Chapter 12. Cellular Networks

This chapter introduces Global System for Mobile communications (GSM), which is the most popular digital cellular network standard in terms of architecture, discusses interfaces and protocols, and concludes by presenting examples of mobility management and call processing in the network. The protocols that are found in GSM to perform these functions—namely, Base Station Subsystem Application Part (BSSAP) and Mobile Application Part (MAP)—are applications (subsystems) that utilize the underlying functionality of the SS7 protocols and network. This chapter aims to provide enough background on GSM cellular networks for you to understand the MAP that is used for mobility management and call processing within the GSM network, which is discussed in Chapter 13, "GSM and ANSI-41 Mobile Application Part (MAP)."

The European Telecommunication Standard Institute (ETSI) formulated GSM. Phase one of the GSM specifications was published in 1990, and the commercial operation using the 900 Mhz range began in 1991. The same year, a derivative of GSM, known as Digital Cellular System 1800 (DCS 1800), which translated GSM to the 1800 Mhz range, appeared. The United States adapted DCS 1800 into the 1900 Mhz range and called it Personal Communication System 1900 (PCS 1900). By 1993, 36 GSM networks existed in 22 countries [119].

Pre-GSM cellular networks are analog and vary from country to country—for example, the United States still uses Advanced/American Mobile Phone Service (AMPS), and the UK used Total Access Communication System (TACS). With these older analog standards, it was impossible to have one phone work in more than one country. In addition, because of the analog nature of the speech, quality could be relatively poor, and there were no provisions for supplementary services (such as call waiting). Although it is standardized in Europe, GSM is not just a European standard. At the time of this writing, there are more than 509 GSM networks (including DCS 1800 and PCS 1900) operating in 182 countries around the world, with 684.2 million subscribers [Source: GSM Association]. See Appendix I for a list of mobile networks by country.

GSM has been released in phases. The following are the features of these phases:

GSM Phase 1 (1992) Features

• Call Forwarding

• All Calls

• No Answer

• Engaged

• Unreachable

• Call Barring

• Outgoing—Bar certain outgoing calls

• Incoming—Bar certain incoming calls

• Global roaming—–If you visit any other country or parts in an existing country with GSM, your cellular phone remains connected without having to change your number or perform any action.

GSM Phase 2 (1995) Features

• Short Message Service (SMS)— Allows you to send and receive text messages.

• Multiparty Calling— Talk to five other parties and yourself at the same time.

• Call Holding— Place a call on hold.

• Calling Line Identity Service— This facility allows you to see the incoming caller's telephone number on your handset before answering.

• Advice of Charge— Allows you to keep track of call costs.

• Cell Broadcast— Allows you to subscribe to local news channels.

• Mobile Terminating Fax— Another number you are issued that can receive faxes.

• Call Waiting— Notifies you of another call while you are on a call.

• Mobile Data Services— Allows handsets to communicate with computers.

• Mobile Fax Service— Allows handsets to send, retrieve, and receive faxes.

GSM Phase 2 + (1996) Features

• Upgrades and improvements to existing services; the majority of the upgrade concerns data transmission, including bearer services and packet switched data at 64 kbps and above

• DECT access to GSM

• PMR/Public Access Mobile Radio (PAMR)-like capabilities to GSM in the local loop

• SIM enhancements

• Premium rate services

• Virtual Private Networks Packet Radio

Unlike Europe (and most of the world), which only pursued GSM for digital cellular networks, North America has pursued a mix of TDMA (IS-54, IS-136), CDMA, and GSM. At the time of this writing, TDMA and CDMA have been more widely deployed in North America than GSM. However, this situation is rapidly beginning to reverse with GSM continually gaining ground.

One benefit of 3G technology is that it unifies these diverse cellular standards. Although three different air interface modes exist—wideband CDMA, CDMA 2000, and the Universal Wireless Communication (UWC-136) interfaces—each should be able to work over both current GSM network architectures.