF influences the standards bodies such as 3GPP and 3GPP2 to successfully adopt new implementations.
In particular, Figure 1 shows where Cisco Systems' GGSN product for GSM networks fits into the model.
Figure 1 IP Integration Phases in Mobile Wireless
The top two quadrants in Figure 1 show where we are today in the telecommunications and IP data services infrastructures. The first quadrant represents the first phase of these infrastructures based on circuit-switched voice and data services. The beginnings of a core IP transport for voice and data integration can be built using Cisco Systems V.110 solutions.
The second quadrant depicts the implementation phase of 2G+ technologies, such as GPRS, supporting higher transmission speeds. In this quadrant, the Cisco Systems GGSN provides IP packet data services. It acts as an IP gateway for access to the internet and other public and private data networks for traffic that is initiated in a GSM-based mobile environment. The services anticipated in this phase include implementing always-on data services and enabling operators to charge by packet rather than connect time. Similar services are supported by Packet Data Services Node (PDSN), for CDMA-based wireless networks.
The third quadrant represents phase three of the integration of IP networking where voice and data are consolidated onto a packet-based infrastructure from the RAN or radio network control (RNC) outward. This is considered a 3G solution. Phase three enables integrated voice and data applications and reduces costs. In addition, some of the components or functions of the MSC are distributed.
The fourth quadrant represents the final phase, which includes 3G services plus the implementation of IP-based radio and mobility components to develop a true end-to-end, all-IP wireless network solution.
Mobile Wireless in Cisco IOS Software
Cisco Systems has a variety of products that provide wireless communications services and that can be used together as solutions for different network environments and needs. Some of these products provide fixed wireless IP data services and others address mobile wireless IP data services. Some reside in Cisco IOS software and others do not.
The Cisco IOS Mobile Wireless Configuration Guide focuses on a portion of the wireless communications services provided by the Cisco IOS software. It describes the segment of wireless products that provide mobile wireless communications services. This first version of the book describes a product that supports IP data services in a mobile environment.
Note The Cisco IOS software also supports the mobile IP protocol, which is not documented in this book. For more information about mobile IP, refer to the Cisco IOS IP Configuration Guide.
IP Data Services
This section describes the first GSM-based technology implemented in the Cisco IOS software for IP data services in mobile wireless networks—GPRS.
GPRS is a new service designed for GSM networks. GSM is a digital cellular technology that is used worldwide, predominantly in Europe and Asia, with current estimates of 400 million subscribers and growing. GSM is the world's leading standard in digital wireless communications.
GPRS is standardized by the European Telecommunications Standards Institute (ETSI). The most common application of GPRS is expected to be Internet/intranet access. Cisco Systems' GPRS solution enables mobile wireless service providers to supply their mobile subscribers with packet data services.
A GPRS network has two essential elements:
•Serving GPRS Support Node (SGSN)—Sends data to and receives data from mobile stations, and maintains information about the location of a mobile station (MS). The SGSN communicates between the MS and the GGSN. SGSN support is available from Cisco partners or other vendors.
•Gateway GPRS Support Node (GGSN)—A wireless gateway that allows mobile cell phone users to access the public data network (PDN) or specified private IP networks. The GGSN function is implemented on the Cisco Systems' router.
Cisco Systems is recognized as the first to market a viable GGSN product. GGSN support is available in the GPRS feature in Cisco IOS software.
The GPRS part of this Cisco IOS Mobile Wireless Configuration Guide describes how to configure a Cisco Systems router to function as a GGSN. While the documentation provides a brief overview of the GPRS technology and its benefits, the primary purpose of this documentation is to provide you with the necessary information to configure, verify, and monitor the GGSN portion of your GPRS network. It does not describe all of the planning considerations that might be involved in setting up your GPRS network.